import AppKit
import Observation
import SwiftUI

// MARK: - TrashLaneView

/// The trash quasi-lane: the trailing, visually distinct column tombstoned items live in
/// (03-board-ui.md § Trash).
///
/// ### A pure view, and a quasi-lane
///
/// **Nothing here moves anything on disk.** Tombstoned items keep their `deleted:` key and stay
/// exactly where they are; this column is a rendering of `TrashModel.entries(of:)` and nothing more.
/// It is a *quasi*-lane because it wears a lane's shape while sharing none of a lane's machinery:
///
/// - it spans a **fixed one width unit** — no `width` frontmatter, no stepper, no resize handle, and
///   the edge drag never reaches it (`LaneLayoutMath.totalUnits(of:trashUnits:)` supplies the unit,
///   so there is no `Lane` value for any of those to act on);
/// - it is **not draggable and not reorderable** — the header carries no gesture, and it is absent
///   from the drop proposal's slot list by construction, since `BoardView` builds that from the
///   snapshot's live lanes;
/// - it is **no destination for a move** — "no move or paste ever targets the trash"
///   (04-interactions.md ▸ The trash). It is a destination for exactly one thing, below;
/// - it has **no new-card button**: nothing is created in the trash.
///
/// ### The one drop it takes: the delete gesture
///
/// **"Dropping a live card on the shown trash deletes it"** (04-interactions.md ▸ The trash, settled
/// 2026-07-28) — "the drag becomes the pointer's delete gesture; release tombstones the dragged
/// card(s), exactly the ⌫ tombstone". So the column does declare an `onDrop`
/// (`TrashDropDelegate`), and it is the narrowest one on the board: a **live** card drag from **this**
/// board, unmodified. Lanes are not deliverable this way, a foreign board's card is not (that would
/// be a transfer-and-delete compound), ⌥ is not (copying into the trash is not a thing), and hidden
/// the column is not rendered at all, so it has no region to enter. Every one of those refusals hands
/// the session back to the strip's own logic, which is exactly what happened here before this target
/// existed — so nothing about the column's behaviour changed except the gesture that is new
/// (`TrashDrop`).
///
/// It diverges from every other drop on the board in one way, and the sort is what makes the
/// divergence honest: **the shadow always takes the topmost row**, because the trash orders by
/// `deleted` newest-first and a fresh tombstone genuinely lands on top. The drop still lands exactly
/// where the shadow shows.
///
/// **Finder file drops stay inert** — "attachment import on tombstoned cards is inert" (▸ The trash)
/// — and now say so directly: the delegate clears the file highlight over the column rather than
/// relying on the strip resolving to no lane.
///
/// ### No editing in the trash
///
/// "Tombstoned cards don't open — double-click does nothing beyond selection; Put Back or drag out
/// first." There is deliberately no double-tap recogniser, no rename editor, and no Style… row: the
/// trash is for restoring or purging, not working.
///
/// ### What is still a later card's
///
/// **⌘C copy-out** is still owed. The **search filter** ("shown, it participates in the filter like
/// any lane") arrived with m5 and is one line — see `entries`, which every other surface here reads
/// through. The *pointer* grammar is here: a row's click runs the same `SelectionGrammar` the
/// board does, and the column's empty space rubber-bands on the trashed side. So is the drop, with
/// the target lane highlighted and the source row dimmed in place; the drag's replica is not. The
/// **keyboard** reaches the column entirely through the frames the rows register — arrow walks in
/// and out, ⇧-arrows inert at both the liveness and the kind boundary — so nothing in this file
/// implements it beyond keeping every row drawn and registered (see `rows`).
struct TrashLaneView: View {

    let store: BoardStore

    /// The window's purge-alert host, threaded down rather than read from the focus system: a
    /// context menu's content is built in its own host, where a `@FocusedValue` is not reliably the
    /// board window's, and the row's Delete Immediately must raise the *same* alert the menu bar's
    /// does.
    let confirmations: TrashConfirmations

    /// The board window's drop machinery — a row's drag is an ordinary card session on the
    /// **trashed** side (`DragSession`, 04-interactions.md ▸ The trash).
    let drops: BoardDropContext

    /// The strip's rubber band. The column's empty space is its third surface, on the **trashed**
    /// side — "a rubber-band stays on the side of the boundary it started on" (04-interactions.md ▸
    /// The trash) — and every row registers its frame into the same registry.
    let marquee: MarqueeControl

