# Section Index

An A to Z bar on the side of a scrolling list that jumps to sections on tap or drag.

Section Index is an open-source mobile interaction from suiss/uim for React Native and Expo, with SwiftUI and Jetpack Compose versions built from the same design tokens. The @esuiss/uim CLI copies its source into your project, so you own the code.

Source: https://uim.suiss.app/docs/interactions/section-index

![Preview](https://uim.suiss.app/previews/interactions-section-index--default.light.webp)

```tsx
import * as React from "react"
import { Pressable, View } from "react-native"
import { SectionIndex, SectionIndexBar, SectionIndexHeader, SectionIndexScrollView, SectionIndexSection } from "@/components/interactions/section-index"
import { Text } from "@/components/ui/text"

const UPPERCASE = /[A-Z]/

const names = [
  "Aaron Price",
  "Abby Chen",
  "Alex Morgan",
  "Amira Haddad",
  "Ben Carter",
  "Bianca Rossi",
  "Carla Diaz",
  "Chris Evans",
  "Cody Brooks",
  "Dana Scott",
  "Derek Hale",
  "Elena Petrova",
  "Ethan Wright",
  "Fatima Khan",
  "Felix Wagner",
  "Grace Kim",
  "Hana Sato",
  "Henry Ford",
  "Ivy Turner",
  "Jack Miller",
  "Jade Wilson",
  "Jonas Berg",
  "Kai Nakamura",
  "Laura Bell",
  "Leo Martin",
  "Lina Costa",
  "Maya Patel",
  "Mia Novak",
  "Noah Fischer",
  "Nora Lind",
  "Omar Aziz",
  "Paula Silva",
  "Quinn Avery",
  "Rosa Lopez",
  "Ryan Cole",
  "Sara Ahmed",
  "Sofia Greco",
  "Tom Baker",
  "Uma Rao",
  "Victor Hugo",
  "Will Jensen",
  "Yara Nasser",
  "Zoe Adams",
  "8 Ball Club",
]

function groupByLetter() {
  const groups = new Map<string, string[]>()
  for (const name of names) {
    const first = name.charAt(0).toUpperCase()
    const letter = UPPERCASE.test(first) ? first : "#"
    groups.set(letter, [...(groups.get(letter) ?? []), name])
  }
  return [...groups.entries()].sort(([a], [b]) => {
    if (a === "#") return 1
    if (b === "#") return -1
    return a.localeCompare(b)
  })
}

function ContactsExample({ className }: { className: string }) {
  const [log, setLog] = React.useState("Tap or drag the letters.")
  return (
    <View className="gap-3">
      <SectionIndex className={className}>
        <SectionIndexScrollView className="rounded-2xl border border-separator">
          {groupByLetter().map(([letter, group]) => (
            <SectionIndexSection key={letter} value={letter}>
              <SectionIndexHeader>{letter}</SectionIndexHeader>
              {group.map((name, index) => (
                <Pressable
                  key={name}
                  onPress={() => setLog(`Opened ${name}`)}
                  className={`ms-4 me-10 py-3 active:opacity-60 ${index > 0 ? "border-t border-separator" : ""}`}
                >
                  <Text>{name}</Text>
                </Pressable>
              ))}
            </SectionIndexSection>
          ))}
        </SectionIndexScrollView>
        <SectionIndexBar
          onValueChange={(letter) => setLog(`Jumped to ${letter}`)}
        />
      </SectionIndex>
      <Text variant="muted">{log}</Text>
    </View>
  )
}

export function SectionIndexExample() {
  return (
    <ContactsExample className="h-[520px]" />
  )
}
```

```swift
import EsuissUI
import SwiftUI

struct SectionIndexExample: View {
  var body: some View {
    SectionIndexContacts(height: 520)
  }
}

let sectionIndexNames = [
  "Aaron Price", "Abby Chen", "Alex Morgan", "Amira Haddad", "Ben Carter", "Bianca Rossi",
  "Carla Diaz", "Chris Evans", "Cody Brooks", "Dana Scott", "Derek Hale", "Elena Petrova",
  "Ethan Wright", "Fatima Khan", "Felix Wagner", "Grace Kim", "Hana Sato", "Henry Ford",
  "Ivy Turner", "Jack Miller", "Jade Wilson", "Jonas Berg", "Kai Nakamura", "Laura Bell",
  "Leo Martin", "Lina Costa", "Maya Patel", "Mia Novak", "Noah Fischer", "Nora Lind",
  "Omar Aziz", "Paula Silva", "Quinn Avery", "Rosa Lopez", "Ryan Cole", "Sara Ahmed",
  "Sofia Greco", "Tom Baker", "Uma Rao", "Victor Hugo", "Will Jensen", "Yara Nasser",
  "Zoe Adams", "8 Ball Club",
]

let sectionIndexGroups: [(String, [String])] = {
  var groups: [String: [String]] = [:]
  for name in sectionIndexNames {
    let first = name.prefix(1).uppercased()
    let letter = first.range(of: "^[A-Z]$", options: .regularExpression) != nil ? first : "#"
    groups[letter, default: []].append(name)
  }
  return groups.sorted { lhs, rhs in
    if lhs.key == "#" { return false }
    if rhs.key == "#" { return true }
    return lhs.key < rhs.key
  }
  .map { ($0.key, $0.value) }
}()

struct SectionIndexContacts: View {
  let height: CGFloat

  @State private var log: LocalizedStringKey = "Tap or drag the letters."

  var body: some View {
    let shape = RoundedRectangle(cornerRadius: Radius.xl2, style: .continuous)
    VStack(alignment: .leading, spacing: 12) {
      SectionIndex {
        ScrollView {
          LazyVStack(alignment: .leading, spacing: 0, pinnedViews: .sectionHeaders) {
            ForEach(sectionIndexGroups, id: \.0) { entry in
              SectionIndexSection(entry.0) {
                ForEach(Array(entry.1.enumerated()), id: \.element) { index, name in
                  Button {
                    log = "Opened \(name)"
                  } label: {
                    Text(verbatim: name)
                      .textStyle(.base)
                      .foregroundStyle(Color.label)
                      .padding(.vertical, 12)
                      .frame(maxWidth: .infinity, alignment: .leading)
                      .contentShape(Rectangle())
                  }
                  .buttonStyle(SectionIndexRowStyle())
                  .overlay(alignment: .top) {
                    if index > 0 {
                      Color.separator.frame(height: 1)
                    }
                  }
                  .padding(.leading, 16)
                  .padding(.trailing, 40)
                }
              }
            }
          }
        }
        .clipShape(shape)
        .overlay { shape.strokeBorder(Color.separator) }
        SectionIndexBar { letter in
          log = "Jumped to \(letter)"
        }
      }
      .frame(height: height)
      Text(log)
        .textVariant(.muted)
    }
  }
}

struct SectionIndexRowStyle: ButtonStyle {
  func makeBody(configuration: Configuration) -> some View {
    configuration.label
      .opacity(configuration.isPressed ? 0.6 : 1)
  }
}
```

```kotlin
import androidx.compose.foundation.background
import androidx.compose.foundation.border
import androidx.compose.foundation.clickable
import androidx.compose.foundation.interaction.MutableInteractionSource
import androidx.compose.foundation.interaction.collectIsPressedAsState
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.saveable.rememberSaveable
import androidx.compose.runtime.setValue
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.alpha
import androidx.compose.ui.draw.clip
import androidx.compose.ui.semantics.Role
import androidx.compose.ui.unit.Dp
import androidx.compose.ui.unit.dp
import com.esuiss.ui.components.Text
import com.esuiss.ui.components.TextVariant
import com.esuiss.ui.interactions.SectionIndex
import com.esuiss.ui.theme.EsuissTheme
import com.esuiss.ui.theme.Radius

@Composable
fun SectionIndexExample() {
    SectionIndexContacts(height = 520.dp)
}

val sectionIndexNames = listOf(
    "Aaron Price",
    "Abby Chen",
    "Alex Morgan",
    "Amira Haddad",
    "Ben Carter",
    "Bianca Rossi",
    "Carla Diaz",
    "Chris Evans",
    "Cody Brooks",
    "Dana Scott",
    "Derek Hale",
    "Elena Petrova",
    "Ethan Wright",
    "Fatima Khan",
    "Felix Wagner",
    "Grace Kim",
    "Hana Sato",
    "Henry Ford",
    "Ivy Turner",
    "Jack Miller",
    "Jade Wilson",
    "Jonas Berg",
    "Kai Nakamura",
    "Laura Bell",
    "Leo Martin",
    "Lina Costa",
    "Maya Patel",
    "Mia Novak",
    "Noah Fischer",
    "Nora Lind",
    "Omar Aziz",
    "Paula Silva",
    "Quinn Avery",
    "Rosa Lopez",
    "Ryan Cole",
    "Sara Ahmed",
    "Sofia Greco",
    "Tom Baker",
    "Uma Rao",
    "Victor Hugo",
    "Will Jensen",
    "Yara Nasser",
    "Zoe Adams",
    "8 Ball Club",
)

val sectionIndexGroups: List<Pair<String, List<String>>> =
    sectionIndexNames
        .groupBy { name ->
            val first = name.first().uppercaseChar()
            if (first in 'A'..'Z') first.toString() else "#"
        }
        .toList()
        .sortedWith(compareBy({ it.first == "#" }, { it.first }))

@Composable
fun SectionIndexContacts(height: Dp) {
    val colors = EsuissTheme.colors
    var log by rememberSaveable { mutableStateOf("Tap or drag the letters.") }
    val shape = RoundedCornerShape(Radius.xl2)
    Column(verticalArrangement = Arrangement.spacedBy(12.dp)) {
        SectionIndex(
            modifier = Modifier
                .fillMaxWidth()
                .height(height)
                .clip(shape)
                .border(1.dp, colors.separator, shape),
            onValueChange = { letter -> log = "Jumped to $letter" },
        ) {
            sectionIndexGroups.forEach { (letter, group) ->
                SectionIndexSection(letter) {
                    items(group.size, key = { group[it] }) { index ->
                        SectionIndexRow(group[index], divided = index > 0) { log = "Opened ${group[index]}" }
                    }
                }
            }
        }
        Text(log, variant = TextVariant.Muted)
    }
}

@Composable
fun SectionIndexRow(name: String, divided: Boolean, onClick: () -> Unit) {
    val colors = EsuissTheme.colors
    val interaction = remember { MutableInteractionSource() }
    val pressed by interaction.collectIsPressedAsState()
    Column(
        Modifier
            .fillMaxWidth()
            .padding(start = 16.dp, end = 40.dp)
            .clickable(interactionSource = interaction, indication = null, role = Role.Button, onClick = onClick),
    ) {
        if (divided) Box(Modifier.fillMaxWidth().height(1.dp).background(colors.separator))
        Text(name, modifier = Modifier.alpha(if (pressed) 0.6f else 1f).padding(vertical = 12.dp))
    }
}
```

`SectionIndex` pairs a scroll view of lettered sections with `SectionIndexBar`, a column of letters on the end edge. Tapping a letter scrolls to that section; dragging along the bar scrubs through sections and shows the current letter in a large bubble beside the finger.

When the bar is too short for every letter, it shows a subset with `•` between them. Use it for long alphabetical lists such as contacts.

## Installation

```bash title="Terminal"
npx @esuiss/uim@latest add section-index
```

```bash title="Terminal"
npx @esuiss/uim@latest add section-index --platform swift
```

```bash title="Terminal"
npx @esuiss/uim@latest add section-index --platform kotlin
```

The CLI also adds what it builds on: [Text](/docs/components/text).

### Manual

**Uniwind**

1. Install the dependencies:

```bash title="Terminal"
npx expo install cn react-native-reanimated react-native-worklets
```

2. Add the pieces it builds on: [Text](/docs/components/text), and the primitives `components/primitives/section-index.tsx`, `components/primitives/use-render.tsx`.

3. Copy the source into `components/interactions/section-index.tsx`:

```tsx title="uniwind/components/interactions/section-index.tsx"
import { cn } from "cn"
import type * as React from "react"
import { View } from "react-native"
import { FadeOut, ReduceMotion, ZoomIn } from "react-native-reanimated"
import * as SectionIndexPrimitive from "@/components/primitives/section-index"
import { resolveClassName } from "@/components/primitives/use-render"
import { AnimatedView } from "@/components/ui/animated-view"
import { Text } from "@/components/ui/text"

function SectionIndex({
  className,
  ...props
}: React.ComponentProps<typeof SectionIndexPrimitive.Root>) {
  return (
    <SectionIndexPrimitive.Root
      className={(state) => cn("relative", resolveClassName(className, state))}
      {...props}
    />
  )
}

function SectionIndexScrollView({
  className,
  ...props
}: React.ComponentProps<typeof SectionIndexPrimitive.ScrollView>) {
  return (
    <SectionIndexPrimitive.ScrollView
      className={cn("flex-1", className)}
      {...props}
    />
  )
}

function SectionIndexSection(
  props: React.ComponentProps<typeof SectionIndexPrimitive.Section>
) {
  return <SectionIndexPrimitive.Section {...props} />
}

function SectionIndexHeader({
  className,
  children,
  ...props
}: React.ComponentProps<typeof View>) {
  return (
    <View
      role="heading"
      className={cn("bg-surface px-4 py-1.5", className)}
      {...props}
    >
      {typeof children === "string" || typeof children === "number" ? (
        <Text className="text-sm font-semibold text-label-secondary">
          {children}
        </Text>
      ) : (
        children
      )}
    </View>
  )
}

function SectionIndexBar({
  className,
  ...props
}: Omit<React.ComponentProps<typeof SectionIndexPrimitive.Bar>, "children">) {
  return (
    <View
      className="absolute top-0 bottom-0 end-3 justify-center"
      style={{ pointerEvents: "box-none" }}
    >
      <SectionIndexPrimitive.Bar
        className={(state) =>
          cn(
            "items-center rounded-full px-1.5",
            resolveClassName(className, state)
          )
        }
        {...props}
      >
        {(state) => (
          <>
            {state.items.map((item) => (
              <View
                key={item.key}
                className="h-4 min-w-3 items-center justify-center"
                style={{ pointerEvents: "none" }}
              >
                <Text className="text-2xs font-semibold text-link">
                  {item.label}
                </Text>
              </View>
            ))}
            {state.dragging ? (
              <AnimatedView
                entering={ZoomIn.duration(200).reduceMotion(
                  ReduceMotion.System
                )}
                exiting={FadeOut.duration(150).reduceMotion(
                  ReduceMotion.System
                )}
                className="absolute end-full me-4 size-14 items-center justify-center rounded-full border border-separator bg-surface-raised shadow-xl"
                style={{ top: state.dragY - 28, pointerEvents: "none" }}
              >
                <Text className="text-3xl font-semibold text-label">
                  {state.letter}
                </Text>
              </AnimatedView>
            ) : null}
          </>
        )}
      </SectionIndexPrimitive.Bar>
    </View>
  )
}

export {
  SectionIndex,
  SectionIndexBar,
  SectionIndexHeader,
  SectionIndexScrollView,
  SectionIndexSection,
}
```

4. Update the import paths to match your project.

**NativeWind**

1. Install the dependencies:

```bash title="Terminal"
npx expo install cn react-native-reanimated react-native-worklets
```

2. Add the pieces it builds on: [Text](/docs/components/text), and the primitives `components/primitives/section-index.tsx`, `components/primitives/use-render.tsx`.

