import Foundation
import Testing
@testable import Kanban

// MARK: - Fixture builder

/// A tiny in-memory-driven builder for synthetic board trees under a temp directory. Smoke
/// coverage only (per 02-architecture.md § Testing) — a comprehensive golden-fixture suite
/// over real trees under `Fixtures/` is a separate, later card.
private struct BoardFixture {
    let root: URL

    init() throws {
        root = FileManager.default.temporaryDirectory
            .appendingPathComponent("BoardLoaderTests-\(UUID().uuidString)", isDirectory: true)
        try FileManager.default.createDirectory(at: root, withIntermediateDirectories: true)
    }

    func tearDown() {
        try? FileManager.default.removeItem(at: root)
    }

    /// Writes `index.md` at `relativePath` (created if needed), with `body` after the
    /// frontmatter delimiters.
    @discardableResult
    func index(_ relativePath: String, _ frontmatter: String, body: String = "") throws -> URL {
        let folder = relativePath.isEmpty ? root : root.appendingPathComponent(relativePath, isDirectory: true)
        try FileManager.default.createDirectory(at: folder, withIntermediateDirectories: true)
        let text = "---\n\(frontmatter)---\n\(body)"
        try text.write(to: folder.appendingPathComponent("index.md"), atomically: true, encoding: .utf8)
        return folder
    }

    /// Creates a folder with no `index.md` — the "interrupted two-step create" shape.
    @discardableResult
    func emptyFolder(_ relativePath: String) throws -> URL {
        let folder = root.appendingPathComponent(relativePath, isDirectory: true)
        try FileManager.default.createDirectory(at: folder, withIntermediateDirectories: true)
        return folder
    }

    /// A stray file, not a folder — never a level candidate regardless of its name.
    func strayFile(_ relativePath: String, contents: String = "stray") throws {
        let url = root.appendingPathComponent(relativePath)
        try FileManager.default.createDirectory(at: url.deletingLastPathComponent(), withIntermediateDirectories: true)
        try contents.write(to: url, atomically: true, encoding: .utf8)
    }
}

/// A fresh folder name in the app's own emission spelling — lowercase v4. The loader's gate is
/// shape-only (hex, `8-4-4-4-12`, any case, any version — 01-storage-format.md § Fractal layout
/// ▸ Rules, "Name shape gates level detection"), so this is *a* valid identity rather than the
/// only kind; the case tests below cover the rest. Used wherever a test just needs some lane/card
/// identity and doesn't care about the exact value; tests that need a specific lexicographic
/// ordering use literal UUID-shaped strings instead.
private func uuidFolderName() -> String {
    UUID().uuidString.lowercased()
}

private func expectFailure(
    _ expectedReason: BoardLoadError.Reason,
    path: String,
    _ operation: () throws -> Void
) {
    do {
        try operation()
        Issue.record("expected BoardLoadError(\(path), \(expectedReason)) but load succeeded")
    } catch let error as BoardLoadError {
        #expect(error.path == path)
        #expect(error.reason == expectedReason)
    } catch {
        Issue.record("expected a BoardLoadError, got \(error)")
    }
}

// MARK: - Well-formed board

struct BoardLoaderWellFormedTests {
    @Test func loadsCompleteStructureWithOrderingAndTombstoneFlags() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let laneA = uuidFolderName()
        let laneB = uuidFolderName()
        let cardFirst = uuidFolderName()
        let cardSecond = uuidFolderName()
        let cardDeleted = uuidFolderName()

        try fixture.index("", "schema: 1\ntitle: Demo Board\ntemplate: {order: 3}\n")
        try fixture.index(laneB, "schema: 1\norder: 2048\ntitle: B Lane\n")
        try fixture.index(laneA, "schema: 1\norder: 1024\ntitle: A Lane\n")

        try fixture.index("\(laneA)/\(cardSecond)", "schema: 1\norder: 2048\ntitle: Second\n")
        try fixture.index("\(laneA)/\(cardFirst)", "schema: 1\norder: 1024\ntitle: First\n")
        try fixture.index(
            "\(laneA)/\(cardDeleted)",
            "schema: 1\norder: 512\ntitle: Gone\ndeleted: 2026-01-01T00:00:00Z\n"
        )

        let result = try BoardLoader.load(boardRoot: fixture.root)
        let model = result.model

