// UITextView/NSTextView
let nsRange = NSRange(location: 0, length: 10)

// Via content manager
let startLocation = textContentManager.location(
    textContentManager.documentRange.location,
    offsetBy: nsRange.location
)!
let endLocation = textContentManager.location(
    startLocation,
    offsetBy: nsRange.length
)!
let textRange = NSTextRange(location: startLocation, end: endLocation)

let startOffset = textContentManager.offset(
    from: textContentManager.documentRange.location,
    to: textRange.location
)
let length = textContentManager.offset(
    from: textRange.location,
    to: textRange.endLocation
)
let nsRange = NSRange(location: startOffset, length: length)

// TextKit 1 - iterate glyphs
var lineCount = 0
let glyphRange = layoutManager.glyphRange(for: textContainer)
for glyphIndex in glyphRange.location..<NSMaxRange(glyphRange) {
    let lineRect = layoutManager.lineFragmentRect(
        forGlyphAt: glyphIndex,
        effectiveRange: nil
    )
    // Count unique rects...
}

// TextKit 2 - enumerate layout fragments
var lineCount = 0
textLayoutManager.enumerateTextLayoutFragments(
    from: textLayoutManager.documentRange.location,
    options: [.ensuresLayout]
) { fragment in
    lineCount += fragment.textLineFragments.count
    return true
}

// Check TextKit 2 first
if let textLayoutManager = textView.textLayoutManager {
    // TextKit 2 code
} else if let layoutManager = textView.layoutManager {
    // TextKit 1 fallback (old OS versions)
}

let textLayoutManager = NSTextLayoutManager()
let textContainer = NSTextContainer()
textLayoutManager.textContainer = textContainer

let textView = NSTextView(frame: .zero, textContainer: textContainer)
// textView.textLayoutManager now available

// iOS 16+ / macOS 13+
let textView = UITextView(usingTextLayoutManager: true)
let nsTextView = NSTextView(usingTextLayoutManager: true)

func textContentStorage(
    _ textContentStorage: NSTextContentStorage,
    textParagraphWith range: NSRange
) -> NSTextParagraph? {
    // Modify attributes for display
    var attributedString = textContentStorage.attributedString!
        .attributedSubstring(from: range)

    // Add custom attributes
    if isComment(range) {
        attributedString.addAttribute(
            .foregroundColor,
            value: UIColor.systemIndigo,
            range: NSRange(location: 0, length: attributedString.length)
        )
    }

    return NSTextParagraph(attributedString: attributedString)
}

func textContentManager(
    _ textContentManager: NSTextContentManager,
    shouldEnumerate textElement: NSTextElement,
    options: NSTextContentManager.EnumerationOptions
) -> Bool {
    // Return false to hide element
    if hideComments && isComment(textElement) {
        return false
    }
    return true
}

func textLayoutManager(
    _ textLayoutManager: NSTextLayoutManager,
    textLayoutFragmentFor location: NSTextLocation,
    in textElement: NSTextElement
) -> NSTextLayoutFragment {
    // Return custom fragment for special styling
    if isComment(textElement) {
        return BubbleLayoutFragment(
            textElement: textElement,
            range: textElement.elementRange
        )
    }
    return NSTextLayoutFragment(
        textElement: textElement,
        range: textElement.elementRange
    )
}

func textViewportLayoutControllerWillLayout(_ controller: NSTextViewportLayoutController) {
    // Prepare for layout: clear sublayers, begin animation
}

func textViewportLayoutController(
    _ controller: NSTextViewportLayoutController,
    configureRenderingSurfaceFor textLayoutFragment: NSTextLayoutFragment
) {
    // Update geometry for each visible fragment
    let layer = getOrCreateLayer(for: textLayoutFragment)
    layer.frame = textLayoutFragment.layoutFragmentFrame
    // Animate to new position if needed
}

func textViewportLayoutControllerDidLayout(_ controller: NSTextViewportLayoutController) {
    // Finish: commit animations, update scroll indicators
}

class BubbleLayoutFragment: NSTextLayoutFragment {
    override func draw(at point: CGPoint, in context: CGContext) {
        // Draw custom background
        context.setFillColor(UIColor.systemIndigo.cgColor)
        let bubblePath = UIBezierPath(
            roundedRect: layoutFragmentFrame,
            cornerRadius: 8
        )
        context.addPath(bubblePath.cgPath)
        context.fillPath()

