import { describe, it, expect, beforeEach, spyOn } from "bun:test";
import { chessPlugin } from "./chess.plugin";
import type { ChessState, ChessAction, ChessPlayerView, ChessSpectatorView } from "./chess.types";
import type { GameResult } from "../types";

// ── Helpers ──

function createState(overrides?: Partial<Parameters<typeof chessPlugin.createInitialState>[1]>): ChessState {
    // Use a fixed seed by mocking Math.random so white/black assignment is deterministic
    const spy = spyOn(Math, "random").mockReturnValue(0.1); // < 0.5 → players[0] = white
    const state = chessPlugin.createInitialState(["alice", "bob"], overrides);
    spy.mockRestore();
    return state;
}

function act(state: ChessState, action: ChessAction, playerId: string): ChessState {
    const result = chessPlugin.handleAction(state, action, playerId);
    if (!result.ok) throw new Error(`Action failed: ${result.error}`);
    return result.state;
}

function tryAct(state: ChessState, action: ChessAction, playerId: string): GameResult<ChessState> {
    return chessPlugin.handleAction(state, action, playerId);
}

/** Play a Scholar's Mate: 1. e4 e5 2. Qh5 Nc6 3. Bc4 Nf6 4. Qxf7# */
function playScholarsMate(state: ChessState): ChessState {
    const white = state.players.white;
    const black = state.players.black;
    state = act(state, { type: "move", from: "e2", to: "e4" }, white);
    state = act(state, { type: "move", from: "e7", to: "e5" }, black);
    state = act(state, { type: "move", from: "d1", to: "h5" }, white);
    state = act(state, { type: "move", from: "b8", to: "c6" }, black);
    state = act(state, { type: "move", from: "f1", to: "c4" }, white);
    state = act(state, { type: "move", from: "g8", to: "f6" }, black);
    state = act(state, { type: "move", from: "h5", to: "f7" }, white); // Checkmate
    return state;
}

// ── Tests ──

describe("chessPlugin", () => {
    describe("createInitialState", () => {
        it("should create a valid starting position", () => {
            const state = createState();
            expect(state.fen).toBe("rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1");
            expect(state.result).toBeNull();
            expect(state.drawOffer).toBeNull();
            expect(state.moveHistory).toEqual([]);
        });

        it("should assign players to white and black", () => {
            const state = createState();
            expect(state.players.white).toBe("alice");
            expect(state.players.black).toBe("bob");
        });

        it("should randomize color assignment", () => {
            const spy = spyOn(Math, "random").mockReturnValue(0.9); // > 0.5 → swap
            const state = chessPlugin.createInitialState(["alice", "bob"]);
            spy.mockRestore();
            expect(state.players.white).toBe("bob");
            expect(state.players.black).toBe("alice");
        });

        it("should default to blitz 5+3 time control", () => {
            const state = createState();
            expect(state.clock).not.toBeNull();
            expect(state.clock!.white).toBe(5 * 60_000);
            expect(state.clock!.black).toBe(5 * 60_000);
            expect(state.clock!.increment).toBe(3_000);
        });

        it("should apply custom time control from options", () => {
            const state = createState({ timeControl: "bullet_1_0" });
            expect(state.clock!.white).toBe(60_000);
            expect(state.clock!.increment).toBe(0);
        });

        it("should create no clock when timeControl is 'none'", () => {
            const state = createState({ timeControl: "none" });
            expect(state.clock).toBeNull();
        });

        it("should fall back to blitz 5+3 for unknown time control", () => {
            const state = createState({ timeControl: "invalid_key" });
            expect(state.clock!.white).toBe(5 * 60_000);
            expect(state.clock!.increment).toBe(3_000);
        });
    });

    describe("handleAction — move", () => {
        let state: ChessState;

        beforeEach(() => {
            state = createState({ timeControl: "none" });
        });

