import AppKit
import Foundation
import Testing
@testable import Kanban

/// The drag session's **value** halves — the pasteboard payload, the locality model, and the
/// committed overlay's hand-off condition (DRAG-REORDER.md; 04-interactions.md ▸ Drag and drop).
///
/// The session object itself, the drop delegates and the gestures are not unit-testable — they are
/// deliberately thin over these three, plus `DropSlotMath`'s arithmetic, which is why the split falls
/// where it does.

// MARK: - The payload

@Suite("DragPayload")
struct DragPayloadTests {

    private static func payload(kind: DragKind = .cards, side: Liveness = .live) -> DragPayload {
        DragPayload(
            boardRoot: URL(fileURLWithPath: "/Boards/Work.kanban", isDirectory: true),
            kind: kind,
            side: side,
            items: [
                DragPayload.Item(id: "aaa", folder: "/Boards/Work.kanban/lane/aaa", title: "First"),
                DragPayload.Item(id: "bbb", folder: "/Boards/Work.kanban/lane/bbb", title: nil)
            ]
        )
    }

    @Test("A payload round-trips through its JSON representation unchanged")
    func roundTrip() throws {
        for kind in [DragKind.cards, .lanes] {
            for side in [Liveness.live, .trashed] {
                let original = Self.payload(kind: kind, side: side)
                let data = try #require(original.encoded())
                #expect(DragPayload(data: data) == original)
            }
        }
    }

    @Test("Garbage decodes to nothing rather than to an empty drag")
    func garbageDecodesToNil() {
        #expect(DragPayload(data: Data("not json".utf8)) == nil)
        #expect(DragPayload(data: Data()) == nil)
    }

    @Test("The ids, folders and root are read back off the strings, in flatten order")
    func derivedValues() {
        let payload = Self.payload()
        #expect(payload.ids == [ItemID(rawValue: "aaa"), ItemID(rawValue: "bbb")])
        #expect(payload.folders.map(\.path) == [
            "/Boards/Work.kanban/lane/aaa",
            "/Boards/Work.kanban/lane/bbb"
        ])
        #expect(payload.rootURL.path == "/Boards/Work.kanban")
    }

    @Test("The plain-text representation is the dragged titles, one per line")
    func plainText() {
        // The stray-drop-into-a-text-editor fallback. An untitled item renders as the board renders
        // it — "Untitled" is a rendering, never a value (03-board-ui.md § Card face).
        #expect(Self.payload().plainText == "First\nUntitled")
    }

    @Test("The side survives the round trip, because it is what makes a trash drag a trash drag")
    func sideSurvives() throws {
        let data = try #require(Self.payload(side: .trashed).encoded())
        #expect(DragPayload(data: data)?.side.liveness == .trashed)
    }
}

// MARK: - Locality

@Suite("DragLocality")
struct DragLocalityTests {

    private static let here = URL(fileURLWithPath: "/Boards/Work.kanban", isDirectory: true)
    private static let there = URL(fileURLWithPath: "/Boards/Home.kanban", isDirectory: true)

    private static let none: NSEvent.ModifierFlags = []
    private static let option: NSEvent.ModifierFlags = [.option]
    private static let command: NSEvent.ModifierFlags = [.command]

    @Test("Roots compare by their standardized path, so the same board is the same board")
    func rootComparison() {
        #expect(DragLocality.isSameBoard(here, here))
        #expect(DragLocality.isSameBoard(here, URL(fileURLWithPath: "/Boards/./Work.kanban/")))
        #expect(DragLocality.isSameBoard(here, URL(fileURLWithPath: "/Boards/Other/../Work.kanban")))
        #expect(!DragLocality.isSameBoard(here, there))
    }

    /// The Finder volume model: within a board a drag rearranges, between boards it transfers.
    @Test("Locality picks the default — within is a move, across is a copy")
    func theDefault() {
        #expect(DragLocality.operation(kind: .cards, side: .live, isWithinBoard: true, modifiers: none) == .move)
        #expect(DragLocality.operation(kind: .cards, side: .live, isWithinBoard: false, modifiers: none) == .copy)
        #expect(DragLocality.operation(kind: .lanes, side: .live, isWithinBoard: false, modifiers: none) == .copy)
    }