    /// Reduce Motion, for the row transition below — 10-accessibility.md names the trash
    /// specifically ("and trash animations all get reduced variants").
    @Environment(\.accessibilityReduceMotion) private var reduceMotion

    /// The lane plate's corner radius — matched to `LaneView`'s so the column reads as a sibling of
    /// the lanes rather than as a different kind of object.
    private let cornerRadius: CGFloat = 10

    private let rowSpacing: CGFloat = 6

    /// The height a shadow row holds open. A trash row's height is content-driven (one or two title
    /// lines, plus a lane entry's count line) and the cards being proposed have no row yet to be
    /// measured, so the shadow is drawn at the nominal single-line plate — `LaneDropRegistry`'s own
    /// answer to the same question, in this column's smaller idiom.
    private let nominalRowHeight: CGFloat = 32

    var body: some View {
        VStack(alignment: .leading, spacing: 0) {
            header
            rows
        }
        .background(
            RoundedRectangle(cornerRadius: cornerRadius)
                .fill(.quaternary.opacity(0.35))
        )
        // **The delete gesture's drop target**, over the whole column — the header included, since
        // the ruling is "dropping a live card on the shown trash", not on one of its rows. It
        // declares every type the board's other targets do, because single-target dispatch hands the
        // deepest region whatever session is in flight and a narrower target would strand the rest
        // (`TrashDropDelegate`).
        .onDrop(of: boardDropTypes, delegate: TrashDropDelegate(context: drops))
    }

    /// The rows the column shows.
    ///
    /// **The shown trash "participates in the filter like any lane"** (03-board-ui.md § Trash), so
    /// the search predicate narrows this collection exactly as it narrows `LaneView.renderedCards`
    /// — card rows and lane rows alike, each by its own title and body (`SearchFilter`) — and the
    /// count badge follows for free, because it reads this same value. Hidden, the column renders
    /// nothing and registers nothing, so "hidden trash is invisible to search" needs no code at all.
    private var entries: [TrashEntry] {
        let filter = store.searchFilter
        return TrashModel.entries(of: store.snapshot).filter { filter.matches($0) }
    }

    // MARK: - The delete gesture's landing

    /// Where the delete gesture's shadow run opens in this column — always the topmost row — or `nil`
    /// when no proposal names the trash, which is every other moment of the app's life.
    private var proposal: Int? {
        drops.session.trashProposal(onBoardRooted: store.rootURL)
    }

    /// The rows the `VStack` lays out: the entries, with the delete gesture's shadow run opened at
    /// the top.
    ///
    /// The run stands until the echo reload brings the real tombstones — the committed-overlay hold
    /// keeps the arrangement the release proposed on screen for that round trip, exactly as every
    /// other container's does (`CommittedHold`).
    private var slots: [TrashSlot] {
        var result = entries.map(TrashSlot.entry)
        guard let proposal else { return result }
        let run = (0..<drops.session.shadowCount).map(TrashSlot.shadow)
        result.insert(contentsOf: run, at: min(max(0, proposal), result.count))
        return result
    }

    // MARK: - Header

    /// Dimmed and hatched, with the trash symbol, the stable "Trash" title and a count badge
    /// (03-board-ui.md § Trash ▸ Rendering).
    ///
    /// The hatching is what makes the column read as *not a lane* at a glance — the design asks for
    /// "visually distinct", and a lane's header is the surface this must not be mistaken for. It
    /// carries no gesture at all: no selection (the quasi-lane "is never selectable as a lane"), no
    /// reorder drag, no context menu.
    private var header: some View {
        HStack(alignment: .firstTextBaseline, spacing: 6) {
            Image(systemName: "trash")
                .foregroundStyle(.secondary)
                .imageScale(.medium)
            Text("Trash")
                .font(.headline)
                .foregroundStyle(.secondary)
                .lineLimit(1)
                .truncationMode(.tail)
            countBadge
            Spacer(minLength: 0)
        }
        .padding(.horizontal, 10)
        .padding(.vertical, 8)
        .background {
            UnevenRoundedRectangle(topLeadingRadius: cornerRadius, topTrailingRadius: cornerRadius)
                .fill(.quaternary.opacity(0.5))
                .overlay {
                    DiagonalHatch()
                        .stroke(.quaternary, lineWidth: 1)
                        .clipShape(UnevenRoundedRectangle(
                            topLeadingRadius: cornerRadius,
                            topTrailingRadius: cornerRadius
                        ))
                }
        }
        .accessibilityElement(children: .combine)
    }