        #expect(model.title.value == "Demo Board")
        #expect(model.schema == 1)
        if case let .mapping(pairs) = model.template {
            #expect(pairs.count == 1)
        } else {
            Issue.record("expected template to be a mapping, got \(String(describing: model.template))")
        }

        #expect(model.lanes.map(\.id.rawValue) == [laneA, laneB])

        let lane = try #require(model.lanes.first { $0.id.rawValue == laneA })
        #expect(lane.cards.map(\.id.rawValue) == [cardDeleted, cardFirst, cardSecond])
        #expect(lane.cards.map(\.isDeleted) == [true, false, false])
        #expect(result.warnings.isEmpty)
    }

    /// Tombstone semantics key on the `deleted` key's *presence*, not its validity
    /// (01-storage-format.md § Frontmatter, § Deletion): a `deleted` value with no sensible
    /// date reading still tombstones — the user's intent to delete outranks the broken date.
    @Test func malformedDeletedValueStillTombstonesLaneAndCard() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()
        let card = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: 1024\ndeleted: yesterday\n")
        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\ndeleted: yesterday\n")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        let loadedLane = try #require(result.model.lanes.first { $0.id.rawValue == lane })
        #expect(loadedLane.deleted == .malformed(raw: "yesterday"))
        #expect(loadedLane.isDeleted)

        let loadedCard = try #require(loadedLane.cards.first { $0.id.rawValue == card })
        #expect(loadedCard.deleted == .malformed(raw: "yesterday"))
        #expect(loadedCard.isDeleted)
    }

    @Test func tiesAreBrokenByFolderNameNotTitle() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        // Both UUID-shaped so both are lane candidates; chosen so their lexicographic order
        // ('0' < 'f') is known ahead of time.
        let laneFirst = "00000000-0000-4000-8000-000000000000"
        let laneSecond = "ffffffff-ffff-4fff-8fff-ffffffffffff"

        try fixture.index("", "schema: 1\n")
        // Same order; titles are reversed relative to folder-name order, to catch a loader
        // that accidentally wires title into the tie-break instead of the folder name.
        try fixture.index(laneSecond, "schema: 1\norder: 1024\ntitle: Should Be Second\n")
        try fixture.index(laneFirst, "schema: 1\norder: 1024\ntitle: Should Be First\n")

        let model = try BoardLoader.load(boardRoot: fixture.root).model
        #expect(model.lanes.map(\.id.rawValue) == [laneFirst, laneSecond])
    }
}

// MARK: - Skip rules (UUID-shaped candidates only)

struct BoardLoaderSkipTests {
    @Test func indexlessUUIDFolderBelowRootIsSkippedWithMissingIndexWarning() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()
        let orphanLane = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: 1024\n")
        try fixture.emptyFolder(orphanLane)

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.map(\.id.rawValue) == [lane])
        #expect(result.warnings.contains(.missingIndex(path: orphanLane)))
    }

    @Test func indexlessUUIDCardFolderIsSkippedWithWarningAndRestOfBoardStillLoads() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()
        let card = uuidFolderName()
        let orphanCard = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: 1024\n")
        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\n")
        try fixture.emptyFolder("\(lane)/\(orphanCard)")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        let loadedLane = try #require(result.model.lanes.first)
        #expect(loadedLane.cards.map(\.id.rawValue) == [card])
        #expect(result.warnings.contains(.missingIndex(path: "\(lane)/\(orphanCard)")))
    }
}

