import AppKit
import Foundation
import Observation
import os

// MARK: - ClipboardStore

/// Cut / copy / paste for cards **and lanes** — the hybrid clipboard (04-interactions.md ▸
/// Clipboard).
///
/// ### Hybrid, and what each half is for
///
/// The pasteboard carries a small JSON manifest plus a plain-text rendering; the *content* — whole
/// folder trees, attachments and strays and all — is **staged** under
/// `<Application Support>/<bundle id>/Clipboard/<copyID>/`, so a paste reproduces the item
/// byte-for-byte across boards rather than reconstructing it from a summary. The manifest's embedded
/// `index.md` per entry is the fallback when a snapshot is missing, and a fallback paste is **loud**:
/// a banner names exactly what was lost.
///
/// ### The staging lifecycle, settled
///
/// - **Eager**: the snapshot is taken at ⌘C/⌘X time, so a copy captures the source as it was at the
///   gesture and is immune to a later deletion or unmount.
/// - **At most the current copy**: every copy sweeps, and a sweep keeps only the `copyID` the
///   pasteboard still names. A launch sweeps too, which is what collects the trees another app
///   orphaned by taking the pasteboard while this app was not running.
/// - **Survives relaunch exactly as long as the pasteboard points at it** — which is the sweep rule
///   read from the other side, not a second mechanism.
///
/// The copies run **off the main actor** on a serialized chain (`stagingChain`): a card holding a
/// large video would otherwise freeze the app for the length of the ⌘C. The pasteboard is written
/// synchronously in front of that — ⌘C is instant and Edit ▸ Paste lights up immediately — and a
/// paste awaits the same chain, so it can never read a half-written snapshot, and a sweep can never
/// delete a tree a copy is still writing.
///
/// ### The deferred cut
///
/// ⌘X stages, writes the pasteboard, and arms the source board's `transient.pendingCut` — the items
/// dim in place. The cut is **armed** while the pasteboard still holds its `copyID`, the source store
/// is still open, and the pending cut still names something; "deletion voids per item" needs no code
/// here at all, because `TransientBoardState.resolve` already ejects a tombstoned or vanished member
/// on every reload, so "paste moves only the survivors" is the reload rule read at paste time.
/// Voiding undims and downgrades the paste to a copy from staging.
///
/// ### Takeover detection is lazy, and there is no timer
///
/// `NSPasteboard.changeCount` is a machine-wide counter, so a value that moved without this store
/// moving it means another app owns the pasteboard now. It is checked exactly where 04 says — menu
/// validation (which reads the cached `payload`), app activation, and before every paste — and
/// nowhere else. `payload` is observable state rather than a computed pasteboard read precisely so
/// the menu items' enablement re-evaluates when it changes rather than whenever SwiftUI happens to
/// rebuild them.
@MainActor
@Observable
public final class ClipboardStore {

    // MARK: State

    /// What the pasteboard offers this app, as of the last `refresh()` — `nil` when it holds
    /// somebody else's content, or nothing this build can read.
    ///
    /// **Observed**, which is the whole point: Edit ▸ Paste's availability is a function of this
    /// value, and a computed pasteboard read would leave the item stale until something else
    /// happened to invalidate the menu.
    public private(set) var payload: ClipboardManifest?

    /// The staging directory — public because the tests assert on what it holds after a copy, a
    /// paste and a sweep, exactly as `BoardRegistry.storageURL` is public for its tests.
    @ObservationIgnored public let stagingRoot: URL

    @ObservationIgnored private let pasteboard: any ClipboardPasteboard

    /// The `changeCount` at the last refresh. Starts below any real value so the first refresh always
    /// reads through.
    @ObservationIgnored private var lastChangeCount = Int.min

    /// The deferred cut awaiting its paste, or `nil` when the clipboard holds a copy (or a cut has
    /// been consumed or voided).
    ///
    /// The *members* are not here: they live in the source board's `transient.pendingCut`, where the
    /// reload rule can eject vanished ones and where the dimming reads them. This is only the pairing
    /// — which copy, and whose board.
    @ObservationIgnored private var armedCut: ArmedCut?

    private struct ArmedCut {
        let copyID: String
        /// Weak: a board window can close mid-cut, and a closed board voids the cut by definition.
        weak var source: BoardStore?
    }

    /// Tail of the serialized staging chain. Every mutation of the staging directory — a copy's
    /// snapshots, a sweep — is appended here and runs strictly after the previous one, which is what
    /// makes "a sweep can never delete a tree a copy is still writing" a property of the code rather
    /// than a race nobody has lost yet.
    @ObservationIgnored private var stagingChain: Task<Void, Never>?

