import SwiftUI
import os

/// The launch-time restoration pass, wearing a window because that is the only place SwiftUI lets
/// work like this run.
///
/// ### Why a window at all
///
/// Restoration has to open windows, and opening a window needs `openWindow`, which is only readable
/// from a view. An `App.init()` cannot do it and `AppDelegate` has no environment. So the app
/// presents one throwaway window at launch — 1×1, plain, ordered straight back out, absent from the
/// Window menu — whose only job is to run the pass and then dismiss itself. It exists for a few
/// hundred milliseconds and never draws.
///
/// It is presented **only** when there is something to restore (`KanbanApp` decides), so the ordinary
/// launch-to-welcome path never creates it.
///
/// ### What the pass does
///
/// Reads the registry's flagged records in `lastOpened` order (`BoardRegistry.restorables()`), opens
/// the available ones, and records the unavailable ones as failures — 02 § Launch and window
/// lifecycle: "Other restorations proceed unaffected — never a launch-time modal chain, never a
/// silent drop." Welcome comes up only if nothing was even attempted; a board that *was* attempted
/// and then failed to load opens welcome from its own host, which is the same rule applied one layer
/// down and keeps this pass from having to wait on loads it did not perform.
struct RestoreBootstrapView: View {

    @Environment(AppModel.self) private var appModel
    @Environment(\.openWindow) private var openWindow
    @Environment(\.dismissWindow) private var dismissWindow

    @State private var windowController = HostedWindowController()

    private static let logger = Logger(subsystem: "dev.rzen.indie.Kanban", category: "launch")

    var body: some View {
        Color.clear
            .frame(width: 1, height: 1)
            .background(WindowAccessor(controller: windowController))
            .onAppear {
                // Out of sight before it can be seen. `orderOut` rather than a hidden style because
                // the scene must still exist — a window SwiftUI never presents never runs its task.
                windowController.onAttach = { window in
                    window.alphaValue = 0
                    window.orderOut(nil)
                }
                if let window = windowController.window {
                    windowController.onAttach?(window)
                }
            }
            .task { await restore() }
    }

    private func restore() async {
        // Captured directly rather than waiting for `CaptureOpenWindow`'s `onAppear`: this task is
        // the app's first act, and `openBoard` needs the action now.
        appModel.captureWindowActions(open: openWindow, dismiss: dismissWindow)

        var attempted = 0
        for board in appModel.boardRegistry.restorables() {
            switch board {
            case let .available(_, url):
                appModel.openBoard(at: url)
                attempted += 1
            case let .unavailable(record):
                Self.logger.error("a flagged board could not be restored — its bookmark no longer resolves")
                appModel.recordLaunchFailure(
                    path: record.lastKnownPath,
                    message: "This board is unavailable. Its volume may be offline, or it may have been moved or deleted."
                )
            }
        }

        if attempted == 0 {
            appModel.showWelcome()
        }
        dismissWindow(id: WindowID.restoreBootstrap)
    }
}