// MARK: - Strays ignored (non-directories, hidden entries, symlinks)

struct BoardLoaderStrayTests {
    @Test func strayFilesAndHiddenEntriesAreIgnoredWithoutWarning() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()
        let card = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: 1024\n")
        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\n")

        try fixture.strayFile("notes.txt")
        try fixture.strayFile(".DS_Store")
        try fixture.strayFile("\(lane)/notes.txt")
        _ = try fixture.emptyFolder(".git")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.map(\.id.rawValue) == [lane])
        #expect(result.model.lanes[0].cards.map(\.id.rawValue) == [card])
        #expect(result.warnings.isEmpty)
    }

    @Test func directorySymlinkIsTreatedAsStrayNotFollowed() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let realLane = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        let realLaneURL = try fixture.index(realLane, "schema: 1\norder: 1024\n")
        try FileManager.default.createSymbolicLink(
            at: fixture.root.appendingPathComponent("linked-lane"),
            withDestinationURL: realLaneURL
        )

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.map(\.id.rawValue) == [realLane])
        #expect(result.warnings.isEmpty)
    }

    /// The identity predicate is shape-only — "identity-shaped name or not" (01-storage-format.md
    /// § Fractal layout ▸ Rules, "Symlinks are never traversed", settled). This pins the case the
    /// previous test's non-UUID name doesn't: a symlink whose *name itself* would pass
    /// `isUUIDShaped` and which points at a real directory must still be excluded before that
    /// name shape is ever consulted — `directoryCandidates` filters on `isSymbolicLink` ahead of
    /// `isDirectory`, so a link is never mistaken for the directory it points to, UUID-shaped name
    /// or not.
    @Test func uuidShapedSymlinkToADirectoryIsTreatedAsStrayNotFollowed() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let realLane = uuidFolderName()
        let linkedName = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        let realLaneURL = try fixture.index(realLane, "schema: 1\norder: 1024\n")
        try FileManager.default.createSymbolicLink(
            at: fixture.root.appendingPathComponent(linkedName),
            withDestinationURL: realLaneURL
        )

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.map(\.id.rawValue) == [realLane])
        #expect(!result.model.lanes.map(\.id.rawValue).contains(linkedName))
        #expect(result.warnings.isEmpty)
    }
}

// MARK: - Non-UUID-shaped folders are strays (01-storage-format.md § Fractal layout ▸ Rules,
// "Name shape gates level detection")

struct BoardLoaderNonUUIDStrayTests {
    /// A non-UUID-shaped folder is a stray even when its `index.md` is perfectly valid
    /// lane-shaped content — the name shape gates candidacy before the file is ever read.
    @Test func nonUUIDFolderWithValidLaneShapedIndexIsIgnoredWithWarningAndBoardLoads() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let realLane = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(realLane, "schema: 1\norder: 1024\n")
        try fixture.index("todo", "schema: 1\norder: 2048\ntitle: Hand-authored lane\n")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.map(\.id.rawValue) == [realLane])
        #expect(result.warnings.contains(.nonUUIDFolderIgnored(path: "todo")))
    }

    /// The motivating case: before this rule, a non-UUID folder with a broken `index.md`
    /// (missing required `order`) would fail-fast the whole load. Now the name shape gates it
    /// out as a stray before the loader ever parses the file, so the rest of the board still
    /// loads.
    @Test func nonUUIDFolderWithBrokenIndexIsIgnoredWithWarningAndBoardStillLoads() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let realLane = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(realLane, "schema: 1\norder: 1024\n")
        // Missing 'order' — would be a fail-fast .missingOrder if this were UUID-shaped.
        try fixture.index("todo", "schema: 1\ntitle: Broken hand-authored lane\n")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.map(\.id.rawValue) == [realLane])
        #expect(result.warnings.contains(.nonUUIDFolderIgnored(path: "todo")))
    }

