import AppKit
import SwiftUI
import os

// MARK: - Fate

/// Where a card window's card is right now: the card itself, and the lane it is currently in.
///
/// **One resolution answers both of the window's questions**, which is why the lane rides along
/// rather than being looked up a second time: the card is what the window renders, and the lane is
/// half of its subtitle ("⟨board⟩ › ⟨lane⟩", live-updating as the card moves — 05-card-window.md
/// ▸ Window). Two walks over the snapshot could disagree about which lane a card is in for exactly
/// one frame, and that frame is the one where the card just moved.
public struct CardPlacement: Equatable {
    public let card: Card
    public let lane: Lane
}

/// 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(CardPlacement)
    case dismisses
}

// MARK: - The session seam

/// A card window's editor session — still a no-op stand-in for the thing 05-card-window.md will
/// build, and deliberately so: **the shell has no Edit session to flush yet.**
///
/// 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-card-body: commit the open Edit session here (06-history-undo.md's session
        // granularity), flushing the debounced body save first — and, on a dismissal caused by a
        // tombstone, the surgical body write 05 ▸ Deletion & lifecycle promises ("dismissal never
        // eats typed work silently where a save can land"). Nothing exists to flush until the
        // editor does; the hook's *position* in the sequence is what this milestone pins.
    }
}

// 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).
///
/// ### It is the window; `CardWindowView` is the content
///
/// This file owns identity, lifecycle, the title and subtitle, and where the window opens. The
/// two-column composition inside it is `CardWindowView`'s, and what fills those columns — the title
/// field, Preview/Edit, the raw-source outlet, the sidebar's five sections — arrives card by card
/// underneath a composition that does not move.
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
    /// This window's body column — the Preview/Edit mode, and the ⌘F hook a menu item reaches
    /// through the focus system (`CardBodyPresentation`).
    @State private var bodyPresentation = CardBodyPresentation()

    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(CardPlacement(card: card, lane: lane))
        }
        return .dismisses
    }

    /// The window's subtitle: "⟨board⟩ › ⟨lane⟩" (05-card-window.md ▸ Window).
    ///
    /// Pure, and taking both names as strings, because the *live* half is what matters and is the
    /// easy half to lose: the board name follows a board rename through
    /// `AppModel.displayName(of:)`, and the lane name follows the card between lanes because it is
    /// re-derived from every snapshot rather than captured when the window opened. A window that
    /// kept showing the lane its card was in an hour ago would be wrong in exactly the case the
    /// subtitle exists for.
    ///
    /// Untitled lanes render the same placeholder the board's lane header does — "Untitled" is a
    /// rendering, never a value (03-board-ui.md § Card face).
    static func subtitle(board: String, lane: String?) -> String {
        "\(board) › \(lane ?? "Untitled")"
    }

    // MARK: - View

    var body: some View {
        content
            // Derived, like every other measurement in this window: the minimum is what the two
            // columns need at the current text size, not a number chosen once at 13pt
            // (`CardWindowMetrics`).
            .frame(minWidth: minimumSize.width, minHeight: minimumSize.height)
            .background(WindowAccessor(controller: windowController))
            .navigationTitle(windowTitle)
            // The window follows its card: both of these are re-derived from every snapshot, so a
            // rename retitles the window and a lane move re-subtitles it with no notification of
            // our own (05-card-window.md ▸ Window).
            .navigationSubtitle(windowSubtitle)
            // Edit ▸ Find (⌘F) is find-in-text in a card window (11-command-nexus.md) — the menu
            // item reaches the frontmost one's body surface through this, exactly as board-window
            // items reach their window's store (`FocusedBoardStoreKey`).
            .focusedSceneValue(\.cardBody, bodyPresentation)
            .task { start() }
            .onChange(of: shouldDismiss, initial: true) { _, dismisses in
                guard dismisses else { return }
                dismissWindow(id: WindowID.card, value: ref)
            }
            .onDisappear { finish() }
    }

    private var minimumSize: CGSize {
        CardWindowMetrics.minimumSize(bodyPointSize: CardWindowMetrics.bodyPointSize)
    }

