portico/Sources/PorticoGen/Generator.swift

/// Emits the import block shared by every generated file.
/// - Parameter isPorticoGtk: When `true`, adds `@_spi(Portico) import Portico`
///   because the file lives in the separate `PorticoGtk` module.
func generateHeader(isPorticoGtk: Bool) -> String {
    var out = "// Generated by PorticoGen. DO NOT EDIT. See Sources/PorticoGen to make changes.\n\n"
    out += "import Adw\nimport Gtk\nimport Gio\nimport Gdk\n"
    if isPorticoGtk { out += "@_spi(Portico) import Portico\n" }
    return out + "\n"
}

/// Converts a Swift wrapper property name to the most likely canonical GObject
/// property name, such as `useMarkup` to `use-markup`.
///
/// Backticks are dropped because Swift keyword properties are emitted as
/// `` `open` ``, while the corresponding GObject property is named `open`.
/// The result is only a candidate; the runtime verifies it against the widget
/// class before using it as a `notify` detail.
func gobjectPropertyName(_ swiftName: String) -> String {
    var out = ""
    for character in swiftName where character != "`" {
        if character.isUppercase {
            if !out.isEmpty { out.append("-") }
            out.append(contentsOf: character.lowercased())
        } else {
            out.append(character)
        }
    }
    return out
}


// MARK: - Doc emission

/// Renders a non-DocC provenance marker plus a DocC comment block.
///
/// The marker is a plain `//` line placed above the `///` block, so the Swift
/// compiler's doc extraction (and therefore DocC's rendered HTML/PDF) ignores it
/// while it stays greppable in the generated source.
///
/// - Parameters:
///   - indent: Leading whitespace for every emitted line (`"    "` for members, `""` for top level).
///   - chain: PorticoGen function names, outermost first; joined with `" -> "`.
///   - sources: Upstream symbols the prose came from; joined with `", "`.
///     Emits `| source: synthesized` when empty.
///   - summary: Carried-over doc lines, verbatim.
///   - notes: Portico-specific paragraphs appended after `summary`, one line each.
///   - parameters: `- Parameter` entries, in declaration order.
///   - returns: `- Returns:` text, or `nil` for initializers.
func docBlock(
    indent: String,
    chain: [String],
    sources: [String],
    summary: [String],
    notes: [String] = [],
    parameters: [(name: String, text: String)] = [],
    returns: String? = nil
) -> String {
    var out = ""
    let chainStr = chain.joined(separator: " -> ")
    let srcStr = sources.isEmpty ? "synthesized" : sources.joined(separator: ", ")
    out += "\(indent)// PorticoGen: \(chainStr) | source: \(srcStr)\n"

    func emitDoc(_ lines: [String]) {
        for line in lines {
            if line.isEmpty {
                out += "\(indent)///\n"
            } else {
                out += "\(indent)/// \(line)\n"
            }
        }
    }

    emitDoc(summary)
    if !notes.isEmpty {
        // Blank separator between summary and notes.
        if !summary.isEmpty { out += "\(indent)///\n" }
        emitDoc(notes)
    }
    if !parameters.isEmpty || returns != nil {
        // Blank separator before parameter/returns group.
        out += "\(indent)///\n"
        for (name, text) in parameters {
            out += "\(indent)/// - Parameter \(name): \(text)\n"
        }
        if let r = returns {
            out += "\(indent)/// - Returns: \(r)\n"
        }
    }
    return out
}

/// Best available one-line description for a value parameter named `label` on `widget`.
///
/// Lookup order: the same-named property's doc, then `set<Label>`, then `get<Label>`,
/// each reduced by `firstParagraph(of:)`. Falls back to
/// `"The \`<label>\` value forwarded to \`<Module>.<Class>\`."`
func parameterDoc(_ label: String, widget: WidgetModel) -> String {
    let propertyName = label
    let setterName = "set" + label.prefix(1).uppercased() + label.dropFirst()
    let getterName = "get" + label.prefix(1).uppercased() + label.dropFirst()

    if let lines = widget.memberDocs[propertyName], let fp = firstParagraph(of: lines) {
        return fp
    }
    if let lines = widget.memberDocs[setterName], let fp = firstParagraph(of: lines) {
        return fp
    }
    if let lines = widget.memberDocs[getterName], let fp = firstParagraph(of: lines) {
        return fp
    }
    return "The `\(label)` value forwarded to `\(widget.module).\(widget.className)`."
}

/// Emits the widget struct, its `WidgetView` conformance and its `Mountable`
/// extension. No imports, so the block can be concatenated into a shared file.
func generateStruct(widget: WidgetModel, structName: String) -> String {
    var out = ""
    let qualifiedType = "\(widget.module).\(widget.className)"

    // Struct doc
    if widget.docLines.isEmpty {
        out += docBlock(
            indent: "",
            chain: ["generateStruct"],
            sources: ["\(widget.module).\(widget.className)"],
            summary: ["A \(structName) widget backed by `\(qualifiedType)`."]
        )
    } else {
        out += docBlock(
            indent: "",
            chain: ["generateStruct"],
            sources: ["\(widget.module).\(widget.className)"],
            summary: widget.docLines,
            notes: ["A Portico view that mounts a `\(qualifiedType)`."]
        )
    }

    // Struct declaration
    out += "@MainActor public struct \(structName): View {\n"
    out += "    private let make: (MountContext) -> \(qualifiedType)\n"
    out += "    private var configure: [(\(qualifiedType), MountContext) -> Void] = []\n"
    out += "\n"
    out += "    public var body: Never { fatalError() }\n"
    out += "\n"

    // Inits
    if let noArg = widget.noArgInit {
        out += generateInits(widget: widget, initModel: noArg)
    }
    for initModel in widget.inits {
        out += generateInits(widget: widget, initModel: initModel)
    }

    out += "}\n"
    out += "\n"

    // WidgetView conformance
    out += "extension \(structName): WidgetView {\n"
    out += "    public typealias Target = \(qualifiedType)\n"
    out += "\n"
    out += "    @_spi(Portico) public func appending(\n"
    out += "        _ step: @escaping (\(qualifiedType), MountContext) -> Void\n"
    out += "    ) -> Self {\n"
    out += "        var c = self\n"
    out += "        c.configure.append(step)\n"
    out += "        return c\n"
    out += "    }\n"
    out += "}\n"
    out += "\n"

    // Mountable extension
    out += "@_spi(Portico) extension \(structName): Mountable {\n"
    out += "    @_spi(Portico) public func mount(_ ctx: MountContext) -> Gtk.Widget {\n"
    out += "        let w = make(ctx)\n"
    out += "        for step in configure { step(w, ctx) }\n"
    out += "        return w\n"
    out += "    }\n"
    out += "}\n"

    return out
}

// MARK: - Type qualification

/// Standard library types that should not be module-qualified.
private let stdlibTypes: Set<String> = [
    "String", "Int", "Int8", "Int16", "Int32", "Int64",
    "UInt", "UInt8", "UInt16", "UInt32", "UInt64",
    "Bool", "Double", "Float", "Float80", "Void", "Never",
    "Any", "Self", "Character", "StaticString", "NSObject",
]