3. Copy the source into `components/interactions/section-index.tsx`:

```tsx title="nativewind/components/interactions/section-index.tsx"
import { cn } from "cn"
import type * as React from "react"
import { View } from "react-native"
import { FadeOut, ReduceMotion, ZoomIn } from "react-native-reanimated"
import * as SectionIndexPrimitive from "@/components/primitives/section-index"
import { resolveClassName } from "@/components/primitives/use-render"
import { AnimatedView } from "@/components/ui/animated-view"
import { Text } from "@/components/ui/text"

function SectionIndex({
  className,
  ...props
}: React.ComponentProps<typeof SectionIndexPrimitive.Root>) {
  return (
    <SectionIndexPrimitive.Root
      className={(state) => cn("relative", resolveClassName(className, state))}
      {...props}
    />
  )
}

function SectionIndexScrollView({
  className,
  ...props
}: React.ComponentProps<typeof SectionIndexPrimitive.ScrollView>) {
  return (
    <SectionIndexPrimitive.ScrollView
      className={cn("flex-1", className)}
      {...props}
    />
  )
}

function SectionIndexSection(
  props: React.ComponentProps<typeof SectionIndexPrimitive.Section>
) {
  return <SectionIndexPrimitive.Section {...props} />
}

function SectionIndexHeader({
  className,
  children,
  ...props
}: React.ComponentProps<typeof View>) {
  return (
    <View
      role="heading"
      className={cn("bg-surface px-4 py-1.5", className)}
      {...props}
    >
      {typeof children === "string" || typeof children === "number" ? (
        <Text className="text-sm font-semibold text-label-secondary">
          {children}
        </Text>
      ) : (
        children
      )}
    </View>
  )
}

function SectionIndexBar({
  className,
  ...props
}: Omit<React.ComponentProps<typeof SectionIndexPrimitive.Bar>, "children">) {
  return (
    <View
      className="absolute top-0 bottom-0 end-3 justify-center"
      style={{ pointerEvents: "box-none" }}
    >
      <SectionIndexPrimitive.Bar
        className={(state) =>
          cn(
            "items-center rounded-full px-1.5",
            resolveClassName(className, state)
          )
        }
        {...props}
      >
        {(state) => (
          <>
            {state.items.map((item) => (
              <View
                key={item.key}
                className="h-4 min-w-3 items-center justify-center"
                style={{ pointerEvents: "none" }}
              >
                <Text className="text-2xs font-semibold text-link">
                  {item.label}
                </Text>
              </View>
            ))}
            {state.dragging ? (
              <AnimatedView
                entering={ZoomIn.duration(200).reduceMotion(
                  ReduceMotion.System
                )}
                exiting={FadeOut.duration(150).reduceMotion(
                  ReduceMotion.System
                )}
                className="absolute end-full me-4 size-14 items-center justify-center rounded-full border border-separator bg-surface-raised shadow-xl"
                style={{ top: state.dragY - 28, pointerEvents: "none" }}
              >
                <Text className="text-3xl font-semibold text-label">
                  {state.letter}
                </Text>
              </AnimatedView>
            ) : null}
          </>
        )}
      </SectionIndexPrimitive.Bar>
    </View>
  )
}

export {
  SectionIndex,
  SectionIndexBar,
  SectionIndexHeader,
  SectionIndexScrollView,
  SectionIndexSection,
}
```

4. Update the import paths to match your project.

**StyleSheet**

1. Install the dependencies:

```bash title="Terminal"
npx expo install react-native-reanimated react-native-worklets
```

2. Add the pieces it builds on: [Text](/docs/components/text), and the primitives `components/primitives/section-index.tsx`, `components/primitives/use-render.tsx`.

3. Copy the source into `components/interactions/section-index.tsx`:

```tsx title="stylesheet/components/interactions/section-index.tsx"
import type * as React from "react"
import { StyleSheet, View, type ViewStyle } from "react-native"
import { FadeOut, ReduceMotion, ZoomIn } from "react-native-reanimated"
import * as SectionIndexPrimitive from "@/components/primitives/section-index"
import { resolveStyle } from "@/components/primitives/use-render"
import { AnimatedView } from "@/components/ui/animated-view"
import { Text } from "@/components/ui/text"
import { fontSize, radius, shadow, useTheme } from "@/components/ui/theme"

const styles = StyleSheet.create({
  root: { position: "relative" },
  scroll: { flex: 1 },
  header: { paddingHorizontal: 16, paddingVertical: 6 },
  headerText: { ...fontSize.sm, fontWeight: "600" },
  barFrame: {
    position: "absolute",
    top: 0,
    bottom: 0,
    end: 12,
    justifyContent: "center",
    pointerEvents: "box-none",
  },
  bar: {
    alignItems: "center",
    borderRadius: radius.full,
    paddingHorizontal: 6,
  },
  letter: {
    height: 16,
    minWidth: 12,
    alignItems: "center",
    justifyContent: "center",
    pointerEvents: "none",
  },
  letterText: { ...fontSize["2xs"], fontWeight: "600" },
  bubble: {
    position: "absolute",
    end: "100%",
    marginEnd: 16,
    width: 56,
    height: 56,
    alignItems: "center",
    justifyContent: "center",
    borderRadius: radius.full,
    borderWidth: 1,
    pointerEvents: "none",
    ...shadow.xl,
  },
  bubbleText: { ...fontSize["3xl"], fontWeight: "600" },
})

function SectionIndex({
  style,
  ...props
}: React.ComponentProps<typeof SectionIndexPrimitive.Root>) {
  return (
    <SectionIndexPrimitive.Root
      style={(state) => [styles.root, resolveStyle(style, state) as ViewStyle]}
      {...props}
    />
  )
}

function SectionIndexScrollView({
  style,
  ...props
}: React.ComponentProps<typeof SectionIndexPrimitive.ScrollView>) {
  return (
    <SectionIndexPrimitive.ScrollView
      style={[styles.scroll, style]}
      {...props}
    />
  )
}

function SectionIndexSection(
  props: React.ComponentProps<typeof SectionIndexPrimitive.Section>
) {
  return <SectionIndexPrimitive.Section {...props} />
}

function SectionIndexHeader({
  style,
  children,
  ...props
}: React.ComponentProps<typeof View>) {
  const { colors } = useTheme()
  return (
    <View
      role="heading"
      style={[styles.header, { backgroundColor: colors.surface }, style]}
      {...props}
    >
      {typeof children === "string" || typeof children === "number" ? (
        <Text style={[styles.headerText, { color: colors.labelSecondary }]}>
          {children}
        </Text>
      ) : (
        children
      )}
    </View>
  )
}

function SectionIndexBar({
  style,
  ...props
}: Omit<React.ComponentProps<typeof SectionIndexPrimitive.Bar>, "children">) {
  const { colors } = useTheme()
  return (
    <View style={styles.barFrame}>
      <SectionIndexPrimitive.Bar
        style={(state) => [styles.bar, resolveStyle(style, state) as ViewStyle]}
        {...props}
      >
        {(state) => (
          <>
            {state.items.map((item) => (
              <View key={item.key} style={styles.letter}>
                <Text style={[styles.letterText, { color: colors.link }]}>
                  {item.label}
                </Text>
              </View>
            ))}
            {state.dragging ? (
              <AnimatedView
                entering={ZoomIn.duration(200).reduceMotion(
                  ReduceMotion.System
                )}
                exiting={FadeOut.duration(150).reduceMotion(
                  ReduceMotion.System
                )}
                style={[
                  styles.bubble,
                  {
                    top: state.dragY - 28,
                    backgroundColor: colors.surfaceRaised,
                    borderColor: colors.separator,
                  },
                ]}
              >
                <Text style={[styles.bubbleText, { color: colors.label }]}>
                  {state.letter}
                </Text>
              </AnimatedView>
            ) : null}
          </>
        )}
      </SectionIndexPrimitive.Bar>
    </View>
  )
}

export {
  SectionIndex,
  SectionIndexBar,
  SectionIndexHeader,
  SectionIndexScrollView,
  SectionIndexSection,
}
```

4. Update the import paths to match your project.

**SwiftUI**

1. Target iOS 17 or later.

2. Add the Swift package to your app:

```swift title="Package.swift"
.package(url: "https://github.com/phosphor-icons/swift", from: "2.1.0")
```

3. Copy the theme files every view uses:

```swift title="swift/Theme/Theme.swift"
import SwiftUI
import UIKit

struct RGBA: Sendable {
  let red: CGFloat
  let green: CGFloat
  let blue: CGFloat
  let alpha: CGFloat

  init(_ hex: UInt32, _ alpha: CGFloat = 1) {
    red = CGFloat((hex >> 16) & 0xFF) / 255
    green = CGFloat((hex >> 8) & 0xFF) / 255
    blue = CGFloat(hex & 0xFF) / 255
    self.alpha = alpha
  }

  var uiColor: UIColor {
    UIColor(red: red, green: green, blue: blue, alpha: alpha)
  }
}

extension Color {
  static func adaptive(light: RGBA, dark: RGBA) -> Color {
    let lightColor = light.uiColor
    let darkColor = dark.uiColor
    return Color(uiColor: UIColor { traits in
      traits.userInterfaceStyle == .dark ? darkColor : lightColor
    })
  }
}

public struct TextStyle: Sendable, Hashable {
  public let size: CGFloat
  public let lineHeight: CGFloat
  public let letterSpacing: CGFloat

  public init(size: CGFloat, lineHeight: CGFloat, letterSpacing: CGFloat) {
    self.size = size
    self.lineHeight = lineHeight
    self.letterSpacing = letterSpacing
  }

  public func font(weight: Font.Weight = .regular) -> Font {
    .system(size: size, weight: weight)
  }

  public var lineSpacing: CGFloat {
    max(0, lineHeight - UIFont.systemFont(ofSize: size).lineHeight)
  }
}

extension Hashable where Self == Font {
  public static func textStyle(_ style: TextStyle, weight: Font.Weight = .regular) -> Font {
    style.font(weight: weight)
  }
}

private struct TextStyleModifier: ViewModifier {
  let style: TextStyle
  let weight: Font.Weight

  func body(content: Content) -> some View {
    content
      .font(style.font(weight: weight))
      .tracking(style.letterSpacing)
      .lineSpacing(style.lineSpacing)
      .padding(.vertical, style.lineSpacing / 2)
  }
}

extension View {
  public func textStyle(_ style: TextStyle, weight: Font.Weight = .regular) -> some View {
    modifier(TextStyleModifier(style: style, weight: weight))
  }
}

public struct Shadow: Sendable, Hashable {
  public let color: Color
  public let radius: CGFloat
  public let x: CGFloat
  public let y: CGFloat

  public init(color: Color, radius: CGFloat, x: CGFloat = 0, y: CGFloat = 0) {
    self.color = color
    self.radius = radius
    self.x = x
    self.y = y
  }
}

extension View {
  public func shadow(_ shadow: Shadow) -> some View {
    self.shadow(color: shadow.color, radius: shadow.radius, x: shadow.x, y: shadow.y)
  }
}
```

```swift title="swift/Theme/Tokens.swift"
import SwiftUI

extension Color {
  public static let surface = Color.adaptive(light: .init(0xFFFFFF), dark: .init(0x000000))
  public static let surfaceSecondary = Color.adaptive(light: .init(0xF5F5F7), dark: .init(0x161617))
  public static let surfaceTertiary = Color.adaptive(light: .init(0xE8E8ED), dark: .init(0x2C2C2E))
  public static let surfaceRaised = Color.adaptive(light: .init(0xFFFFFF), dark: .init(0x1D1D1F))
  public static let label = Color.adaptive(light: .init(0x1D1D1F), dark: .init(0xF5F5F7))
  public static let labelSecondary = Color.adaptive(light: .init(0x6E6E73), dark: .init(0xA1A1A6))
  public static let labelTertiary = Color.adaptive(light: .init(0x86868B), dark: .init(0x86868B))
  public static let labelQuaternary = Color.adaptive(light: .init(0xD2D2D7), dark: .init(0x424245))
  public static let control = Color.adaptive(light: .init(0x000000, 0.04), dark: .init(0xFFFFFF, 0.1))
  public static let controlPressed = Color.adaptive(light: .init(0x000000, 0.12), dark: .init(0xFFFFFF, 0.22))
  public static let controlSelected = Color.adaptive(light: .init(0x1D1D1F), dark: .init(0xF5F5F7))
  public static let controlDisabled = Color.adaptive(light: .init(0x000000, 0.03), dark: .init(0xFFFFFF, 0.05))
  public static let onControlSelected = Color.adaptive(light: .init(0xFFFFFF), dark: .init(0x000000))
  public static let itemPressed = Color.adaptive(light: .init(0x000000, 0.08), dark: .init(0xFFFFFF, 0.12))
  public static let itemSelected = Color.adaptive(light: .init(0x000000, 0.06), dark: .init(0xFFFFFF, 0.1))
  public static let separator = Color.adaptive(light: .init(0xD2D2D7), dark: .init(0x424245))
  public static let separatorStrong = Color.adaptive(light: .init(0x86868B), dark: .init(0x6E6E73))
  public static let accent = Color.adaptive(light: .init(0x0071E3), dark: .init(0x0071E3))
  public static let accentPressed = Color.adaptive(light: .init(0x005BB8), dark: .init(0x004D9E))
  public static let accentSelected = Color.adaptive(light: .init(0x0071E3), dark: .init(0x0071E3))
  public static let accentDisabled = Color.adaptive(light: .init(0x0071E3, 0.4), dark: .init(0x0071E3, 0.4))
  public static let onAccent = Color.adaptive(light: .init(0xFFFFFF), dark: .init(0xFFFFFF))
  public static let accentSurface = Color.adaptive(light: .init(0x0071E3, 0.09), dark: .init(0x0071E3, 0.18))
  public static let accentSurfacePressed = Color.adaptive(light: .init(0x0071E3, 0.18), dark: .init(0x0071E3, 0.3))
  public static let link = Color.adaptive(light: .init(0x0066CC), dark: .init(0x2997FF))
  public static let focus = Color.adaptive(light: .init(0x0071E3), dark: .init(0x0071E3))
  public static let scrim = Color.adaptive(light: .init(0x000000, 0.48), dark: .init(0x000000, 0.48))
  public static let media = Color.adaptive(light: .init(0x000000), dark: .init(0x000000))
  public static let onMedia = Color.adaptive(light: .init(0xFFFFFF), dark: .init(0xFFFFFF))
  public static let danger = Color.adaptive(light: .init(0xD0000A), dark: .init(0xFF5447))
  public static let dangerSurface = Color.adaptive(light: .init(0xD70015, 0.08), dark: .init(0xFF453A, 0.2))
  public static let dangerSurfacePressed = Color.adaptive(light: .init(0xD70015, 0.16), dark: .init(0xFF453A, 0.36))
  public static let success = Color.adaptive(light: .init(0x008009), dark: .init(0x30D158))
  public static let successSurface = Color.adaptive(light: .init(0xEFFAF1), dark: .init(0x30D158, 0.16))
  public static let warning = Color.adaptive(light: .init(0xB64400), dark: .init(0xFF9F0A))
  public static let warningSurface = Color.adaptive(light: .init(0xFFF5EA), dark: .init(0xFF9F0A, 0.16))
}

public enum Radius {
  public static let xs: CGFloat = 3
  public static let sm: CGFloat = 5
  public static let md: CGFloat = 8
  public static let lg: CGFloat = 10
  public static let xl: CGFloat = 12
  public static let xl2: CGFloat = 18
  public static let xl3: CGFloat = 28
  public static let full: CGFloat = 9999
}

extension TextStyle {
  public static let xs3 = TextStyle(size: 11, lineHeight: 13, letterSpacing: 0.066)
  public static let xs2 = TextStyle(size: 12, lineHeight: 16, letterSpacing: 0)
  public static let xs = TextStyle(size: 13, lineHeight: 18, letterSpacing: -0.078)
  public static let sm = TextStyle(size: 15, lineHeight: 20, letterSpacing: -0.24)
  public static let md = TextStyle(size: 16, lineHeight: 21, letterSpacing: -0.32)
  public static let base = TextStyle(size: 17, lineHeight: 22, letterSpacing: -0.442)
  public static let lg = TextStyle(size: 20, lineHeight: 25, letterSpacing: -0.46)
  public static let xl = TextStyle(size: 22, lineHeight: 28, letterSpacing: -0.264)
  public static let xl2 = TextStyle(size: 28, lineHeight: 34, letterSpacing: 0.392)
  public static let xl3 = TextStyle(size: 34, lineHeight: 41, letterSpacing: 0.408)

  public static let allCases: [TextStyle] = [.xs3, .xs2, .xs, .sm, .md, .base, .lg, .xl, .xl2, .xl3]
}

extension Shadow {
  public static let md = Shadow(color: .black.opacity(0.08), radius: 6, x: 2, y: 4)
  public static let lg = Shadow(color: .black.opacity(0.12), radius: 12, y: 4)
}
```

