import AppKit
import SwiftUI
import os

// MARK: - Fate

/// What the current snapshot says about a card window: render this card, or go away.
///
/// A named decision rather than a scattering of `if`s, because 05-card-window.md ▸ Deletion &
/// lifecycle and 02-architecture.md § Live-reload resilience state the same rule from two directions
/// and both have to be true of one piece of code. Making it a value also makes it a *pure* function
/// of a snapshot, which is the only way the tombstoned-lane case gets tested without a window.
public enum CardWindowFate: Equatable {
    case shows(Card)
    case dismisses
}

// MARK: - The session seam

/// A card window's editor session — m4's no-op stand-in for the thing 05-card-window.md will build.
///
/// It exists so the close flush has something real to call and something real to be *ordered against*
/// (see `CardSessionFlushing`). The only behaviour it has is the one the ordering depends on: ending
/// twice does nothing the second time, which matters because two paths legitimately end a session —
/// the board's close flush drives it for every card window, and a card window closed on its own runs
/// it from its disappear.
@MainActor
final class CardWindowSession: CardSessionFlushing {

    private var hasEnded = false

    func endSession() async {
        guard !hasEnded else { return }
        hasEnded = true
        // m6: commit the open Edit session here (06-history-undo.md's session granularity), flushing
        // the debounced body save first.
    }
}

// MARK: - CardWindowHost

/// One card window (05-card-window.md).
///
/// ### Its whole identity is `(board, card)`
///
/// Which is why this host is mostly a set of dismissal rules. The window follows its card between
/// lanes for free — the key names neither — and it dismisses in the three cases where the key stops
/// naming anything: the card is tombstoned, its *lane* is tombstoned (effective liveness is
/// ancestor-walked, 02 § Live-reload resilience), or the card is simply not in this board's snapshot
/// any more, which is what a cross-board move looks like from here.
///
/// ### It can never outlive its board window
///
/// "The board window owns the board" (02 § Components) — so a card window whose board has no live
/// store, or whose board session has gone, dismisses immediately rather than becoming an orphan with
/// a store it acquired by itself. That covers the ordinary case (the board window closed and its
/// flush dismissed this one) and the odd one (the system restoring a card window from a previous
/// launch, which scene restoration is disabled precisely to prevent).
///
/// The content is a placeholder — the two-column composition, the sidebar, Edit/Preview and the rest
/// are the card-window milestone's.
struct CardWindowHost: View {

    let ref: CardWindowRef

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

    @State private var windowController = HostedWindowController()
    @State private var session = CardWindowSession()
    @State private var phase: Phase = .opening

    private enum Phase {
        case opening
        case open(BoardStore)
        case closing
    }

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

    // MARK: - The lifecycle rule

    /// Whether a card window keyed on `cardID` still has a card, given this board's snapshot.
    ///
    /// The three dismissal cases collapse into two lines: a card that is not in the snapshot is gone
    /// (deleted outright, or moved to another board — the board half of the key no longer names it),
    /// and a card whose **effective** liveness is trashed renders nowhere, whether the tombstone is
    /// its own or its lane's. Only a live card in a live lane keeps its window.
    ///
    /// Takes the id as the ref stores it — a raw folder name — and compares it as an `ItemID`, so two
    /// case-spellings of one UUID are one card here exactly as they are everywhere else.
    static func cardWindowFate(cardID: String, in snapshot: BoardModel) -> CardWindowFate {
        let identity = ItemID(rawValue: cardID)
        for lane in snapshot.lanes {
            guard let card = lane.cards.first(where: { $0.id == identity }) else { continue }
            return lane.isDeleted || card.isDeleted ? .dismisses : .shows(card)
        }
        return .dismisses
    }

    // MARK: - View

    var body: some View {
        content
            .frame(minWidth: 360, minHeight: 240)
            .background(WindowAccessor(controller: windowController))
            .navigationTitle(windowTitle)
            .task { start() }
            .onChange(of: shouldDismiss, initial: true) { _, dismisses in
                guard dismisses else { return }
                dismissWindow(id: WindowID.card, value: ref)
            }
            .onDisappear { finish() }
    }