    /// `nonisolated(unsafe)` for one reason and one only: `deinit` is nonisolated and this is the
    /// token it has to hand back. It is written exactly once, in `init` on the main actor, and read
    /// exactly once, in `deinit` after the last reference is gone — there is no window in which two
    /// contexts could touch it.
    @ObservationIgnored private nonisolated(unsafe) var activationObserver: (any NSObjectProtocol)?

    private static let logger = Logger(subsystem: "dev.rzen.indie.Kanban", category: "clipboard")

    /// `~/Library/Application Support/<bundle id>/Clipboard/`, beside the board registry — the same
    /// container convention, for the same reason (02-architecture.md § Per-board app state, "App-wide
    /// state has the same home").
    public static var defaultStagingRoot: URL {
        let support = FileManager.default.urls(for: .applicationSupportDirectory, in: .userDomainMask).first
            ?? URL(fileURLWithPath: NSHomeDirectory(), isDirectory: true)
                .appendingPathComponent("Library/Application Support", isDirectory: true)
        let bundleIdentifier = Bundle.main.bundleIdentifier ?? "dev.rzen.indie.Kanban"
        return support
            .appendingPathComponent(bundleIdentifier, isDirectory: true)
            .appendingPathComponent("Clipboard", isDirectory: true)
    }

    /// The app builds one of these with the system pasteboard and the real staging directory; a test
    /// passes its own of each, for the reason `BoardRegistry` takes a storage URL at all — injecting
    /// them is how a suite stays out of Application Support *and* off the machine's one pasteboard.
    ///
    /// **The launch sweep is here** (04: "a sweep at launch and on each copy"): a fresh store reads
    /// the pasteboard once and collects every staged tree it no longer names, which is exactly the
    /// residue a crash or a previous launch leaves behind.
    public init(
        pasteboard: any ClipboardPasteboard = SystemPasteboard(),
        stagingRoot: URL = ClipboardStore.defaultStagingRoot,
        observesActivation: Bool = true
    ) {
        self.pasteboard = pasteboard
        self.stagingRoot = stagingRoot
        refresh()
        sweep()

        guard observesActivation else { return }
        // Returning to the foreground is when another app's copy becomes this app's problem: the
        // cached payload is re-read, a cut whose pasteboard entry is gone is voided and undimmed, and
        // the staged tree that can never be pasted again goes now rather than lingering.
        activationObserver = NotificationCenter.default.addObserver(
            forName: NSApplication.didBecomeActiveNotification,
            object: nil,
            queue: .main
        ) { [weak self] _ in
            MainActor.assumeIsolated {
                guard let self else { return }
                self.refresh()
                self.sweep()
            }
        }
    }

    deinit {
        if let activationObserver {
            NotificationCenter.default.removeObserver(activationObserver)
        }
    }

    // MARK: - Copy and cut

    /// ⌘C — stages `store`'s selection and writes the pasteboard. Any pending cut is voided: its
    /// pasteboard entry has just been overwritten, so the items it dimmed are staying put.
    public func copy(from store: BoardStore) {
        write(from: store, cut: false)
    }

    /// ⌘X — the same write, plus the deferred move: the items stay where they are, dimmed, until a
    /// paste relocates them (04: "Cut is Finder-style deferred").
    public func cut(from store: BoardStore) {
        write(from: store, cut: true)
    }

    /// The one write both gestures share.
    ///
    /// The order is the contract: capture from the snapshot (main actor, no I/O — every item's
    /// `index.md` is already parsed into the snapshot and `FrontmatterDocument.serialized()` returns
    /// it verbatim), schedule the snapshots behind it, then write the pasteboard, then sweep. The
    /// pasteboard is written *before* the copies land, which is safe precisely because the manifest
    /// carries the fallback text: a paste that somehow beat the chain would still materialize the
    /// right items.
    private func write(from store: BoardStore, cut: Bool) {
        guard let capture = Self.capture(selection: store.selection, snapshot: store.snapshot) else { return }

        let copyID = UUID().uuidString.lowercased()
        let stagingDir = stagingRoot.appendingPathComponent(copyID, isDirectory: true)
        let jobs = capture.subjects.map { subject in
            StagingJob(
                source: subject.path.folder(under: store.rootURL),
                destination: stagingDir.appendingPathComponent(subject.id.rawValue, isDirectory: true)
            )
        }
        let manifest = ClipboardManifest(
            copyID: copyID,
            boardRoot: store.rootURL,
            kind: capture.kind,
            side: capture.side,
            entries: capture.subjects.map(\.entry)
        )
        guard let data = manifest.encoded() else { return }

        stage(jobs, into: stagingDir)