4. Copy the source and every file it uses:

```swift title="swift/Interactions/SectionIndex.swift"
import SwiftUI

struct SectionIndexItem: Equatable, Sendable {
  let key: String
  let label: String
}

enum SectionIndexMath {
  static let letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".map(String.init) + ["#"]
  static let rowHeight: CGFloat = 16

  static func capacity(height: CGFloat) -> Int {
    max(0, Int(((height - rowHeight) / rowHeight).rounded(.down)))
  }

  static func displayItems(_ letters: [String], capacity: Int) -> [SectionIndexItem] {
    guard capacity < letters.count, letters.count > 1 else {
      return letters.map { SectionIndexItem(key: $0, label: $0) }
    }
    let slots = max(3, capacity % 2 == 0 ? capacity - 1 : capacity)
    func letter(at slot: Int) -> String {
      letters[Int((Double(slot) / Double(slots - 1) * Double(letters.count - 1)).rounded())]
    }
    return (0..<slots).map { slot in
      slot % 2 == 0
        ? SectionIndexItem(key: letter(at: slot), label: letter(at: slot))
        : SectionIndexItem(key: "after-\(letter(at: slot - 1))", label: "•")
    }
  }

  static func index(at y: CGFloat, height: CGFloat, count: Int) -> Int {
    guard count > 0, height > 0 else { return 0 }
    let fraction = min(max(y / height, 0), 0.9999)
    return Int((fraction * CGFloat(count)).rounded(.down))
  }

  static func merge(_ known: [String], _ seen: [String]) -> [String] {
    var result = known
    for value in seen where !result.contains(value) { result.append(value) }
    return result.enumerated().sorted { lhs, rhs in
      let left = letters.firstIndex(of: lhs.element) ?? letters.count
      let right = letters.firstIndex(of: rhs.element) ?? letters.count
      return left == right ? lhs.offset < rhs.offset : left < right
    }.map(\.element)
  }

  static func target(sections: [String], letters: [String], index: Int) -> String? {
    sections.first { value in
      guard let position = letters.firstIndex(of: value) else { return false }
      return position >= index
    } ?? sections.last
  }
}

struct SectionIndexContext: @unchecked Sendable {
  var sections: [String] = []
  var jump: @MainActor @Sendable (String) -> Void = { _ in }
}

extension EnvironmentValues {
  @Entry var sectionIndex = SectionIndexContext()
}

struct SectionIndexSectionsKey: PreferenceKey {
  static var defaultValue: [String] { [] }

  static func reduce(value: inout [String], nextValue: () -> [String]) {
    value.append(contentsOf: nextValue())
  }
}

public struct SectionIndex<Content: View>: View {
  let known: [String]?
  let content: Content

  @State private var sections: [String] = []

  public init(sections: [String]? = nil, @ViewBuilder content: () -> Content) {
    self.known = sections
    self.content = content()
  }

  public var body: some View {
    ScrollViewReader { proxy in
      let context = SectionIndexContext(sections: known ?? sections) { value in
        proxy.scrollTo(value, anchor: .top)
      }
      ZStack(alignment: .trailing) {
        content
      }
      .environment(\.sectionIndex, context)
    }
    .onPreferenceChange(SectionIndexSectionsKey.self) { value in sections = SectionIndexMath.merge(sections, value) }
  }
}

public struct SectionIndexSection<Content: View, Header: View>: View {
  let value: String
  let content: Content
  let header: Header

  public init(value: String, @ViewBuilder content: () -> Content, @ViewBuilder header: () -> Header) {
    self.value = value
    self.content = content()
    self.header = header()
  }

  public var body: some View {
    Section {
      content
    } header: {
      header
        .id(value)
        .preference(key: SectionIndexSectionsKey.self, value: [value])
    }
  }
}

extension SectionIndexSection where Header == SectionIndexHeader {
  public init(_ value: String, @ViewBuilder content: () -> Content) {
    self.init(value: value, content: content) { SectionIndexHeader(verbatim: value) }
  }
}

public struct SectionIndexHeader: View {
  let title: Text

  @Environment(\.screenBackground) private var background

  public init(_ title: LocalizedStringKey) {
    self.title = Text(title)
  }

  public init(verbatim title: String) {
    self.title = Text(verbatim: title)
  }

  public var body: some View {
    title
      .scaledFont(.sm, weight: .semibold)
      .foregroundStyle(Color.labelSecondary)
      .padding(.horizontal, 16)
      .padding(.vertical, 6)
      .frame(maxWidth: .infinity, alignment: .leading)
      .background(background.opacity(0.95))
      .accessibilityAddTraits(.isHeader)
  }
}

public struct SectionIndexBar: View {
  let letters: [String]
  let onValueChange: ((String) -> Void)?

  @State private var current = 0
  @State private var drag: SectionIndexDrag?
  @State private var height: CGFloat = 0
  @State private var available: CGFloat = 0
  @Environment(\.sectionIndex) private var sectionIndex

  public init(letters: [String]? = nil, onValueChange: ((String) -> Void)? = nil) {
    self.letters = letters ?? SectionIndexMath.letters
    self.onValueChange = onValueChange
  }

  init(letters: [String]? = nil, dragging index: Int, at y: CGFloat) {
    self.letters = letters ?? SectionIndexMath.letters
    self.onValueChange = nil
    _current = State(initialValue: index)
    _drag = State(initialValue: SectionIndexDrag(index: index, y: y))
  }

  public var body: some View {
    let capacity = available > 0 ? SectionIndexMath.capacity(height: available) : letters.count
    let items = SectionIndexMath.displayItems(letters, capacity: capacity)
    VStack(spacing: 0) {
      ForEach(items, id: \.key) { item in
        Text(verbatim: item.label)
          .font(TextStyle.xs3.font(weight: .semibold))
          .foregroundStyle(Color.link)
          .frame(minWidth: 12, minHeight: SectionIndexMath.rowHeight, maxHeight: SectionIndexMath.rowHeight)
      }
    }
    .padding(.horizontal, 6)
    .onGeometryChange(for: CGFloat.self) { $0.size.height } action: { height = $0 }
    .padding(.leading, 12)
    .contentShape(Rectangle())
    .gesture(
      DragGesture(minimumDistance: 0, coordinateSpace: .local)
        .onChanged { value in track(value.location.y) }
        .onEnded { _ in drag = nil }
    )
    .overlay(alignment: .topLeading) {
      if let drag, letters.indices.contains(drag.index) {
        SectionIndexBubble(letter: letters[drag.index])
          .offset(x: -72, y: drag.y - 28)
          .transition(.scale(scale: 0.5).combined(with: .opacity))
      }
    }
    .animation(.timingCurve(0.32, 0.72, 0, 1, duration: 0.2), value: drag == nil)
    .hapticFeedback(.selection, trigger: drag?.index) { old, new in HapticMoments.lifted(old, new) }
    .frame(maxHeight: .infinity)
    .padding(.vertical, 8)
    .padding(.trailing, 6)
    .onGeometryChange(for: CGFloat.self) { $0.size.height - 16 } action: { available = $0 }
    .accessibilityElement(children: .ignore)
    .accessibilityLabel(Text("Section index"))
    .accessibilityValue(Text(verbatim: letters.indices.contains(current) ? letters[current] : ""))
    .accessibilityAdjustableAction { direction in
      switch direction {
      case .increment: jump(min(current + 1, letters.count - 1))
      case .decrement: jump(max(current - 1, 0))
      @unknown default: break
      }
    }
  }

  private func track(_ y: CGFloat) {
    let index = SectionIndexMath.index(at: y, height: height, count: letters.count)
    let clamped = min(max(y, 0), height)
    let first = drag == nil
    drag = SectionIndexDrag(index: index, y: clamped)
    if index != current || first { jump(index) }
  }

  private func jump(_ index: Int) {
    current = index
    guard let target = SectionIndexMath.target(sections: sectionIndex.sections, letters: letters, index: index) else { return }
    sectionIndex.jump(target)
    if letters.indices.contains(index) { onValueChange?(letters[index]) }
  }
}

struct SectionIndexDrag: Equatable {
  let index: Int
  let y: CGFloat
}

private struct SectionIndexBubble: View {
  let letter: String

  var body: some View {
    Text(verbatim: letter)
      .font(TextStyle.xl2.font(weight: .semibold))
      .foregroundStyle(Color.label)
      .frame(width: 56, height: 56)
      .background(Circle().fill(Color.surfaceRaised).shadow(.lg))
      .overlay(Circle().strokeBorder(Color.separator))
      .allowsHitTesting(false)
      .accessibilityHidden(true)
  }
}
```

```swift title="swift/Components/Button.swift"
import SwiftUI

public struct VariantButtonStyle: ButtonStyle {
  public enum Variant: CaseIterable, Sendable {
    case `default`, outline, secondary, tinted, ghost, plain, destructive, link
  }

  public enum Size: CaseIterable, Sendable {
    case `default`, xs, sm, lg, xl, icon, iconXs, iconSm, iconLg, iconXl

    var height: CGFloat {
      switch self {
      case .xs, .iconXs: 24
      case .sm, .iconSm: 32
      case .default, .icon: 36
      case .lg, .iconLg: 44
      case .xl, .iconXl: 56
      }
    }

    var horizontalPadding: CGFloat {
      switch self {
      case .xs: 11
      case .sm: 12
      case .default: 16
      case .lg: 22
      case .xl: 31
      case .icon, .iconXs, .iconSm, .iconLg, .iconXl: 0
      }
    }

    var spacing: CGFloat {
      switch self {
      case .xs, .sm, .iconXs, .iconSm: 4
      case .xl, .iconXl: 8
      default: 6
      }
    }

    var textStyle: TextStyle {
      switch self {
      case .xs, .iconXs: .xs2
      case .lg, .xl: .base
      default: .sm
      }
    }

    public var iconSize: CGFloat {
      switch self {
      case .xs, .iconXs: 12
      default: 16
      }
    }

    var blockRadius: CGFloat {
      switch self {
      case .xs, .iconXs: Radius.sm
      case .lg, .iconLg: Radius.lg
      case .xl, .iconXl: Radius.xl
      default: Radius.md
      }
    }

    var isIcon: Bool {
      switch self {
      case .icon, .iconXs, .iconSm, .iconLg, .iconXl: true
      default: false
      }
    }
  }

  let variant: Variant
  let size: Size
  let block: Bool
  var metrics: ButtonMetrics?

  public init(_ variant: Variant = .default, size: Size = .default, block: Bool = false) {
    self.variant = variant
    self.size = size
    self.block = block
  }

  init(_ variant: Variant, size: Size, metrics: ButtonMetrics) {
    self.variant = variant
    self.size = size
    self.block = false
    self.metrics = metrics
  }

  public func makeBody(configuration: Configuration) -> some View {
    StyledButton(configuration: configuration, variant: variant, size: size, block: block, metrics: metrics)
  }
}

struct ButtonMetrics: Sendable {
  var horizontalPadding: CGFloat
  var spacing: CGFloat
  var iconSize: CGFloat
  var textStyle: TextStyle
}

private struct StyledButton: View {
  let configuration: ButtonStyleConfiguration
  let variant: VariantButtonStyle.Variant
  let size: VariantButtonStyle.Size
  let block: Bool
  let metrics: ButtonMetrics?

  @Environment(\.colorScheme) private var colorScheme
  @Environment(\.isEnabled) private var isEnabled
  @Environment(\.buttonGroup) private var group

  var body: some View {
    let joined = group != nil && variant != .ghost && variant != .plain
    let rounded = RoundedRectangle(
      cornerRadius: block ? size.blockRadius : Radius.full,
      style: .continuous
    )
    let shape = joined ? AnyShape(Rectangle()) : AnyShape(rounded)
    configuration.label
      .labelStyle(ButtonLabelStyle(spacing: metrics?.spacing ?? size.spacing, iconSize: metrics?.iconSize ?? size.iconSize))
    .font((metrics?.textStyle ?? size.textStyle).font())
    .tracking((metrics?.textStyle ?? size.textStyle).letterSpacing)
    .underline(variant == .link && pressed && isEnabled)
    .lineLimit(1)
    .foregroundStyle(foreground)
    .padding(.horizontal, metrics?.horizontalPadding ?? size.horizontalPadding)
    .frame(width: size.isIcon && !block ? size.height : nil, height: size.height)
    .frame(maxWidth: block || group == .vertical ? .infinity : nil)
    .background(background, in: shape)
    .overlay {
      if variant == .outline && !joined {
        rounded.strokeBorder(Color.separator)
      }
    }
    .contentShape(shape)
    .anchorPreference(key: ButtonGroupFramesKey.self, value: .bounds) { anchor in
      joined ? [ButtonGroupFrame(bounds: anchor, outlined: variant == .outline)] : []
    }
  }

  private var isDark: Bool { colorScheme == .dark }
  private var pressed: Bool { configuration.isPressed }

  private var foreground: Color {
    switch variant {
    case .default:
      .onAccent
    case .outline, .secondary, .ghost:
      isEnabled ? .label : .labelQuaternary
    case .tinted, .plain:
      isEnabled ? .link : .link.opacity(0.4)
    case .destructive:
      isEnabled ? .danger : .danger.opacity(0.4)
    case .link:
      isEnabled ? .link : .labelQuaternary
    }
  }

  private var background: Color {
    switch variant {
    case .default:
      !isEnabled ? .accentDisabled : pressed ? .accentPressed : .accent
    case .outline:
      isEnabled && pressed ? .itemPressed : isDark ? .clear : .surface
    case .secondary:
      !isEnabled ? .controlDisabled : pressed ? .controlPressed : .control
    case .tinted:
      isEnabled && pressed ? .accentSurfacePressed : .accentSurface
    case .ghost:
      isEnabled && pressed ? .itemPressed : .clear
    case .plain:
      isEnabled && pressed ? .itemPressed : .clear
    case .destructive:
      isEnabled && pressed ? .dangerSurfacePressed : .dangerSurface
    case .link:
      .clear
    }
  }
}

struct ButtonLabelStyle: LabelStyle {
  let spacing: CGFloat
  let iconSize: CGFloat

  func makeBody(configuration: Configuration) -> some View {
    HStack(spacing: spacing) {
      configuration.icon
        .frame(width: iconSize, height: iconSize)
      configuration.title
    }
  }
}

extension ButtonStyle where Self == VariantButtonStyle {
  public static func variant(
    _ variant: VariantButtonStyle.Variant = .default,
    size: VariantButtonStyle.Size = .default,
    block: Bool = false
  ) -> VariantButtonStyle {
    VariantButtonStyle(variant, size: size, block: block)
  }
}
```

```swift title="swift/Components/ButtonGroup.swift"
import SwiftUI

extension EnvironmentValues {
  @Entry var buttonGroup: Axis? = nil
  @Entry var buttonGroupSize: CGSize = .zero
}

enum ButtonGroupSpace: Hashable {
  case group
}

struct ButtonGroupFrame {
  let bounds: Anchor<CGRect>
  let outlined: Bool
}

struct ButtonGroupFramesKey: PreferenceKey {
  static var defaultValue: [ButtonGroupFrame] { [] }

  static func reduce(value: inout [ButtonGroupFrame], nextValue: () -> [ButtonGroupFrame]) {
    value.append(contentsOf: nextValue())
  }
}

struct ButtonGroupNestedKey: PreferenceKey {
  static var defaultValue: Bool { false }

  static func reduce(value: inout Bool, nextValue: () -> Bool) {
    value = value || nextValue()
  }
}

public struct ButtonGroup<Content: View>: View {
  let orientation: Axis
  let content: Content

  @State private var nested = false
  @State private var size: CGSize = .zero

  public init(orientation: Axis = .horizontal, @ViewBuilder content: () -> Content) {
    self.orientation = orientation
    self.content = content()
  }

  public var body: some View {
    let shape = orientation == .horizontal
      ? AnyShape(Capsule())
      : AnyShape(RoundedRectangle(cornerRadius: Radius.xl2, style: .continuous))
    stack
      .coordinateSpace(.named(ButtonGroupSpace.group))
      .onGeometryChange(for: CGSize.self) { $0.size } action: { size = $0 }
      .environment(\.buttonGroup, nested ? nil : orientation)
      .environment(\.buttonGroupSize, size)
      .onPreferenceChange(ButtonGroupNestedKey.self) { nested = $0 }
      .modifier(ButtonGroupClip(shape: nested ? nil : shape))
      .overlayPreferenceValue(ButtonGroupFramesKey.self) { frames in
        if !nested {
          GeometryReader { proxy in
            outline(frames.map { (proxy[$0.bounds], $0.outlined) }, shape: shape)
          }
        }
      }
      .transformPreference(ButtonGroupFramesKey.self) { $0 = [] }
      .transformPreference(ButtonGroupNestedKey.self) { $0 = true }