    @Test("⌥ forces copy and ⌘ forces move, each a no-op where it is already the default")
    func modifiersOverride() {
        #expect(DragLocality.operation(kind: .cards, side: .live, isWithinBoard: true, modifiers: option) == .copy)
        #expect(DragLocality.operation(kind: .cards, side: .live, isWithinBoard: false, modifiers: command) == .move)
        // The no-ops.
        #expect(DragLocality.operation(kind: .cards, side: .live, isWithinBoard: true, modifiers: command) == .move)
        #expect(DragLocality.operation(kind: .cards, side: .live, isWithinBoard: false, modifiers: option) == .copy)
    }

    @Test("⌘ wins over ⌥ when both are held")
    func commandWinsOverOption() {
        // Finder's own reduction, and the same precedence `ClickModifier.current` applies to clicks.
        #expect(DragLocality.operation(
            kind: .cards, side: .live, isWithinBoard: false, modifiers: [.option, .command]) == .move)
    }

    /// The first carve-out: "Lane drags never copy *within their board*. ⌥ is simply ignored there:
    /// the drag stays a clean reorder and the badge never shows copy."
    @Test("A within-board lane drag ignores ⌥ entirely")
    func laneDragsNeverCopyWithinTheirBoard() {
        for modifiers in [none, option, command, [.option, .command] as NSEvent.ModifierFlags] {
            #expect(
                DragLocality.operation(kind: .lanes, side: .live, isWithinBoard: true, modifiers: modifiers) == .move,
                "a within-board lane drag is a reorder whatever is held"
            )
        }
        // Across boards the lane obeys the ordinary grammar again.
        #expect(DragLocality.operation(kind: .lanes, side: .live, isWithinBoard: false, modifiers: option) == .copy)
        #expect(DragLocality.operation(kind: .lanes, side: .live, isWithinBoard: false, modifiers: command) == .move)
    }

    /// The second: a trash row's drag is copy-out grammar (04-interactions.md ▸ The trash). Within its
    /// own board the default is the restore — a move, no badge; across boards the default is the live
    /// copy that leaves the tombstone standing. ⌘ forces the true restore-move either way, and ⌥ the
    /// live copy either way.
    @Test("A trash row drags as a restore at home and as a copy-out abroad")
    func trashDragDefaults() {
        #expect(DragLocality.operation(kind: .cards, side: .trashed, isWithinBoard: true, modifiers: none) == .move)
        #expect(DragLocality.operation(kind: .cards, side: .trashed, isWithinBoard: false, modifiers: none) == .copy)
        #expect(DragLocality.operation(
            kind: .cards, side: .trashed, isWithinBoard: false, modifiers: command) == .move)
        #expect(DragLocality.operation(kind: .cards, side: .trashed, isWithinBoard: true, modifiers: option) == .copy)
    }
}

// MARK: - The committed-overlay hold

@Suite("CommittedHold")
struct CommittedHoldTests {

    private static let here = URL(fileURLWithPath: "/Boards/Work.kanban", isDirectory: true)
    private static let there = URL(fileURLWithPath: "/Boards/Home.kanban", isDirectory: true)

    private static let hold = CommittedHold(boardRoot: here, generation: 7)

    @Test("The hold stands until the destination board applies a *newer* snapshot")
    func retiredByTheNextSnapshot() {
        // The generation at the commit is the one already on screen — it is the pre-drop arrangement,
        // and retiring on it would drop the overlay before the write has round-tripped.
        #expect(!Self.hold.isRetired(byRoot: Self.here, generation: 7))
        #expect(Self.hold.isRetired(byRoot: Self.here, generation: 8))
        // *Any* snapshot hands off, not just the app-mediated echo: a foreign one that lands first
        // re-grounds everything anyway.
        #expect(Self.hold.isRetired(byRoot: Self.here, generation: 99))
    }

    @Test("A reload on another board says nothing about this one")
    func otherBoardsDoNotRetireIt() {
        #expect(!Self.hold.isRetired(byRoot: Self.there, generation: 99))
    }

    @Test("The board is matched by identity, not by string")
    func rootMatchingUsesTheLocalityComparison() {
        #expect(Self.hold.isRetired(byRoot: URL(fileURLWithPath: "/Boards/./Work.kanban/"), generation: 8))
    }

    @Test("A stale generation never retires it")
    func staleGenerations() {
        #expect(!Self.hold.isRetired(byRoot: Self.here, generation: 0))
        #expect(!Self.hold.isRetired(byRoot: Self.here, generation: 6))
    }
}