        // Whatever was armed is void the instant its copyID leaves the pasteboard — done here rather
        // than discovered later so the old board undims in the same turn as the new copy.
        voidCut()
        lastChangeCount = pasteboard.write(manifest: data, text: manifest.plainText)
        payload = manifest

        if cut {
            armedCut = ArmedCut(copyID: copyID, source: store)
            store.transient.pendingCut = ItemReferenceSet(
                ids: Set(capture.subjects.map(\.id)),
                liveness: capture.side
            )
        }
        // "A sweep at launch and on each copy purges entries the pasteboard no longer references."
        // Queued behind the snapshots above, so it can only ever collect trees older than this one.
        sweep()
    }

    // MARK: - Availability

    /// Whether Edit ▸ Copy applies — a non-empty selection that still names something the board
    /// renders, on either side of the live/tombstoned boundary.
    ///
    /// **The read-only lock deliberately does not close it**: "reading, selecting, searching and
    /// copying out all stay live" (02-architecture.md § The lock's scope) — a copy is a read. The
    /// focused-editor rule does close it: while an inline title editor holds the keyboard, ⌘C acts on
    /// the text (04 ▸ Grammar). The field consumes the selector natively, so this guard is belt over
    /// braces — but a board command that stayed armed under an editor would be exactly the kind of
    /// fall-through 04 is careful about.
    public func canCopy(from store: BoardStore) -> Bool {
        guard !store.isEditingInline else { return false }
        return SelectionGrammar.kind(of: store.selection, in: store.snapshot) != nil
    }

    /// Whether Edit ▸ Cut applies. Copy's conditions, plus the two a *move* adds: the board must
    /// accept writes (a cut mutates its source), and the selection must be **live** — "⌘X is
    /// disabled: the move-out vocabulary is Put Back or drag-to-restore, nothing else" (04 ▸ The
    /// trash).
    public func canCut(from store: BoardStore) -> Bool {
        canCopy(from: store) && !store.isReadOnly && store.selection.liveness == .live
    }

    /// Whether Edit ▸ Paste applies to `store`.
    ///
    /// Three clauses, all 04's: the board accepts board mutations (the lock and the focused-editor
    /// rule, `acceptsBoardMutations`); there is a payload at all; and — for a **card** payload only —
    /// there is somewhere to put it, which is false on a zero-lane board. A **lane** payload is
    /// always enabled, zero-lane board included: it is the other way out of one.
    public func canPaste(into store: BoardStore) -> Bool {
        guard store.acceptsBoardMutations, let payload else { return false }
        switch payload.kind {
        case .lane:
            return true
        case .card:
            return PasteTarget.cards(
                selection: store.selection,
                lastActiveLaneID: store.transient.lastActiveLaneID,
                snapshot: store.snapshot
            ) != nil
        }
    }

    // MARK: - Paste

    /// Where this paste is going, resolved **now** — from the selection as it stands when ⌘V is
    /// pressed, even though the paste itself completes once the staging chain has settled.
    private enum Plan {
        case cards(PasteTarget.Cards)
        case lanes(index: Int)
    }

    /// ⌘V — pastes into `store`, once the snapshots this pasteboard promised are actually on disk.
    ///
    /// Returns the task so a caller that must observe the end state (the tests) can await it; the app
    /// discards it. `nil` means there was nothing to do — no payload, or no target — which is the
    /// same condition the menu item's `disabled` reads, so a disabled command that somehow fires is a
    /// silent no-op rather than a surprise.
    @discardableResult
    public func paste(into store: BoardStore) -> Task<Void, Never>? {
        refresh()
        guard canPaste(into: store), let manifest = payload else { return nil }

        let plan: Plan
        switch manifest.kind {
        case .card:
            guard let target = PasteTarget.cards(
                selection: store.selection,
                lastActiveLaneID: store.transient.lastActiveLaneID,
                snapshot: store.snapshot
            ) else { return nil }
            plan = .cards(target)
        case .lane:
            plan = .lanes(index: PasteTarget.lanes(selection: store.selection, snapshot: store.snapshot))
        }

        let staging = stagingChain
        return Task { @MainActor [weak self, weak store] in
            await staging?.value
            guard let self, let store else { return }
            perform(manifest, plan: plan, into: store)
            // The snapshots just did their job — reclaim everything the pasteboard no longer points
            // at rather than waiting for the next copy or launch. The current copy survives: ⌘V twice
            // is a legitimate flow, and the second one needs it.
            sweep()
        }
    }