    @ViewBuilder
    private var content: some View {
        if case let .open(store) = phase, let placement {
            CardWindowView(
                card: placement.card,
                cardFolder: Self.cardFolder(root: store.rootURL, placement: placement),
                bodyPresentation: bodyPresentation,
                // "Under the read-only lock the controls disable in place — an in-content mutation
                // menu validation can't reach" (05 ▸ Preview). The checkbox is that control, and
                // the store's own lock is the whole predicate.
                isEditable: !store.isReadOnly,
                onToggleTask: { offset, checked in
                    store.toggleTaskMarker(inCard: placement.card.id, bodyOffset: offset, checked: checked)
                }
            )
        } else {
            // Nothing to render and nothing worth animating: this window is on its way out.
            Color.clear
        }
    }

    /// `<root>/<lane>/<card>` — the card's own folder, which is what its body's relative images and
    /// links resolve against (05-card-window.md ▸ Preview).
    ///
    /// Built off the store's *current* `rootURL` rather than the ref's captured one, for
    /// `BoardStore.liveItem`'s reason: a mid-session folder rename moves the board, and a preview
    /// resolving images against where the board used to be would quietly stop showing them.
    static func cardFolder(root: URL, placement: CardPlacement) -> URL {
        root
            .appendingPathComponent(placement.lane.id.rawValue, isDirectory: true)
            .appendingPathComponent(placement.card.id.rawValue, isDirectory: true)
    }

    /// Where this window's card is in this board's snapshot, or `nil` when it is not — which is the
    /// same condition `shouldDismiss` reads, one moment before the window goes.
    private var placement: CardPlacement? {
        guard case let .open(store) = phase,
              case let .shows(placement) = Self.cardWindowFate(cardID: ref.cardID, in: store.snapshot)
        else { return nil }
        return placement
    }

    /// The card's title, with the face's own untitled rendering — a card with no `title` key is
    /// "Untitled" in the title bar and the Window menu, never a blank strip.
    private var windowTitle: String {
        guard let placement else { return "" }
        return placement.card.title.value ?? "Untitled"
    }

    private var windowSubtitle: String {
        guard case let .open(store) = phase, let placement else { return "" }
        return Self.subtitle(
            board: AppModel.displayName(of: store),
            lane: placement.lane.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 remembered frame first, the cascade second** (05-card-window.md
    /// ▸ Window: "New windows open at the last-used card-window size, cascaded; frames restore per
    /// card across relaunch where state restoration allows").
    ///
    /// Two memories, and they answer different questions:
    ///
    /// - **The last-used size is app-wide.** 02 § Per-board app state files "the last-used
    ///   card-window size" under App-wide state explicitly, so it lives in `AppPreferences` and a
    ///   card window opened on any board inherits the size of the last one the user sized.
    /// - **The frame is per card**, and lives on the board's registry record beside the board
    ///   window's own frame — same home, same identity-keyed record, same files-first rule (nothing
    ///   app-private is ever written into the board folder). "Where state restoration allows" is
    ///   this: AppKit's scene restoration is disabled app-wide on purpose (`KanbanApp`), so a card
    ///   window does not come back by itself at relaunch — but the *next* time the user opens that
    ///   card, it opens where they left it.
    ///
    /// A card with a remembered frame therefore does **not** cascade: a cascade over a deliberate
    /// placement would move a window the user had already put somewhere. Only the windows with
    /// nothing remembered take the running cascade point, which is what keeps a burst of freshly
    /// opened cards from landing on top of each other.
    private func configureWindow() {
        // Read once here rather than per callback: this window's board has a session by now (the
        // caller just registered against it), and the record id is what both memories are keyed on.
        let recordID = appModel.session(for: ref.board)?.recordID

        windowController.onAttach = { window in
            if let recordID,
               let saved = appModel.boardRegistry.cardWindowFrame(id: recordID, cardID: ref.cardIdentity) {
                // Repositioned onto a live screen when the saved one is gone — the board window's
                // own rule, shared rather than restated (`HostedWindowController.placement`).
                window.setFrame(HostedWindowController.placementOnCurrentScreens(for: saved), display: true)
                return
            }
            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
            if let recordID {
                appModel.boardRegistry.updateCardWindowFrame(
                    id: recordID,
                    cardID: ref.cardIdentity,
                    frame: WindowFrame(x: frame.origin.x, y: frame.origin.y, width: frame.width, height: frame.height)
                )
            }
            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)
        }
    }
}