import AppKit

// MARK: - BoardUndoManager

/// What AppKit is handed for a board's windows: an `UndoManager` that owns no stack and answers
/// every question from the session's `HistoryProviding`.
///
/// ### Why an adapter exists at all
///
/// The responder chain speaks one currency. `NSWindow` implements `undo:`/`redo:` and validates
/// those menu items itself, reading `canUndo`, `canRedo` and `undoMenuItemTitle` off whatever
/// `UndoManager` the window's delegate hands back (`windowWillReturnUndoManager(_:)`) — which is
/// exactly how the system's Edit ▸ Undo row and the toolbar's nil-target pair (`BoardToolbar`) light
/// up, disable and retitle with no code of the app's own.
///
/// The seam, though, must not be an `NSUndoManager`: the free tier's stack is one, Pro's is git
/// (12-editions.md ▸ The provider seam), and a protocol that vended one could only ever have had a
/// single implementation. So the substrate stays behind `HistoryProviding` and *this* object is the
/// translation — one per board session, over whichever provider that session was composed with. Pro
/// inherits the whole command surface (enablement, dynamic titles, ⌘Z, the toolbar pair) by binding
/// its provider and changing nothing here, which is what "a user subscribing (or lapsing) relearns
/// nothing" (12) has to mean in code.
///
/// ### It deliberately keeps its inherited stack empty
///
/// Every question is overridden, so anything that *did* register into this manager by accident (a
/// stray AppKit client finding it through the window) would be invisible rather than half-live: it
/// could never enable Undo, retitle it, or be crossed by ⌘Z. Nothing registers here today; the
/// overrides are what make that safe rather than lucky.
///
/// `removeAllActions()` is deliberately **not** forwarded to `HistoryProviding.clear()`: AppKit
/// clears a window's undo manager on paths this app does not control, and a card window closing must
/// not empty the board's stack (13-native-undo.md ▸ Rules — the stack belongs to the *session*, and
/// its one clearing point is that session's teardown).
///
/// ### The read-only lock disables Undo and Redo here
///
/// "Every read-only lock (vanished root, failed reload after wholesale ops, unwritable location)
/// disables Undo/Redo with the other mutating commands; **the stack itself survives the lock and
/// resumes when it clears**" (13 ▸ Rules). This is the right place for it and the only one: every
/// surface that offers ⌘Z — the Edit menu's nil-target row, the toolbar pair, a card window's
/// responder chain — validates through this object, so answering `false` here disables all of them
/// at once, exactly as the lock's other victims disable through menu validation (02-architecture.md
/// § "The lock's scope"). Putting it in the *provider* would have been the same answer in the wrong
/// place: the stack is not the thing that is locked, the board is, and a Pro session binding the git
/// provider must inherit the rule without reimplementing it.
public final class BoardUndoManager: UndoManager {

    /// The substrate this manager is a face for. Strong: the session owns both, and the manager is
    /// only ever reachable while the session that made it is alive.
    private let history: any HistoryProviding

    /// Whether the board is refusing writes — `BoardStore.isReadOnly`, read through a closure rather
    /// than by holding the store. The adapter is deliberately store-free (it is a face for a *seam*,
    /// and Pro binds a different substrate behind the same one), and a closure is what lets the
    /// composition root wire the board's own truth in without this file learning what a `BoardStore`
    /// is. The default answers "writable", which is what a manager built without a board — a test of
    /// the adapter's own grammar — should have.
    private let isReadOnly: @MainActor () -> Bool

    public init(history: any HistoryProviding, isReadOnly: @escaping @MainActor () -> Bool = { false }) {
        self.history = history
        self.isReadOnly = isReadOnly
        super.init()
    }