/// How a generated modifier wraps its configuration step.
enum ModifierStyle {
    /// `WidgetView` extension: `appending { … }`, returns `Self`.
    case widgetView
    /// `View` extension: builds an `AnyView` mount thunk, returns `AnyView`.
    case erasingView
}


/// Qualifies a type string with the widget's module if it is an unqualified
/// GTK/Adw type reference.
func qualifyType(_ type: String, module: String) -> String {
    if type.contains(".") { return type }
    if type.hasSuffix("?") {
        let base = String(type.dropLast())
        return qualifyType(base, module: module) + "?"
    }
    if type.hasSuffix("!") {
        let base = String(type.dropLast())
        return qualifyType(base, module: module) + "!"
    }
    if stdlibTypes.contains(type) { return type }
    if type.hasPrefix("[") && type.hasSuffix("]") {
        let inner = String(type.dropFirst().dropLast())
        return "[\(qualifyType(inner, module: module))]"
    }
    if type.hasPrefix("(") { return type }
    if let first = type.first, first.isLowercase { return type }
    return "\(module).\(type)"
}

/// True when `type` denotes a GTK widget slot; i.e. `Widget`, `Widget?`, `Gtk.Widget?`,
/// `Adw` re-exports `Gtk`, so `Adw.Widget` and `Gtk.Widget` are the same type.
func isWidgetType(_ type: String, module: String) -> Bool {
    var t = qualifyType(type, module: module)
    while t.hasSuffix("?") || t.hasSuffix("!") { t = String(t.dropLast()) }
    return t == "Gtk.Widget" || t == "Adw.Widget"
}

/// Every parsed class that descends from `Gtk.Widget`, keyed `"Module.ClassName"`.
///
/// Populated once by `main()` after the inheritance walk, before any generation runs.
/// ``isWidgetType(_:module:)`` recognizes only the exact base class, which is the right
/// test for a mountable slot; this set additionally recognizes subclass-typed properties
/// such as `Gtk.StackSidebar.stack` (typed `Gtk.Stack`).
var widgetClassKeys: Set<String> = []
/// Every parsed class/interface model, keyed "Module.ClassName".
///
/// Populated once by `main()` before any generation runs.
var widgetModelMap: [String: WidgetModel] = [:]

/// Raw parent-class string for every parsed class, keyed "Module.ClassName".
///
/// Populated once by `main()`; mirrors the parent registry used by widget-set resolution.
var widgetParentMap: [String: String] = [:]
/// Resolves a raw parent-class string to a fully-qualified `Module.Class` key.
///
/// The lookup mirrors `main()`'s widget inheritance walk, including same-name
/// GTK/Adwaita resolution and module-qualified fallbacks.
func resolveParentKey(currentKey: String, parentRaw: String) -> String? {
    var parent = parentRaw
    if let idx = parent.firstIndex(where: { $0 == " " || $0 == "," }) {
        parent = String(parent[..<idx])
    }
    guard !parent.isEmpty else { return nil }
    if parent.contains(".") { return parent }
    let components = currentKey.split(separator: ".")
    guard components.count == 2 else { return nil }
    let module = String(components[0])
    let className = String(components[1])
    if parent == className {
        // Adw.Window : Gtk.Window style: try the other GTK module first.
        let other = (module == "Adw") ? "Gtk" : "Adw"
        if widgetModelMap["\(other).\(parent)"] != nil { return "\(other).\(parent)" }
    }
    if widgetModelMap["\(module).\(parent)"] != nil { return "\(module).\(parent)" }
    if widgetModelMap["Gtk.\(parent)"] != nil { return "Gtk.\(parent)" }
    if widgetModelMap["Adw.\(parent)"] != nil { return "Adw.\(parent)" }
    return nil
}

/// Returns nearest-first widget-class ancestors, excluding `Gtk.Widget` and
/// `Adw.Widget`. The walk stops when it reaches an unresolvable or non-widget
/// parent and guards against malformed cyclic model data.
func ancestorModels(for widget: WidgetModel) -> [WidgetModel] {
    let stop = Set(["Gtk.Widget", "Adw.Widget"])
    var result: [WidgetModel] = []
    var current = "\(widget.module).\(widget.className)"
    var visited: Set<String> = [current]
    while let raw = widgetParentMap[current],
          let parentKey = resolveParentKey(currentKey: current, parentRaw: raw) {
        if stop.contains(parentKey) { break }
        guard let model = widgetModelMap[parentKey], model.kind == .widgetClass else { break }
        if !visited.insert(parentKey).inserted { break }
        result.append(model)
        current = parentKey
    }
    return result
}

/// Returns own properties followed by nearest-first ancestor properties,
/// retaining the first definition for each property name.
func effectiveProperties(for widget: WidgetModel) -> [(prop: PropertyModel, owner: WidgetModel)] {
    var seen = Set<String>()
    var result: [(prop: PropertyModel, owner: WidgetModel)] = []
    for prop in widget.properties where seen.insert(prop.name).inserted {
        result.append((prop, widget))
    }
    for ancestor in ancestorModels(for: widget) {
        for prop in ancestor.properties where seen.insert(prop.name).inserted {
            result.append((prop, ancestor))
        }
    }
    return result
}

/// Returns own signals followed by nearest-first ancestor signals, retaining
/// the first definition for each signal base name.
func effectiveSignals(for widget: WidgetModel) -> [(signal: SignalModel, owner: WidgetModel)] {
    var seen = Set<String>()
    var result: [(signal: SignalModel, owner: WidgetModel)] = []
    for signal in widget.signals where seen.insert(signal.baseName).inserted {
        result.append((signal, widget))
    }
    for ancestor in ancestorModels(for: widget) {
        for signal in ancestor.signals where seen.insert(signal.baseName).inserted {
            result.append((signal, ancestor))
        }
    }
    return result
}

/// The qualified widget class a `Binding` overload for `type` can be made generic over,
/// or `nil` when `type` is not a widget class.
///
/// `Binding` is invariant, so an overload fixed at the property's declared type rejects
/// the `Binding<Subclass?>` that a `WidgetRef<Subclass>` projects. Constraining a generic
/// parameter to the returned class restores the subtype relationship the property's own
/// type already has, and every such value upcasts to the setter's parameter type.
func widgetClassConstraint(_ type: String, module: String) -> String? {
    var t = qualifyType(type, module: module)
    while t.hasSuffix("?") || t.hasSuffix("!") { t = String(t.dropLast()) }
    // `Adw` re-exports `Gtk`, so both spellings name the same base class.
    if t == "Gtk.Widget" || t == "Adw.Widget" { return "Gtk.Widget" }
    return widgetClassKeys.contains(t) ? t : nil
}

/// True when `qualifiedType` is `String` or `String?`.
func isStringType(_ qualifiedType: String) -> Bool {
    return qualifiedType == "String" || qualifiedType == "String?"
}