        it("should accept a legal move", () => {
            const result = tryAct(state, { type: "move", from: "e2", to: "e4" }, "alice");
            expect(result.ok).toBe(true);
            if (result.ok) {
                // After 1. e4, FEN should show pawn on e4 (4th rank) and it's black's turn
                expect(result.state.fen).toContain("4P3"); // Pawn on e4 in FEN notation
                expect(result.state.fen).toContain(" b "); // Black to move
                expect(result.state.moveHistory).toHaveLength(1);
                expect(result.state.moveHistory[0]!.san).toBe("e4");
                expect(result.state.moveHistory[0]!.color).toBe("w");
            }
        });

        it("should reject a move when it's not your turn", () => {
            const result = tryAct(state, { type: "move", from: "e7", to: "e5" }, "bob");
            // bob is black, white moves first — but bob is trying to move a black piece on white's turn
            // Actually, the check is playerColor !== turn, so bob (black) can't move when turn is white
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("It's not your turn");
        });

        it("should reject an illegal move", () => {
            const result = tryAct(state, { type: "move", from: "e2", to: "e5" }, "alice");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("Illegal move");
        });

        it("should reject a move from a nonsense square", () => {
            const result = tryAct(state, { type: "move", from: "z9", to: "z8" }, "alice");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("Illegal move");
        });

        it("should detect checkmate", () => {
            const final = playScholarsMate(state);
            expect(final.result).toBe("white");
            expect(final.resultReason).toBe("Checkmate");
        });

        it("should clear a pending draw offer on move", () => {
            state = act(state, { type: "offer_draw" }, "alice");
            expect(state.drawOffer).toBe("white");
            state = act(state, { type: "move", from: "e2", to: "e4" }, "alice");
            expect(state.drawOffer).toBeNull();
        });

        it("should track move history for both colors", () => {
            state = act(state, { type: "move", from: "e2", to: "e4" }, "alice");
            state = act(state, { type: "move", from: "e7", to: "e5" }, "bob");
            expect(state.moveHistory).toHaveLength(2);
            expect(state.moveHistory[0]!.color).toBe("w");
            expect(state.moveHistory[1]!.color).toBe("b");
        });

        it("should handle pawn promotion", () => {
            // Set up a position where white pawn is on the 7th rank
            const promoState: ChessState = {
                ...state,
                fen: "8/P7/8/8/8/8/8/4K2k w - - 0 1", // White pawn on a7, kings
            };
            const result = tryAct(promoState, { type: "move", from: "a7", to: "a8", promotion: "q" }, "alice");
            expect(result.ok).toBe(true);
            if (result.ok) {
                expect(result.state.fen).toContain("Q"); // Promoted to queen
            }
        });

        it("should detect stalemate", () => {
            // Classic stalemate: black king in corner, no legal moves
            const stalemateState: ChessState = {
                ...state,
                fen: "k7/2Q5/1K6/8/8/8/8/8 w - - 0 1",
            };
            // White plays Qc8 — but that's check not stalemate. Use Qb7 stalemate pattern.
            // Actually use: king a8, white queen a6, white king c8 → Qa7# is checkmate not stalemate
            // Classic stalemate: Ka1, Qb3 with Kc2
            const state2: ChessState = {
                ...state,
                fen: "k7/8/1K6/8/8/8/8/2Q5 w - - 0 1", // Kc1 → Qc7 creates stalemate? No.
            };
            // Let's use a known stalemate position where it's black to move and has no legal moves
            const state3: ChessState = {
                ...state,
                fen: "k7/2Q5/K7/8/8/8/8/8 b - - 0 1", // Black to move, king on a8, blocked
            };
            // In this position it's actually stalemate for black — black king has no legal moves
            // But wait, Qa7 is not played, the queen is on c7.
            // Ka8 can go to b8 (not attacked by Qc7? Qc7 attacks b8? c7 queen attacks b8 yes).
            // Ka8 also blocked by Ka6. So a8 king: a7 attacked by K and Q, b8 attacked by Q, b7 attacked by Q.
            // That IS stalemate — black king has no legal moves and is not in check.
            // But we need white to deliver the stalemate on their move, then the position detection happens.
            // Actually, chess.js checks stalemate from the new position. So we need a position where
            // after white's move, it's black's turn and black is stalemated.

