import Foundation

// MARK: - TrashModel

/// What is left of the trash as a *model* once the trash became a folder — 03-board-ui.md § Trash's
/// **materialized** container (resettled 2026-07-28).
///
/// ### Almost nothing, and that is the point of the pivot
///
/// The tombstone model needed a whole derivation layer: an entry type, an absolute ancestor walk, a
/// returning-card count, a deterministic `deleted`-timestamp sort, and a paths function that had to
/// restate which items were addressable. All of it is gone. A trashed card is "an ordinary card in a
/// special place", so the trash's contents *are* `snapshot.trash` — already parsed by the same card
/// parse the lanes use, already in `order` display order, already newest-first because every arrival
/// mints a rank above the current top. There is nothing to derive, and no second definition to keep
/// in step with the loader's.
///
/// What genuinely remains is what the *commands* need and no view can answer: the two purge
/// confirmations' phrasing, and the menu validation that stages Delete by place. Both are pure
/// functions of a snapshot and a selection (`TrashModelTests`), so an alert's sentence is testable
/// without an alert on screen.
public enum TrashModel {

    // MARK: - Counts and phrasing

    /// "41 cards", "1 card" — 06-history-undo.md's **plural folding**, which is all the folding a
    /// cards-only container can need ("Cards only. Lanes are never trashed" — 03-board-ui.md).
    public static func phrase(_ count: Int) -> String {
        "\(count) card\(count == 1 ? "" : "s")"
    }

    // MARK: - Confirmations

    /// A purge confirmation's three strings, built once and rendered by the window's alert.
    ///
    /// A value rather than a view so the phrasing rules — plural folding, naming a sole item, and
    /// whether the loss is actually irreversible — are testable without an alert on screen.
    public struct PurgePrompt: Sendable, Equatable {
        public let title: String
        public let message: String
        public let confirmTitle: String
    }

    /// The alert in front of a **permanent** card delete — the trash's own ⌫/⌘⌫ (03-board-ui.md §
    /// Trash: "confirms exactly where the loss is real: the alert stands between one keystroke and
    /// unrecoverable deletion").
    ///
    /// A sole card is **named**; several fold into a count. `nil` when the ids name nothing in the
    /// trash, which is also the command's own refusal — so the prompt and the action can never
    /// disagree about whether there is anything to purge.
    public static func purgePrompt(
        for ids: Set<ItemID>,
        snapshot: BoardModel,
        unrecoverable: Bool
    ) -> PurgePrompt? {
        let targets = ItemPath.resolve(ids, in: .trash, snapshot: snapshot).filter { !$0.isLane }
        guard !targets.isEmpty else { return nil }

        let subject: String
        if targets.count == 1, let only = targets.first {
            subject = "\u{201C}\(displayName(of: only, in: snapshot))\u{201D}"
        } else {
            subject = phrase(targets.count)
        }
        return PurgePrompt(
            title: "Permanently delete \(subject)?",
            message: message(unrecoverable: unrecoverable),
            confirmTitle: "Delete"
        )
    }

    /// Empty Trash…'s alert — **always shown** ("Empty Trash… confirms everywhere"), and always
    /// naming the **true count**: every card in `.trash/`, never the filtered view (03-board-ui.md §
    /// Trash: "search-independent, the confirmation naming the card count").
    ///
    /// Counts rather than names even for a single card, because the command is about the trash
    /// rather than about an item: "Permanently delete 41 cards" is the design's own example phrasing.
    public static func emptyTrashPrompt(in snapshot: BoardModel, unrecoverable: Bool) -> PurgePrompt? {
        guard !snapshot.trash.isEmpty else { return nil }
        return PurgePrompt(
            title: "Permanently delete \(phrase(snapshot.trash.count))?",
            message: message(unrecoverable: unrecoverable),
            confirmTitle: "Delete"
        )
    }

    /// The alert's body: whether any of it comes back.
    ///
    /// The tombstone era's second sentence — "Deleting a lane also deletes every card inside it" —
    /// is gone with the lane entries it warned about: no purge path reaches a lane any more
    /// (`ItemPath.isLane` is filtered out above, and lane deletion is its own physical command with
    /// undo as its net).
    private static func message(unrecoverable: Bool) -> String {
        // m7-git: on a git board the content stays reachable in history, so the second sentence is
        // the honest one — and the trash's own Delete does not confirm there at all
        // (`BoardStore.purgeIsUnrecoverable`).
        unrecoverable
            ? "This can\u{2019}t be undone."
            : "The board\u{2019}s history still has them."
    }

    /// What to call a card in a prompt — its title, or the "Untitled" rendering.
    ///
    /// Total by construction: a path whose card has gone since the prompt was asked for reads
    /// "Untitled" rather than failing, which is the same shrug every other vanished-target rule in
    /// the app gives.
    private static func displayName(of path: ItemPath, in snapshot: BoardModel) -> String {
        switch path {
        case let .lane(id):
            return snapshot.lanes.first { $0.id == id }?.title.value ?? "Untitled"
        case let .card(lane, id):
            return snapshot.lanes.first { $0.id == lane }?
                .cards.first { $0.id == id }?.title.value ?? "Untitled"
        case let .trashCard(id):
            return snapshot.trash.first { $0.id == id }?.title.value ?? "Untitled"
        }
    }

    // MARK: - Menu validation

    /// Whether File ▸ Delete has something to act on — **staged by place, but validated once**
    /// (04-interactions.md ▸ The map, resettled 2026-07-28: "File ▸ Delete is the chord's only
    /// owner — no twin menu items, no shared-equivalent routing").
    ///
    /// One predicate for both stagings, because there is only one item now: a board selection moves
    /// into the trash, a trash selection deletes permanently, and the command is enabled whenever
    /// either names something the board still holds. The old mirror-image pair
    /// (which existed to make two ⌘⌫ twins enable exactly one of themselves) retired with Put Back.
    public static func canDelete(selection: ItemReferenceSet, in snapshot: BoardModel) -> Bool {
        !ItemPath.resolve(selection.ids, in: selection.container, snapshot: snapshot).isEmpty
    }
}