/// Returns the safe expression used to read a property from a mounted widget.
///
/// A `String` property without a generated getter has no safe computed-property read:
/// the wrapper's C-string conversion traps when the underlying GObject value is NULL.
func readBackExpr(_ prop: PropertyModel, module: String) -> String? {
    if let g = prop.getterName { return "w.\(g)()" }
    if qualifyType(prop.type, module: module) == "String" { return nil }
    return "w.\(prop.name)"
}

/// The single `String`/`String?` parameter of `params` that can be lifted to
/// `Portico.InterpolatedText`, plus the setter used to push later values.
struct InterpolationSlot {
    let param: Param
    let optional: Bool
    let setterName: String
    let setterLabel: String
}

/// Returns the lone interpolatable parameter of `params`, or `nil`.
///
/// Eligible only when exactly one parameter's qualified type is `String` or `String?`
/// **and** its label matches a settable property of the same type. Two or more `String`
/// parameters are rejected on purpose: Swift then ranks the all-`String` overload above
/// the interpolated one even for interpolated literals, which would silently drop
/// reactivity.
func interpolationSlot(params: [Param], widget: WidgetModel) -> InterpolationSlot? {
    let stringParams = params.filter { isStringType(qualifyType($0.type, module: widget.module)) }
    guard stringParams.count == 1, let p = stringParams.first else { return nil }
    let qt = qualifyType(p.type, module: widget.module)
    let propOwner = Dictionary(
        effectiveProperties(for: widget).map { ($0.prop.name, ($0.prop, $0.owner.module)) },
        uniquingKeysWith: { a, _ in a }
    )
    guard let (prop, ownerModule) = propOwner[p.label],
          qualifyType(prop.type, module: ownerModule) == qt else { return nil }
    let isOpt = qt.hasSuffix("?")
    return InterpolationSlot(param: p, optional: isOpt, setterName: prop.setterName, setterLabel: prop.setterLabel)
}

// MARK: - Init generation

/// Orders widget slots so the main content regions receive trailing-closure priority.
func slotRank(_ name: String) -> Int {
    switch name {
    case "content": return 0
    case "child": return 1
    default: return 2
    }
}

/// Categories 2, 3, 4 and 6 of an emitted initializer.
struct InitExtras {
    var paramDecls: [String] = []
    var docs: [(name: String, text: String)] = []
    var preludeLines: [String] = []
    var makeArgs: [String: String] = [:]
    var configureLines: [String] = []
    var makeUsesCtx = false
    var configureUsesCtx = false
    var sources: [String] = []
}

/// Returns the documentation shared by signal initializers and modifiers.
func signalHandlerDoc(_ signal: SignalModel) -> String {
    var text = "Invoked when the widget emits the `\(signal.signalName)` signal."
    if !signal.argTypes.isEmpty {
        text += " The closure receives the signal's arguments in order."
    }
    if signal.returnType != "Void" {
        text += " Its return value is forwarded to GTK as the signal's result."
    }
    return text
}
/// Builds the defaulted properties, slots, child builder and signal parameters shared by
/// every initializer flavor for one wrapper initializer.
func initExtras(widget: WidgetModel, initModel: InitModel, bindingValues: Bool) -> InitExtras {
    var extras = InitExtras()
    let effProps = effectiveProperties(for: widget)

    // Optional value properties, including inherited members.
    for entry in effProps where
        !isWidgetType(entry.prop.type, module: entry.owner.module) &&
        !widget.reservedInitLabels.contains(entry.prop.name) {
        let prop = entry.prop
        let owner = entry.owner
        let name = prop.name
        let qt = qualifyType(prop.type, module: owner.module)
        if bindingValues {
            extras.paramDecls.append("\(name): Portico.Binding<\(qt)>? = nil")
            if let read = readBackExpr(prop, module: owner.module) {
                extras.configureLines += [
                    "            if let \(name) {",
                    "                Portico.bindProperty(w, \(name), registry: ctx.registry, notifyDetail: \"\(gobjectPropertyName(name))\", read: { [w] in \(read) }, write: { [w] v in w.\(prop.setterName)(\(prop.setterLabel): v) })",
                    "            }",
                ]
            } else {
                extras.configureLines += [
                    "            if let \(name) {",
                    "                w.\(prop.setterName)(\(prop.setterLabel): \(name).untrackedValue)",
                    "                ctx.registry.add(\(name).subscribe { [w] v in w.\(prop.setterName)(\(prop.setterLabel): v) })",
                    "            }",
                ]
            }
            extras.configureUsesCtx = true
        } else {
            let parameterType = qt.hasSuffix("?") ? qt : qt + "?"
            extras.paramDecls.append("\(name): \(parameterType) = nil")
            extras.configureLines.append("            if let \(name) { w.\(prop.setterName)(\(prop.setterLabel): \(name)) }")
        }
        extras.docs.append((name, parameterDoc(name, widget: owner)))
    }

    // Required widget parameters become strict single-view builders.
    for param in initModel.params where isWidgetType(param.type, module: widget.module) {
        let label = param.label
        extras.paramDecls.append("@SingleViewBuilder \(label): () -> AnyView")
        extras.preludeLines.append("        let \(label)View = \(label)()")
        extras.makeArgs[label] = "\(label)View.makeWidget(ctx)"
        extras.makeUsesCtx = true
        extras.docs.append((label, "A closure supplying the single view passed to `\(widget.module).\(widget.className).init` as `\(label)`. Exactly one view is required; an empty closure is a compile-time error."))
    }

    // Optional generic child builder.
    if let primary = widget.primaryAdder {
        extras.paramDecls.append("@ViewBuilder children: () -> [AnyView] = { [] }")
        extras.preludeLines.append("        let childrenViews = children()")
        let discard = primary.returnsValue ? "_ = " : ""
        extras.configureLines.append("            Portico.mountChildren(childrenViews, into: w, ctx) { c in \(discard)w.\(primary.methodName)(\(primary.label): c) }")
        extras.configureUsesCtx = true
        extras.sources.append("\(widget.module).\(widget.className).\(primary.methodName)(\(primary.label):)")
        extras.docs.append(("children", "A `ViewBuilder` closure whose views are added in order."))
    }

    // Optional widget slots, ordered by semantic region and declaration order.
    let matchedSlots = effProps.enumerated().filter { _, entry in
        isWidgetType(entry.prop.type, module: entry.owner.module) &&
        !nonSlotWidgetProperties.contains("\(entry.owner.module).\(entry.owner.className).\(entry.prop.name)") &&
        !widget.reservedInitLabels.contains(entry.prop.name)
    }.sorted {
        let leftRank = slotRank($0.element.prop.name)
        let rightRank = slotRank($1.element.prop.name)
        return leftRank == rightRank ? $0.offset < $1.offset : leftRank < rightRank
    }.map(\.element)
    for entry in matchedSlots {
        let prop = entry.prop
        let owner = entry.owner
        let name = prop.name
        extras.paramDecls.append("@ViewBuilder \(name): () -> [AnyView] = { [] }")
        extras.preludeLines.append("        let \(name)Views = \(name)()")
        extras.configureLines.append("            if let v = \(name)Views.first { w.\(prop.setterName)(\(prop.setterLabel): v.makeWidget(ctx)) }")
        extras.configureUsesCtx = true
        extras.sources.append("\(owner.module).\(owner.className).\(prop.setterName)(\(prop.setterLabel):)")
        extras.docs.append((name, "A `ViewBuilder` closure whose first view is mounted into the `\(name)` slot."))
    }