            // Simpler: use position where white's move leads to stalemate
            const stalemateSetup: ChessState = {
                ...state,
                fen: "k7/8/1K6/2Q5/8/8/8/8 w - - 0 1",
            };
            // White plays Qc7 → position is k7/2Q5/1K6/8/8/8/8/8 b - - 1 1
            // Black king on a8: a7 attacked by K+Q, b8 attacked by Q, b7 attacked by K → stalemate!
            const result = tryAct(stalemateSetup, { type: "move", from: "c5", to: "c7" }, "alice");
            expect(result.ok).toBe(true);
            if (result.ok) {
                expect(result.state.result).toBe("draw");
                expect(result.state.resultReason).toBe("Stalemate");
            }
        });

        it("should detect insufficient material", () => {
            // King vs King — after a capture leaves only kings
            const kvk: ChessState = {
                ...state,
                fen: "8/8/8/8/8/8/1p6/K1k5 b - - 0 1", // Black pawn can't create insufficiency easily
            };
            // Simpler: just set up K vs K directly after a capture
            // Actually, let's set up KN vs K where white captures last black piece
            const setup: ChessState = {
                ...state,
                fen: "8/8/8/8/8/2n5/8/KN5k w - - 0 1",
            };
            // White Nb1 captures Nc3 → only K+N vs K (insufficient material? Actually K+N vs K IS insufficient)
            const result = tryAct(setup, { type: "move", from: "b1", to: "c3" }, "alice");
            expect(result.ok).toBe(true);
            if (result.ok) {
                expect(result.state.result).toBe("draw");
                expect(result.state.resultReason).toBe("Insufficient material");
            }
        });
    });

    describe("handleAction — move with clock", () => {
        it("should deduct time and add increment on move", () => {
            const state = createState({ timeControl: "blitz_5_3" });
            const now = Date.now();
            // Simulate 1 second passing
            const stateWithOldClock: ChessState = {
                ...state,
                clock: { ...state.clock!, lastMoveAt: now - 1000 },
            };
            const result = tryAct(stateWithOldClock, { type: "move", from: "e2", to: "e4" }, "alice");
            expect(result.ok).toBe(true);
            if (result.ok) {
                // White had 300_000ms, spent ~1000ms, got 3000ms increment
                // Should be approximately 300_000 - 1000 + 3000 = 302_000
                expect(result.state.clock!.white).toBeGreaterThan(300_000);
                expect(result.state.clock!.white).toBeLessThanOrEqual(302_100); // small tolerance
            }
        });

        it("should trigger timeout if player's clock has expired when they try to move", () => {
            const state = createState({ timeControl: "bullet_1_0" });
            const stateWithExpiredClock: ChessState = {
                ...state,
                clock: { ...state.clock!, white: 500, lastMoveAt: Date.now() - 1000 },
            };
            // White tries to move but their clock is at 500ms with 1000ms elapsed → expired
            const result = tryAct(stateWithExpiredClock, { type: "move", from: "e2", to: "e4" }, "alice");
            expect(result.ok).toBe(true);
            if (result.ok) {
                expect(result.state.result).toBe("black"); // Black wins on time
                expect(result.state.resultReason).toBe("Timeout");
            }
        });
    });

    describe("handleAction — resign", () => {
        it("should let white resign (black wins)", () => {
            const state = createState({ timeControl: "none" });
            const result = tryAct(state, { type: "resign" }, "alice");
            expect(result.ok).toBe(true);
            if (result.ok) {
                expect(result.state.result).toBe("black");
                expect(result.state.resultReason).toBe("Resignation");
            }
        });