      .fixedSize(horizontal: orientation == .vertical, vertical: orientation == .horizontal)
      .accessibilityElement(children: .contain)
  }

  @ViewBuilder private var stack: some View {
    switch orientation {
    case .horizontal:
      HStack(spacing: nested ? 8 : 0) { content }
    case .vertical:
      VStack(spacing: nested ? 8 : 0) { content }
    }
  }

  @ViewBuilder private func outline(_ frames: [(CGRect, Bool)], shape: AnyShape) -> some View {
    if frames.contains(where: \.1) {
      ZStack(alignment: .topLeading) {
        shape
          .stroke(Color.separator, lineWidth: 1)
          .padding(0.5)
          .mask {
            Path { path in
              for (rect, outlined) in frames where outlined {
                path.addRect(rect)
              }
            }
          }
        ForEach(Array(frames.dropLast().enumerated()), id: \.offset) { _, frame in
          if frame.1 {
            divider(frame.0)
          }
        }
      }
      .clipShape(shape)
      .allowsHitTesting(false)
    }
  }

  private func divider(_ rect: CGRect) -> some View {
    let horizontal = orientation == .horizontal
    return Rectangle()
      .fill(Color.separator)
      .frame(width: horizontal ? 1 : rect.width, height: horizontal ? rect.height : 1)
      .position(
        x: horizontal ? rect.maxX - 0.5 : rect.midX,
        y: horizontal ? rect.midY : rect.maxY - 0.5
      )
  }
}

struct ButtonGroupItem<Content: View>: View {
  let radius: CGFloat
  let content: (UnevenRoundedRectangle) -> Content

  @State private var frame: CGRect = .zero
  @Environment(\.buttonGroup) private var group
  @Environment(\.buttonGroupSize) private var groupSize

  init(radius: CGFloat, @ViewBuilder content: @escaping (UnevenRoundedRectangle) -> Content) {
    self.radius = radius
    self.content = content
  }

  var body: some View {
    if let group {
      content(shape(group))
        .onGeometryChange(for: CGRect.self) { $0.frame(in: .named(ButtonGroupSpace.group)) } action: { frame = $0 }
    } else {
      content(UnevenRoundedRectangle(cornerRadii: RectangleCornerRadii(
        topLeading: radius,
        bottomLeading: radius,
        bottomTrailing: radius,
        topTrailing: radius
      ), style: .continuous))
    }
  }

  private func shape(_ group: Axis) -> UnevenRoundedRectangle {
    let horizontal = group == .horizontal
    let first = horizontal ? frame.minX <= 0.5 : frame.minY <= 0.5
    let last = horizontal
      ? frame.maxX >= groupSize.width - 0.5
      : frame.maxY >= groupSize.height - 0.5
    let round = horizontal ? frame.height / 2 : Radius.xl2
    let start: CGFloat = first ? round : 0
    let end: CGFloat = last ? round : 0
    let radii = horizontal
      ? RectangleCornerRadii(topLeading: start, bottomLeading: start, bottomTrailing: end, topTrailing: end)
      : RectangleCornerRadii(topLeading: start, bottomLeading: end, bottomTrailing: end, topTrailing: start)
    return UnevenRoundedRectangle(cornerRadii: radii, style: .continuous)
  }
}

private struct ButtonGroupClip: ViewModifier {
  let shape: AnyShape?

  func body(content: Content) -> some View {
    if let shape {
      content.clipShape(shape)
    } else {
      content
    }
  }
}

public struct ButtonGroupText<Content: View>: View {
  let content: Content

  @Environment(\.buttonGroup) private var group

  public init(@ViewBuilder content: () -> Content) {
    self.content = content()
  }

  public var body: some View {
    let shape = group == nil ? AnyShape(Capsule()) : AnyShape(Rectangle())
    HStack(spacing: 8) {
      content
    }
    .labelStyle(ButtonLabelStyle(spacing: 8, iconSize: 16))
    .scaledFont(.sm)
    .lineLimit(1)
    .foregroundStyle(Color.label)
    .padding(.horizontal, 10)
    .frame(minHeight: 36)
    .frame(maxWidth: group == .vertical ? .infinity : nil, maxHeight: group == .horizontal ? .infinity : nil)
    .background(Color.control, in: shape)
    .anchorPreference(key: ButtonGroupFramesKey.self, value: .bounds) { anchor in
      group == nil ? [] : [ButtonGroupFrame(bounds: anchor, outlined: false)]
    }
  }
}

extension ButtonGroupText where Content == Text {
  public init(_ title: LocalizedStringKey) {
    self.init { Text(title) }
  }

  public init(verbatim title: String) {
    self.init { Text(verbatim: title) }
  }
}

public struct ButtonGroupSeparator: View {
  let orientation: Axis

  public init(_ orientation: Axis = .vertical) {
    self.orientation = orientation
  }

  public var body: some View {
    let vertical = orientation == .vertical
    Rectangle()
      .fill(Color.label.opacity(0.2))
      .frame(width: vertical ? 1 : nil, height: vertical ? nil : 1)
      .padding(vertical ? .vertical : .horizontal, 9)
      .frame(maxWidth: vertical ? nil : .infinity, maxHeight: vertical ? .infinity : nil)
      .padding(vertical ? .trailing : .bottom, -1)
      .zIndex(1)
      .accessibilityHidden(true)
  }
}
```

```swift title="swift/Components/Checkbox.swift"
import PhosphorSwift
import SwiftUI

extension Shadow {
  static let control = Shadow(color: .black.opacity(0.08), radius: 0.5, y: 0.5)
  static let thumb = Shadow(color: .black.opacity(0.12), radius: 1.5, y: 1)
}

struct SelectionIndicator<Mark: View>: View {
  let checked: Bool
  let pressed: Bool
  let cornerRadius: CGFloat
  let mark: Mark

  @Environment(\.isEnabled) private var isEnabled
  @Environment(\.isInvalid) private var invalid
  @Environment(\.colorScheme) private var colorScheme

  init(checked: Bool, pressed: Bool, cornerRadius: CGFloat, @ViewBuilder mark: () -> Mark) {
    self.checked = checked
    self.pressed = pressed
    self.cornerRadius = cornerRadius
    self.mark = mark()
  }

  var body: some View {
    let shape = RoundedRectangle(cornerRadius: cornerRadius, style: .continuous)
    ZStack {
      shape.fill(fill)
      shape.strokeBorder(border, lineWidth: 1)
      if checked {
        mark
      }
    }
    .frame(width: 16, height: 16)
    .shadow(raised ? .control : Shadow(color: .clear, radius: 0))
  }

  private var isDark: Bool { colorScheme == .dark }

  private var raised: Bool { !checked && isEnabled && !isDark }

  private var fill: Color {
    if checked {
      return !isEnabled ? .accentDisabled : pressed ? .accentPressed : .accent
    }
    if !isEnabled { return .controlDisabled }
    if isDark { return pressed ? .labelTertiary.opacity(0.6) : .labelQuaternary }
    return pressed ? .control : .surface
  }

  private var border: Color {
    if checked {
      return !isEnabled ? .clear : pressed ? .accentPressed : .accent
    }
    if !isEnabled { return isDark ? .clear : .label.opacity(0.1) }
    if invalid { return .danger }
    return isDark ? .clear : .label.opacity(0.25)
  }
}

struct PressReader<Content: View>: ButtonStyle {
  let content: (Bool) -> Content

  init(@ViewBuilder content: @escaping (Bool) -> Content) {
    self.content = content
  }

  func makeBody(configuration: Configuration) -> some View {
    content(configuration.isPressed)
  }
}

public struct CheckboxStyle: ToggleStyle {
  public init() {}

  public func makeBody(configuration: Configuration) -> some View {
    HapticButton(style: PressReader { pressed in
      HStack(spacing: 12) {
        SelectionIndicator(
          checked: configuration.isOn || configuration.isMixed,
          pressed: pressed,
          cornerRadius: 4
        ) {
          (configuration.isMixed ? Ph.minus.regular : Ph.check.regular)
            .frame(width: 14, height: 14)
            .foregroundStyle(Color.onAccent)
        }
        configuration.label
      }
      .contentShape(Rectangle().inset(by: -8))
    }) {
      configuration.isOn.toggle()
      return true
    }
    .accessibilityElement(children: .combine)
    .accessibilityRemoveTraits(.isButton)
    .accessibilityAddTraits(.isToggle)
    .accessibilityValue(
      configuration.isMixed
        ? Text("Mixed")
        : configuration.isOn ? Text("Checked") : Text("Unchecked")
    )
  }
}

extension ToggleStyle where Self == CheckboxStyle {
  public static var checkbox: CheckboxStyle { CheckboxStyle() }
}
```

```swift title="swift/Components/Field.swift"
import SwiftUI

extension EnvironmentValues {
  @Entry public var isInvalid = false
  @Entry var fieldInset = false
  @Entry var fieldGroupInset = false
  @Entry var fieldSetInset = false
}

extension View {
  public func invalid(_ isInvalid: Bool = true) -> some View {
    environment(\.isInvalid, isInvalid)
  }
}

public enum FieldOrientation: CaseIterable, Sendable {
  case vertical, horizontal
}

public struct Field<Content: View>: View {
  let orientation: FieldOrientation
  let invalid: Bool?
  let content: Content

  @Environment(\.fieldGroupInset) private var inset
  @Environment(\.isInvalid) private var inheritedInvalid

  public init(
    orientation: FieldOrientation = .vertical,
    invalid: Bool? = nil,
    @ViewBuilder content: () -> Content
  ) {
    self.orientation = orientation
    self.invalid = invalid
    self.content = content()
  }

  public var body: some View {
    Group {
      switch orientation {
      case .vertical:
        VStack(alignment: .leading, spacing: 12) { content }
      case .horizontal:
        HStack(alignment: .center, spacing: 12) { content }
      }
    }
    .frame(maxWidth: .infinity, alignment: .leading)
    .padding(.horizontal, inset ? 16 : 0)
    .padding(.vertical, inset ? 6 : 0)
    .frame(minHeight: inset ? 44 : nil)
    .overlay(alignment: .top) {
      if inset {
        Color.separator
          .frame(height: 1)
          .padding(.leading, 16)
          .offset(y: -1)
      }
    }
    .environment(\.fieldInset, inset)
    .environment(\.fieldGroupInset, false)
    .environment(\.isInvalid, invalid ?? inheritedInvalid)
  }
}

public struct FieldContent<Content: View>: View {
  let content: Content

  public init(@ViewBuilder content: () -> Content) {
    self.content = content()
  }

  public var body: some View {
    VStack(alignment: .leading, spacing: 4) {
      content
    }
    .frame(maxWidth: .infinity, alignment: .leading)
  }
}

public struct FieldTitle: View {
  let text: Text

  @Environment(\.isEnabled) private var isEnabled

  public init(_ title: LocalizedStringKey) {
    text = Text(title)
  }

  public init<S: StringProtocol>(_ title: S) {
    text = Text(title)
  }

  public var body: some View {
    text
      .scaledTextStyle(.base, weight: .semibold)
      .foregroundStyle(isEnabled ? Color.label : .labelQuaternary)
  }
}

public struct FieldDescription: View {
  let text: Text

  @Environment(\.fieldSetInset) private var inset

  public init(_ description: LocalizedStringKey) {
    text = Text(description)
  }

  public init<S: StringProtocol>(_ description: S) {
    text = Text(description)
  }

  public var body: some View {
    text
      .scaledTextStyle(inset ? .xs : .sm)
      .foregroundStyle(Color.labelSecondary)
      .multilineTextAlignment(.leading)
      .fixedSize(horizontal: false, vertical: true)
      .padding(.leading, inset ? 16 : 0)
  }
}

public struct FieldError: View {
  let messages: [String]
  let text: Text?

  public init(_ message: LocalizedStringKey) {
    messages = []
    text = Text(message)
  }

  public init(errors: [String?]) {
    var seen = Set<String>()
    messages = errors.compactMap { $0 }.filter { !$0.isEmpty && seen.insert($0).inserted }
    text = nil
  }

  public var body: some View {
    if let content {
      content
        .scaledTextStyle(.sm)
        .foregroundStyle(Color.danger)
        .multilineTextAlignment(.leading)
        .fixedSize(horizontal: false, vertical: true)
    }
  }

  private var content: Text? {
    if let text { return text }
    switch messages.count {
    case 0: return nil
    case 1: return Text(verbatim: messages[0])
    default: return Text(verbatim: messages.map { "\u{2022} \($0)" }.joined(separator: "\n"))
    }
  }
}

public enum FieldGroupVariant: CaseIterable, Sendable {
  case `default`, inset
}

public struct FieldGroup<Content: View>: View {
  let variant: FieldGroupVariant
  let content: Content

  public init(_ variant: FieldGroupVariant = .default, @ViewBuilder content: () -> Content) {
    self.variant = variant
    self.content = content()
  }

  public var body: some View {
    styled
      .environment(\.fieldGroupInset, variant == .inset)
      .environment(\.fieldSetInset, false)
      .transformPreference(FieldSetInsetKey.self) { $0 = variant == .inset }
  }

  @ViewBuilder private var styled: some View {
    let stack = VStack(alignment: .leading, spacing: variant == .inset ? 0 : 28) {
      content
    }
    .frame(maxWidth: .infinity, alignment: .leading)
    if variant == .inset {
      let shape = RoundedRectangle(cornerRadius: Radius.xl2, style: .continuous)
      stack
        .background(Color.surfaceSecondary, in: shape)
        .clipShape(shape)
    } else {
      stack
    }
  }
}

struct FieldSetInsetKey: PreferenceKey {
  static let defaultValue = false

  static func reduce(value: inout Bool, nextValue: () -> Bool) {
    value = value || nextValue()
  }
}

public struct FieldSet<Content: View>: View {
  let content: Content

  @State private var inset = false

  public init(@ViewBuilder content: () -> Content) {
    self.content = content()
  }

  public var body: some View {
    VStack(alignment: .leading, spacing: inset ? 8 : 24) {
      content
    }
    .frame(maxWidth: .infinity, alignment: .leading)
    .environment(\.fieldSetInset, inset)
    .onPreferenceChange(FieldSetInsetKey.self) { inset = $0 }
    .transformPreference(FieldSetInsetKey.self) { $0 = false }
    .accessibilityElement(children: .contain)
  }
}

public struct FieldLegend: View {
  public enum Variant: CaseIterable, Sendable {
    case legend, label
  }

  let text: Text
  let variant: Variant

  @Environment(\.fieldSetInset) private var inset
  @Environment(\.isEnabled) private var isEnabled

  public init(_ title: LocalizedStringKey, variant: Variant = .legend) {
    text = Text(title)
    self.variant = variant
  }

  public init<S: StringProtocol>(_ title: S, variant: Variant = .legend) {
    text = Text(title)
    self.variant = variant
  }

  public var body: some View {
    Group {
      if inset {
        text
          .textCase(.uppercase)
          .scaledTextStyle(.xs)
          .foregroundStyle(isEnabled ? Color.labelSecondary : .labelQuaternary)
          .padding(.leading, 16)
      } else {
        text
          .scaledTextStyle(.base, weight: .semibold)
          .foregroundStyle(isEnabled ? Color.label : .labelQuaternary)
          .padding(.bottom, 12)
      }
    }
    .accessibilityAddTraits(variant == .legend ? .isHeader : [])
  }
}

public struct FieldSeparator<Content: View>: View {
  let content: Content

  public init(@ViewBuilder content: () -> Content) {
    self.content = content()
  }

  public var body: some View {
    ZStack {
      Separator()
      content
        .scaledTextStyle(.sm)
        .foregroundStyle(Color.labelSecondary)
        .padding(.horizontal, 8)
        .background(Color.surface)
    }
    .frame(minHeight: 20)
    .padding(.vertical, -8)
  }
}

extension FieldSeparator where Content == EmptyView {
  public init() {
    self.init { EmptyView() }
  }
}

extension FieldSeparator where Content == Text {
  public init(_ title: LocalizedStringKey) {
    self.init { Text(title) }
  }
}
```

```swift title="swift/Components/Haptics.swift"
import SwiftUI

extension EnvironmentValues {
  @Entry public var hapticsEnabled = true
}

extension View {
  public func haptics(_ enabled: Bool) -> some View {
    environment(\.hapticsEnabled, enabled)
  }

  func hapticFeedback<Trigger: Equatable>(_ feedback: SensoryFeedback, trigger: Trigger) -> some View {
    modifier(HapticFeedbackModifier(feedback: feedback, trigger: trigger) { _, _ in true })
  }

  func hapticFeedback<Trigger: Equatable>(
    _ feedback: SensoryFeedback,
    trigger: Trigger,
    condition: @escaping (Trigger, Trigger) -> Bool
  ) -> some View {
    modifier(HapticFeedbackModifier(feedback: feedback, trigger: trigger, condition: condition))