    // MARK: Enablement

    /// **False under the lock, whatever the stack holds.** The steps are still there — this is an
    /// enablement answer, not a clearing — so the first ⌘Z after the lock clears crosses the step it
    /// would have crossed before it landed.
    public override var canUndo: Bool { !isReadOnly() && history.canUndo }

    public override var canRedo: Bool { !isReadOnly() && history.canRedo }

    // MARK: Crossing

    /// Not gated on the lock, deliberately: `undo:` reaches a manager only through a menu item or
    /// toolbar button that has already validated against `canUndo`, and a crossing that somehow
    /// started anyway is refused one layer down by `performWrite` — which leaves the step on the
    /// stack (`HistoryStepOutcome.failed`), the same place this enablement rule keeps it. A second
    /// guard here would be a second answer to one question.
    public override func undo() { history.undo() }

    public override func redo() { history.redo() }

    // MARK: Titles

    /// `NSUndoManager`'s own vocabulary for "the phrase, without the verb" — `""` when there is
    /// nothing to cross, which is what its menu-title composition expects.
    public override var undoActionName: String { history.undoActionName ?? "" }

    public override var redoActionName: String { history.redoActionName ?? "" }

    /// "Undo Move 3 Cards" — composed and localized by the platform (`undoMenuTitle(forUndoActionName:)`
    /// reads the `undo.strings` pattern), so the step vocabulary stays the bare phrase and this app
    /// never spells the word "Undo" in a title.
    ///
    /// The trim is for the nameless case: the pattern is `Undo %@`, so an empty action name would
    /// otherwise leave a trailing space where `NSUndoManager` itself answers a bare "Undo".
    public override var undoMenuItemTitle: String {
        undoMenuTitle(forUndoActionName: undoActionName).trimmingCharacters(in: .whitespaces)
    }

    public override var redoMenuItemTitle: String {
        redoMenuTitle(forUndoActionName: redoActionName).trimmingCharacters(in: .whitespaces)
    }
}

// MARK: - BoardUndoRouting

/// Which undo a hosted window answers with, given what holds the keyboard — 06-history-undo.md
/// ▸ Undo routing, which 12 records as **tier-independent**: "focus decides text-undo vs
/// board-undo; only the substrate behind board-undo differs".
///
/// ### Most of the rule is AppKit's, and is not here
///
/// "While a text-editing surface is focused ... ⌘Z/⇧⌘Z are that editor's own text undo" is the
/// platform's own behaviour for a text view that vends a manager: `NSWindow.undo:` crosses the
/// *first responder's* `undoManager`, and both of this app's real editors vend their own through the
/// text-view delegate (`CardBodySurface`, `CardRawSourceView` — each with an `UndoManager` created
/// per editor, emptied when the session ends). Those never reach this file.
///
/// ### What is here is the case AppKit gets wrong
///
/// A **field editor** — the shared `NSTextView` that appears inside every focused `NSTextField` and
/// `NSSearchField` — vends no manager of its own to the window, so `undo:` falls through to the
/// window's, and a reflexive ⌘Z over a typo in the search field or the board-rename field would
/// cross a *board* step. 06 rules that out by name: "Control-class text fields route the same way
/// (settled): the search field ... and the popover's text fields ... own ⌘Z/⇧⌘Z as field-local text
/// undo while focused — a reflexive undo over a typo must never become a tree checkout." So the
/// window-level answer is the board's stack **only when no text-editing surface holds the
/// keyboard**, and a per-window text manager otherwise — which is also exactly what AppKit would
/// have created for such a window on its own, so nothing about typing in a field changes.
///
/// Pure and free of windows on purpose: the decision is three lines that are invisible until they
/// are wrong, and the responder it reads is the only part a test cannot conjure.
public enum BoardUndoRouting {

    /// Whether `responder` is a text-editing surface — every `NSTextView`, field editors included,
    /// which `NSText` is precisely the ancestor of. An `NSTextField` that has focus without editing
    /// is *not* one: AppKit installs the field editor the moment editing begins, and until then the
    /// board is what the keyboard is acting on.
    public static func isTextEditing(_ responder: NSResponder?) -> Bool {
        responder is NSText
    }

    /// The manager a window's delegate should answer with.
    ///
    /// `board` is `nil` for every window that is not showing a board — welcome, the restore
    /// bootstrap, the template chooser, and a board or card window whose session has already been
    /// torn down. Those get the text manager too, which is the platform default they had before this
    /// seam existed.
    public static func undoManager(
        isTextEditing: Bool,
        board: UndoManager?,
        textFallback: UndoManager
    ) -> UndoManager {
        guard !isTextEditing, let board else { return textFallback }
        return board
    }
}