        it("should let black resign (white wins)", () => {
            const state = createState({ timeControl: "none" });
            const result = tryAct(state, { type: "resign" }, "bob");
            expect(result.ok).toBe(true);
            if (result.ok) {
                expect(result.state.result).toBe("white");
                expect(result.state.resultReason).toBe("Resignation");
            }
        });
    });

    describe("handleAction — draw offers", () => {
        let state: ChessState;

        beforeEach(() => {
            state = createState({ timeControl: "none" });
        });

        it("should allow offering a draw", () => {
            const result = tryAct(state, { type: "offer_draw" }, "alice");
            expect(result.ok).toBe(true);
            if (result.ok) expect(result.state.drawOffer).toBe("white");
        });

        it("should reject duplicate draw offer from same player", () => {
            state = act(state, { type: "offer_draw" }, "alice");
            const result = tryAct(state, { type: "offer_draw" }, "alice");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("You already offered a draw");
        });

        it("should allow opponent to accept a draw", () => {
            state = act(state, { type: "offer_draw" }, "alice");
            const result = tryAct(state, { type: "accept_draw" }, "bob");
            expect(result.ok).toBe(true);
            if (result.ok) {
                expect(result.state.result).toBe("draw");
                expect(result.state.resultReason).toBe("Agreement");
                expect(result.state.drawOffer).toBeNull();
            }
        });

        it("should reject accepting when no draw offer exists", () => {
            const result = tryAct(state, { type: "accept_draw" }, "bob");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("No draw offer to accept");
        });

        it("should reject accepting your own draw offer", () => {
            state = act(state, { type: "offer_draw" }, "alice");
            const result = tryAct(state, { type: "accept_draw" }, "alice");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("No draw offer to accept");
        });

        it("should allow opponent to decline a draw", () => {
            state = act(state, { type: "offer_draw" }, "alice");
            const result = tryAct(state, { type: "decline_draw" }, "bob");
            expect(result.ok).toBe(true);
            if (result.ok) expect(result.state.drawOffer).toBeNull();
        });

        it("should reject declining when no draw offer exists", () => {
            const result = tryAct(state, { type: "decline_draw" }, "bob");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("No draw offer to decline");
        });

        it("should reject declining your own draw offer", () => {
            state = act(state, { type: "offer_draw" }, "alice");
            const result = tryAct(state, { type: "decline_draw" }, "alice");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("No draw offer to decline");
        });
    });

    describe("handleAction — claim_timeout", () => {
        it("should reject when there is no clock", () => {
            const state = createState({ timeControl: "none" });
            const result = tryAct(state, { type: "claim_timeout" }, "alice");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("No clock in this game");
        });

        it("should reject when opponent still has time", () => {
            const state = createState({ timeControl: "blitz_5_3" });
            const result = tryAct(state, { type: "claim_timeout" }, "bob");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("Opponent still has time remaining");
        });

        it("should succeed when opponent's time has expired", () => {
            const state = createState({ timeControl: "bullet_1_0" });
            // White's clock is 60_000ms — set lastMoveAt far in the past
            const expiredState: ChessState = {
                ...state,
                clock: { ...state.clock!, lastMoveAt: Date.now() - 120_000 },
            };
            // It's white's turn, so white's clock is ticking. Bob (black) claims timeout.
            const result = tryAct(expiredState, { type: "claim_timeout" }, "bob");
            expect(result.ok).toBe(true);
            if (result.ok) {
                expect(result.state.result).toBe("black");
                expect(result.state.resultReason).toBe("Timeout");
            }
        });
    });

    describe("handleAction — guards", () => {
        it("should reject any action after game is over", () => {
            let state = createState({ timeControl: "none" });
            state = act(state, { type: "resign" }, "alice");
            expect(state.result).toBe("black");

            const moveResult = tryAct(state, { type: "move", from: "e2", to: "e4" }, "bob");
            expect(moveResult.ok).toBe(false);
            if (!moveResult.ok) expect(moveResult.error).toBe("Game is already over");