    /// The entry count — the same collection the body renders, so the badge cannot disagree with
    /// what is on screen (`LaneView.countBadge`'s rule, and it is why m5's filter needs no second
    /// change here).
    private var countBadge: some View {
        Text("\(entries.count)")
            .font(.caption)
            .monospacedDigit()
            .foregroundStyle(.secondary)
            .padding(.horizontal, 6)
            .padding(.vertical, 1)
            .background(Capsule().fill(.quaternary))
    }

    // MARK: - Rows

    /// The rows, scrollable, with the navigation head kept in view.
    ///
    /// **"Selection scrolls into view"** (04-interactions.md ▸ Grammar), watching the head rather
    /// than the whole selection so exactly one column responds to any one arrow — `LaneView`'s rule,
    /// on the trash side.
    private var rows: some View {
        ScrollViewReader { proxy in
            scrollableRows
                .onChange(of: store.transient.selectionHead) { _, head in
                    guard let head, entries.contains(where: { $0.id == head }) else { return }
                    proxy.scrollTo(TrashSlot.identity(of: head))
                }
        }
    }

    private var scrollableRows: some View {
        ScrollView(.vertical) {
            // **A plain `VStack`, deliberately not lazy.** Every row must keep its drawn frame
            // registered in `MarqueeTargetRegistry` — the rubber band sweeps those frames and the
            // arrows navigate by them (`NavigationMath`) — and a lazy stack only builds the rows it
            // has scrolled to, so an unbuilt row is invisible to both. The constraint is affordable
            // because a trash is small: it holds one board's tombstones, and Empty Trash… exists.
            VStack(alignment: .leading, spacing: rowSpacing) {
                ForEach(slots) { slot in
                    Group {
                        switch slot {
                        case let .entry(entry):
                            TrashEntryRow(
                                store: store,
                                entry: entry,
                                confirmations: confirmations,
                                drops: drops,
                                registry: marquee.registry
                            )
                        case .shadow:
                            // The delete gesture's shadow, holding the topmost row open
                            // (04-interactions.md ▸ The trash).
                            DragShadow(cornerRadius: 6)
                                .frame(maxWidth: .infinity)
                                .frame(height: nominalRowHeight)
                        }
                    }
                    // A row is a tombstoned item, so it arrives and leaves in the card's dialect —
                    // a delete files one in, a Put Back or a purge takes one out, and both halves of
                    // that pair should read alike from either side of the strip. The transaction is
                    // the reload's, like the lanes' (`Motion.reloadAnimates`).
                    .transition(Motion.cardTransition(reduced: reduceMotion))
                    // The scroll target — `LaneView`'s rule, and outermost for its reason.
                    .id(slot.id)
                }
            }
            // The reflow that opens the topmost row for the shadow, keyed on **the drop proposal and
            // nothing else** (03-board-ui.md § Motion's narrow keys) — the trash column's own copy of
            // the rule `BoardView` applies to the strip and `LaneView` to its masonry.
            .animation(Motion.dragReflow(reduced: reduceMotion), value: proposal)
            // `maxHeight: .infinity` here, not just `maxWidth`, is what makes the gesture surface
            // below reach the column's full height rather than stopping where the last row ends —
            // the same fix `LaneView.scrollableCards` applies to its masonry, and for the identical
            // reason: a `ScrollView` proposes its content only the height that content asks for, so a
            // view sized to fit its rows leaves the blank space beneath them un-hit-testable. "The
            // column's gesture surface is full height" (04-interactions.md ▸ The trash, settled)
            // needs that blank space to actually belong to the view the gesture below is on.
            .frame(maxWidth: .infinity, maxHeight: .infinity, alignment: .topLeading)
            .padding(6)
            .contentShape(Rectangle())
            // The band's trash-side surface. It arms from the column's empty space, full height
            // (above) included, so a drag can start from the blank area below the last row exactly
            // as the board background allows on the live side — a drag begun on a row instead is that
            // row's drag-out, and the begin guard makes that geometric rather than a matter of
            // gesture priority (`MarqueeControl`).
            .simultaneousGesture(marquee.gesture(side: .trashed))
        }
    }
}