    // Optional signal handlers, including inherited signals.
    for entry in effectiveSignals(for: widget) {
        let signal = entry.signal
        let args = signal.argTypes.map { qualifyType($0, module: entry.owner.module) }
        let returnType = qualifyType(signal.returnType, module: entry.owner.module)
        let handlerType = args.isEmpty
            ? "() -> \(returnType)"
            : "(\(args.joined(separator: ", "))) -> \(returnType)"
        let label = "on\(signal.baseName)"
        extras.paramDecls.append("\(label): (\(handlerType))? = nil")
        if args.isEmpty {
            extras.configureLines.append("            if let \(label) { ctx.registry.add(w.connect\(signal.baseName) { _ in \(label)() }) }")
        } else {
            let names = args.indices.map { "a\($0)" }.joined(separator: ", ")
            extras.configureLines.append("            if let \(label) { ctx.registry.add(w.connect\(signal.baseName) { _, \(names) in \(label)(\(names)) }) }")
        }
        extras.configureUsesCtx = true
        extras.docs.append((label, signalHandlerDoc(signal)))
    }

    return extras
}

func generateInits(widget: WidgetModel, initModel: InitModel) -> String {
    let qualifiedType = "\(widget.module).\(widget.className)"
    let params = initModel.params
    let valueParams = params.filter { !isWidgetType($0.type, module: widget.module) }
    var out = ""

    let effPropMap = Dictionary(
        effectiveProperties(for: widget).map { ($0.prop.name, ($0.prop, $0.owner.module)) },
        uniquingKeysWith: { a, _ in a }
    )
    let qualifiedValueTypes = valueParams.map { qualifyType($0.type, module: widget.module) }
    let reactiveParams: [(Param, String)] = valueParams.compactMap { p in
        guard let (prop, ownerModule) = effPropMap[p.label] else { return nil }
        let propType = qualifyType(prop.type, module: ownerModule)
        let paramType = qualifyType(p.type, module: widget.module)
        guard propType == paramType else { return nil }
        return (p, paramType)
    }
    let allReactive = !valueParams.isEmpty && reactiveParams.count == valueParams.count
    let interpSlot = interpolationSlot(params: valueParams, widget: widget)
    let initLabels = params.map { "\($0.label):" }.joined()
    let baseDocs = valueParams.map { (name: $0.label, text: parameterDoc($0.label, widget: widget)) }

    func notes(_ base: [String], extras: InitExtras, binding: Bool) -> [String] {
        var result = base
        if !extras.paramDecls.filter({ $0.hasPrefix("@") }).isEmpty {
            result.append("Each closure is evaluated once; children are added in order and slot closures mount their first view.")
            result.append("An empty closure adds no children and leaves slots unset.")
            if widget.primaryAdder != nil {
                result.append("A `ForEach` in the `children:` closure spreads its rows directly into this widget, with no wrapper, when the widget supports ordered insertion.")
            }
        }
        result.append("Optional value parameters are applied only when non-`nil`; a `nil` argument leaves the widget's own default in place and cannot clear a nullable property - use the matching modifier for that.")
        if binding {
            result.append("Optional `Binding` parameters bind through `Portico.bindProperty`, so they are two-way wherever the wrapper exposes a safe getter.")
        }
        return result
    }

    func argumentExpressions(_ valueExpression: (Param) -> String, extras: InitExtras) -> String {
        params.map { param in
            "\(param.label): \(extras.makeArgs[param.label] ?? valueExpression(param))"
        }.joined(separator: ", ")
    }

    func emitFlavor(
        chain: String,
        sources: [String],
        summary: [String],
        flavorNotes: [String],
        parameterDecls: [String],
        parameterDocs: [(name: String, text: String)],
        arguments: String,
        prelude: [String],
        flavorConfigure: [String],
        extras: InitExtras,
        genericPrefix: String = "",
        disfavored: Bool = false
    ) {
        out += docBlock(
            indent: "    ",
            chain: [chain],
            sources: sources,
            summary: summary,
            notes: notes(flavorNotes, extras: extras, binding: chain.contains("binding")),
            parameters: parameterDocs
        )
        if disfavored { out += "    @_disfavoredOverload\n" }
        out += "    public init\(genericPrefix)(\(parameterDecls.joined(separator: ", "))) {\n"
        out += prelude.map { "\($0)\n" }.joined()
        let makeContext = extras.makeUsesCtx ? "ctx" : "_"
        out += "        make = { \(makeContext) in \(qualifiedType)(\(arguments)) }\n"
        let configureLines = flavorConfigure + extras.configureLines
        if !configureLines.isEmpty {
            let configureContext = extras.configureUsesCtx || chain.contains("binding") || chain.contains("closure") || chain.contains("interpolation") ? "ctx" : "_"
            out += "        configure.append { w, \(configureContext) in\n"
            out += configureLines.map { "\($0)\n" }.joined()
            out += "        }\n"
        }
        out += "    }\n\n"
    }

    // --- Static init ---
    let staticExtras = initExtras(widget: widget, initModel: initModel, bindingValues: false)
    let staticArgs = argumentExpressions({ "\($0.label)" }, extras: staticExtras)
    if let slot = interpSlot {
        let slotLabel = slot.param.label
        let typeParam = slot.optional ? "S?" : "S"
        let valueDecls = zip(valueParams, qualifiedValueTypes).map { p, type in
            p.label == slotLabel ? "\(p.label): \(typeParam)" : "\(p.label): \(type)"
        }
        let staticArgsWithCast = argumentExpressions({ param in
            if param.label == slotLabel {
                return slot.optional ? "\(param.label).map { String($0) }" : "String(\(param.label))"
            }
            return param.label
        }, extras: staticExtras)
        emitFlavor(
            chain: "generateInits(static)",
            sources: ["\(widget.module).\(widget.className).init(\(initLabels))"],
            summary: initModel.doc,
            flavorNotes: ["Applied once at mount; use the `Binding`, closure, or `InterpolatedText` overload for values that change.", "A string literal containing interpolation selects the `InterpolatedText` overload instead, which updates live."],
            parameterDecls: valueDecls + staticExtras.paramDecls,
            parameterDocs: baseDocs + staticExtras.docs,
            arguments: staticArgsWithCast,
            prelude: staticExtras.preludeLines,
            flavorConfigure: [],
            extras: staticExtras,
            genericPrefix: "<S: StringProtocol>",
            disfavored: true
        )
    } else {
        emitFlavor(
            chain: "generateInits(static)",
            sources: ["\(widget.module).\(widget.className).init(\(initLabels))"],
            summary: initModel.doc,
            flavorNotes: ["Applied once at mount; use the `Binding` or closure overload for values that change."],
            parameterDecls: zip(valueParams, qualifiedValueTypes).map { "\($0.label): \($1)" } + staticExtras.paramDecls,
            parameterDocs: baseDocs + staticExtras.docs,
            arguments: staticArgs,
            prelude: staticExtras.preludeLines,
            flavorConfigure: [],
            extras: staticExtras
        )
    }