            const resignResult = tryAct(state, { type: "resign" }, "bob");
            expect(resignResult.ok).toBe(false);

            const drawResult = tryAct(state, { type: "offer_draw" }, "bob");
            expect(drawResult.ok).toBe(false);
        });

        it("should reject actions from a non-player", () => {
            const state = createState({ timeControl: "none" });
            const result = tryAct(state, { type: "move", from: "e2", to: "e4" }, "charlie");
            expect(result.ok).toBe(false);
            if (!result.ok) expect(result.error).toBe("You are not a player in this game");
        });
    });

    describe("getPlayerView", () => {
        it("should return the correct color for each player", () => {
            const state = createState({ timeControl: "none" });
            const aliceView = chessPlugin.getPlayerView(state, "alice") as ChessPlayerView;
            const bobView = chessPlugin.getPlayerView(state, "bob") as ChessPlayerView;
            expect(aliceView.myColor).toBe("white");
            expect(bobView.myColor).toBe("black");
        });

        it("should include legal moves only for the active player", () => {
            const state = createState({ timeControl: "none" });
            const whiteView = chessPlugin.getPlayerView(state, "alice") as ChessPlayerView;
            const blackView = chessPlugin.getPlayerView(state, "bob") as ChessPlayerView;
            expect(whiteView.legalMoves.length).toBeGreaterThan(0); // White has 20 opening moves
            expect(blackView.legalMoves).toEqual([]); // Not black's turn
        });

        it("should return 20 legal moves in starting position", () => {
            const state = createState({ timeControl: "none" });
            const view = chessPlugin.getPlayerView(state, "alice") as ChessPlayerView;
            expect(view.legalMoves.length).toBe(20); // 16 pawn moves + 4 knight moves
        });

        it("should return no legal moves after game is over", () => {
            let state = createState({ timeControl: "none" });
            state = playScholarsMate(state);
            const view = chessPlugin.getPlayerView(state, "alice") as ChessPlayerView;
            expect(view.legalMoves).toEqual([]);
        });

        it("should detect check in the view", () => {
            const state = createState({ timeControl: "none" });
            // After 1. e4 e5 2. Qh5 — queen attacks f7, not check yet.
            // Use a direct check position: white queen on e7 checking black king on e8
            const checkState: ChessState = {
                ...state,
                fen: "rnbqkbnr/ppppQppp/8/8/4P3/8/PPPP1PPP/RNB1KBNR b KQkq - 0 1",
            };
            const view = chessPlugin.getPlayerView(checkState, "bob") as ChessPlayerView;
            expect(view.isCheck).toBe(true);
        });

        it("should include clock with activeColor when game is in progress", () => {
            const state = createState({ timeControl: "blitz_5_3" });
            const view = chessPlugin.getPlayerView(state, "alice") as ChessPlayerView;
            expect(view.clock).not.toBeNull();
            expect(view.clock!.activeColor).toBe("white");
        });

        it("should set clock activeColor to null when game is over", () => {
            let state = createState({ timeControl: "blitz_5_3" });
            state = act(state, { type: "resign" }, "alice");
            const view = chessPlugin.getPlayerView(state, "alice") as ChessPlayerView;
            expect(view.clock!.activeColor).toBeNull();
        });

        it("should default to white for an unknown player", () => {
            const state = createState({ timeControl: "none" });
            const view = chessPlugin.getPlayerView(state, "unknown") as ChessPlayerView;
            expect(view.myColor).toBe("white");
        });
    });

    describe("getSpectatorView", () => {
        it("should include both player identifiers", () => {
            const state = createState({ timeControl: "none" });
            const view = chessPlugin.getSpectatorView(state) as ChessSpectatorView;
            expect(view.players.white).toBe("alice");
            expect(view.players.black).toBe("bob");
        });