// MARK: - The plate

/// The trash row's *appearance*, with none of anybody's behaviour — the compact, dimmed plate a
/// tombstone wears.
///
/// **Two views draw it and neither may drift**: the row itself, and its own drag replica (a drag
/// image is a snapshot, and one built out of the live plate would re-register the row's frame from
/// inside the preview's geometry and then deregister it when the image went away — quietly stealing
/// the row from the rubber band and the arrow keys).
private struct TrashRowPlate: View {

    let symbol: String

    /// The title as written, or `nil` for an untitled item — "Untitled" is a rendering, never a value
    /// (03-board-ui.md § Card face).
    let title: String?

    /// A lane entry's returning-card count, and nothing else takes a second line.
    let subtitle: String?

    var isSelected: Bool = false

    private let cornerRadius: CGFloat = 6

    var body: some View {
        HStack(alignment: .firstTextBaseline, spacing: 6) {
            Image(systemName: symbol)
                .foregroundStyle(.secondary)
                .imageScale(.small)
            VStack(alignment: .leading, spacing: 2) {
                Text(title ?? "Untitled")
                    .font(.callout)
                    .foregroundStyle(.secondary)
                    .lineLimit(2)
                if let subtitle {
                    Text(subtitle)
                        .font(.caption)
                        .foregroundStyle(.tertiary)
                }
            }
            .frame(maxWidth: .infinity, alignment: .leading)
        }
        .padding(.horizontal, 8)
        .padding(.vertical, 6)
        .background(RoundedRectangle(cornerRadius: cornerRadius).fill(.background.secondary.opacity(0.6)))
        .overlay(
            RoundedRectangle(cornerRadius: cornerRadius)
                .strokeBorder(isSelected ? AnyShapeStyle(Color.accentColor) : AnyShapeStyle(.clear), lineWidth: 1.5)
        )
    }
}

// MARK: - What the column lays out

/// One row of the trash column — an entry, or one slot of the delete gesture's run.
///
/// `LaneSlot`'s smaller sibling, and keyed on the same principle: a slot's id decides whether the
/// echo reload reads as a *swap* or as a removal and an insertion.
private enum TrashSlot: Identifiable {

    /// A tombstone the snapshot already holds.
    case entry(TrashEntry)

    /// One of the drag's N shadows, holding the topmost rows open (04-interactions.md ▸ The trash).
    case shadow(index: Int)

    var id: String {
        switch self {
        case let .entry(entry): Self.identity(of: entry.id)
        // Constant per position in the run, so a run that grows or shrinks animates as slots rather
        // than blinking (`LaneSlot`'s rule).
        case let .shadow(index): "shadow:\(index)"
        }
    }

    /// An entry slot's id, spelled once so `scrollTo` and the slot cannot disagree about what the
    /// scroll reader is looking for (`LaneSlot.identity(of:)`).
    static func identity(of item: ItemID) -> String { "entry:\(item.rawValue)" }
}

// MARK: - The hatch

/// Diagonal hatching for the trash header — the "dimmed/hatched" treatment 03-board-ui.md asks for,
/// drawn rather than imaged so it takes whatever width the division gives the column.
///
/// The lines start a full header-height to the left of the leading edge so the first stroke reaches
/// the top-left corner instead of beginning partway across.
private struct DiagonalHatch: Shape {
    var spacing: CGFloat = 7

    func path(in rect: CGRect) -> Path {
        var path = Path()
        guard spacing > 0, rect.height > 0 else { return path }
        var x = rect.minX - rect.height
        while x < rect.maxX {
            path.move(to: CGPoint(x: x, y: rect.maxY))
            path.addLine(to: CGPoint(x: x + rect.height, y: rect.minY))
            x += spacing
        }
        return path
    }
}

// MARK: - Rows

/// One trash row: a compact, dimmed plate carrying the item's symbol and title — and, for a lane
/// entry, the count of cards Put Back would return with it.
///
/// **Face-like but not a card face.** It shares the plate, the symbol and the title, and it
/// deliberately shares none of the face's *editing* affordances: no rename editor, no Open, no
/// Style…. That is 03-board-ui.md's no-editing-in-the-trash rule expressed as an absence rather
/// than as a pile of `disabled` modifiers.
private struct TrashEntryRow: View {

    let store: BoardStore
    let entry: TrashEntry
    let confirmations: TrashConfirmations
    let drops: BoardDropContext