    /// Same motivating case, one level down: a non-UUID card-depth folder with a broken
    /// `index.md` is a stray, not a fail-fast, and doesn't stop its lane's other cards loading.
    @Test func nonUUIDCardFolderWithBrokenIndexIsIgnoredWithWarningAndLaneStillLoads() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()
        let realCard = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: 1024\n")
        try fixture.index("\(lane)/\(realCard)", "schema: 1\norder: 1024\n")
        try fixture.index("\(lane)/scratch", "schema: 1\n") // missing 'order' too

        let result = try BoardLoader.load(boardRoot: fixture.root)
        let loadedLane = try #require(result.model.lanes.first)
        #expect(loadedLane.cards.map(\.id.rawValue) == [realCard])
        #expect(result.warnings.contains(.nonUUIDFolderIgnored(path: "\(lane)/scratch")))
    }

    /// The identity predicate is **shape-only, any case** (01-storage-format.md § Fractal layout
    /// ▸ Rules, settled): `uuidgen` and `UUID().uuidString` both print uppercase, so an
    /// uppercase folder is an ordinary lane — never a silently skipped stray. Its `rawValue`
    /// keeps the exact spelling: the app accepts liberally and never renames to canonicalize.
    @Test func uppercaseUUIDFolderIsALaneWithItsSpellingPreserved() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lowercaseLane = uuidFolderName()
        let uppercaseLane = UUID().uuidString // Foundation renders this uppercase.

        try fixture.index("", "schema: 1\n")
        try fixture.index(lowercaseLane, "schema: 1\norder: 1024\n")
        try fixture.index(uppercaseLane, "schema: 1\norder: 2048\n")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.map(\.id.rawValue) == [lowercaseLane, uppercaseLane])
        #expect(result.warnings.isEmpty)
    }

    /// One level down, and mixed case rather than uniform: an agent's `uuidgen`-named card
    /// folder loads as a card, spelling intact.
    @Test func mixedCaseUUIDCardFolderLoadsAsACardWithItsSpellingPreserved() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()
        let mixedCaseCard = "AbCdEf01-2345-6789-aBcD-EF0123456789"

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: 1024\n")
        try fixture.index("\(lane)/\(mixedCaseCard)", "schema: 1\norder: 1024\ntitle: From an agent\n")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        let loadedLane = try #require(result.model.lanes.first)
        #expect(loadedLane.cards.map(\.id.rawValue) == [mixedCaseCard])
        #expect(loadedLane.cards.first?.title.value == "From an agent")
        #expect(result.warnings.isEmpty)
    }

    /// **Any version**, not just v4: the version nibble protects no invariant here — a v7 (or a
    /// nibble no RFC ever assigned) is exactly as unique as a v4, so it is an identity, not a
    /// stray. Only the shape is checked.
    @Test func oddVersionAndVariantNibblesAreStillIdentities() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let v7Lane = "01912d5e-7c00-7000-8000-abcdefabcdef"    // version nibble 7
        let oddLane = "01912d5e-7c00-c000-f000-abcdefabcdef"   // version c, variant f — no RFC's

        try fixture.index("", "schema: 1\n")
        try fixture.index(v7Lane, "schema: 1\norder: 1024\n")
        try fixture.index(oddLane, "schema: 1\norder: 2048\n")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.map(\.id.rawValue) == [v7Lane, oddLane])
        #expect(result.warnings.isEmpty)
    }

    /// The shape itself is still strict: near-misses stay strays. Hex only, exact group lengths,
    /// hyphens exactly where they belong.
    @Test func nearMissUUIDShapesAreStillStrays() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let realLane = uuidFolderName()
        let strays = [
            "GGGGGGGG-0000-4000-8000-000000000000",   // not hex
            "00000000-0000-4000-8000-00000000000",    // one digit short
            "000000000-000-4000-8000-000000000000",   // hyphens misplaced
            "00000000-0000-4000-8000-000000000000-",  // trailing hyphen
        ]

        try fixture.index("", "schema: 1\n")
        try fixture.index(realLane, "schema: 1\norder: 1024\n")
        for (offset, stray) in strays.enumerated() {
            try fixture.index(stray, "schema: 1\norder: \(2048 + offset)\n")
        }