  }
}

private struct HapticFeedbackModifier<Trigger: Equatable>: ViewModifier {
  let feedback: SensoryFeedback
  let trigger: Trigger
  let condition: (Trigger, Trigger) -> Bool

  @Environment(\.hapticsEnabled) private var enabled

  func body(content: Content) -> some View {
    let enabled = enabled
    let condition = condition
    content.sensoryFeedback(feedback, trigger: trigger) { old, new in
      enabled && condition(old, new)
    }
  }
}

enum HapticMoments {
  static func step(_ value: Double, bounds: ClosedRange<Double>, step: Double?) -> Int? {
    guard let step, step > 0 else { return nil }
    return Int(((value - bounds.lowerBound) / step).rounded())
  }

  static func lifted<Value: Equatable>(_ old: Value?, _ new: Value?) -> Bool {
    new != nil && old != new
  }

  static func crossed<Value: Equatable>(_ old: Value?, _ new: Value?) -> Bool {
    old == nil && new != nil
  }

  static func moved(_ old: Int?, _ new: Int?) -> Bool {
    guard let old, let new else { return false }
    return old != new
  }
}

struct HapticButton<Style: ButtonStyle>: View {
  let feedback: SensoryFeedback
  let action: () -> Bool
  let style: Style

  @State private var count = 0

  init(_ feedback: SensoryFeedback = .selection, style: Style, action: @escaping () -> Bool) {
    self.feedback = feedback
    self.style = style
    self.action = action
  }

  var body: some View {
    Button {
      if action() { count += 1 }
    } label: {
      EmptyView()
    }
    .buttonStyle(style)
    .hapticFeedback(feedback, trigger: count)
  }
}
```

```swift title="swift/Components/Header.swift"
import PhosphorSwift
import SwiftUI

extension EnvironmentValues {
  @Entry var headerProgress: CGFloat?
  @Entry var headerReport: ((CGFloat) -> Void)?
}

enum HeaderMath {
  static func progress(minY: CGFloat, height: CGFloat) -> CGFloat {
    guard height > 0 else { return 0 }
    return min(max(-minY / height, 0), 1)
  }
}

public struct Header<Title: View, Leading: View, Trailing: View>: View {
  let title: Title
  let leading: Leading
  let trailing: Trailing

  @Environment(\.headerProgress) private var progress
  @Environment(\.screenBackground) private var background

  public init(
    @ViewBuilder title: () -> Title,
    @ViewBuilder leading: () -> Leading,
    @ViewBuilder trailing: () -> Trailing
  ) {
    self.title = title()
    self.leading = leading()
    self.trailing = trailing()
  }

  public var body: some View {
    HeaderLayout {
      HStack(spacing: 0) { leading }
        .frame(maxHeight: .infinity)
      ZStack { title }
        .frame(maxWidth: .infinity, maxHeight: .infinity)
      HStack(spacing: 0) { trailing }
        .frame(maxHeight: .infinity)
    }
    .padding(.horizontal, 8)
    .frame(height: 44)
    .frame(maxWidth: .infinity)
    .background(background.ignoresSafeArea(.container, edges: .top))
    .overlay(alignment: .bottom) {
      Color.separator
        .frame(height: 1)
        .opacity(progress ?? 0)
    }
    .accessibilityElement(children: .contain)
    .accessibilityAddTraits(.isHeader)
  }
}

extension Header where Leading == EmptyView {
  public init(@ViewBuilder title: () -> Title, @ViewBuilder trailing: () -> Trailing) {
    self.init(title: title, leading: { EmptyView() }, trailing: trailing)
  }
}

extension Header where Trailing == EmptyView {
  public init(@ViewBuilder title: () -> Title, @ViewBuilder leading: () -> Leading) {
    self.init(title: title, leading: leading, trailing: { EmptyView() })
  }
}

extension Header where Leading == EmptyView, Trailing == EmptyView {
  public init(@ViewBuilder title: () -> Title) {
    self.init(title: title, leading: { EmptyView() }, trailing: { EmptyView() })
  }
}

struct HeaderLayout: Layout {
  var spacing: CGFloat = 8
  var minSide: CGFloat = 44

  func sizeThatFits(proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) -> CGSize {
    let ideal = subviews.reduce(0) { $0 + $1.sizeThatFits(.unspecified).width }
    return CGSize(width: proposal.width ?? ideal, height: proposal.height ?? 44)
  }

  func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) {
    guard subviews.count == 3 else { return }
    let leading = subviews[0]
    let title = subviews[1]
    let trailing = subviews[2]
    let trailingWidth = trailing.sizeThatFits(.unspecified).width
    let leadingIdeal = leading.sizeThatFits(.unspecified).width
    let leadingMinimum = leading.sizeThatFits(ProposedViewSize(width: 0, height: nil)).width
    let reserve = max(minSide, trailingWidth, leadingMinimum) + spacing
    let titleWidth = max(0, min(title.sizeThatFits(.unspecified).width, bounds.width - reserve * 2))
    let side = max(0, (bounds.width - titleWidth) / 2 - spacing)
    let leadingProposal = ProposedViewSize(width: min(side, leadingIdeal), height: nil)
    let leadingWidth = leading.sizeThatFits(leadingProposal).width
    let titleInset = max(leadingWidth, trailingWidth) + spacing
    leading.place(
      at: CGPoint(x: bounds.minX, y: bounds.minY),
      anchor: .topLeading,
      proposal: ProposedViewSize(width: leadingProposal.width, height: bounds.height)
    )
    title.place(
      at: CGPoint(x: bounds.minX + titleInset, y: bounds.minY),
      anchor: .topLeading,
      proposal: ProposedViewSize(width: max(0, bounds.width - titleInset * 2), height: bounds.height)
    )
    trailing.place(
      at: CGPoint(x: bounds.maxX - trailingWidth, y: bounds.minY),
      anchor: .topLeading,
      proposal: ProposedViewSize(width: trailingWidth, height: bounds.height)
    )
  }
}

public struct HeaderTitle: View {
  let title: Text
  let subtitle: Text?

  @Environment(\.headerProgress) private var progress

  public init(_ title: LocalizedStringKey, subtitle: LocalizedStringKey? = nil) {
    self.title = Text(title)
    self.subtitle = subtitle.map { Text($0) }
  }

  public init(verbatim title: String, subtitle: String? = nil) {
    self.title = Text(verbatim: title)
    self.subtitle = subtitle.map { Text(verbatim: $0) }
  }

  public var body: some View {
    VStack(spacing: 0) {
      title
        .scaledFont(.base, weight: .semibold)
        .foregroundStyle(Color.label)
      if let subtitle {
        subtitle
          .scaledFont(.xs2)
          .foregroundStyle(Color.labelSecondary)
      }
    }
    .lineLimit(1)
    .multilineTextAlignment(.center)
    .opacity(progress ?? 1)
    .accessibilityElement(children: .combine)
    .accessibilityHidden((progress ?? 1) < 0.5)
  }
}

public struct HeaderLargeTitle: View {
  let title: Text
  let subtitle: Text?

  @Environment(\.headerReport) private var report

  public init(_ title: LocalizedStringKey, subtitle: LocalizedStringKey? = nil) {
    self.title = Text(title)
    self.subtitle = subtitle.map { Text($0) }
  }

  public init(verbatim title: String, subtitle: String? = nil) {
    self.title = Text(verbatim: title)
    self.subtitle = subtitle.map { Text(verbatim: $0) }
  }

  public var body: some View {
    VStack(alignment: .leading, spacing: 2) {
      title
        .scaledFont(.xl3, weight: .bold)
        .foregroundStyle(Color.label)
        .accessibilityAddTraits(.isHeader)
      if let subtitle {
        subtitle
          .scaledFont(.sm)
          .foregroundStyle(Color.labelSecondary)
      }
    }
    .lineLimit(2)
    .padding(.horizontal, 16)
    .padding(.top, 4)
    .padding(.bottom, 8)
    .frame(maxWidth: .infinity, alignment: .leading)
    .onGeometryChange(for: CGFloat.self) { proxy in
      HeaderMath.progress(minY: proxy.frame(in: .scrollView).minY, height: proxy.size.height)
    } action: { value in
      report?(value)
    }
  }
}

public struct HeaderBack: View {
  let label: Text?
  let action: (() -> Void)?

  @Environment(\.dismiss) private var dismiss
  @Environment(\.isEnabled) private var isEnabled

  public init(_ label: LocalizedStringKey? = nil, action: (() -> Void)? = nil) {
    self.label = label.map { Text($0) }
    self.action = action
  }

  public init(verbatim label: String, action: (() -> Void)? = nil) {
    self.label = Text(verbatim: label)
    self.action = action
  }

  public var body: some View {
    Button {
      if let action {
        action()
      } else {
        dismiss()
      }
    } label: {
      EmptyView()
    }
    .buttonStyle(PressReader { pressed in
      HStack(spacing: 2) {
        Ph.caretLeft.bold
          .frame(width: 20, height: 20)
          .flipsForRightToLeftLayoutDirection(true)
        if let label {
          label
            .scaledFont(.base)
            .lineLimit(1)
        }
      }
      .foregroundStyle(!isEnabled ? Color.labelQuaternary : pressed ? .link.opacity(0.4) : .link)
      .padding(.horizontal, 4)
      .frame(minWidth: 44, minHeight: 44, alignment: .leading)
      .contentShape(Rectangle())
    })
    .accessibilityLabel(label ?? Text("Back"))
  }
}

public struct HeaderActions<Content: View>: View {
  let content: Content

  public init(@ViewBuilder content: () -> Content) {
    self.content = content()
  }

  public var body: some View {
    HStack(spacing: 4) {
      content
    }
    .buttonStyle(.variant(.ghost, size: .icon))
  }
}

public struct HeaderScrollView<HeaderContent: View, Content: View>: View {
  let header: HeaderContent
  let content: Content

  @State private var progress: CGFloat?

  public init(@ViewBuilder content: () -> Content, @ViewBuilder header: () -> HeaderContent) {
    self.content = content()
    self.header = header()
  }

  public var body: some View {
    VStack(spacing: 0) {
      header
        .environment(\.headerProgress, progress)
        .zIndex(1)
      KeyboardScrollView {
        VStack(alignment: .leading, spacing: 0) {
          content
        }
      }
      .environment(\.headerReport) { value in
        if progress != value { progress = value }
      }
    }
  }
}
```

```swift title="swift/Components/KeyboardScrollView.swift"
import SwiftUI
import UIKit

public struct KeyboardScrollView<Content: View>: View {
  let showsIndicators: Bool
  let content: Content

  public init(showsIndicators: Bool = true, @ViewBuilder content: () -> Content) {
    self.showsIndicators = showsIndicators
    self.content = content()
  }

  public var body: some View {
    ScrollView(.vertical, showsIndicators: showsIndicators) {
      content
        .frame(maxWidth: .infinity, alignment: .topLeading)
        .background {
          Color.clear
            .contentShape(Rectangle())
            .onTapGesture { KeyboardScrollView.dismissKeyboard() }
        }
    }
    .scrollDismissesKeyboard(.interactively)
  }

  @MainActor
  static func dismissKeyboard() {
    UIApplication.shared.sendAction(#selector(UIResponder.resignFirstResponder), to: nil, from: nil, for: nil)
  }
}
```

```swift title="swift/Components/Screen.swift"
import SwiftUI

extension EnvironmentValues {
  @Entry var screenBackground: Color = .surface
}

public struct Screen<Content: View>: View {
  public enum Background: CaseIterable, Sendable {
    case surface, surfaceSecondary

    var color: Color {
      switch self {
      case .surface: .surface
      case .surfaceSecondary: .surfaceSecondary
      }
    }
  }

  let edges: Edge.Set
  let background: Background
  let content: Content

  public init(
    edges: Edge.Set = .all,
    background: Background = .surface,
    @ViewBuilder content: () -> Content
  ) {
    self.edges = edges
    self.background = background
    self.content = content()
  }

  public var body: some View {
    VStack(spacing: 0) {
      content
    }
    .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .top)
    .ignoresSafeArea(.container, edges: Edge.Set.all.subtracting(edges))
    .foregroundStyle(Color.label)
    .background(background.color.ignoresSafeArea())
    .environment(\.screenBackground, background.color)
  }
}

public struct ScreenContent<Content: View>: View {
  let scroll: Bool
  let padded: Bool
  let content: Content

  public init(scroll: Bool = true, padded: Bool = true, @ViewBuilder content: () -> Content) {
    self.scroll = scroll
    self.padded = padded
    self.content = content()
  }

  public var body: some View {
    if scroll {
      KeyboardScrollView {
        stack
      }
    } else {
      stack
        .frame(maxHeight: .infinity, alignment: .top)
    }
  }

  private var stack: some View {
    VStack(alignment: .leading, spacing: 16) {
      content
    }
    .padding(padded ? 16 : 0)
    .frame(maxWidth: .infinity, alignment: .leading)
  }
}
```

```swift title="swift/Components/Separator.swift"
import SwiftUI

public struct Separator: View {
  let orientation: Axis

  public init(_ orientation: Axis = .horizontal) {
    self.orientation = orientation
  }

  public var body: some View {
    Rectangle()
      .fill(Color.separator)
      .frame(width: orientation == .vertical ? 1 : nil, height: orientation == .horizontal ? 1 : nil)
      .frame(maxWidth: orientation == .horizontal ? .infinity : nil, maxHeight: orientation == .vertical ? .infinity : nil)
      .accessibilityHidden(true)
  }
}
```

```swift title="swift/Components/TextVariant.swift"
import SwiftUI

public enum TextVariant: CaseIterable, Sendable {
  case `default`, h1, h2, h3, h4, p, blockquote, code, lead, large, small, muted

  var style: TextStyle {
    switch self {
    case .h1: .xl3
    case .h2: .xl2
    case .h3: .xl
    case .h4, .lead, .large: .lg
    case .code, .small, .muted: .sm
    default: .base
    }
  }

  var weight: Font.Weight {
    switch self {
    case .h1, .h2: .bold
    case .h3, .h4, .large, .code: .semibold
    case .small: .medium
    default: .regular
    }
  }

  var color: Color {
    switch self {
    case .lead, .muted: .labelSecondary
    default: .label
    }
  }

  var isHeading: Bool {
    switch self {
    case .h1, .h2, .h3, .h4: true
    default: false
    }
  }
}

private struct TextVariantModifier: ViewModifier {
  let variant: TextVariant

  func body(content: Content) -> some View {
    switch variant {
    case .blockquote:
      styled(content)
        .italic()
        .padding(.leading, 12)
        .overlay(alignment: .leading) {
          Rectangle().fill(Color.separator).frame(width: 2)
        }
        .padding(.top, 16)
    case .code:
      styled(content)
        .monospaced()
        .padding(.horizontal, 4)
        .padding(.vertical, 2)
        .background(Color.surfaceSecondary, in: RoundedRectangle(cornerRadius: Radius.sm, style: .continuous))
    case .p:
      styled(content).padding(.top, 12)
    default:
      styled(content)
    }
  }

  private func styled(_ content: Content) -> some View {
    content
      .scaledTextStyle(variant.style, weight: variant.weight)
      .foregroundStyle(variant.color)
      .accessibilityAddTraits(variant.isHeading ? .isHeader : [])
  }
}

extension View {
  public func textVariant(_ variant: TextVariant) -> some View {
    modifier(TextVariantModifier(variant: variant))
  }
}

private struct ScaledTextStyleModifier: ViewModifier {
  let style: TextStyle
  let weight: Font.Weight

  @ScaledMetric(relativeTo: .body) private var scale: CGFloat = 1

  func body(content: Content) -> some View {
    let size = style.size * scale
    let lineSpacing = max(0, style.lineHeight * scale - UIFont.systemFont(ofSize: size).lineHeight)
    content
      .font(.system(size: size, weight: weight))
      .tracking(style.letterSpacing)
      .lineSpacing(lineSpacing)
      .padding(.vertical, lineSpacing / 2)
  }
}

extension View {
  func scaledTextStyle(_ style: TextStyle, weight: Font.Weight = .regular) -> some View {
    modifier(ScaledTextStyleModifier(style: style, weight: weight))
  }

  func scaledFont(_ style: TextStyle, weight: Font.Weight = .regular) -> some View {
    modifier(ScaledFontModifier(style: style, weight: weight))
  }
}

private struct ScaledFontModifier: ViewModifier {
  let style: TextStyle
  let weight: Font.Weight

  @ScaledMetric(relativeTo: .body) private var scale: CGFloat = 1

  func body(content: Content) -> some View {
    content
      .font(.system(size: style.size * scale, weight: weight))
      .tracking(style.letterSpacing)
  }
}
```