    /// Where the rubber band looks up what it is sweeping — the card face's rule, on the trashed
    /// side (`View.marqueeTarget`).
    let registry: MarqueeTargetRegistry

    /// **Lane entries are not draggable** (03-board-ui.md § Trash: "a lane entry is not draggable —
    /// its entry is a compact row, not the lane; its move-out is Put Back"), so the drag half is
    /// simply *absent* for them rather than refused — no session, no image, no snap-back. A click
    /// still selects either way.
    @ViewBuilder
    var body: some View {
        if entry.isLaneEntry {
            plate
        } else {
            plate.onDrag(startRowDrag, preview: { dragReplica })
        }
    }

    private var plate: some View {
        rowFace
            // The row being dragged out dims in place — the source stays visible in the trash,
            // because a restore is not a removal until the write lands.
            .opacity(drops.session.isDragging(entry.id) ? ClipboardTreatment.dimmedOpacity : 1)
            // The deferred cut wears the same dim wherever it lands, so the treatment is stated for
            // every surface a `pendingCut` could name rather than for two of the three. In practice
            // it never fires here: ⌘X is disabled on tombstoned selections (04-interactions.md ▸ The
            // trash), and a pending cut is homogeneous by liveness — a reload that tombstones a cut
            // card *ejects* it from the set rather than moving it to the other side.
            .cutTreatment(of: entry.id, in: store)
            .contentShape(Rectangle())
            .onTapGesture { select() }
            .marqueeTarget(entry.id, kind: entry.isLaneEntry ? .lane : .card, side: .trashed, in: registry)
            .contextMenu { menu }
    }

    /// This entry as the shared plate draws it — appearance only, no gesture, no context menu and
    /// crucially no marquee registration, which is what makes it safe for the drag replica to render
    /// (see `TrashRowPlate`).
    private var rowFace: some View {
        TrashRowPlate(
            symbol: ItemSymbol.name(entry.icon, fallback: symbolFallback),
            title: entry.title,
            subtitle: laneSubtitle,
            isSelected: isSelected
        )
    }

    private var symbolFallback: String {
        entry.isLaneEntry ? ItemSymbol.lane : ItemSymbol.card
    }

    /// "N cards" — what Put Back brings back with a tombstoned lane, not how many folders sit inside
    /// it (`TrashModel.entries`' returning-count rule). Card entries have no second line.
    private var laneSubtitle: String? {
        guard case let .lane(_, returning) = entry else { return nil }
        return "\(returning) card\(returning == 1 ? "" : "s")"
    }

    // MARK: - Selection

    private var isSelected: Bool {
        store.selection.liveness == .trashed && store.selection.ids.contains(entry.id)
    }

    /// A click selects this row on the **trashed** side, through the same grammar the board's
    /// surfaces use — plain replaces, ⌘ toggles, ⇧ ranges (`SelectionGrammar`).
    ///
    /// The row's kind travels with the click, and that is what keeps the trash's second homogeneity
    /// axis true: a ⌘-click across the card/lane-entry boundary replaces rather than mixing, and a
    /// ⇧-range walks only its own kind's rows (04-interactions.md ▸ The trash). No `togglesOnRepeat`
    /// — click-again-to-unselect is the lane's behaviour, not a row's.
    ///
    /// **A double click is two of these and nothing more**: no editor, no card window, no timer.
    private func select() {
        store.click(
            SelectionTarget(id: entry.id, kind: entry.isLaneEntry ? .lane : .card, side: .trashed),
            modifier: .current
        )
    }

