import CoreGraphics
import Foundation
import Testing
@testable import Kanban

/// **The card drag's resting layout, built once per snapshot rather than once per mouse sample**
/// (`RestingLayoutCache`; DRAG-REORDER.md § The mid-drag re-grounding trio, rule 1).
///
/// The cache is transparent by construction — `BoardDropContext.retargetCards` hands
/// `DropSlotMath.cardSlot` the same heights it always did — so what is worth pinning is not the
/// arithmetic (that is `DropSlotMathTests`') but the **key**: every input the layout derives from is
/// either in it or provably still for the drag's duration, and a missing one would be stale
/// proposals rather than a slow drag.
///
/// Boards are real loads off real temp trees, `ViewEquatableTests`' reason: a hand-assembled `Lane`
/// would be caching something `BoardLoader` can never produce, and "a reload mid-drag re-grounds the
/// zones" is only worth asserting against the snapshots a reload actually lands.

// MARK: - Fixtures

/// Two lanes, three cards in the first — enough for a layout with an interior card to lift out of,
/// and a second lane to prove the entries are per lane.
@MainActor
private func makeFixture() throws -> WriterFixture {
    let fixture = try WriterFixture()
    try fixture.board()
    try fixture.lane(Ident.lane1, order: "1024", title: "Todo")
    try fixture.card(Ident.card1, in: Ident.lane1, order: "1024", title: "First")
    try fixture.card(Ident.card2, in: Ident.lane1, order: "2048", title: "Second")
    try fixture.card(Ident.card3, in: Ident.lane1, order: "3072", title: "Third")
    try fixture.lane(Ident.lane2, order: "2048", title: "Doing")
    try fixture.card(Ident.card4, in: Ident.lane2, order: "1024", title: "Fourth")
    return fixture
}

/// An identity neither fixture board has seen — what an agent files into a lane mid-drag.
private let foreignName = "abcdabcd-abcd-4bcd-8bcd-abcdabcdabcd"
private let foreignCard = ItemID(rawValue: foreignName)

private let lane1 = ItemID(rawValue: Ident.lane1)
private let lane2 = ItemID(rawValue: Ident.lane2)
private let card1 = ItemID(rawValue: Ident.card1)
private let card2 = ItemID(rawValue: Ident.card2)
private let card3 = ItemID(rawValue: Ident.card3)
private let card4 = ItemID(rawValue: Ident.card4)

/// A registry with every card's height registered — a board that has finished laying out, which is
/// the state a drag spends all but its first frames in.
@MainActor
private func makeRegistry(_ heights: [ItemID: CGFloat] = [card1: 40, card2: 60, card3: 80, card4: 50])
    -> LaneDropRegistry {
    let registry = LaneDropRegistry()
    for (id, height) in heights { registry.update(height: height, for: id) }
    return registry
}

/// One reload through the store's one inbound door — a foreign one, the mid-drag case the
/// re-grounding trio is written for.
@MainActor
private func reload(_ store: BoardStore) async {
    store.handleWatcherEvent(.treeChanged(.foreign))
    await store.awaitQuiescence()
}

// MARK: - The key

@MainActor
@Suite("The card drag's resting-layout cache")
struct RestingLayoutCacheTests {

    @Test("A second sample against the same snapshot rebuilds nothing")
    func sameKeyReuses() throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let cache = RestingLayoutCache()

        let first = cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])
        let second = cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])

        #expect(first?.cardIDs == [card1, card2, card3])
        #expect(first?.heights == [40, 60, 80])
        #expect(second == first)
        #expect(cache.builds == 1)
        #expect(cache.reuses == 1)
    }

    @Test("An unmeasured card tiles at the nominal height, exactly as the uncached path did")
    func unmeasuredCardsFallBack() throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry([card1: 40])
        let cache = RestingLayoutCache()

        let layout = cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])

        let nominal = LaneDropRegistry.nominalCardHeight
        #expect(layout?.heights == [40, nominal, nominal])
    }

    @Test("The dragged run is lifted out of the layout, and the hidden set is part of the key")
    func hiddenMembersAreKeyed() throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let cache = RestingLayoutCache()

        // A move: the run is out of the layout the zones are counted in.
        let moving = cache.layout(inLane: lane1, of: store, registry: registry, hidden: [card2])
        #expect(moving?.cardIDs == [card1, card3])
        #expect(moving?.heights == [40, 80])

        // ⌥ mid-drag — `hiddenMembers` answers the empty set for a copy, because the originals stay
        // (`DragSession.hiddenMembers`). A key that missed the flip would keep proposing in the
        // move's index space while the user is looking at the copy's.
        let copying = cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])
        #expect(copying?.cardIDs == [card1, card2, card3])
        #expect(cache.builds == 2)
        #expect(cache.reuses == 0)