    /// The paste itself: main actor, snapshots settled.
    ///
    /// **The armed cut is tried first and consumed on success** — "first armed paste MOVES the
    /// surviving originals … a second paste materializes copies from staging" — and everything else
    /// is the copy path, which is also where a voided cut lands.
    ///
    /// **A paste is a user-initiated creation, so it clears the destination's search**
    /// (04-interactions.md § Search, stated by mechanism — "⌘N, Return-creation, the header button,
    /// empty-space double-click, paste, and Finder file drops alike"). Cards and lanes alike — the
    /// clipboard holds one or the other, and either arrives as an item the query may well not match.
    /// Unqualified, too: 04 names the *mechanism*, so the armed cut's move clears exactly as the copy
    /// does rather than earning a sub-rule for the one case where the items were already on this
    /// board. It is cleared here rather than at ⌘V so the two staleness guards keep their meaning: a
    /// paste the pasteboard moved under lands nothing, and so clears nothing.
    ///
    /// **A paste is an import boundary, so normalization applies** (04 ▸ Clipboard, settled
    /// 2026-07-28 — 01-storage-format.md's loose-file carve-out): every arrival below passes
    /// `normalizingLooseFiles: true`, so a loose file the staged snapshot faithfully carried beside
    /// a card's `index.md` lands inside the pasted card's `attachments/`, Finder-renamed on
    /// collision. Both branches and both operations, unqualified, because 04's sentence is
    /// unqualified. Nothing is dropped and nothing is announced: the snapshot preserved the file,
    /// the paste kept it, and it is where the schema says it belongs — the carve-out's notice is for
    /// files the app moves *without* being asked, which is the loader's path, not this one.
    private func perform(_ manifest: ClipboardManifest, plan: Plan, into store: BoardStore) {
        refresh()
        // The pasteboard moved under this paste (another app copied while the chain settled): the
        // payload the user asked to paste is no longer the payload, and inventing one is worse than
        // doing nothing.
        guard payload?.copyID == manifest.copyID else { return }

        store.transient.noteUserCreation()

        if let move = armedMove(for: manifest) {
            let sources = move.folders.map(BoardStore.ItemSource.folder)
            switch plan {
            case let .cards(target):
                store.receiveCards(
                    sources,
                    operation: .move,
                    toLane: target.laneID,
                    at: target.index,
                    clearingTombstones: false,
                    normalizingLooseFiles: true
                )
            case let .lanes(index):
                store.receiveLanes(
                    sources,
                    operation: .move,
                    at: index,
                    clearingTombstones: false,
                    normalizingLooseFiles: true
                )
            }
            consumeCut()
            return
        }

        // The copy path — the staged snapshot per entry, or the embedded `index.md` where that
        // snapshot is missing or unreadable. Mixed is legal and is the honest outcome of a partial
        // staging failure: the entries that have snapshots arrive whole.
        let stagingDir = stagingRoot.appendingPathComponent(manifest.copyID, isDirectory: true)
        var sources: [BoardStore.ItemSource] = []
        var losses: [BannerCenter.AttachmentLoss] = []
        for entry in manifest.entries {
            let staged = stagingDir.appendingPathComponent(entry.folder, isDirectory: true)
            if FileManager.default.fileExists(
                atPath: staged.appendingPathComponent(BoardLoader.indexFileName).path
            ) {
                sources.append(.folder(staged))
                continue
            }
            sources.append(.text(index: entry.index, cards: entry.cards.map(\.index)))
            // "A degraded paste is loud, never silent … a one-shot banner names exactly what was
            // lost." An entry with no attachments lost nothing — its content is intact and its bytes
            // are the source bytes — so it contributes no row.
            if entry.lostAttachmentCount > 0 {
                losses.append(BannerCenter.AttachmentLoss(
                    title: entry.title,
                    attachments: entry.lostAttachmentCount
                ))
            }
        }