        // Draw text on top
        super.draw(at: point, in: context)
    }
}

textLayoutManager.addRenderingAttribute(
    .foregroundColor,
    value: UIColor.green,
    for: ingredientRange
)

// Remove when no longer needed
textLayoutManager.removeRenderingAttribute(
    .foregroundColor,
    for: ingredientRange
)

// iOS 15+
let attachment = NSTextAttachment()
attachment.image = UIImage(systemName: "star.fill")

// Provide view for interaction
class AttachmentViewProvider: NSTextAttachmentViewProvider {
    override func loadView() {
        super.loadView()
        let button = UIButton(type: .system)
        button.setTitle("Tap me", for: .normal)
        button.addTarget(self, action: #selector(didTap), for: .touchUpInside)
        view = button
    }

    @objc func didTap() {
        // Handle tap
    }
}

// Create list
let listItem = NSTextList(markerFormat: .disc, options: 0)
let paragraphStyle = NSMutableParagraphStyle()
paragraphStyle.textLists = [listItem]

attributedString.addAttribute(
    .paragraphStyle,
    value: paragraphStyle,
    range: range
)

// Get text range at point
let location = textLayoutManager.location(
    interactingAt: point,
    inContainerAt: textContainer.location
)

// Get bounding rect for range
var boundingRect = CGRect.zero
textLayoutManager.enumerateTextSegments(
    in: textRange,
    type: .standard,
    options: []
) { segmentRange, segmentRect, baselinePosition, textContainer in
    boundingRect = boundingRect.union(segmentRect)
    return true
}

// UITextView, NSTextView, WKWebView
// Writing Tools appears automatically

func textViewWritingToolsWillBegin(_ textView: UITextView) {
    // Pause syncing, prevent edits
    isSyncing = false
}

func textViewWritingToolsDidEnd(_ textView: UITextView) {
    // Resume syncing
    isSyncing = true
}

// Check if active
if textView.isWritingToolsActive {
    // Don't persist text storage
}

// Opt out completely
textView.writingToolsBehavior = .none

// Panel-only experience (no in-line edits)
textView.writingToolsBehavior = .limited

// Full experience (default)
textView.writingToolsBehavior = .default

// Plain text only
textView.writingToolsResultOptions = [.plainText]

// Rich text
textView.writingToolsResultOptions = [.richText]

// Rich text + tables
textView.writingToolsResultOptions = [.richText, .table]

// Rich text + lists
textView.writingToolsResultOptions = [.richText, .list]

// UITextViewDelegate / NSTextViewDelegate
func textView(
    _ textView: UITextView,
    writingToolsIgnoredRangesIn enclosingRange: NSRange
) -> [NSRange] {
    // Return ranges that Writing Tools should not modify
    return codeBlockRanges + quoteRanges
}

// UIKit
let coordinator = UIWritingToolsCoordinator()
coordinator.delegate = self
textView.addInteraction(coordinator)
coordinator.writingToolsBehavior = .default
coordinator.writingToolsResultOptions = [.richText]

// AppKit
let coordinator = NSWritingToolsCoordinator()
coordinator.delegate = self
customView.writingToolsCoordinator = coordinator

func writingToolsCoordinator(
    _ coordinator: NSWritingToolsCoordinator,
    requestContexts scope: NSWritingToolsCoordinator.ContextScope
) async -> [NSWritingToolsCoordinator.Context] {
    // Return attributed string + selection range
    let context = NSWritingToolsCoordinator.Context(
        attributedString: currentText,
        range: currentSelection
    )
    return [context]
}

func writingToolsCoordinator(
    _ coordinator: NSWritingToolsCoordinator,
    replace context: NSWritingToolsCoordinator.Context,
    range: NSRange,
    with attributedString: NSAttributedString
) async {
    // Update text storage
    textStorage.replaceCharacters(in: range, with: attributedString)
}

func writingToolsCoordinator(
    _ coordinator: NSWritingToolsCoordinator,
    updateSelectedRange selectedRange: NSRange,
    in context: NSWritingToolsCoordinator.Context
) async {
    // Update selection
    self.selectedRange = selectedRange
}