        // And back: the flip is a key change in both directions, not a one-way invalidation.
        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [card2]) == moving)
        #expect(cache.builds == 3)
    }

    @Test("Each lane is its own entry, so crossing lanes and coming back rebuilds neither")
    func lanesAreSeparateEntries() throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let cache = RestingLayoutCache()

        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])?.cardIDs
            == [card1, card2, card3])
        #expect(cache.layout(inLane: lane2, of: store, registry: registry, hidden: [])?.cardIDs
            == [card4])
        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])?.cardIDs
            == [card1, card2, card3])

        #expect(cache.builds == 2)
        #expect(cache.reuses == 1)
    }

    @Test("A lane that is not in the snapshot answers nothing, and leaves no entry behind")
    func aVanishedLaneAnswersNothing() throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let cache = RestingLayoutCache()

        // The caller's cue to run rule 2's revalidation (`BoardDropContext.retargetCards`), and it
        // has to arrive on *every* sample rather than once — so nothing may be cached for it.
        #expect(cache.layout(inLane: ItemID(rawValue: Ident.lane3), of: store,
                             registry: registry, hidden: []) == nil)
        #expect(cache.layout(inLane: ItemID(rawValue: Ident.lane3), of: store,
                             registry: registry, hidden: []) == nil)
        #expect(cache.builds == 0)
        #expect(cache.reuses == 0)
    }
}

// MARK: - The snapshot, and which counter answers for it

/// **Rule 1 of the mid-drag re-grounding trio, under a cache** (DRAG-REORDER.md): "the resting zones
/// are recomputed against each new snapshot … nothing is cached across a reload because nothing
/// needs to be".
@MainActor
@Suite("The resting-layout cache ▸ re-grounding")
struct RestingLayoutRegroundingTests {

    @Test("A foreign card arriving mid-drag re-derives the layout against the new snapshot")
    func aReloadRegroundsTheLayout() async throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let cache = RestingLayoutCache()

        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])?.cardIDs
            == [card1, card2, card3])

        // An agent files a card between First and Second while the drag is in flight.
        try fixture.card(foreignName, in: Ident.lane1, order: "1536", title: "Foreign")
        await reload(store)
        #expect(store.snapshotGeneration == 1)

        // The next sample proposes against the board as it now is, not as it was at pickup — and
        // the arrival tiles at the nominal height until its face measures itself, exactly as the
        // uncached path left it.
        let reground = cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])
        #expect(reground?.cardIDs == [card1, foreignCard, card2, card3])
        #expect(reground?.heights == [40, LaneDropRegistry.nominalCardHeight, 60, 80])
        #expect(cache.builds == 2)
        #expect(cache.reuses == 0)
    }

    @Test("A value-equal reload rebuilds nothing — the applied counter is the key, not the walk")
    func aValueEqualReloadKeepsTheLayout() async throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let cache = RestingLayoutCache()

        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: []) != nil)

        // A walk that landed and found nothing to assign (`BoardStore.landedReloads` vs
        // `snapshotGeneration`, split 2026-07-31). The same cards in the same order cannot move a
        // zone, so keying on the walk counter would throw the layout away for a reload that
        // provably changed nothing — which, under a watcher, is most of them.
        await reload(store)
        #expect(store.landedReloads == 1)
        #expect(store.snapshotGeneration == 0)

        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])?.cardIDs
            == [card1, card2, card3])
        #expect(cache.builds == 1)
        #expect(cache.reuses == 1)
    }

    @Test("A lane deleted mid-drag stops answering, which is what withdraws the proposal")
    func aDeletedLaneStopsAnswering() async throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let cache = RestingLayoutCache()

        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: []) != nil)

        try fixture.moveFolder(Ident.lane1, to: ".trash/\(Ident.lane1)")
        await reload(store)

        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: []) == nil)
    }
}

// MARK: - The heights, and the two board windows

/// The inputs that move **without** a snapshot behind them: a face measuring itself for the first
/// time, and a second window drawing the same board at a different size.
@MainActor
@Suite("The resting-layout cache ▸ measured heights and board identity")
struct RestingLayoutMeasurementTests {

    @Test("A height that actually changes re-derives the layout; one that repeats does not")
    func heightsAreKeyed() throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let cache = RestingLayoutCache()

        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])?.heights
            == [40, 60, 80])

        // The re-register a layout pass makes with nothing to say — the common case, and the one
        // that must not cost a rebuild.
        registry.update(height: 60, for: card2)
        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])?.heights
            == [40, 60, 80])
        #expect(cache.builds == 1)
        #expect(cache.reuses == 1)