    @ViewBuilder
    private var content: some View {
        if let card {
            VStack(alignment: .leading, spacing: 12) {
                Text(card.title.value ?? "Untitled")
                    .font(.title)
                    // The untitled placeholder is styling, not a title: a card with no `title` key
                    // shows the word in secondary, never as if somebody had typed it
                    // (01-storage-format.md § Frontmatter).
                    .foregroundStyle(card.title.value == nil ? .secondary : .primary)
                Spacer(minLength: 0)
            }
            .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)
            .padding(24)
        } else {
            Color.clear
        }
    }

    private var card: Card? {
        guard case let .open(store) = phase,
              case let .shows(card) = Self.cardWindowFate(cardID: ref.cardID, in: store.snapshot)
        else { return nil }
        return card
    }

    private var windowTitle: String {
        card?.title.value ?? ""
    }

    /// The dismissal decision, re-evaluated on every snapshot the store applies.
    ///
    /// Two clauses, and the second is the safety net: the board's session vanishing means the board
    /// window has finished tearing down, and a card window still on screen at that point has nothing
    /// behind it. It is deliberately redundant with the close flush, which dismisses these windows
    /// itself — a net is only useful when the thing it backs up has already failed.
    private var shouldDismiss: Bool {
        guard case let .open(store) = phase else { return false }
        guard appModel.session(for: ref.board) != nil else { return true }
        return Self.cardWindowFate(cardID: ref.cardID, in: store.snapshot) == .dismisses
    }

    // MARK: - Opening

    /// Joins the board's session, or dismisses.
    ///
    /// **`liveStore(for:)` first, and no fallback to `acquire` on a closed board.** A card window
    /// never opens a board: doing so would put a store — and a watcher — behind a window that,
    /// by 02's ownership rule, is not allowed to exist. The `acquire` below can only hit the
    /// already-open path, which is why its failure is logged rather than surfaced.
    private func start() {
        guard case .opening = phase else { return }

        guard appModel.storeRegistry.liveStore(for: ref.boardURL) != nil else {
            Self.logger.debug("card window has no live board — dismissing")
            phase = .closing
            dismissWindow(id: WindowID.card, value: ref)
            return
        }

        let store: BoardStore
        do throws(BoardLoadError) {
            store = try appModel.storeRegistry.acquire(ref.boardURL)
        } catch {
            Self.logger.error("card window could not acquire its board: \(error.description, privacy: .public)")
            phase = .closing
            dismissWindow(id: WindowID.card, value: ref)
            return
        }

        appModel.registerCardWindow(ref, session: session)
        phase = .open(store)
        configureWindow()
    }

    /// Size and placement: the last-used card-window size, cascaded (05-card-window.md, "New windows
    /// open at the last-used card-window size, cascaded").
    ///
    /// The size is app-wide rather than per-board or per-card — 02 § Per-board app state files "the
    /// last-used card-window size" under App-wide state explicitly. Per-*card* frame restoration is a
    /// separate promise in 05 ("frames restore per card across relaunch where state restoration
    /// allows") and belongs to the card-window milestone, which owns the per-card record it needs.
    private func configureWindow() {
        windowController.onAttach = { window in
            if let size = AppPreferences.lastCardWindowSize {
                window.setContentSize(size)
            }
            // `cascadeTopLeft(from:)` both places this window and returns the origin for the next
            // one, so the running point is the whole cascade.
            appModel.cardCascadePoint = window.cascadeTopLeft(from: appModel.cardCascadePoint)
        }
        if let window = windowController.window {
            windowController.onAttach?(window)
        }

        windowController.onFrameChanged = { frame in
            guard let window = windowController.window else { return }
            let size = window.contentRect(forFrameRect: frame).size
            guard size != AppPreferences.lastCardWindowSize else { return }
            AppPreferences.setLastCardWindowSize(size)
        }
    }

    // MARK: - Closing

    /// Leaves the session and lets the store go.
    ///
    /// The release rides **behind** the session's end rather than beside it: a session that has
    /// something to commit (m6) needs the store it is committing through, and a refcount that hit
    /// zero first would have stopped the watcher underneath it. In m4 the hook is a no-op and the
    /// ordering costs one run-loop turn — the point is that the shape is already right.
    private func finish() {
        guard case let .open(store) = phase else { return }
        phase = .closing
        appModel.unregisterCardWindow(ref)
        Task { @MainActor in
            await session.endSession()
            appModel.storeRegistry.release(store)
        }
    }
}