DebugLayoutLog.swift

import SwiftUI

@available(macOS 13.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *)
func logLayoutStep(_ label: String, step: LogEntry.Step) {
    DispatchQueue.main.async {
        guard let prevEntry = LogStore.shared.log.last else {
            // First log entry → start at indent 0.
            LogStore.shared.log.append(LogEntry(label: label, step: step, indent: 0))
            return
        }

        var newEntry = LogEntry(label: label, step: step, indent: prevEntry.indent)
        let isSameView = prevEntry.label == label
        switch (isSameView, prevEntry.step, step) {
        case (true, .proposal(let prop), .response(let resp)):
            // Response follows immediately after proposal for the same view.
            // → We want to display them in a single row.
            // → Coalesce both layout steps.
            LogStore.shared.log.removeLast()
            newEntry = prevEntry
            newEntry.step = .proposalAndResponse(proposal: prop, response: resp)
            LogStore.shared.log.append(newEntry)

        case (_, .proposal, .proposal):
            // A proposal follows a proposal → nested view → increment indent.
            newEntry.indent += 1
            LogStore.shared.log.append(newEntry)

        case (_, .response, .response),
            (_, .proposalAndResponse, .response):
            // A response follows a response → last child returns to parent → decrement indent.
            newEntry.indent -= 1
            LogStore.shared.log.append(newEntry)

        default:
            // Keep current indentation.
            LogStore.shared.log.append(newEntry)
        }
    }
}

/// A custom layout that clears the DebugLayout log
/// at the point where it's placed in the view tree.
@available(macOS 13.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *)
struct ClearDebugLayoutLog: Layout {
    func sizeThatFits(proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) -> CGSize {
        assert(subviews.count == 1)
        DispatchQueue.main.async {
            LogStore.shared.log.removeAll()
            LogStore.shared.viewLabels.removeAll()
        }
        return subviews[0].sizeThatFits(proposal)
    }

    func placeSubviews(in bounds: CGRect, proposal: ProposedViewSize, subviews: Subviews, cache: inout ()) {
        assert(subviews.count == 1)
        subviews[0].place(at: bounds.origin, proposal: proposal)
    }
}

@available(macOS 13.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *)
public final class LogStore: ObservableObject {
    public static let shared: LogStore = .init()

    @Published public var log: [LogEntry] = []
    var viewLabels: Set<String> = []

    func registerViewLabelAndWarnIfNotUnique(_ label: String, file: StaticString, line: UInt) {
        DispatchQueue.main.async {
            if self.viewLabels.contains(label) {
                let message: StaticString = "Duplicate view label '%s' detected. Use unique labels in debugLayout() calls"
                runtimeWarning(message, [label], file: file, line: line)
            }
            self.viewLabels.insert(label)
        }
    }
}

@available(macOS 13.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *)
struct DebugLayoutSelectedViewID: EnvironmentKey {
    static var defaultValue: String? { nil }
}

@available(macOS 13.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *)
extension EnvironmentValues {
    var debugLayoutSelectedViewID: String? {
        get { self[DebugLayoutSelectedViewID.self] }
        set { self[DebugLayoutSelectedViewID.self] = newValue }
    }
}