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.map(\.id.rawValue) == [realLane])
        for stray in strays {
            #expect(result.warnings.contains(.nonUUIDFolderIgnored(path: stray)))
        }
    }

    /// Reserved card children are covered "by construction": `attachments/` and `comments/` are
    /// non-UUID-shaped, and the *level walk* stops at depth 2 — so neither can ever be mistaken
    /// for an item, and neither may surface a warning. (`attachments/` is read for its file
    /// names, which is a listing, not a descent — see `CardAttachmentListingTests` below.)
    @Test func reservedAttachmentsAndCommentsUnderCardProduceNoWarning() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()
        let card = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index("\(lane)", "schema: 1\norder: 1024\n")
        try fixture.index("\(lane)/\(card)", "schema: 1\norder: 1024\n")
        try fixture.strayFile("\(lane)/\(card)/attachments/sketch.png")
        try fixture.strayFile("\(lane)/\(card)/comments/whatever.md")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.first?.cards.map(\.id.rawValue) == [card])
        #expect(result.warnings.isEmpty)
    }
}

// MARK: - Card attachments (01-storage-format.md § Attachments)

/// `Card.attachments` — the loader's one read *inside* a card folder. The golden-fixture suite
/// pins the everyday shapes on real committed trees (`FixtureBoardTests`); these cover what a git
/// fixture can't carry (a symlink) and what only a synthetic tree can arrange (a card folder whose
/// `attachments` is a *file*, an empty folder, Finder's numeric ordering).
struct CardAttachmentListingTests {

    /// Builds a one-card board and returns that card, so each test below is one arrangement plus
    /// one assertion.
    private func card(in fixture: BoardFixture) throws -> Card {
        let result = try BoardLoader.load(boardRoot: fixture.root)
        return try #require(result.model.lanes.first?.cards.first)
    }

    private func boardWithOneCard(_ fixture: BoardFixture) throws -> String {
        let lane = "10000000-0000-4000-8000-000000000001"
        let cardID = "20000000-0000-4000-8000-000000000002"
        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: 1024\n")
        try fixture.index("\(lane)/\(cardID)", "schema: 1\norder: 1024\n")
        return "\(lane)/\(cardID)"
    }

    /// **Symlinks are not surfaced** — the same never-resolve stance the level walk takes
    /// (`directoryCandidates`), so a link into another volume or a cycle can't turn a listing
    /// into a traversal. The link itself stays on disk untouched; it just isn't an attachment.
    @Test func symlinksInAttachmentsAreNotSurfaced() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }
        let cardPath = try boardWithOneCard(fixture)

        try fixture.strayFile("\(cardPath)/attachments/real.png")
        try fixture.strayFile("outside.png")
        let attachments = fixture.root.appendingPathComponent("\(cardPath)/attachments", isDirectory: true)
        try FileManager.default.createSymbolicLink(
            at: attachments.appendingPathComponent("link-to-file.png"),
            withDestinationURL: fixture.root.appendingPathComponent("outside.png")
        )
        try FileManager.default.createSymbolicLink(
            at: attachments.appendingPathComponent("link-to-folder"),
            withDestinationURL: fixture.root
        )

        #expect(try card(in: fixture).attachments == ["real.png"])
    }

    /// The four shapes in one folder — the fixture board's assertion restated synthetically, so
    /// the rule is pinned even if the bundled fixture tree ever loses a file to a copy phase.
    @Test func onlyTopLevelNonHiddenRegularFilesAreListed() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }
        let cardPath = try boardWithOneCard(fixture)

        try fixture.strayFile("\(cardPath)/attachments/sketch.png")
        try fixture.strayFile("\(cardPath)/attachments/notes.txt")
        try fixture.strayFile("\(cardPath)/attachments/.DS_Store")
        try fixture.strayFile("\(cardPath)/attachments/sub/nested.txt")