    // MARK: - Drag out

    /// Begins the row's drag out of the trash — an ordinary **card session on the trashed side**,
    /// which is the whole of what makes it a restore rather than a move (04-interactions.md ▸ The
    /// trash; `DragLocality.operation`).
    ///
    /// Where it lands is the ordinary drop model's answer: `DropSlotMath.cardSlot` over the
    /// destination lane's masonry, so "restores it at the drop position" is the same arithmetic every
    /// other card drop uses. What a release *means* differs by locality and modifier, and that lives
    /// in one place (`BoardDropContext.commitDrop`): within the board a restore, ⌥ a live copy-out,
    /// across boards a live copy with ⌘ forcing the true restore-move.
    ///
    /// **Multi-drag carries the whole trashed selection**, in the trash's own sorted order — the
    /// order the rows are drawn in, which is the only relative order a set of tombstones has.
    ///
    /// Refused under the read-only lock and while an inline editor is focused, like every other
    /// mutating gesture.
    private func startRowDrag() -> NSItemProvider {
        guard !store.isReadOnly, !store.isEditingInline else { return NSItemProvider() }
        let selection = store.selection
        let ids: Set<ItemID> = selection.liveness == .trashed
            && selection.ids.contains(entry.id)
            && selection.ids.count > 1
            ? selection.ids
            : [entry.id]

        // Card entries only: a lane entry cannot be dragged at all, so one caught up in a mixed
        // selection is simply not carried. (The selection is homogeneous by kind anyway — this is
        // belt over braces.)
        let rows: [(id: ItemID, laneID: ItemID, title: String?)] = TrashModel.entries(of: store.snapshot)
            .compactMap { candidate in
                guard ids.contains(candidate.id), case let .card(card, laneID) = candidate else { return nil }
                return (card.id, laneID, card.title.value)
            }
        guard !rows.isEmpty else { return NSItemProvider() }

        let root = store.rootURL
        let payload = DragPayload(
            boardRoot: root,
            kind: .cards,
            side: .trashed,
            items: rows.map {
                DragPayload.Item(
                    id: $0.id.rawValue,
                    folder: TrashModel.ItemPath(laneID: $0.laneID, cardID: $0.id).folder(under: root).path,
                    title: $0.title
                )
            }
        )
        drops.session.beginCards(
            rows.map(\.id),
            folders: payload.folders,
            heights: rows.map { _ in LaneDropRegistry.nominalCardHeight },
            side: .trashed,
            source: store
        )
        return payload.itemProvider()
    }

    /// The image under the cursor: the row as it is drawn, fanned with a count badge for a
    /// multi-drag — the card replica's treatment, at a trash row's size.
    private var dragReplica: some View {
        let count = store.selection.liveness == .trashed && store.selection.ids.contains(entry.id)
            ? max(1, store.selection.ids.count)
            : 1
        return ZStack {
            if count > 2 { rowFace.offset(x: 10, y: 10).opacity(0.45) }
            if count > 1 { rowFace.offset(x: 5, y: 5).opacity(0.7) }
            rowFace
        }
        .frame(width: 200)
        .overlay(alignment: .topTrailing) { DragCountBadge(count: count) }
        .padding(12)
    }

    // MARK: - The trash entry's context menu

    /// Put Back, Delete Immediately, Reveal in Finder — the three rows 11-command-nexus.md gives a
    /// trash entry, and no others.
    ///
    /// Reveal in Finder is the odd one out and deliberately so: it is "not edit-shaped and stays
    /// enabled on tombstoned selections", read-only lock included — inspecting a folder before a
    /// purge is exactly the errand it exists for.
    @ViewBuilder
    private var menu: some View {
        Button("Put Back") {
            store.putBack(targetIDs)
        }
        .disabled(!store.acceptsBoardMutations)

        Button("Delete Immediately") {
            confirmations.requestPurge(of: targetIDs, in: store)
        }
        .disabled(!store.acceptsBoardMutations)

        Divider()

        Button("Reveal in Finder") {
            NSWorkspace.shared.activateFileViewerSelecting(targetFolders)
        }
    }

    /// What this row's menu acts on: the whole selection when this row is part of it, else this row
    /// alone — standard macOS context-menu targeting, and the same rule the card face and the lane
    /// header apply to Style…. Right-clicking something outside the selection acts on what was
    /// clicked, which is also what keeps a cross-kind menu from ever acting on a mixed set.
    private var targetIDs: Set<ItemID> {
        guard store.selection.liveness == .trashed, store.selection.ids.contains(entry.id) else {
            return [entry.id]
        }
        return store.selection.ids
    }

    private var targetFolders: [URL] {
        TrashModel.paths(of: targetIDs, on: .trashed, in: store.snapshot)
            .map { $0.folder(under: store.rootURL) }
    }
}