5. Add the files to your app target.

**Jetpack Compose**

1. Set `minSdk` to 24 or higher and add the dependencies:

```kotlin title="build.gradle.kts"
implementation(platform("androidx.compose:compose-bom:2026.09.00"))
implementation("androidx.compose.foundation:foundation")
implementation("androidx.compose.ui:ui")
```

2. Copy the theme files every view uses:

```kt title="kotlin/theme/Theme.kt"
package com.esuiss.ui.theme

import androidx.compose.foundation.isSystemInDarkTheme
import androidx.compose.runtime.Composable
import androidx.compose.runtime.CompositionLocalProvider
import androidx.compose.runtime.Immutable
import androidx.compose.runtime.staticCompositionLocalOf
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.dropShadow
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.graphics.Shape
import androidx.compose.ui.graphics.shadow.Shadow as DropShadow
import androidx.compose.ui.text.TextStyle
import androidx.compose.ui.text.style.LineHeightStyle
import androidx.compose.ui.unit.Dp
import androidx.compose.ui.unit.DpOffset
import androidx.compose.ui.unit.em
import androidx.compose.ui.unit.sp

internal fun textStyle(size: Double, lineHeight: Double, letterSpacing: Double) = TextStyle(
    fontSize = size.sp,
    lineHeight = lineHeight.sp,
    letterSpacing = letterSpacing.em,
    lineHeightStyle = LineHeightStyle(
        alignment = LineHeightStyle.Alignment.Center,
        trim = LineHeightStyle.Trim.None,
    ),
)

@Immutable
data class Shadow(
    val offsetX: Dp,
    val offsetY: Dp,
    val blur: Dp,
    val color: Color,
)

fun Modifier.shadow(shadow: Shadow, shape: Shape): Modifier = dropShadow(
    shape,
    DropShadow(
        radius = shadow.blur,
        color = shadow.color,
        offset = DpOffset(shadow.offsetX, shadow.offsetY),
    ),
)

val LocalColors = staticCompositionLocalOf { LightColors }

object EsuissTheme {
    val colors: Colors
        @Composable get() = LocalColors.current

    val typography: Typography
        get() = Typography

    val radius: Radius
        get() = Radius

    val shadows: Shadows
        get() = Shadows
}

@Composable
fun EsuissTheme(
    darkTheme: Boolean = isSystemInDarkTheme(),
    content: @Composable () -> Unit,
) {
    CompositionLocalProvider(
        LocalColors provides if (darkTheme) DarkColors else LightColors,
        content = content,
    )
}
```

```kt title="kotlin/theme/Tokens.kt"
package com.esuiss.ui.theme

import androidx.compose.runtime.Immutable
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.unit.dp

@Immutable
data class Colors(
    val surface: Color,
    val surfaceSecondary: Color,
    val surfaceTertiary: Color,
    val surfaceRaised: Color,
    val label: Color,
    val labelSecondary: Color,
    val labelTertiary: Color,
    val labelQuaternary: Color,
    val control: Color,
    val controlPressed: Color,
    val controlSelected: Color,
    val controlDisabled: Color,
    val onControlSelected: Color,
    val itemPressed: Color,
    val itemSelected: Color,
    val separator: Color,
    val separatorStrong: Color,
    val accent: Color,
    val accentPressed: Color,
    val accentSelected: Color,
    val accentDisabled: Color,
    val onAccent: Color,
    val accentSurface: Color,
    val accentSurfacePressed: Color,
    val link: Color,
    val focus: Color,
    val scrim: Color,
    val media: Color,
    val onMedia: Color,
    val danger: Color,
    val dangerSurface: Color,
    val dangerSurfacePressed: Color,
    val success: Color,
    val successSurface: Color,
    val warning: Color,
    val warningSurface: Color,
    val blue: Color,
    val green: Color,
    val orange: Color,
    val red: Color,
    val yellow: Color,
    val purple: Color,
    val pink: Color,
    val indigo: Color,
    val teal: Color,
    val mint: Color,
    val cyan: Color,
    val brown: Color,
    val gray: Color,
    val isDark: Boolean,
)

val LightColors = Colors(
    surface = Color(0xFFFFFFFF),
    surfaceSecondary = Color(0xFFF5F5F7),
    surfaceTertiary = Color(0xFFE8E8ED),
    surfaceRaised = Color(0xFFFFFFFF),
    label = Color(0xFF1D1D1F),
    labelSecondary = Color(0xFF6E6E73),
    labelTertiary = Color(0xFF86868B),
    labelQuaternary = Color(0xFFD2D2D7),
    control = Color(0xFF000000).copy(alpha = 0.04f),
    controlPressed = Color(0xFF000000).copy(alpha = 0.12f),
    controlSelected = Color(0xFF1D1D1F),
    controlDisabled = Color(0xFF000000).copy(alpha = 0.03f),
    onControlSelected = Color(0xFFFFFFFF),
    itemPressed = Color(0xFF000000).copy(alpha = 0.08f),
    itemSelected = Color(0xFF000000).copy(alpha = 0.06f),
    separator = Color(0xFFD2D2D7),
    separatorStrong = Color(0xFF86868B),
    accent = Color(0xFF0071E3),
    accentPressed = Color(0xFF005BB8),
    accentSelected = Color(0xFF0071E3),
    accentDisabled = Color(0xFF0071E3).copy(alpha = 0.4f),
    onAccent = Color(0xFFFFFFFF),
    accentSurface = Color(0xFF0071E3).copy(alpha = 0.09f),
    accentSurfacePressed = Color(0xFF0071E3).copy(alpha = 0.18f),
    link = Color(0xFF0066CC),
    focus = Color(0xFF0071E3),
    scrim = Color(0xFF000000).copy(alpha = 0.48f),
    media = Color(0xFF000000),
    onMedia = Color(0xFFFFFFFF),
    danger = Color(0xFFD0000A),
    dangerSurface = Color(0xFFD70015).copy(alpha = 0.08f),
    dangerSurfacePressed = Color(0xFFD70015).copy(alpha = 0.16f),
    success = Color(0xFF008009),
    successSurface = Color(0xFFEFFAF1),
    warning = Color(0xFFB64400),
    warningSurface = Color(0xFFFFF5EA),
    blue = Color(0xFF007AFF),
    green = Color(0xFF34C759),
    orange = Color(0xFFFF9500),
    red = Color(0xFFFF3B30),
    yellow = Color(0xFFFFCC00),
    purple = Color(0xFFAF52DE),
    pink = Color(0xFFFF2D55),
    indigo = Color(0xFF5856D6),
    teal = Color(0xFF30B0C7),
    mint = Color(0xFF00C7BE),
    cyan = Color(0xFF32ADE6),
    brown = Color(0xFFA2845E),
    gray = Color(0xFF8E8E93),
    isDark = false,
)

val DarkColors = Colors(
    surface = Color(0xFF000000),
    surfaceSecondary = Color(0xFF161617),
    surfaceTertiary = Color(0xFF2C2C2E),
    surfaceRaised = Color(0xFF1D1D1F),
    label = Color(0xFFF5F5F7),
    labelSecondary = Color(0xFFA1A1A6),
    labelTertiary = Color(0xFF86868B),
    labelQuaternary = Color(0xFF424245),
    control = Color(0xFFFFFFFF).copy(alpha = 0.1f),
    controlPressed = Color(0xFFFFFFFF).copy(alpha = 0.22f),
    controlSelected = Color(0xFFF5F5F7),
    controlDisabled = Color(0xFFFFFFFF).copy(alpha = 0.05f),
    onControlSelected = Color(0xFF000000),
    itemPressed = Color(0xFFFFFFFF).copy(alpha = 0.12f),
    itemSelected = Color(0xFFFFFFFF).copy(alpha = 0.1f),
    separator = Color(0xFF424245),
    separatorStrong = Color(0xFF6E6E73),
    accent = Color(0xFF0071E3),
    accentPressed = Color(0xFF004D9E),
    accentSelected = Color(0xFF0071E3),
    accentDisabled = Color(0xFF0071E3).copy(alpha = 0.4f),
    onAccent = Color(0xFFFFFFFF),
    accentSurface = Color(0xFF0071E3).copy(alpha = 0.18f),
    accentSurfacePressed = Color(0xFF0071E3).copy(alpha = 0.3f),
    link = Color(0xFF2997FF),
    focus = Color(0xFF0071E3),
    scrim = Color(0xFF000000).copy(alpha = 0.48f),
    media = Color(0xFF000000),
    onMedia = Color(0xFFFFFFFF),
    danger = Color(0xFFFF5447),
    dangerSurface = Color(0xFFFF453A).copy(alpha = 0.2f),
    dangerSurfacePressed = Color(0xFFFF453A).copy(alpha = 0.36f),
    success = Color(0xFF30D158),
    successSurface = Color(0xFF30D158).copy(alpha = 0.16f),
    warning = Color(0xFFFF9F0A),
    warningSurface = Color(0xFFFF9F0A).copy(alpha = 0.16f),
    blue = Color(0xFF0A84FF),
    green = Color(0xFF30D158),
    orange = Color(0xFFFF9F0A),
    red = Color(0xFFFF453A),
    yellow = Color(0xFFFFD60A),
    purple = Color(0xFFBF5AF2),
    pink = Color(0xFFFF375F),
    indigo = Color(0xFF5E5CE6),
    teal = Color(0xFF40C8E0),
    mint = Color(0xFF66D4CF),
    cyan = Color(0xFF64D2FF),
    brown = Color(0xFFAC8E68),
    gray = Color(0xFF8E8E93),
    isDark = true,
)

object Radius {
    val xs = 3.dp
    val sm = 5.dp
    val md = 8.dp
    val lg = 10.dp
    val xl = 12.dp
    val xl2 = 18.dp
    val xl3 = 28.dp
    val full = 9999.dp
}

object Typography {
    val xs3 = textStyle(11.0, 13.0, 0.006)
    val xs2 = textStyle(12.0, 16.0, 0.0)
    val xs = textStyle(13.0, 18.0, -0.006)
    val sm = textStyle(15.0, 20.0, -0.016)
    val md = textStyle(16.0, 21.0, -0.02)
    val base = textStyle(17.0, 22.0, -0.026)
    val lg = textStyle(20.0, 25.0, -0.023)
    val xl = textStyle(22.0, 28.0, -0.012)
    val xl2 = textStyle(28.0, 34.0, 0.014)
    val xl3 = textStyle(34.0, 41.0, 0.012)

    val all = listOf(xs3, xs2, xs, sm, md, base, lg, xl, xl2, xl3)
}

object Shadows {
    val md = Shadow(2.dp, 4.dp, 12.dp, Color.Black.copy(alpha = 0.08f))
    val lg = Shadow(0.dp, 4.dp, 24.dp, Color.Black.copy(alpha = 0.12f))
}
```

3. Copy the source and every file it uses:

```kt title="kotlin/interactions/SectionIndex.kt"
package com.esuiss.ui.interactions

import androidx.compose.animation.AnimatedVisibility
import androidx.compose.animation.core.tween
import androidx.compose.animation.fadeIn
import androidx.compose.animation.fadeOut
import androidx.compose.animation.scaleIn
import androidx.compose.animation.scaleOut
import androidx.compose.foundation.background
import androidx.compose.foundation.border
import androidx.compose.foundation.gestures.awaitEachGesture
import androidx.compose.foundation.gestures.awaitFirstDown
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.BoxWithConstraints
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.PaddingValues
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.layout.size
import androidx.compose.foundation.layout.widthIn
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.LazyItemScope
import androidx.compose.foundation.lazy.LazyListState
import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.foundation.shape.CircleShape
import androidx.compose.foundation.text.BasicText
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableFloatStateOf
import androidx.compose.runtime.mutableIntStateOf
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.rememberCoroutineScope
import androidx.compose.runtime.rememberUpdatedState
import androidx.compose.runtime.setValue
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.input.pointer.pointerInput
import androidx.compose.ui.layout.layout
import androidx.compose.ui.layout.onSizeChanged
import androidx.compose.ui.platform.LocalDensity
import androidx.compose.ui.semantics.contentDescription
import androidx.compose.ui.semantics.heading
import androidx.compose.ui.semantics.progressBarRangeInfo
import androidx.compose.ui.semantics.ProgressBarRangeInfo
import androidx.compose.ui.semantics.semantics
import androidx.compose.ui.semantics.setProgress
import androidx.compose.ui.semantics.stateDescription
