import SwiftUI

/// The lane list for one board — `BoardRoute.lanes`'s destination.
///
/// Holds only `boardRoot`, never a `BoardSummary`/`BoardModel` value: the session and its
/// snapshot are pulled from the environment's index store fresh on every body evaluation, so a
/// write from anywhere in the stack (a lane created, a card moved) reaches this screen the moment
/// the session's reload lands. A segmented control above the lane rows lets the list be sorted by
/// name or by most recent change, on top of the board's own manual arrangement, remembered across
/// launches.
struct BoardScreen: View {
    let boardRoot: URL

    @Environment(BoardIndexStore.self) private var index
    @State private var isPresentingNewLane = false

    /// Persisted as its raw value, not the enum itself — same reasoning as `BoardsTabView`'s
    /// `sortOrderRaw`.
    @AppStorage("laneListSortOrder") private var sortOrderRaw = ItemSortOrder.manual.rawValue

    private var session: BoardSession { index.session(forBoardAt: boardRoot) }

    /// The stored raw value as the enum, defaulting to `.manual` on anything the store didn't
    /// write itself — an unset key or a stale raw value from a build that no longer has this case.
    private var sortOrder: Binding<ItemSortOrder> {
        Binding(
            get: { ItemSortOrder(rawValue: sortOrderRaw) ?? .manual },
            set: { sortOrderRaw = $0.rawValue }
        )
    }

    var body: some View {
        content
            .navigationTitle(title)
            .toolbar {
                if case .ready = session.phase {
                    Button("New Lane", systemImage: "plus") {
                        isPresentingNewLane = true
                    }
                }
            }
            .task { session.open() }
            .onDisappear {
                // Stops the materializing/downloading retry timer. In practice a no-op here: a
                // lane row (the only thing on this screen that pushes forward) only renders in
                // `.ready`, the one phase where `close()`'s `cancelRetry()` has nothing to cancel —
                // so pushing deeper into the board costs nothing, and popping back out to the
                // board list is where this actually stops the timer.
                session.close()
            }
            .titlePromptAlert("New Lane", isPresented: $isPresentingNewLane, placeholder: "Lane Title") { title in
                let newTitle: String? = title.isEmpty ? nil : title
                Task {
                    // The closure's throws type must be spelled out — a trailing closure literal
                    // does not pick up `perform`'s `throws(BoardWriteError)` from context alone.
                    await session.perform { (root: URL) throws(BoardWriteError) -> ItemID in
                        try BoardWriter.createLane(inBoard: root, title: newTitle)
                    }
                }
            }
    }

    private var title: String {
        // The same fallback `BoardSummaryScanner` uses — the folder name minus `.kanban` — so the
        // title never blanks out while the session is still opening.
        session.snapshot?.title.value ?? boardRoot.deletingPathExtension().lastPathComponent
    }

    /// The row's display title, "Untitled Lane" fallback included — fed to `ItemSortOrder.sorted`
    /// so `.name` sorts on exactly what the row shows.
    private func displayTitle(of lane: Lane) -> String {
        guard let title = lane.title.value, !title.isEmpty else { return "Untitled Lane" }
        return title
    }

    @ViewBuilder
    private var content: some View {
        switch session.phase {
        case .idle, .loading:
            ProgressView("Opening board")

        case let .materializing(progress):
            ProgressView(value: progress.fractionMaterialized) {
                Text("Downloading board")
            }
            .padding()

        case let .failed(error):
            ContentUnavailableView {
                Label("Can't Open Board", systemImage: "exclamationmark.triangle")
            } description: {
                Text(error.description)
            } actions: {
                Button("Try Again") { session.reload() }
            }

        case .ready:
            if let snapshot = session.snapshot {
                laneList(snapshot)
            } else {
                // Unreachable in practice — `.ready` is only ever set alongside a landed load,
                // which sets `snapshot` in the same step (`BoardSession.apply`). Kept so the
                // switch is exhaustive without a force-unwrap.
                ProgressView("Opening board")
            }
        }
    }

    @ViewBuilder
    private func laneList(_ snapshot: BoardModel) -> some View {
        List {
            if session.lastError != nil {
                Section {
                    Label("Showing the last saved version — a recent update didn't load.", systemImage: "exclamationmark.triangle")
                        .font(.footnote)
                        .foregroundStyle(.secondary)
                }
            }
            if snapshot.lanes.isEmpty {
                ContentUnavailableView(
                    "No Lanes Yet",
                    systemImage: "rectangle.split.3x1",
                    description: Text("Add a lane to start organizing cards.")
                )
            } else {
                Picker("Sort", selection: sortOrder) {
                    Text("Manual").tag(ItemSortOrder.manual)
                    Text("Name").tag(ItemSortOrder.name)
                    Text("Recent").tag(ItemSortOrder.recent)
                }
                .pickerStyle(.segmented)
                .listRowBackground(Color.clear)
                .listRowSeparator(.hidden)

                // The trusted order is `.manual`'s base — `BoardModel.lanes` is already in display
                // order (the loader's `Ranks.sortedForDisplay`) — and `.name`/`.recent` layer a
                // display-only re-sort on top, never touching that base or what's on disk.
                ForEach(sortOrder.wrappedValue.sorted(snapshot.lanes, title: displayTitle(of:), modified: { $0.modified.value })) { lane in
                    NavigationLink(value: BoardRoute.cards(boardRoot: boardRoot, laneID: lane.id)) {
                        LaneSummaryRow(lane: lane)
                    }
                }
            }
        }
        .refreshable { session.reload() }
    }
}

/// One lane row: its icon when it has one, title, and its card count.
private struct LaneSummaryRow: View {
    let lane: Lane

    var body: some View {
        HStack {
            ItemIconView(icon: lane.icon.value, iconColor: lane.iconColor.value)
            VStack(alignment: .leading, spacing: 2) {
                Text(displayTitle)
                Text("\(lane.cards.count) card\(lane.cards.count == 1 ? "" : "s")")
                    .font(.caption)
                    .foregroundStyle(.secondary)
            }
        }
    }

    private var displayTitle: String {
        guard let title = lane.title.value, !title.isEmpty else { return "Untitled Lane" }
        return title
    }
}