        #expect(try card(in: fixture).attachments == ["notes.txt", "sketch.png"])
    }

    /// **Finder order** (`localizedStandardCompare`), not plain lexicographic — digits inside a
    /// name *count* rather than collate, so the run `importAttachments` itself produces on a
    /// collision (`shot.png` → `shot 2.png` → `shot 10.png`) sorts 2-before-10, matching the card
    /// window sidebar's listing, which answers through this same enumeration. (`shot.png` trailing
    /// its own numbered copies is Finder's own ordering of a space against a dot, not a quirk of
    /// ours.)
    @Test func namesSortInFinderOrderSoNumbersCountRatherThanCollate() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }
        let cardPath = try boardWithOneCard(fixture)

        for name in ["shot 10.png", "shot 2.png", "shot.png", "page-10.txt", "page-2.txt"] {
            try fixture.strayFile("\(cardPath)/attachments/\(name)")
        }

        #expect(try card(in: fixture).attachments == [
            "page-2.txt", "page-10.txt", "shot 2.png", "shot 10.png", "shot.png",
        ])
    }

    @Test func anEmptyAttachmentsFolderListsNothing() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }
        let cardPath = try boardWithOneCard(fixture)
        try fixture.emptyFolder("\(cardPath)/attachments")

        #expect(try card(in: fixture).attachments.isEmpty)
    }

    /// A listing that *cannot* be made degrades to `[]` — here because a hand-editor left a
    /// `attachments` **file** where the folder would be. Fail-fast is reserved for structure
    /// (01-storage-format.md § Malformed input); a cosmetic field must never be why a board
    /// refuses to open, and the file itself is preserved verbatim like any other stray.
    @Test func anAttachmentsThatIsNotADirectoryDegradesToAnEmptyListing() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }
        let cardPath = try boardWithOneCard(fixture)
        try fixture.strayFile("\(cardPath)/attachments", contents: "not a folder")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.first?.cards.first?.attachments.isEmpty == true)
        #expect(result.warnings.isEmpty)
    }

    /// `BoardWriter.listAttachments` — the card window sidebar's authoritative listing — and
    /// `Card.attachments` are **one enumeration**, so a sidebar and a face looking at the same
    /// card can never disagree about its files or their order.
    @Test func theSnapshotsListingAndTheWritersAreTheSameAnswer() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }
        let cardPath = try boardWithOneCard(fixture)

        for name in ["shot 10.png", "shot 2.png", "shot.png", ".hidden"] {
            try fixture.strayFile("\(cardPath)/attachments/\(name)")
        }
        try fixture.strayFile("\(cardPath)/attachments/sub/nested.txt")

        let cardFolder = fixture.root.appendingPathComponent(cardPath, isDirectory: true)
        #expect(try card(in: fixture).attachments == BoardWriter.listAttachments(ofCard: cardFolder))
    }
}

// MARK: - ItemID value semantics (01-storage-format.md § Fractal layout ▸ Rules, "Identity
// comparison is UUID-value equality, never string equality")

/// `ItemID` stores the folder's exact spelling — it builds URLs — but *compares* as a UUID
/// value: two case-spellings of one UUID are one identity everywhere.
struct ItemIDValueSemanticsTests {
    private static let lower = "abcdef01-2345-6789-abcd-ef0123456789"
    private static let upper = "ABCDEF01-2345-6789-ABCD-EF0123456789"
    private static let mixed = "AbCdEf01-2345-6789-aBcD-eF0123456789"

    @Test func caseSpellingsOfOneUUIDAreEqualAndHashAlike() {
        let lower = ItemID(rawValue: Self.lower)
        let upper = ItemID(rawValue: Self.upper)
        let mixed = ItemID(rawValue: Self.mixed)

        #expect(lower == upper)
        #expect(lower == mixed)
        #expect(upper == mixed)
        #expect(lower.hashValue == upper.hashValue)
        #expect(upper.hashValue == mixed.hashValue)
    }