// macOS
func writingToolsCoordinator(
    _ coordinator: NSWritingToolsCoordinator,
    previewsFor context: NSWritingToolsCoordinator.Context,
    range: NSRange
) async -> [NSTextPreview] {
    // Return one preview per line for smooth animation
    return textLines.map { line in
        NSTextPreview(
            image: renderImage(for: line),
            frame: line.frame
        )
    }
}

// iOS
func writingToolsCoordinator(
    _ coordinator: UIWritingToolsCoordinator,
    previewFor context: UIWritingToolsCoordinator.Context,
    range: NSRange
) async -> UITargetedPreview {
    // Return single preview
    return UITargetedPreview(
        view: previewView,
        parameters: parameters
    )
}

func writingToolsCoordinator(
    _ coordinator: NSWritingToolsCoordinator,
    underlinesFor context: NSWritingToolsCoordinator.Context,
    range: NSRange
) async -> [NSValue] {
    // Return bezier paths for underlines
    return ranges.map { range in
        let path = bezierPath(for: range)
        return NSValue(bytes: &path, objCType: "CGPath")
    }
}

coordinator.writingToolsResultOptions = [.richText, .presentationIntent]

// Check for presentation intent
if attributedString.runs[\.presentationIntent].contains(where: { $0?.components.contains(.header(level: 1)) == true }) {
    // This is a heading
}

struct RecipeEditor: View {
    @State private var text: AttributedString = "Recipe text"

    var body: some View {
        TextEditor(text: $text)
    }
}

@State private var selection: AttributedTextSelection?

TextEditor(text: $text, selection: $selection)

enum AttributedTextSelection {
    case none
    case single(NSRange)
    case multiple(Set<NSRange>) // For bidirectional text
}

if let selection {
    let selectedText: AttributedSubstring
    switch selection.indices {
    case .none:
        selectedText = text[...]
    case .single(let range):
        selectedText = text[range]
    case .multiple(let ranges):
        // Discontiguous substring from RangeSet
        selectedText = text[selection]
    }
}

struct RecipeFormattingDefinition: AttributedTextFormattingDefinition {
    typealias FormatScope = RecipeAttributeScope

    static let constraints: [any AttributedTextValueConstraint<RecipeFormattingDefinition>] = [
        IngredientsAreGreen()
    ]
}

struct RecipeAttributeScope: AttributedScope {
    var ingredient: IngredientAttribute
    var foregroundColor: ForegroundColorAttribute
    var genmoji: GenmojiAttribute
}

TextEditor(text: $text)
    .attributedTextFormattingDefinition(RecipeFormattingDefinition.self)

struct IngredientsAreGreen: AttributedTextValueConstraint {
    typealias Definition = RecipeFormattingDefinition
    typealias AttributeKey = ForegroundColorAttribute

    func constrain(
        _ value: inout Color?,
        in scope: RecipeFormattingDefinition.FormatScope
    ) {
        if scope.ingredient != nil {
            value = .green // Ingredients are always green
        } else {
            value = nil // Others use default
        }
    }
}

struct IngredientAttribute: CodableAttributedStringKey {
    typealias Value = UUID // Ingredient ID

    static let name = "ingredient"
}

extension AttributeScopes.RecipeAttributeScope {
    var ingredient: IngredientAttribute.Type { IngredientAttribute.self }
}

extension IngredientAttribute {
    // Don't expand when typing after ingredient
    static let inheritedByAddedText = false

    // Remove if text in run changes
    static let invalidationConditions: [AttributedString.InvalidationCondition] = [
        .textChanged
    ]

    // Optional: constrain to paragraph boundaries
    static let runBoundaries: AttributedString.RunBoundaries = .paragraph
}

// Transform updates indices/selection during mutation
text.transform(updating: &selection) { mutableText in
    // Find ranges
    let ranges = mutableText.characters.ranges(of: "butter")

    // Set attribute for all ranges at once
    for range in ranges {
        mutableText[range].ingredient = ingredientID
    }
}

// selection is now updated to match transformed text

// BAD - indices invalidated by mutation
let range = text.characters.range(of: "butter")!
text[range].foregroundColor = .green
text.append(" (unsalted)") // range is now invalid!