    if allReactive {
        let bindingExtras = initExtras(widget: widget, initModel: initModel, bindingValues: true)
        let bindingParams = valueParams.map { "\($0.label): Portico.Binding<\(qualifyType($0.type, module: widget.module))>" } + bindingExtras.paramDecls
        let bindingArgs = argumentExpressions({ "\($0.label).wrappedValue" }, extras: bindingExtras)
        let setters = reactiveParams.map { rp in
            let setter = effPropMap[rp.0.label]!.0
            return "\(qualifiedType).\(setter.setterName)(\(setter.setterLabel):)"
        }.joined(separator: ", ")
        var bindSources = ["\(widget.module).\(widget.className).init(\(initLabels))"]
        bindSources += reactiveParams.map { rp in
            let setter = effPropMap[rp.0.label]!.0
            return "\(widget.module).\(widget.className).\(setter.setterName)(\(setter.setterLabel):)"
        }
        let bindingConfigure = reactiveParams.map { p, _ -> String in
            let setter = effPropMap[p.label]!.0
            return "            ctx.registry.add(\(p.label).subscribe { [w] v in w.\(setter.setterName)(\(setter.setterLabel): v) })"
        }
        emitFlavor(
            chain: "generateInits(binding)",
            sources: bindSources,
            summary: initModel.doc,
            flavorNotes: ["The initial value is the binding's current value; every later change is pushed into the widget through `\(setters)` without rebuilding the view."],
            parameterDecls: bindingParams,
            parameterDocs: baseDocs + bindingExtras.docs,
            arguments: bindingArgs,
            prelude: bindingExtras.preludeLines,
            flavorConfigure: bindingConfigure,
            extras: bindingExtras
        )

        let closureExtras = staticExtras
        let closureParams = valueParams.map { "\($0.label): @escaping () -> \(qualifyType($0.type, module: widget.module))" } + closureExtras.paramDecls
        let closureArgs = argumentExpressions({ "\($0.label)()" }, extras: closureExtras)
        let closureConfigure = reactiveParams.enumerated().flatMap { i, rp -> [String] in
            let setter = effPropMap[rp.0.label]!.0
            return [
                "            let t\(i) = DependencyTracker { [w] in w.\(setter.setterName)(\(setter.setterLabel): \(rp.0.label)()) }",
                "            t\(i).run()",
                "            ctx.registry.add(t\(i))",
            ]
        }
        emitFlavor(
            chain: "generateInits(closure)",
            sources: bindSources,
            summary: initModel.doc,
            flavorNotes: ["Each closure runs inside a `DependencyTracker`, so any `@State` it reads re-runs it and pushes the new value through `\(setters)`."],
            parameterDecls: closureParams,
            parameterDocs: baseDocs + closureExtras.docs,
            arguments: closureArgs,
            prelude: closureExtras.preludeLines,
            flavorConfigure: closureConfigure,
            extras: closureExtras
        )
    }

    // --- Interpolated init ---
    if let slot = interpSlot {
        let interpExtras = staticExtras
        let slotLabel = slot.param.label
        let interpType = slot.optional ? "Portico.InterpolatedText?" : "Portico.InterpolatedText"
        let interpParams = valueParams.map { param in
            "\(param.label): \(param.label == slotLabel ? interpType : qualifyType(param.type, module: widget.module))"
        } + interpExtras.paramDecls
        let interpArgs = argumentExpressions({ param in
            param.label == slotLabel
                ? (slot.optional ? "\(param.label)?.untrackedText" : "\(param.label).untrackedText")
                : param.label
        }, extras: interpExtras)
        let bindFn = slot.optional ? "Portico.bindOptionalInterpolation" : "Portico.bindInterpolation"
        let setter = "\(qualifiedType).\(slot.setterName)(\(slot.setterLabel):)"
        let interpConfigure = ["            \(bindFn)(\(slotLabel), registry: ctx.registry) { [w] v in w.\(slot.setterName)(\(slot.setterLabel): v) }"]
        emitFlavor(
            chain: "generateInits(interpolation)",
            sources: ["\(widget.module).\(widget.className).init(\(initLabels))", setter],
            summary: initModel.doc,
            flavorNotes: ["Interpolated segments are captured unevaluated and re-read inside a `DependencyTracker`, so any `@State` they read pushes a new value through `\(setter)`. A literal with no interpolation is applied once, with no subscription."],
            parameterDecls: interpParams,
            parameterDocs: baseDocs + interpExtras.docs,
            arguments: interpArgs,
            prelude: interpExtras.preludeLines,
            flavorConfigure: interpConfigure,
            extras: interpExtras
        )
    }

    return out
}

/// `Module.Class.property` names that must never become a `@ViewBuilder` slot.
///
/// `setVisibleChild` requires a widget that is already a child of the container, so a slot
/// that mounts a fresh view would always violate the GTK precondition. The leading
/// `children:` builder covers these classes: GTK makes the first added child visible.
let nonSlotWidgetProperties: Set<String> = [
    "Adw.Leaflet.visibleChild",
    "Adw.ViewStack.visibleChild",
    "Gtk.Stack.visibleChild",
]




/// Generates static and ViewBuilder modifiers for child-adder methods.
func generateChildAdderModifiers(widget: WidgetModel) -> String {
    var out = ""
    for adder in widget.childAdders {
        let source = "\(widget.module).\(widget.className).\(adder.methodName)(\(adder.label):)"
        let summary = widget.memberDocs[adder.methodName] ?? ["Adds a child to `\(widget.module).\(widget.className)`." ]
        let discard = adder.returnsValue ? "_ = " : ""
        out += docBlock(indent: "    ", chain: ["generateModifierExtension", "generateChildAdderModifiers(static)"], sources: [source], summary: summary, notes: ["Applied once at mount; use the `@ViewBuilder` overload for multiple children."], parameters: [(name: "child", text: "A child widget to add.")], returns: "A copy of this view with the modifier applied.")
        out += "    public func \(adder.methodName)(_ child: Gtk.Widget) -> Self {\n"
        emitWrapperStart(&out, style: .widgetView, usesCtx: false)
        out += "            \(discard)w.\(adder.methodName)(\(adder.label): child)\n"
        emitWrapperEnd(&out, style: .widgetView)
        out += "    }\n\n"
        out += docBlock(indent: "    ", chain: ["generateModifierExtension", "generateChildAdderModifiers(viewBuilder)"], sources: [source], summary: summary, notes: ["Every view the closure produces is added at mount, in order."], parameters: [(name: "child", text: "A closure producing child views.")], returns: "A copy of this view with the modifier applied.")
        out += "    public func \(adder.methodName)(@ViewBuilder _ child: () -> [AnyView]) -> Self {\n"
        out += "        let childViews = child()\n"
        emitWrapperStart(&out, style: .widgetView, lead: "return ")
        out += "            for v in childViews { \(discard)w.\(adder.methodName)(\(adder.label): v.makeWidget(ctx)) }\n"
        emitWrapperEnd(&out, style: .widgetView)
        out += "    }\n\n"
    }
    return out
}