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.text.style.TextAlign
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.dp
import com.esuiss.ui.components.rememberHaptics
import com.esuiss.ui.theme.EsuissTheme
import com.esuiss.ui.theme.Shadows
import com.esuiss.ui.theme.Typography
import com.esuiss.ui.theme.shadow
import kotlin.math.floor
import kotlin.math.roundToInt
import kotlinx.coroutines.launch

val SectionIndexLetters: List<String> = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".map { it.toString() } + "#"

private val RowHeight = 16.dp

interface SectionIndexSectionScope {
    fun item(key: Any? = null, content: @Composable LazyItemScope.() -> Unit)

    fun items(count: Int, key: ((Int) -> Any)? = null, content: @Composable LazyItemScope.(index: Int) -> Unit)
}

interface SectionIndexScope {
    fun SectionIndexSection(value: String, header: String? = value, content: SectionIndexSectionScope.() -> Unit)
}

private class SectionEntry(val count: Int, val key: ((Int) -> Any)?, val content: @Composable LazyItemScope.(Int) -> Unit)

private class SectionSpec(val value: String, val header: String?, val entries: List<SectionEntry>) {
    val size: Int get() = (if (header != null) 1 else 0) + entries.sumOf { it.count }
}

private class SectionIndexSectionScopeImpl : SectionIndexSectionScope {
    val entries = mutableListOf<SectionEntry>()

    override fun item(key: Any?, content: @Composable LazyItemScope.() -> Unit) {
        entries += SectionEntry(1, key?.let { k -> { k } }) { content() }
    }

    override fun items(count: Int, key: ((Int) -> Any)?, content: @Composable LazyItemScope.(index: Int) -> Unit) {
        entries += SectionEntry(count, key, content)
    }
}

private class SectionIndexScopeImpl : SectionIndexScope {
    val sections = mutableListOf<SectionSpec>()

    override fun SectionIndexSection(value: String, header: String?, content: SectionIndexSectionScope.() -> Unit) {
        sections += SectionSpec(value, header, SectionIndexSectionScopeImpl().apply(content).entries.toList())
    }
}

@Composable
fun SectionIndex(
    modifier: Modifier = Modifier,
    state: LazyListState = rememberLazyListState(),
    letters: List<String> = SectionIndexLetters,
    onValueChange: ((String) -> Unit)? = null,
    contentPadding: PaddingValues = PaddingValues(0.dp),
    content: SectionIndexScope.() -> Unit,
) {
    val sections = SectionIndexScopeImpl().apply(content).sections.toList()
    val starts = sections.runningFold(0) { total, section -> total + section.size }
    val scope = rememberCoroutineScope()
    Box(modifier = modifier) {
        LazyColumn(state = state, contentPadding = contentPadding) {
            sections.forEach { section ->
                if (section.header != null) {
                    stickyHeader(key = "section-index-${section.value}", contentType = "section-index-header") {
                        SectionIndexHeader(section.header)
                    }
                }
                section.entries.forEach { entry ->
                    items(entry.count, key = entry.key) { index -> entry.content(this, index) }
                }
            }
        }
        if (sections.isNotEmpty()) {
            SectionIndexBar(
                letters = letters,
                onValueChange = { letter ->
                    val position = letters.indexOf(letter)
                    val target = sections.indexOfFirst { letters.indexOf(it.value) >= position }.takeIf { it >= 0 } ?: sections.lastIndex
                    scope.launch { state.scrollToItem(starts[target]) }
                    onValueChange?.invoke(letter)
                },
                modifier = Modifier.align(Alignment.CenterEnd).padding(end = 12.dp),
            )
        }
    }
}

@Composable
fun SectionIndexHeader(text: String, modifier: Modifier = Modifier) {
    val colors = EsuissTheme.colors
    BasicText(
        text,
        modifier = modifier
            .fillMaxWidth()
            .background(colors.surface.copy(alpha = 0.94f))
            .padding(horizontal = 16.dp, vertical = 6.dp)
            .semantics { heading() },
        style = Typography.sm.copy(color = colors.labelSecondary, fontWeight = FontWeight.SemiBold),
    )
}

private fun displayItems(letters: List<String>, capacity: Int): List<String> {
    if (capacity >= letters.size) return letters
    val slots = maxOf(3, if (capacity % 2 == 0) capacity - 1 else capacity)
    fun letterAt(slot: Int) = letters[((slot.toFloat() / (slots - 1)) * (letters.size - 1)).roundToInt()]
    return List(slots) { slot -> if (slot % 2 == 0) letterAt(slot) else "•" }
}

@Composable
fun SectionIndexBar(
    modifier: Modifier = Modifier,
    letters: List<String> = SectionIndexLetters,
    onValueChange: ((String) -> Unit)? = null,
    accessibilityLabel: String = "Section index",
) {
    if (letters.isEmpty()) return
    val colors = EsuissTheme.colors
    val haptics = rememberHaptics()
    val density = LocalDensity.current
    var current by remember { mutableIntStateOf(0) }
    var dragging by remember { mutableStateOf(false) }
    var dragY by remember { mutableFloatStateOf(0f) }
    var columnHeight by remember { mutableIntStateOf(0) }
    val change by rememberUpdatedState(onValueChange)
    val currentLetters by rememberUpdatedState(letters)

    fun jump(index: Int) {
        if (index != current) haptics.selection()
        current = index
        currentLetters.getOrNull(index)?.let { change?.invoke(it) }
    }

    BoxWithConstraints(modifier = modifier) {
        val available = with(density) { constraints.maxHeight.toDp() } - 16.dp
        val capacity = if (constraints.hasBoundedHeight) floor(((available - RowHeight) / RowHeight)).toInt() else letters.size
        val items = displayItems(letters, capacity)
        Box(
            modifier = Modifier
                .pointerInput(Unit) {
                    fun track(y: Float, first: Boolean) {
                        val height = columnHeight.toFloat().coerceAtLeast(1f)
                        val clamped = y.coerceIn(0f, height)
                        dragY = clamped
                        val fraction = (clamped / height).coerceIn(0f, 0.9999f)
                        val index = (fraction * currentLetters.size).toInt()
                        if (index != current || first) jump(index)
                    }
                    awaitEachGesture {
                        val down = awaitFirstDown()
                        down.consume()
                        dragging = true
                        track(down.position.y, true)
                        while (true) {
                            val event = awaitPointerEvent()
                            val pointer = event.changes.firstOrNull { it.id == down.id } ?: break
                            if (!pointer.pressed) break
                            pointer.consume()
                            track(pointer.position.y, false)
                        }
                        dragging = false
                    }
                }
                .semantics {
                    contentDescription = accessibilityLabel
                    stateDescription = letters.getOrElse(current) { "" }
                    progressBarRangeInfo = ProgressBarRangeInfo(current.toFloat(), 0f..letters.lastIndex.toFloat(), letters.lastIndex - 1)
                    setProgress { value ->
                        jump(value.roundToInt().coerceIn(0, letters.lastIndex))
                        true
                    }
                }
                .padding(start = 12.dp),
        ) {
            Column(
                modifier = Modifier
                    .onSizeChanged { columnHeight = it.height }
                    .padding(horizontal = 6.dp),
                horizontalAlignment = Alignment.CenterHorizontally,
            ) {
                items.forEach { label ->
                    Box(modifier = Modifier.height(RowHeight).widthIn(min = 12.dp), contentAlignment = Alignment.Center) {
                        BasicText(
                            label,
                            style = Typography.xs3.copy(color = colors.link, fontWeight = FontWeight.SemiBold, textAlign = TextAlign.Center),
                        )
                    }
                }
            }
            AnimatedVisibility(
                visible = dragging,
                modifier = Modifier.layout { measurable, _ ->
                    val placeable = measurable.measure(Constraints())
                    layout(0, 0) {
                        placeable.place(-(56.dp + 16.dp).roundToPx(), (dragY - 28.dp.toPx()).roundToInt())
                    }
                },
                enter = fadeIn(tween(200)) + scaleIn(tween(200), initialScale = 0.5f),
                exit = fadeOut(tween(200)) + scaleOut(tween(200), targetScale = 0.5f),
            ) {
                Box(
                    modifier = Modifier
                        .size(56.dp)
                        .shadow(Shadows.lg, CircleShape)
                        .background(colors.surfaceRaised, CircleShape)
                        .border(1.dp, colors.separator, CircleShape),
                    contentAlignment = Alignment.Center,
                ) {
                    BasicText(
                        letters.getOrElse(current) { "" },
                        style = Typography.xl3.copy(color = colors.label, fontWeight = FontWeight.SemiBold, textAlign = TextAlign.Center),
                    )
                }
            }
        }
    }
}
```

```kt title="kotlin/components/Haptics.kt"
package com.esuiss.ui.components

import androidx.compose.runtime.Composable
import androidx.compose.runtime.CompositionLocalProvider
import androidx.compose.runtime.remember
import androidx.compose.runtime.staticCompositionLocalOf
import androidx.compose.ui.hapticfeedback.HapticFeedback
import androidx.compose.ui.hapticfeedback.HapticFeedbackType
import androidx.compose.ui.platform.LocalHapticFeedback

val LocalHapticsEnabled = staticCompositionLocalOf { true }

@Composable
fun ProvideHaptics(enabled: Boolean, content: @Composable () -> Unit) {
    CompositionLocalProvider(LocalHapticsEnabled provides enabled, content = content)
}

internal class Haptics(private val feedback: HapticFeedback, private val enabled: Boolean) {
    fun perform(type: HapticFeedbackType) {
        if (enabled) feedback.performHapticFeedback(type)
    }

    fun toggle(on: Boolean) = perform(if (on) HapticFeedbackType.ToggleOn else HapticFeedbackType.ToggleOff)

    fun selection() = perform(HapticFeedbackType.SegmentTick)
}

@Composable
internal fun rememberHaptics(): Haptics {
    val feedback = LocalHapticFeedback.current
    val enabled = LocalHapticsEnabled.current
    return remember(feedback, enabled) { Haptics(feedback, enabled) }
}
```

