import SwiftUI

// MARK: - The focused board

/// The frontmost board window's store, published into the focus system by `BoardWindowHost` so menu
/// items can act on "the board in front" without the app model keeping a which-window-is-key
/// register of its own.
///
/// `focusedSceneValue` rather than `focusedValue`: the value is the *window's*, not any particular
/// control's, so it stays available whatever inside the board has keyboard focus — which is what a
/// menu item validating against the selection needs.
struct FocusedBoardStoreKey: FocusedValueKey {
    typealias Value = BoardStore
}

extension FocusedValues {
    var boardStore: BoardStore? {
        get { self[FocusedBoardStoreKey.self] }
        set { self[FocusedBoardStoreKey.self] = newValue }
    }
}

// MARK: - Shared validation

/// The two conditions **every** board-mutating menu item disables on, in one place.
///
/// - **The read-only lock** (02-architecture.md § The lock's scope): "every mutating command
///   disables via menu validation" across every window sharing the store. An item that is going to
///   be refused should not look available.
/// - **The focused-editor rule** (04-interactions.md ▸ Grammar, settled): "while an inline title
///   editor — rename or the new-card placeholder — is focused, board-scoped menu commands (Delete,
///   New Card, Paste, Move, Style, …) disable via menu validation" and the keyboard belongs to the
///   text domain. The one carve-out the design names is Open Card ⌘↩, which stays enabled to commit
///   the edit and open the window — it is not a menu item yet (m5), and when it is, it is the one
///   item that must *not* read this property.
///
/// Stated once rather than repeated per item, because the interesting failure mode is an item that
/// quietly forgets half of it.
extension BoardStore {
    var acceptsBoardMutations: Bool {
        !isReadOnly && !isEditingInline
    }
}

// MARK: - Creation items

/// File ▸ New Card (⌘N) and File ▸ New Lane (⇧⌘N) — 11-command-nexus.md's two creation rows.
///
/// **New Card resolves its target through `NewCardTarget`**, the ⌘N target rule as a pure function,
/// and uses the *same* answer for its `disabled` state as for its action: a `nil` resolution is the
/// zero-lane board, where "card creation and card paste have no target — New Card, Return-creation,
/// and Paste with a card payload disable via menu validation until a lane exists"
/// (04-interactions.md ▸ The map). Two derivations of that condition would be two chances to
/// disagree.
///
/// **New Lane is enabled whenever the board accepts writes.** It is the way *out* of a zero-lane
/// board — "New Lane (⇧⌘N) is one way in" — so it can have no selection precondition at all. The
/// lane it creates is untitled and no editor opens on it; see `BoardStore.createLane`.
struct BoardCreationCommands: View {

    @FocusedValue(\.boardStore) private var store

    var body: some View {
        Button("New Card") {
            guard let store, let target = newCardTarget else { return }
            store.transient.beginPlaceholder(inLane: target.laneID, after: target.anchorCardID)
        }
        .keyboardShortcut("n", modifiers: .command)
        .disabled(newCardTarget == nil)

        Button("New Lane") {
            store?.createLane()
        }
        .keyboardShortcut("n", modifiers: [.shift, .command])
        .disabled(store?.acceptsBoardMutations != true)
    }

    /// Where ⌘N would file a card, or `nil` when it cannot — no focused board, a board that refuses
    /// writes, an inline editor holding the keyboard, or a board with no lanes.
    private var newCardTarget: NewCardTarget.Resolution? {
        guard let store, store.acceptsBoardMutations else { return nil }
        return NewCardTarget.resolve(
            selection: store.selection,
            lastActiveLaneID: store.transient.lastActiveLaneID,
            snapshot: store.snapshot
        )
    }
}

// MARK: - Rename

/// Board ▸ Rename — no default chord, deliberately (11-command-nexus.md: "— (cards: Return in
/// place)"), and remappable like any other item.
///
/// It "exists for completeness and remapping" for cards, whose real path is Return, and it is a
/// **lane's only rename path**: Return on a lane creates a card, so without this item a lane could
/// never be renamed at all (04-interactions.md ▸ Selection).
///
/// Validation is the sole-selected-live-item rule — card or lane, either kind, exactly one. A
/// tombstoned selection never enables it: "everything edit-shaped is disabled on tombstoned
/// selections" (04 ▸ The trash), which `ItemReferenceSet`'s liveness side answers directly.
struct BoardRenameCommand: View {

    @FocusedValue(\.boardStore) private var store

    var body: some View {
        Button("Rename") {
            guard let store, let target = renameTarget else { return }
            store.transient.beginRename(of: target.id, currentTitle: target.title)
        }
        .disabled(renameTarget == nil)
    }

    private var renameTarget: (id: ItemID, title: String?)? {
        guard let store, store.acceptsBoardMutations else { return nil }
        let selection = store.selection
        guard selection.liveness == .live, selection.ids.count == 1, let id = selection.ids.first,
              let item = BoardStore.liveItem(id, in: store.snapshot)
        else { return nil }
        return (id: id, title: item.title)
    }
}

// MARK: - Lane width items

/// Increase / Decrease Lane Width — **the width stepper's keyboard face** (03-board-ui.md § Lane,
/// 11-command-nexus.md), and therefore the *re-divide* mechanism: each step re-divides the existing
/// window width across the new unit total, compressing the siblings. They never touch the window's
/// size — window-growing behaviour belongs to the right-edge drag alone — and they are uncapped, so
/// widths beyond what the screen can fit stay reachable here even though the drag hard-stops.
///
/// **Validation is the sole-selected-lane rule.** Both items are enabled only when the focused
/// board's selection resolves to exactly one live lane; a card selection, a multi-selection, a
/// trash-side selection and an empty one all disable them. Decrease additionally disables at one
/// unit, which is the floor.
struct LaneWidthCommands: View {

    @FocusedValue(\.boardStore) private var store

    var body: some View {
        Button("Increase Lane Width") {
            step(by: 1)
        }
        .keyboardShortcut(.rightArrow, modifiers: [.option, .command])
        .disabled(selectedLane == nil)

        Button("Decrease Lane Width") {
            step(by: -1)
        }
        .keyboardShortcut(.leftArrow, modifiers: [.option, .command])
        .disabled(!canDecrease)
    }

    /// The sole selected live lane, or `nil` — the whole of these items' validation.
    ///
    /// The lock and the open-editor rule are folded in through `acceptsBoardMutations` rather than
    /// left for the write to refuse: an item that is going to fail should not look available.
    private var selectedLane: Lane? {
        guard let store, store.acceptsBoardMutations else { return nil }
        let selection = store.selection
        guard selection.liveness == .live, selection.ids.count == 1, let id = selection.ids.first else { return nil }
        return store.snapshot.lanes.first { $0.id == id && !$0.isDeleted }
    }

    /// A one-unit lane cannot shrink: `width` is ≥ 1 (03-board-ui.md § Lane), and an item whose only
    /// outcome is a no-op reads better disabled than dead.
    private var canDecrease: Bool {
        guard let lane = selectedLane else { return false }
        return LaneLayoutMath.displayUnits(of: lane) > 1
    }

    private func step(by delta: Int) {
        guard let store, let lane = selectedLane else { return }
        store.setLaneWidth(lane.id, units: LaneLayoutMath.displayUnits(of: lane) + delta)
    }
}