// MARK: - Property modifier generation

/// Generates the modifier overload set for a settable property.
///
/// - Parameters:
///   - owner: The ``WidgetModel`` that **owns** this modifier extension (used for
///     two-way binding key lookup).
///   - prop: The property to generate modifiers for.
///   - style: Whether to emit `WidgetView`-constrained (`Self`) or erasing
///     `View` (`AnyView`) modifiers.
///
/// Every property gets a static modifier. Widget-typed properties additionally get a
/// ``ViewBuilder`` slot modifier; everything else gets a `Binding` and a tracked-closure
/// modifier. Nullable properties get a second `Binding` overload taking the non-optional
/// value type, because `Binding` is invariant. Properties typed as a widget class emit
/// their `Binding` overloads generically over that class, so a `Binding` of any subclass
/// is accepted; see ``widgetClassConstraint(_:module:)``.
func generatePropertyModifiers(owner: WidgetModel, prop: PropertyModel, style: ModifierStyle) -> String {
    var out = ""
    let qualifiedType = qualifyType(prop.type, module: owner.module)
    let ret = style == .widgetView ? "Self" : "AnyView"
    let interpolatable = !isWidgetType(prop.type, module: owner.module) && isStringType(qualifiedType)

    let root = style == .widgetView ? "generateModifierExtension" : "generateViewExtension"
    let retStr = style == .widgetView
        ? "A copy of this view with the modifier applied."
        : "An `AnyView` wrapping this view with the modifier applied."

    let summaryLines = owner.memberDocs[prop.setterName] ?? owner.memberDocs[prop.name] ?? ["Sets `\(prop.name)`."]
    let sources = ["\(owner.module).\(owner.className).\(prop.setterName)(\(prop.setterLabel):)"]

    let paramText: String
    if let pl = owner.memberDocs[prop.name], let fp = firstParagraph(of: pl) {
        paramText = fp
    } else if let sl = owner.memberDocs[prop.setterName], let fp = firstParagraph(of: sl) {
        paramText = fp
    } else {
        paramText = "The new `\(prop.name)` value."
    }

    // --- Static modifier ---
    if interpolatable {
        let staticNotes = ["Applied once at mount; use the `Binding`, closure, or `InterpolatedText` overload for a value that changes.",
                           "A string literal containing interpolation selects the `InterpolatedText` overload instead, which updates live."]
        out += docBlock(
            indent: "    ",
            chain: [root, "generatePropertyModifiers(static)"],
            sources: sources,
            summary: summaryLines,
            notes: staticNotes,
            parameters: [(name: prop.name, text: paramText)],
            returns: retStr
        )
        let typeParam = qualifiedType.hasSuffix("?") ? "S?" : "S"
        let argExpr = qualifiedType.hasSuffix("?")
            ? "\(prop.name).map { String($0) }"
            : "String(\(prop.name))"
        out += "    @_disfavoredOverload\n"
        out += "    public func \(prop.name)<S: StringProtocol>(_ \(prop.name): \(typeParam)) -> \(ret) {\n"
        emitWrapperStart(&out, style: style, usesCtx: false)
        out += "            w.\(prop.setterName)(\(prop.setterLabel): \(argExpr))\n"
        emitWrapperEnd(&out, style: style)
        out += "    }\n"
    } else {
        out += docBlock(
            indent: "    ",
            chain: [root, "generatePropertyModifiers(static)"],
            sources: sources,
            summary: summaryLines,
            notes: ["Applied once at mount; use the `Binding` or closure overload for a value that changes."],
            parameters: [(name: prop.name, text: paramText)],
            returns: retStr
        )
        out += "    public func \(prop.name)(_ \(prop.name): \(qualifiedType)) -> \(ret) {\n"
        emitWrapperStart(&out, style: style, usesCtx: false)
        out += "            w.\(prop.setterName)(\(prop.setterLabel): \(prop.name))\n"
        emitWrapperEnd(&out, style: style)
        out += "    }\n"
    }
    out += "\n"

    if isWidgetType(prop.type, module: owner.module) && style == .widgetView {
        // --- ViewBuilder modifier ---
        out += docBlock(
            indent: "    ",
            chain: [root, "generatePropertyModifiers(viewBuilder)"],
            sources: sources,
            summary: summaryLines,
            notes: [
                "The closure is evaluated once when the modifier is applied. Its first view is mounted into the slot.",
                "Additional views are ignored; an empty closure leaves the slot unset.",
            ],
            parameters: [(name: prop.name, text: paramText)],
            returns: retStr
        )
        out += "    public func \(prop.name)(@ViewBuilder _ \(prop.name): () -> [AnyView]) -> \(ret) {\n"
        out += "        let \(prop.name)Views = \(prop.name)()\n"
        emitWrapperStart(&out, style: style, lead: "return ")
        out += "            guard let v = \(prop.name)Views.first else { return }\n"
        out += "            w.\(prop.setterName)(\(prop.setterLabel): v.makeWidget(ctx))\n"
        emitWrapperEnd(&out, style: style)
        out += "    }\n"
    }

    // --- Binding modifier ---
    out += bindingModifier(owner: owner, prop: prop, valueType: qualifiedType, variance: .exact, style: style)
    out += "\n"
    if qualifiedType.hasSuffix("?") {
        out += bindingModifier(owner: owner, prop: prop, valueType: String(qualifiedType.dropLast()), variance: .lifted, style: style)
        out += "\n"
    } else if prop.getterIsOptional && !isStringType(qualifiedType) {
        out += bindingModifier(owner: owner, prop: prop, valueType: qualifiedType + "?", variance: .lowered, style: style)
        out += "\n"
    }

    // --- Closure modifier ---
    out += docBlock(
        indent: "    ",
        chain: [root, "generatePropertyModifiers(closure)"],
        sources: sources,
        summary: summaryLines,
        notes: ["The closure runs inside a `DependencyTracker`, so any `@State` it reads re-runs it and pushes the new value through `\(owner.module).\(owner.className).\(prop.setterName)(\(prop.setterLabel):)`."],
        parameters: [(name: prop.name, text: paramText)],
        returns: retStr
    )
    out += "    public func \(prop.name)(_ \(prop.name): @escaping () -> \(qualifiedType)) -> \(ret) {\n"
    emitWrapperStart(&out, style: style)
    out += "            let tracker = DependencyTracker { [w] in w.\(prop.setterName)(\(prop.setterLabel): \(prop.name)()) }\n"
    out += "            tracker.run()\n"
    out += "            ctx.registry.add(tracker)\n"
    emitWrapperEnd(&out, style: style)
    out += "    }\n"
    // --- Interpolated modifier ---
    if interpolatable {
        out += docBlock(
            indent: "    ",
            chain: [root, "generatePropertyModifiers(interpolation)"],
            sources: sources,
            summary: summaryLines,
            notes: ["Interpolated segments are captured unevaluated and re-read inside a `DependencyTracker`, so any `@State` they read pushes a new value through `\(owner.module).\(owner.className).\(prop.setterName)(\(prop.setterLabel):)`. A literal with no interpolation is applied once, with no subscription."],
            parameters: [(name: prop.name, text: paramText)],
            returns: retStr
        )
        let interpType = qualifiedType.hasSuffix("?") ? "Portico.InterpolatedText?" : "Portico.InterpolatedText"
        let bindFn = qualifiedType.hasSuffix("?") ? "Portico.bindOptionalInterpolation" : "Portico.bindInterpolation"
        out += "    public func \(prop.name)(_ \(prop.name): \(interpType)) -> \(ret) {\n"
        emitWrapperStart(&out, style: style)
        out += "            \(bindFn)(\(prop.name), registry: ctx.registry) { [w] v in w.\(prop.setterName)(\(prop.setterLabel): v) }\n"
        emitWrapperEnd(&out, style: style)
        out += "    }\n"
    }
    out += "\n"