    /// Equality is by value, but the spelling is never rewritten — the app accepts liberally and
    /// emits conservatively, and `rawValue` is what builds the folder's URL.
    @Test func rawValueKeepsTheExactSpelling() {
        #expect(ItemID(rawValue: Self.upper).rawValue == Self.upper)
        #expect(ItemID(rawValue: Self.mixed).description == Self.mixed)
    }

    @Test func distinctUUIDsAreUnequalHoweverTheyAreSpelled() {
        let one = ItemID(rawValue: "abcdef01-2345-6789-abcd-ef0123456789")
        let other = ItemID(rawValue: "ABCDEF01-2345-6789-ABCD-EF012345678A")
        #expect(one != other)
    }

    /// The consequence every `Set`/`Dictionary` keyed by `ItemID` inherits — selection
    /// membership included (`ItemReferenceSet`).
    @Test func aSetCollapsesTheTwoSpellingsToOneMember() {
        let set: Set<ItemID> = [ItemID(rawValue: Self.lower), ItemID(rawValue: Self.upper)]
        #expect(set.count == 1)
        #expect(set.contains(ItemID(rawValue: Self.mixed)))

        var byID: [ItemID: String] = [:]
        byID[ItemID(rawValue: Self.upper)] = "written uppercase"
        #expect(byID[ItemID(rawValue: Self.lower)] == "written uppercase")
    }
}

// MARK: - Board-level deleted

struct BoardLoaderBoardLevelDeletedTests {
    @Test func boardLevelDeletedIsIgnoredAndWarned() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        try fixture.index("", "schema: 1\ndeleted: 2026-01-01T00:00:00Z\n")

        let result = try BoardLoader.load(boardRoot: fixture.root)
        #expect(result.model.lanes.isEmpty)
        #expect(result.warnings.contains(.boardLevelDeletedIgnored))
    }
}

// MARK: - Fail-fast

struct BoardLoaderFailFastTests {
    @Test func rootMissingIndexThrows() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        expectFailure(.boardRootMissingIndex, path: "index.md") {
            _ = try BoardLoader.load(boardRoot: fixture.root)
        }
    }

    @Test func rootThatIsAFileThrowsNotADirectory() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let fileRoot = fixture.root.appendingPathComponent("not-a-folder")
        try "hello".write(to: fileRoot, atomically: true, encoding: .utf8)

        expectFailure(.notADirectory, path: ".") {
            _ = try BoardLoader.load(boardRoot: fileRoot)
        }
    }

    @Test func unreadableRootThrows() throws {
        let missing = FileManager.default.temporaryDirectory
            .appendingPathComponent("BoardLoaderTests-does-not-exist-\(UUID().uuidString)")

        do {
            _ = try BoardLoader.load(boardRoot: missing)
            Issue.record("expected a BoardLoadError but load succeeded")
        } catch {
            #expect(error.path == ".")
            if case .unreadableRoot = error.reason {
                // expected
            } else {
                Issue.record("expected .unreadableRoot, got \(error.reason)")
            }
        }
    }

    @Test func unparseableYAMLThrows() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        // No closing delimiter.
        try "---\nschema: 1\n".write(
            to: fixture.root.appendingPathComponent("index.md"),
            atomically: true,
            encoding: .utf8
        )

        do {
            _ = try BoardLoader.load(boardRoot: fixture.root)
            Issue.record("expected a BoardLoadError but load succeeded")
        } catch {
            #expect(error.path == "index.md")
            if case .unparseableYAML = error.reason {
                // expected
            } else {
                Issue.record("expected .unparseableYAML, got \(error.reason)")
            }
        }
    }

    @Test func missingSchemaThrows() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        try fixture.index("", "title: No Schema\n")

        expectFailure(.missingSchema, path: "index.md") {
            _ = try BoardLoader.load(boardRoot: fixture.root)
        }
    }