        // "⌘C strips `deleted:` at materialization" (04 ▸ The trash) — the trash's copy-out-only rule,
        // and the one axis a paste varies that a within-board drop never does.
        let clearingTombstones = manifest.side == .trashed
        switch plan {
        case let .cards(target):
            store.receiveCards(
                sources,
                operation: .copy,
                toLane: target.laneID,
                at: target.index,
                clearingTombstones: clearingTombstones,
                normalizingLooseFiles: true
            )
        case let .lanes(index):
            store.receiveLanes(
                sources,
                operation: .copy,
                at: index,
                clearingTombstones: clearingTombstones,
                normalizingLooseFiles: true
            )
        }
        store.banners.postDegradedPaste(losses)
    }

    /// The armed cut's surviving originals, in flatten order and as folders under the **source**
    /// board's root — or `nil` when the cut is not armed for this manifest.
    ///
    /// The four ways it is not armed are 04's four ways a cut voids, and three of them are simply
    /// the absence of something: another app took the pasteboard (the copyID no longer matches), the
    /// source board closed (the weak reference is gone), and the cut emptied — "a cut voided down to
    /// nothing is simply void". The fourth, per-item deletion, is already applied: the pending cut
    /// has been re-resolved against every reload since, so what is left in it *is* the survivors.
    private func armedMove(for manifest: ClipboardManifest) -> (source: BoardStore, folders: [URL])? {
        guard let cut = armedCut, cut.copyID == manifest.copyID, let source = cut.source else { return nil }
        let survivors = source.transient.pendingCut
        guard !survivors.isEmpty else { return nil }

        // `TrashModel.paths` walks lanes in board order and each lane's cards in card order, which is
        // the flatten order the drop commits insert in — and the pending cut is homogeneous by kind,
        // so only one of its two branches ever contributes.
        let folders = TrashModel.paths(of: survivors.ids, on: .live, in: source.snapshot)
            .map { $0.folder(under: source.rootURL) }
        guard !folders.isEmpty else { return nil }
        return (source, folders)
    }

    /// The cut has been paid out: the originals moved, so nothing is pending and nothing dims. A
    /// second ⌘V then falls through to the copy path, which is exactly what 04 asks for.
    private func consumeCut() {
        armedCut?.source?.transient.pendingCut = .empty
        armedCut = nil
    }

    /// The cut is void: undim and forget it. Clearing the source's pending set is what "voiding
    /// undims" means in code — everything else about a void cut is the absence of an arm.
    private func voidCut() {
        guard let cut = armedCut else { return }
        cut.source?.transient.pendingCut = .empty
        armedCut = nil
        Self.logger.debug("pending cut voided")
    }

    // MARK: - Pasteboard freshness

    /// Re-reads the pasteboard **if and only if it has changed**, and voids a cut the change orphaned.
    ///
    /// One `changeCount` read in the common case, which is what makes it cheap enough for the three
    /// callers 04 names: menu validation (through the cached `payload`), app activation, and the
    /// front of every paste.
    public func refresh() {
        let count = pasteboard.changeCount
        guard count != lastChangeCount else { return }
        lastChangeCount = count
        payload = pasteboard.manifestData().flatMap(ClipboardManifest.init(data:))
        if let cut = armedCut, payload?.copyID != cut.copyID {
            voidCut()
        }
    }

    // MARK: - Staging

    /// One item's snapshot: where it lives, where its copy goes.
    private struct StagingJob: Sendable {
        let source: URL
        let destination: URL
    }

    /// Appends this copy's snapshots to the staging chain. Best-effort per item: one that fails to
    /// copy simply falls back to the manifest's embedded `index.md` at paste time, which is the
    /// degraded paste the banner already has words for.
    private func stage(_ jobs: [StagingJob], into stagingDir: URL) {
        enqueue { [jobs, stagingDir] in
            guard (try? FileManager.default.createDirectory(
                at: stagingDir,
                withIntermediateDirectories: true
            )) != nil else { return }
            for job in jobs {
                try? FileManager.default.copyItem(at: job.source, to: job.destination)
            }
        }
    }

    /// Deletes every staged tree the pasteboard no longer names — **one rule, three callers**: app
    /// launch (trees orphaned by a crash or a previous session), returning to the foreground (another
    /// app took the pasteboard while we were away, so ours can never be pasted again), and the tail
    /// of every copy and every paste.
    ///
    /// Runs on the staging chain, off the main actor: deleting a gigabyte-scale tree is as slow as
    /// writing one, and the chain is what keeps this from ever overtaking the copy that is producing
    /// the tree it is being told to keep.
    public func sweep() {
        refresh()
        let keep = payload?.copyID
        let root = stagingRoot
        enqueue { await Self.prune(root, keeping: keep) }
    }

    private nonisolated static func prune(_ root: URL, keeping keep: String?) async {
        guard let entries = try? FileManager.default.contentsOfDirectory(
            at: root,
            includingPropertiesForKeys: nil,
            options: [.skipsHiddenFiles]
        ) else { return }
        for entry in entries where entry.lastPathComponent != keep {
            try? FileManager.default.removeItem(at: entry)
        }
    }