        it("should include current turn", () => {
            const state = createState({ timeControl: "none" });
            const view = chessPlugin.getSpectatorView(state) as ChessSpectatorView;
            expect(view.turn).toBe("white");
        });

        it("should include clock data when present", () => {
            const state = createState({ timeControl: "rapid_10_0" });
            const view = chessPlugin.getSpectatorView(state) as ChessSpectatorView;
            expect(view.clock).not.toBeNull();
            expect(view.clock!.increment).toBe(0);
        });

        it("should have null clock when time control is none", () => {
            const state = createState({ timeControl: "none" });
            const view = chessPlugin.getSpectatorView(state) as ChessSpectatorView;
            expect(view.clock).toBeNull();
        });
    });

    describe("isGameOver", () => {
        it("should return null when game is in progress", () => {
            const state = createState({ timeControl: "none" });
            expect(chessPlugin.isGameOver!(state)).toBeNull();
        });

        it("should return winner for white victory", () => {
            let state = createState({ timeControl: "none" });
            state = act(state, { type: "resign" }, "bob"); // Bob (black) resigns
            const result = chessPlugin.isGameOver!(state);
            expect(result).not.toBeNull();
            expect(result!.winner).toBe("alice"); // White player ID
            expect(result!.reason).toBe("Resignation");
        });

        it("should return winner for black victory", () => {
            let state = createState({ timeControl: "none" });
            state = act(state, { type: "resign" }, "alice"); // Alice (white) resigns
            const result = chessPlugin.isGameOver!(state);
            expect(result).not.toBeNull();
            expect(result!.winner).toBe("bob"); // Black player ID
        });

        it("should return null winner for draw", () => {
            let state = createState({ timeControl: "none" });
            state = act(state, { type: "offer_draw" }, "alice");
            state = act(state, { type: "accept_draw" }, "bob");
            const result = chessPlugin.isGameOver!(state);
            expect(result).not.toBeNull();
            expect(result!.winner).toBeNull();
            expect(result!.reason).toBe("Agreement");
        });

        it("should return checkmate result with correct winner", () => {
            let state = createState({ timeControl: "none" });
            state = playScholarsMate(state);
            const result = chessPlugin.isGameOver!(state);
            expect(result).not.toBeNull();
            expect(result!.winner).toBe("alice"); // White wins by checkmate
            expect(result!.reason).toBe("Checkmate");
        });
    });

    describe("onPlayerDisconnect", () => {
        it("should award victory to opponent when player disconnects", () => {
            const state = createState({ timeControl: "none" });
            const result = chessPlugin.onPlayerDisconnect!(state, "alice");
            expect(result.result).toBe("black");
            expect(result.resultReason).toBe("Opponent disconnected");
        });

        it("should award victory to white when black disconnects", () => {
            const state = createState({ timeControl: "none" });
            const result = chessPlugin.onPlayerDisconnect!(state, "bob");
            expect(result.result).toBe("white");
            expect(result.resultReason).toBe("Opponent disconnected");
        });

        it("should not change state if game is already over", () => {
            let state = createState({ timeControl: "none" });
            state = act(state, { type: "resign" }, "alice");
            const result = chessPlugin.onPlayerDisconnect!(state, "bob");
            expect(result.result).toBe("black"); // Original result preserved
            expect(result.resultReason).toBe("Resignation"); // Not overwritten
        });

        it("should not change state for unknown player", () => {
            const state = createState({ timeControl: "none" });
            const result = chessPlugin.onPlayerDisconnect!(state, "unknown");
            expect(result.result).toBeNull(); // No change
        });
    });

    describe("plugin metadata", () => {
        it("should have correct slug and name", () => {
            expect(chessPlugin.slug).toBe("chess");
            expect(chessPlugin.name).toBe("Chess");
        });

        it("should require exactly 2 players", () => {
            expect(chessPlugin.minPlayers).toBe(2);
            expect(chessPlugin.maxPlayers).toBe(2);
        });
    });
});