    return out
}

/// Emits one `Binding`-taking reactive modifier for `prop`.
///
/// Uses `Portico.bindProperty` to push the binding's value into the widget at
/// mount and keep them in sync. When the property has a safe read-back path and
/// the value type is `Equatable`, the generated code calls the two-way overload;
/// otherwise it calls the one-way overload.
///
/// How a `Binding`'s value type relates to the property's declared type.
enum BindingVariance { case exact, lifted, lowered }
func bindingModifier(owner: WidgetModel, prop: PropertyModel, valueType: String, variance: BindingVariance, style: ModifierStyle) -> String {
    var out = ""
    let ret = style == .widgetView ? "Self" : "AnyView"

    let root = style == .widgetView ? "generateModifierExtension" : "generateViewExtension"
    let retStr = style == .widgetView
        ? "A copy of this view with the modifier applied."
        : "An `AnyView` wrapping this view with the modifier applied."
    // The expression the write-back reads the widget's current value through.
    // `nil` means there is no safe read path, so the modifier stays one-way.
    let readExpr = readBackExpr(prop, module: owner.module)

    let isLowered: Bool
    if case .lowered = variance { isLowered = true } else { isLowered = false }
    let canReadBack = !isLowered && readExpr != nil

    // Widget-class properties are emitted generically over `W` so a `Binding` of any
    // subclass - what a `WidgetRef<Subclass>` projects - is accepted directly. An
    // implicitly-unwrapped declared type is left concrete; replacing `T!` with `W`
    // would silently drop its optionality.
    let genericBase = valueType.hasSuffix("!")
        ? nil
        : widgetClassConstraint(prop.type, module: owner.module)
    let genericParam = genericBase.map { "<W: \($0)>" } ?? ""
    let boundType = genericBase == nil
        ? valueType
        : (valueType.hasSuffix("?") ? "W?" : "W")
    // The read-back closure must yield the bound type, not the property's declared type.
    let readCast = genericBase == nil ? "" : " as? W"

    let summaryLines = owner.memberDocs[prop.setterName] ?? owner.memberDocs[prop.name] ?? ["Sets `\(prop.name)`."]
    var sources = ["\(owner.module).\(owner.className).\(prop.setterName)(\(prop.setterLabel):)"]

    let paramText: String
    if let pl = owner.memberDocs[prop.name], let fp = firstParagraph(of: pl) {
        paramText = fp
    } else if let sl = owner.memberDocs[prop.setterName], let fp = firstParagraph(of: sl) {
        paramText = fp
    } else {
        paramText = "The new `\(prop.name)` value."
    }

    let chain: [String]
    var notes: [String]

    if canReadBack {
        sources.append("GObject.Object.connectNotify(detail:_:)")
        if let g = prop.getterName {
            sources.append("\(owner.module).\(owner.className).\(g)()")
        }
    }

    switch variance {
    case .exact:
        if canReadBack {
            chain = [root, "generatePropertyModifiers", "bindingModifier(twoWay)"]
            notes = [
                "Applied at mount and re-applied on every change the binding publishes.",
                """
When `\(valueType)` conforms to `Equatable` this binds in both directions: \
the widget's `notify` signal writes its current value back into the binding, \
so changes made in the UI propagate to the bound state. Each direction \
compares before writing, which terminates the echo after one hop. A value type \
that is not `Equatable` binds one way only, because the echo cannot be \
broken.
""",
            ]
        } else {
            chain = [root, "generatePropertyModifiers", "bindingModifier(oneWay)"]
            notes = [
                "Applied at mount and re-applied on every change the binding publishes.",
                "Binds one way only (binding to widget): `\(owner.module).\(owner.className)` exposes no getter for `\(prop.name)` that is safe to read back, so changes made in the UI do not propagate to the binding.",
            ]
        }
    case .lifted:
        let marker = canReadBack ? "twoWay" : "oneWay"
        chain = [root, "generatePropertyModifiers", "bindingModifier(lifted,\(marker))"]
        notes = [
            "Applied at mount and re-applied on every change the binding publishes.",
            "`Binding` is invariant, so a `Binding<\(valueType)>` is not accepted by the nullable overload; this one takes it and promotes each value. Pass a `Binding<\(valueType)?>` to be able to clear the property.",
        ]
        if canReadBack {
            notes.append("""
When `\(valueType)` conforms to `Equatable` this binds in both directions: \
the widget's `notify` signal writes its current value back into the binding, \
so changes made in the UI propagate to the bound state. Each direction \
compares before writing, which terminates the echo after one hop. A value type \
that is not `Equatable` binds one way only, because the echo cannot be \
broken.
""")
            notes.append("A `nil` widget value is never written back into the binding.")
        }
    case .lowered:
        chain = [root, "generatePropertyModifiers", "bindingModifier(lowered)"]
        let nullableSource = genericBase == nil
            ? "this overload accepts a nullable binding"
            : "this overload accepts a nullable binding (what a `WidgetRef` projects)"
        notes = [
            "Applied at mount and re-applied on every change the binding publishes.",
            "`Binding` is invariant and this property has no unset state; \(nullableSource) and ignores `nil` values. Binds one way only.",
        ]
    }


    out += docBlock(
        indent: "    ",
        chain: chain,
        sources: sources,
        summary: summaryLines,
        notes: notes,
        returns: retStr
    )
    out += "    public func \(prop.name)\(genericParam)(_ \(prop.name): Portico.Binding<\(boundType)>) -> \(ret) {\n"