    /// Appends `work` to the staging chain. `Task.detached` rather than `Task { }`: a task created in
    /// a `@MainActor` method inherits that isolation and would run the file work on the main actor —
    /// the exact thing this chain exists to avoid.
    private func enqueue(_ work: @escaping @Sendable () async -> Void) {
        let previous = stagingChain
        stagingChain = Task.detached(priority: .userInitiated) {
            await previous?.value
            await work()
        }
    }

    /// Awaits every snapshot and sweep queued so far. The app never needs this — a paste awaits the
    /// chain itself — but the tests use it to observe the staging directory once the dust has settled.
    public func stagingSettled() async {
        await stagingChain?.value
    }

    // MARK: - What a copy captures

    /// One item a copy is about to stage: its identity, its folder, and the manifest entry it
    /// produces.
    struct Subject {
        let id: ItemID
        let path: TrashModel.ItemPath
        let entry: ClipboardManifest.Entry
    }

    /// The selection, resolved into copy subjects in the order the clipboard records them — or `nil`
    /// when it names nothing the board renders on its own side.
    ///
    /// **The order is `SelectionGrammar.order`'s**, which is already the right answer for all four
    /// (side, kind) pairs: flatten order for live cards, left-to-right for live lanes, and the trash's
    /// own deterministic sort for either kind of entry. Deriving it here would be a fifth definition
    /// of an order the app already states once.
    ///
    /// **The index text comes from the snapshot, not from disk.** `FrontmatterDocument` edits by line
    /// span, so `serialized()` on an untouched document returns the file's bytes exactly — which
    /// makes the manifest's fallback text genuinely *the source bytes* while costing ⌘C no file I/O
    /// at all, even for a lane carrying two hundred cards.
    static func capture(
        selection: ItemReferenceSet,
        snapshot: BoardModel
    ) -> (kind: SelectionKind, side: Liveness, subjects: [Subject])? {
        guard let kind = SelectionGrammar.kind(of: selection, in: snapshot) else { return nil }
        let side = selection.liveness
        let ordered = SelectionGrammar.order(of: kind, on: side, in: snapshot)
            .filter { selection.ids.contains($0) }
        guard !ordered.isEmpty else { return nil }

        var subjects: [ItemID: Subject] = [:]
        for lane in snapshot.lanes {
            if kind == .lane, Liveness(isDeleted: lane.isDeleted) == side {
                subjects[lane.id] = Subject(
                    id: lane.id,
                    path: TrashModel.ItemPath(laneID: lane.id, cardID: nil),
                    entry: ClipboardManifest.Entry(
                        id: lane.id.rawValue,
                        folder: lane.id.rawValue,
                        title: lane.title.value,
                        index: lane.document.serialized(),
                        attachmentCount: 0,
                        // Live cards only — a lane copy strips tombstoned cards, and the fallback
                        // only ever materializes a copy (see `ClipboardManifest.Entry.cards`).
                        cards: lane.cards.filter { !$0.isDeleted }.map { card in
                            ClipboardManifest.Entry.Card(
                                id: card.id.rawValue,
                                title: card.title.value,
                                index: card.document.serialized(),
                                attachmentCount: card.attachments.count
                            )
                        }
                    )
                )
            }
            // A tombstoned lane subsumes its subtree on both sides: its cards render nowhere live and
            // have no trash row of their own, so they are nobody's copy subject.
            guard kind == .card, !lane.isDeleted else { continue }
            for card in lane.cards where Liveness(isDeleted: card.isDeleted) == side {
                subjects[card.id] = Subject(
                    id: card.id,
                    path: TrashModel.ItemPath(laneID: lane.id, cardID: card.id),
                    entry: ClipboardManifest.Entry(
                        id: card.id.rawValue,
                        folder: card.id.rawValue,
                        title: card.title.value,
                        index: card.document.serialized(),
                        attachmentCount: card.attachments.count
                    )
                )
            }
        }

        let resolved = ordered.compactMap { subjects[$0] }
        guard !resolved.isEmpty else { return nil }
        return (kind, side, resolved)
    }
}