4. Update the `com.esuiss.ui` package names to match your project.

## Usage

```tsx
import { SectionIndex, SectionIndexScrollView, SectionIndexSection, SectionIndexHeader, SectionIndexBar } from "@/components/interactions/section-index"
```

```tsx
<ContactsExample className="h-[520px]" />
```

Put a `SectionIndexScrollView` and a `SectionIndexBar` inside `SectionIndex`. Wrap each group in a `SectionIndexSection` with its letter as `value`, and start it with a `SectionIndexHeader`.

The bar shows `A` to `Z` and `#` by default; pass `letters` to match your sections. `onValueChange` is called with the letter when the user jumps.

## Examples

### Compact

A short list where the bar collapses letters into dots.

![Preview](https://uim.suiss.app/previews/interactions-section-index--compact.light.webp)

```tsx
import * as React from "react"
import { Pressable, View } from "react-native"
import { SectionIndex, SectionIndexBar, SectionIndexHeader, SectionIndexScrollView, SectionIndexSection } from "@/components/interactions/section-index"
import { Text } from "@/components/ui/text"

const UPPERCASE = /[A-Z]/

const names = [
  "Aaron Price",
  "Abby Chen",
  "Alex Morgan",
  "Amira Haddad",
  "Ben Carter",
  "Bianca Rossi",
  "Carla Diaz",
  "Chris Evans",
  "Cody Brooks",
  "Dana Scott",
  "Derek Hale",
  "Elena Petrova",
  "Ethan Wright",
  "Fatima Khan",
  "Felix Wagner",
  "Grace Kim",
  "Hana Sato",
  "Henry Ford",
  "Ivy Turner",
  "Jack Miller",
  "Jade Wilson",
  "Jonas Berg",
  "Kai Nakamura",
  "Laura Bell",
  "Leo Martin",
  "Lina Costa",
  "Maya Patel",
  "Mia Novak",
  "Noah Fischer",
  "Nora Lind",
  "Omar Aziz",
  "Paula Silva",
  "Quinn Avery",
  "Rosa Lopez",
  "Ryan Cole",
  "Sara Ahmed",
  "Sofia Greco",
  "Tom Baker",
  "Uma Rao",
  "Victor Hugo",
  "Will Jensen",
  "Yara Nasser",
  "Zoe Adams",
  "8 Ball Club",
]

function groupByLetter() {
  const groups = new Map<string, string[]>()
  for (const name of names) {
    const first = name.charAt(0).toUpperCase()
    const letter = UPPERCASE.test(first) ? first : "#"
    groups.set(letter, [...(groups.get(letter) ?? []), name])
  }
  return [...groups.entries()].sort(([a], [b]) => {
    if (a === "#") return 1
    if (b === "#") return -1
    return a.localeCompare(b)
  })
}

function ContactsExample({ className }: { className: string }) {
  const [log, setLog] = React.useState("Tap or drag the letters.")
  return (
    <View className="gap-3">
      <SectionIndex className={className}>
        <SectionIndexScrollView className="rounded-2xl border border-separator">
          {groupByLetter().map(([letter, group]) => (
            <SectionIndexSection key={letter} value={letter}>
              <SectionIndexHeader>{letter}</SectionIndexHeader>
              {group.map((name, index) => (
                <Pressable
                  key={name}
                  onPress={() => setLog(`Opened ${name}`)}
                  className={`ms-4 me-10 py-3 active:opacity-60 ${index > 0 ? "border-t border-separator" : ""}`}
                >
                  <Text>{name}</Text>
                </Pressable>
              ))}
            </SectionIndexSection>
          ))}
        </SectionIndexScrollView>
        <SectionIndexBar
          onValueChange={(letter) => setLog(`Jumped to ${letter}`)}
        />
      </SectionIndex>
      <Text variant="muted">{log}</Text>
    </View>
  )
}

export function SectionIndexCompactExample() {
  return (
    <ContactsExample className="h-64" />
  )
}
```

```swift
import EsuissUI
import SwiftUI

struct SectionIndexCompactExample: View {
  var body: some View {
    SectionIndexContacts(height: 256)
  }
}

let sectionIndexNames = [
  "Aaron Price", "Abby Chen", "Alex Morgan", "Amira Haddad", "Ben Carter", "Bianca Rossi",
  "Carla Diaz", "Chris Evans", "Cody Brooks", "Dana Scott", "Derek Hale", "Elena Petrova",
  "Ethan Wright", "Fatima Khan", "Felix Wagner", "Grace Kim", "Hana Sato", "Henry Ford",
  "Ivy Turner", "Jack Miller", "Jade Wilson", "Jonas Berg", "Kai Nakamura", "Laura Bell",
  "Leo Martin", "Lina Costa", "Maya Patel", "Mia Novak", "Noah Fischer", "Nora Lind",
  "Omar Aziz", "Paula Silva", "Quinn Avery", "Rosa Lopez", "Ryan Cole", "Sara Ahmed",
  "Sofia Greco", "Tom Baker", "Uma Rao", "Victor Hugo", "Will Jensen", "Yara Nasser",
  "Zoe Adams", "8 Ball Club",
]

let sectionIndexGroups: [(String, [String])] = {
  var groups: [String: [String]] = [:]
  for name in sectionIndexNames {
    let first = name.prefix(1).uppercased()
    let letter = first.range(of: "^[A-Z]$", options: .regularExpression) != nil ? first : "#"
    groups[letter, default: []].append(name)
  }
  return groups.sorted { lhs, rhs in
    if lhs.key == "#" { return false }
    if rhs.key == "#" { return true }
    return lhs.key < rhs.key
  }
  .map { ($0.key, $0.value) }
}()

struct SectionIndexContacts: View {
  let height: CGFloat

  @State private var log: LocalizedStringKey = "Tap or drag the letters."

  var body: some View {
    let shape = RoundedRectangle(cornerRadius: Radius.xl2, style: .continuous)
    VStack(alignment: .leading, spacing: 12) {
      SectionIndex {
        ScrollView {
          LazyVStack(alignment: .leading, spacing: 0, pinnedViews: .sectionHeaders) {
            ForEach(sectionIndexGroups, id: \.0) { entry in
              SectionIndexSection(entry.0) {
                ForEach(Array(entry.1.enumerated()), id: \.element) { index, name in
                  Button {
                    log = "Opened \(name)"
                  } label: {
                    Text(verbatim: name)
                      .textStyle(.base)
                      .foregroundStyle(Color.label)
                      .padding(.vertical, 12)
                      .frame(maxWidth: .infinity, alignment: .leading)
                      .contentShape(Rectangle())
                  }
                  .buttonStyle(SectionIndexRowStyle())
                  .overlay(alignment: .top) {
                    if index > 0 {
                      Color.separator.frame(height: 1)
                    }
                  }
                  .padding(.leading, 16)
                  .padding(.trailing, 40)
                }
              }
            }
          }
        }
        .clipShape(shape)
        .overlay { shape.strokeBorder(Color.separator) }
        SectionIndexBar { letter in
          log = "Jumped to \(letter)"
        }
      }
      .frame(height: height)
      Text(log)
        .textVariant(.muted)
    }
  }
}

struct SectionIndexRowStyle: ButtonStyle {
  func makeBody(configuration: Configuration) -> some View {
    configuration.label
      .opacity(configuration.isPressed ? 0.6 : 1)
  }
}
```

```kotlin
import androidx.compose.foundation.background
import androidx.compose.foundation.border
import androidx.compose.foundation.clickable
import androidx.compose.foundation.interaction.MutableInteractionSource
import androidx.compose.foundation.interaction.collectIsPressedAsState
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.Column
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.layout.padding
import androidx.compose.foundation.shape.RoundedCornerShape
import androidx.compose.runtime.Composable
import androidx.compose.runtime.getValue
import androidx.compose.runtime.mutableStateOf
import androidx.compose.runtime.remember
import androidx.compose.runtime.saveable.rememberSaveable
import androidx.compose.runtime.setValue
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.alpha
import androidx.compose.ui.draw.clip
import androidx.compose.ui.semantics.Role
import androidx.compose.ui.unit.Dp
import androidx.compose.ui.unit.dp
import com.esuiss.ui.components.Text
import com.esuiss.ui.components.TextVariant
import com.esuiss.ui.interactions.SectionIndex
import com.esuiss.ui.theme.EsuissTheme
import com.esuiss.ui.theme.Radius

@Composable
fun SectionIndexCompactExample() {
    SectionIndexContacts(height = 256.dp)
}

val sectionIndexNames = listOf(
    "Aaron Price",
    "Abby Chen",
    "Alex Morgan",
    "Amira Haddad",
    "Ben Carter",
    "Bianca Rossi",
    "Carla Diaz",
    "Chris Evans",
    "Cody Brooks",
    "Dana Scott",
    "Derek Hale",
    "Elena Petrova",
    "Ethan Wright",
    "Fatima Khan",
    "Felix Wagner",
    "Grace Kim",
    "Hana Sato",
    "Henry Ford",
    "Ivy Turner",
    "Jack Miller",
    "Jade Wilson",
    "Jonas Berg",
    "Kai Nakamura",
    "Laura Bell",
    "Leo Martin",
    "Lina Costa",
    "Maya Patel",
    "Mia Novak",
    "Noah Fischer",
    "Nora Lind",
    "Omar Aziz",
    "Paula Silva",
    "Quinn Avery",
    "Rosa Lopez",
    "Ryan Cole",
    "Sara Ahmed",
    "Sofia Greco",
    "Tom Baker",
    "Uma Rao",
    "Victor Hugo",
    "Will Jensen",
    "Yara Nasser",
    "Zoe Adams",
    "8 Ball Club",
)

val sectionIndexGroups: List<Pair<String, List<String>>> =
    sectionIndexNames
        .groupBy { name ->
            val first = name.first().uppercaseChar()
            if (first in 'A'..'Z') first.toString() else "#"
        }
        .toList()
        .sortedWith(compareBy({ it.first == "#" }, { it.first }))

@Composable
fun SectionIndexContacts(height: Dp) {
    val colors = EsuissTheme.colors
    var log by rememberSaveable { mutableStateOf("Tap or drag the letters.") }
    val shape = RoundedCornerShape(Radius.xl2)
    Column(verticalArrangement = Arrangement.spacedBy(12.dp)) {
        SectionIndex(
            modifier = Modifier
                .fillMaxWidth()
                .height(height)
                .clip(shape)
                .border(1.dp, colors.separator, shape),
            onValueChange = { letter -> log = "Jumped to $letter" },
        ) {
            sectionIndexGroups.forEach { (letter, group) ->
                SectionIndexSection(letter) {
                    items(group.size, key = { group[it] }) { index ->
                        SectionIndexRow(group[index], divided = index > 0) { log = "Opened ${group[index]}" }
                    }
                }
            }
        }
        Text(log, variant = TextVariant.Muted)
    }
}

@Composable
fun SectionIndexRow(name: String, divided: Boolean, onClick: () -> Unit) {
    val colors = EsuissTheme.colors
    val interaction = remember { MutableInteractionSource() }
    val pressed by interaction.collectIsPressedAsState()
    Column(
        Modifier
            .fillMaxWidth()
            .padding(start = 16.dp, end = 40.dp)
            .clickable(interactionSource = interaction, indication = null, role = Role.Button, onClick = onClick),
    ) {
        if (divided) Box(Modifier.fillMaxWidth().height(1.dp).background(colors.separator))
        Text(name, modifier = Modifier.alpha(if (pressed) 0.6f else 1f).padding(vertical = 12.dp))
    }
}
```

## API Reference

### SectionIndex

The root that tracks section positions.

### SectionIndexScrollView

The scroll view that holds the sections.

### SectionIndexSection

One section, registered by its `value`.

### SectionIndexHeader

A section heading; string children are styled.

### SectionIndexBar

The letter bar with the drag bubble.

## Accessibility

- The bar is `adjustable`: swiping up or down with a screen reader moves to the previous or next section, and the current letter is announced as its value.
- `SectionIndexHeader` has the `heading` role.

## Notes

- A selection haptic plays on each letter change from touch, if the app provides an adapter through `HapticsProvider`.
- Letters use `text-link`; the bubble uses `bg-surface-raised`.
- The bubble animation respects the system reduce motion setting.