    @Test func malformedSchemaThrows() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        try fixture.index("", "schema: not-a-number\n")

        expectFailure(.malformedSchema(raw: "not-a-number"), path: "index.md") {
            _ = try BoardLoader.load(boardRoot: fixture.root)
        }
    }

    @Test func schemaNewerThanAppThrows() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        try fixture.index("", "schema: 2\n")

        expectFailure(.schemaNewerThanApp(found: 2), path: "index.md") {
            _ = try BoardLoader.load(boardRoot: fixture.root)
        }
    }

    /// A UUID-shaped folder still fails fast on structurally-bad content — the name shape only
    /// gates *candidacy*, never the validity of a folder that qualifies.
    @Test func missingOrderOnUUIDLaneThrows() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\n")

        expectFailure(.missingOrder, path: "\(lane)/index.md") {
            _ = try BoardLoader.load(boardRoot: fixture.root)
        }
    }

    @Test func malformedOrderOnUUIDLaneThrows() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: not-a-number\n")

        expectFailure(.malformedOrder(raw: "not-a-number"), path: "\(lane)/index.md") {
            _ = try BoardLoader.load(boardRoot: fixture.root)
        }
    }

    /// A non-finite `order` (`.nan`, `.inf`) is the same loud rejection as a non-numeric one
    /// (01-storage-format.md § Frontmatter, settled) — NaN has no place in the total order the
    /// tie-break and midpoint math assume.
    @Test func nonFiniteOrderOnUUIDLaneThrows() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: .nan\n")

        expectFailure(.malformedOrder(raw: ".nan"), path: "\(lane)/index.md") {
            _ = try BoardLoader.load(boardRoot: fixture.root)
        }
    }

    @Test func missingOrderOnUUIDCardThrows() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        let lane = uuidFolderName()
        let card = uuidFolderName()

        try fixture.index("", "schema: 1\n")
        try fixture.index(lane, "schema: 1\norder: 1024\n")
        try fixture.index("\(lane)/\(card)", "schema: 1\n")

        expectFailure(.missingOrder, path: "\(lane)/\(card)/index.md") {
            _ = try BoardLoader.load(boardRoot: fixture.root)
        }
    }
}

// MARK: - Encoding strictness

/// The loader decodes byte-faithfully (no NSString BOM-stripping) so the settled encoding
/// contract (01-storage-format.md § Fractal layout ▸ Rules) actually holds at load time: a
/// BOM'd file fails the frontmatter delimiter, a non-UTF-8 file is named as such — the same
/// strict decode `BoardWriter` uses, so a file can never load here and then refuse every write.
struct BoardLoaderEncodingTests {
    @Test func bomPrefixedBoardIndexIsRejected() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        var bytes = Data([0xEF, 0xBB, 0xBF])
        bytes.append(Data("---\nschema: 1\n---\nbody\n".utf8))
        try bytes.write(to: fixture.root.appendingPathComponent("index.md"))

        #expect { try BoardLoader.load(boardRoot: fixture.root) } throws: { error in
            guard let loadError = error as? BoardLoadError,
                  case .unparseableYAML = loadError.reason else { return false }
            return loadError.path == "index.md"
        }
    }

    @Test func nonUTF8BoardIndexIsRejected() throws {
        let fixture = try BoardFixture()
        defer { fixture.tearDown() }

        // "café" in ISO-8859-1 — 0xE9 is not valid UTF-8.
        var bytes = Data("---\nschema: 1\ntitle: caf".utf8)
        bytes.append(0xE9)
        bytes.append(Data("\n---\n".utf8))
        try bytes.write(to: fixture.root.appendingPathComponent("index.md"))

        #expect { try BoardLoader.load(boardRoot: fixture.root) } throws: { error in
            guard let loadError = error as? BoardLoadError,
                  case let .unparseableYAML(message, _) = loadError.reason else { return false }
            return message == "file is not UTF-8"
        }
    }
}