import Foundation

// MARK: - ItemContainer

/// Which of the board's two **card containers** something sits in — the board's lanes, or the
/// board's `.trash/`.
///
/// **This is the materialized trash's replacement for `Liveness`** (02-architecture.md § Changes
/// from Kanban, resettled 2026-07-28; 03-board-ui.md § Trash). Deletion is a *move* now, so there is
/// no flag to read, no ancestor to walk, and no "effective liveness" to compute: an item is in a
/// container or it is not, and which container is a fact about where its folder sits on disk. The
/// tombstone model's two-sided machinery — the absolute ancestor walk, the entry-vs-universe split,
/// kind-homogeneity inside the trash — is retired wholesale with it.
///
/// **An item-referencing set carries one of these** (`ItemReferenceSet`), because 04-interactions.md
/// ▸ The trash keeps exactly one boundary: "a selection never mixes trash cards with board cards — a
/// single container rule replacing the old liveness law, because Delete would otherwise mean two
/// different things in one gesture (move-to-trash vs permanent)".
///
/// **Lanes live only on the board side.** "Cards only. Lanes are never trashed" (03-board-ui.md §
/// Trash), so the trash's universe is cards and nothing else — which is why the trash needs no
/// kind axis of its own any more.
///
/// `String`-backed and `Codable` because the clipboard manifest carries one: a manifest written
/// before a quit is decoded after the relaunch, so these raw spellings are pasteboard API, and they
/// are the case names so nothing has to remember a second vocabulary.
public enum ItemContainer: String, Codable, Sendable, Equatable, CaseIterable {

    /// The board proper — every lane, and every card inside a lane.
    case board

    /// `<root>/.trash/` — the reserved container deletion moves cards into.
    case trash
}

extension ItemContainer {

    /// Every id `snapshot` holds in this container — **the universe** every item-referencing set is
    /// held to (02-architecture.md § Live-reload resilience: "re-resolution matches UUID *and*
    /// container side ... presence in the snapshot is the whole question").
    ///
    /// One walk, no filtering: the board side is the lanes plus their cards, the trash side is
    /// `snapshot.trash`. There is deliberately no liveness predicate anywhere in here — a legacy
    /// `deleted:` key still riding in from an unmigrated board (`BoardLoader`'s migration window)
    /// names an ordinary board card until its folder actually moves, which is the safe direction and
    /// the one the migration then takes (01-storage-format.md § Deletion).
    public func ids(in snapshot: BoardModel) -> Set<ItemID> {
        var universe: Set<ItemID> = []
        switch self {
        case .board:
            for lane in snapshot.lanes {
                universe.insert(lane.id)
                for card in lane.cards {
                    universe.insert(card.id)
                }
            }
        case .trash:
            for card in snapshot.trash {
                universe.insert(card.id)
            }
        }
        return universe
    }
}

// MARK: - ItemPath

/// Where an item's folder sits under a board root, as identity components rather than as a URL.
///
/// **Components, not a URL**, for the reason every path-shaped value in this app is: the caller
/// builds the URL off the store's *current* `rootURL`, so a board renamed or moved mid-session
/// writes at the new location (02-architecture.md § Write-failure surfacing).
///
/// **Three cases, because the board has exactly three places an identity-bearing folder can be** —
/// `<root>/<lane>`, `<root>/<lane>/<card>`, and `<root>/.trash/<card>`. The old two-optional-fields
/// shape could spell a fourth thing that does not exist; this cannot.
public enum ItemPath: Sendable, Equatable {

    /// A lane: `<root>/<lane>/`.
    case lane(ItemID)

    /// A card in a lane: `<root>/<lane>/<card>/`.
    case card(lane: ItemID, id: ItemID)

    /// A card in the board's trash: `<root>/.trash/<card>/`.
    case trashCard(ItemID)

    /// The item this path names.
    public var id: ItemID {
        switch self {
        case let .lane(id): id
        case let .card(_, id): id
        case let .trashCard(id): id
        }
    }

    public var isLane: Bool {
        if case .lane = self { return true }
        return false
    }

    /// Which container this path is in — the board for a lane or a lane's card, the trash for a
    /// trash card. Derived rather than stored: the case *is* the answer.
    public var container: ItemContainer {
        if case .trashCard = self { return .trash }
        return .board
    }

    /// This path resolved under a board root.
    public func folder(under root: URL) -> URL {
        switch self {
        case let .lane(id):
            root.appendingPathComponent(id.rawValue, isDirectory: true)
        case let .card(lane, id):
            root
                .appendingPathComponent(lane.rawValue, isDirectory: true)
                .appendingPathComponent(id.rawValue, isDirectory: true)
        case let .trashCard(id):
            BoardWriter.trashFolder(inBoard: root)
                .appendingPathComponent(id.rawValue, isDirectory: true)
        }
    }
}

extension ItemPath {

    /// The folders `ids` names inside one container, **in display order**.
    ///
    /// Display order — lanes left to right, each lane then its cards; the trash top to bottom —
    /// rather than the caller's set iteration order, which is not an order at all: a batch that
    /// fails partway must fail the same way twice (`BoardStore.styleSubjects` makes the same choice
    /// for the same reason).
    ///
    /// Ids the container does not hold are simply absent, which is every caller's standing posture:
    /// a selection the next reload will drop writes nothing rather than being refused.
    public static func resolve(
        _ ids: Set<ItemID>,
        in container: ItemContainer,
        snapshot: BoardModel
    ) -> [ItemPath] {
        guard !ids.isEmpty else { return [] }
        var result: [ItemPath] = []
        switch container {
        case .board:
            for lane in snapshot.lanes {
                if ids.contains(lane.id) { result.append(.lane(lane.id)) }
                for card in lane.cards where ids.contains(card.id) {
                    result.append(.card(lane: lane.id, id: card.id))
                }
            }
        case .trash:
            for card in snapshot.trash where ids.contains(card.id) {
                result.append(.trashCard(card.id))
            }
        }
        return result
    }

    /// Where one id lives, searching both containers — `nil` when the snapshot does not hold it.
    ///
    /// The board is searched first because that is where the overwhelming majority of lookups land;
    /// an id can only be in one container anyway (board-wide uniqueness spans both —
    /// 01-storage-format.md § Fractal layout ▸ Rules).
    public static func of(_ id: ItemID, in snapshot: BoardModel) -> ItemPath? {
        for lane in snapshot.lanes {
            if lane.id == id { return .lane(id) }
            if lane.cards.contains(where: { $0.id == id }) { return .card(lane: lane.id, id: id) }
        }
        return snapshot.trash.contains { $0.id == id } ? .trashCard(id) : nil
    }
}