        // A real measurement. No snapshot moved for it, so nothing but the registry's own counter
        // can retire the layout that tiled the lane at the old figure.
        registry.update(height: 100, for: card2)
        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])?.heights
            == [40, 100, 80])
        #expect(cache.builds == 2)
    }

    @Test("A card face going away re-derives too")
    func removingAHeightIsAChange() throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let cache = RestingLayoutCache()

        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])?.heights
            == [40, 60, 80])

        registry.removeHeight(card3)
        #expect(cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])?.heights
            == [40, 60, LaneDropRegistry.nominalCardHeight])
        #expect(cache.builds == 2)

        // A second removal of the same card is not a change, and must not cost a rebuild.
        registry.removeHeight(card3)
        _ = cache.layout(inLane: lane1, of: store, registry: registry, hidden: [])
        #expect(cache.builds == 2)
        #expect(cache.reuses == 1)
    }

    @Test("Two board windows are two layouts, even for one board's lane")
    func registriesDoNotCollide() throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let cache = RestingLayoutCache()

        // One store, two `LaneDropRegistry`s — a board open in two windows, whose faces are measured
        // separately and can be mid-layout in one while settled in the other.
        let settled = makeRegistry()
        let opening = makeRegistry([:])

        #expect(cache.layout(inLane: lane1, of: store, registry: settled, hidden: [])?.heights
            == [40, 60, 80])
        let nominal = LaneDropRegistry.nominalCardHeight
        #expect(cache.layout(inLane: lane1, of: store, registry: opening, hidden: [])?.heights
            == [nominal, nominal, nominal])
        #expect(cache.builds == 2)
    }

    @Test("Two boards holding a lane under one id are two layouts")
    func boardsDoNotCollide() throws {
        let here = try makeFixture()
        defer { here.tearDown() }
        // A board duplicated on disk: same lane id, different content. A cross-board drag retargets
        // against the *hovered* board's store, so a layout that answered for the wrong root would
        // propose into a lane the user is not over.
        let there = try WriterFixture()
        defer { there.tearDown() }
        try there.board()
        try there.lane(Ident.lane1, order: "1024", title: "Todo")
        try there.card(Ident.card4, in: Ident.lane1, order: "1024", title: "Only")

        let cache = RestingLayoutCache()
        let registry = makeRegistry()
        let hereStore = try BoardStore(rootURL: here.root)
        let thereStore = try BoardStore(rootURL: there.root)

        // Deliberately the *same* registry for both: the key's registry identity would separate two
        // windows on its own, and this is the entry's `boardRoot` guard being pinned rather than it.
        #expect(cache.layout(inLane: lane1, of: hereStore, registry: registry, hidden: [])?.cardIDs
            == [card1, card2, card3])
        #expect(cache.layout(inLane: lane1, of: thereStore, registry: registry, hidden: [])?.cardIDs
            == [card4])
        #expect(cache.layout(inLane: lane1, of: hereStore, registry: registry, hidden: [])?.cardIDs
            == [card1, card2, card3])
        #expect(cache.builds == 3)
    }
}

// MARK: - The lifecycle

/// The cache is the **drag's**, not the board's: it is filled by one session's samples and must not
/// be readable by the next one's (`DragSession.restingLayouts`).
@MainActor
@Suite("The resting-layout cache ▸ session lifecycle")
struct RestingLayoutLifecycleTests {

    @Test("Beginning and ending a drag both drop every layout")
    func theCacheIsSessionScoped() throws {
        let fixture = try makeFixture()
        defer { fixture.tearDown() }
        let store = try BoardStore(rootURL: fixture.root)
        let registry = makeRegistry()
        let session = DragSession()

        session.beginCards([card1], folders: [], heights: [40], container: .board, source: store)
        _ = session.restingLayouts.layout(inLane: lane1, of: store, registry: registry, hidden: [card1])
        _ = session.restingLayouts.layout(inLane: lane1, of: store, registry: registry, hidden: [card1])
        #expect(session.restingLayouts.builds == 1)
        #expect(session.restingLayouts.reuses == 1)

        session.end()
        #expect(session.restingLayouts.builds == 0)
        #expect(session.restingLayouts.reuses == 0)

        // A second drag starts cold, whatever the first one left standing.
        session.beginCards([card2], folders: [], heights: [60], container: .board, source: store)
        _ = session.restingLayouts.layout(inLane: lane1, of: store, registry: registry, hidden: [card2])
        #expect(session.restingLayouts.builds == 1)
        #expect(session.restingLayouts.reuses == 0)
        session.end()
    }
}