    if canReadBack, let re = readExpr {
        // Two-way capable: call Portico.bindProperty with read/write closures.
        let setterCall = "w.\(prop.setterName)(\(prop.setterLabel): v)"
        if style == .widgetView {
            out += "        appending { w, ctx in\n"
            out += "            Portico.bindProperty(\n"
            out += "                w, \(prop.name), registry: ctx.registry, notifyDetail: \"\(gobjectPropertyName(prop.name))\",\n"
            out += "                read: { [w] in \(re)\(readCast) },\n"
            out += "                write: { [w] v in \(setterCall) }\n"
            out += "            )\n"
            out += "        }\n"
        } else {
            out += "        AnyView(makeWidget: { ctx in\n"
            out += "            let w = AnyView(self).makeWidget(ctx)\n"
            out += "            Portico.bindProperty(\n"
            out += "                w, \(prop.name), registry: ctx.registry, notifyDetail: \"\(gobjectPropertyName(prop.name))\",\n"
            out += "                read: { [w] in \(re)\(readCast) },\n"
            out += "                write: { [w] v in \(setterCall) }\n"
            out += "            )\n"
            out += "            return w\n"
            out += "        })\n"
        }
    } else {
        // One-way: subscribe to binding only.
        emitWrapperStart(&out, style: style)
        if isLowered {
            out += "            if let v = \(prop.name).untrackedValue { w.\(prop.setterName)(\(prop.setterLabel): v) }\n"
            out += "            ctx.registry.add(\(prop.name).subscribe { [w] v in if let v { w.\(prop.setterName)(\(prop.setterLabel): v) } })\n"
        } else {
            out += "            w.\(prop.setterName)(\(prop.setterLabel): \(prop.name).untrackedValue)\n"
            out += "            ctx.registry.add(\(prop.name).subscribe { [w] v in w.\(prop.setterName)(\(prop.setterLabel): v) })\n"
        }
        emitWrapperEnd(&out, style: style)
    }

    out += "    }\n"
    return out
}

// MARK: - Wrapper helpers

/// Emits the opening lines of a modifier body, wrapping the configuration
/// step in either a `WidgetView.appending` call or an `AnyView` mount thunk.
/// - Parameter usesCtx: When `false`, the closure captures `_` instead of `ctx`
///   to avoid an unused-variable warning.
/// - Parameter lead: Text emitted between the indent and the wrapper call, e.g. `"return "`.
func emitWrapperStart(_ out: inout String, style: ModifierStyle, usesCtx: Bool = true, lead: String = "") {
    switch style {
    case .widgetView:
        let ctxParam = usesCtx ? "ctx" : "_"
        out += "        \(lead)appending { w, \(ctxParam) in\n"
    case .erasingView:
        // `ctx` is always used for `makeWidget(ctx)` on the next line.
        out += "        \(lead)AnyView(makeWidget: { ctx in\n"
        out += "            let w = AnyView(self).makeWidget(ctx)\n"
    }
}

/// Emits the closing lines for a wrapper started by ``emitWrapperStart``.
func emitWrapperEnd(_ out: inout String, style: ModifierStyle) {
    switch style {
    case .widgetView:
        out += "        }\n"
    case .erasingView:
        out += "            return w\n"
        out += "        })\n"
    }
}
// MARK: - Signal modifier generation

func generateSignalModifier(widget: WidgetModel, signal: SignalModel, style: ModifierStyle) -> String {
    var out = ""
    let ret = style == .widgetView ? "Self" : "AnyView"

    let root = style == .widgetView ? "generateModifierExtension" : "generateViewExtension"
    let retStr = style == .widgetView
        ? "A copy of this view with the modifier applied."
        : "An `AnyView` wrapping this view with the modifier applied."

    let trampolineArgs: String
    let handlerType: String

    if signal.argTypes.isEmpty {
        trampolineArgs = ""
        handlerType = "() -> \(qualifyType(signal.returnType, module: widget.module))"
    } else {
        let qualifiedArgs = signal.argTypes.map { qualifyType($0, module: widget.module) }
        trampolineArgs = qualifiedArgs.enumerated().map { (i, _) in "a\(i)" }.joined(separator: ", ")
        handlerType = "(\(qualifiedArgs.joined(separator: ", "))) -> \(qualifyType(signal.returnType, module: widget.module))"
    }

    let summaryLines = widget.memberDocs["connect\(signal.baseName)"] ?? ["Connects a handler to the `\(signal.signalName)` signal."]

    let handlerNote = signalHandlerDoc(signal)

    out += docBlock(
        indent: "    ",
        chain: [root, "generateSignalModifier"],
        sources: ["\(widget.module).\(widget.className).connect\(signal.baseName)(_:)"],
        summary: summaryLines,
        parameters: [(name: "handler", text: handlerNote)],
        returns: retStr
    )
    out += "    public func on\(signal.baseName)(_ handler: @escaping \(handlerType)) -> \(ret) {\n"
    emitWrapperStart(&out, style: style)

    if signal.argTypes.isEmpty {
        out += "            ctx.registry.add(w.connect\(signal.baseName) { _ in handler() })\n"
    } else {
        out += "            ctx.registry.add(w.connect\(signal.baseName) { _, \(trampolineArgs) in handler(\(trampolineArgs)) })\n"
    }

    emitWrapperEnd(&out, style: style)
    out += "    }\n"
    out += "\n"

    return out
}

// MARK: - Modifier extension generation

/// Emits `extension WidgetView where Target: <Module>.<Class> { … }` with every
/// property and signal modifier the class owns. Returns `""` when the owner has
/// no settable properties and no signals.
func generateModifierExtension(widget: WidgetModel) -> String {
    guard !widget.properties.isEmpty || !widget.signals.isEmpty || !widget.childAdders.isEmpty else { return "" }

    var out = ""
    let target = "\(widget.module).\(widget.className)"

    out += docBlock(
        indent: "",
        chain: ["generateModifierExtension"],
        sources: ["\(widget.module).\(widget.className)"],
        summary: ["Modifiers for `\(target)`, available on every Portico view whose", "backing widget is `\(target)` or one of its subclasses."]
    )
    out += "extension WidgetView where Target: \(target) {\n"
    out += generateChildAdderModifiers(widget: widget)

    for prop in widget.properties {
        out += generatePropertyModifiers(owner: widget, prop: prop, style: .widgetView)
    }
    for signal in widget.signals {
        out += generateSignalModifier(widget: widget, signal: signal, style: .widgetView)
    }

    out += "}\n"
    return out
}

/// Emits the erasing `extension View { … }` fallback so non-`WidgetView` views
/// (user composites, `AnyView`, raw `Gtk.Widget` values, `VStack`/`ForEach`/…)
/// still accept widget-level modifiers. Invoked only for the `Gtk.Widget` model.
func generateViewExtension(widget: WidgetModel) -> String {
    var out = ""

    out += docBlock(
        indent: "",
        chain: ["generateViewExtension"],
        sources: ["\(widget.module).\(widget.className)"],
        summary: [
            "Widget-level modifiers for any `View`.",
            "",
            "These erase to `AnyView` so they compose with views that do not conform",
            "to `WidgetView`. `WidgetView` conformers prefer the `Self`-returning",
            "`WidgetView where Target: Gtk.Widget` overloads by Swift's overload",
            "resolution, preserving their concrete type for chaining.",
        ]
    )
    out += "extension View {\n"

    for prop in widget.properties {
        out += generatePropertyModifiers(owner: widget, prop: prop, style: .erasingView)
    }
    for signal in widget.signals {
        out += generateSignalModifier(widget: widget, signal: signal, style: .erasingView)
    }

    out += "}\n"
    return out
}