/*!
 * -------------------------------------------------------------------------- *
 *                                                                            *
 *    Kokopu - A JavaScript/TypeScript chess library.                         *
 *    <https://www.npmjs.com/package/kokopu>                                  *
 *    Copyright (C) 2018-2025  Yoann Le Montagner <yo35 -at- melix.net>       *
 *                                                                            *
 *    Kokopu is free software: you can redistribute it and/or                 *
 *    modify it under the terms of the GNU Lesser General Public License      *
 *    as published by the Free Software Foundation, either version 3 of       *
 *    the License, or (at your option) any later version.                     *
 *                                                                            *
 *    Kokopu is distributed in the hope that it will be useful,               *
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of          *
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the            *
 *    GNU Lesser General Public License for more details.                     *
 *                                                                            *
 *    You should have received a copy of the GNU Lesser General               *
 *    Public License along with this program. If not, see                     *
 *    <http://www.gnu.org/licenses/>.                                         *
 *                                                                            *
 * -------------------------------------------------------------------------- */


import { ColorImpl, PieceImpl, CpI, SpI, SquareImpl, GameVariantImpl } from './base_types_impl';


const EMPTY_BOARD = [
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY,
];

const REGULAR_START_BOARD = [
    /* eslint-disable @stylistic/comma-spacing, @stylistic/no-multi-spaces */
    CpI.WR   , CpI.WN   , CpI.WB   , CpI.WQ   , CpI.WK   , CpI.WB   , CpI.WN   , CpI.WR   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    CpI.BR   , CpI.BN   , CpI.BB   , CpI.BQ   , CpI.BK   , CpI.BB   , CpI.BN   , CpI.BR   ,
    /* eslint-enable */
];

const HORDE_START_BOARD = [
    /* eslint-disable @stylistic/comma-spacing, @stylistic/no-multi-spaces */
    CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, CpI.WP   , CpI.WP   , SpI.EMPTY, SpI.EMPTY, CpI.WP   , CpI.WP   , SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
    CpI.BR   , CpI.BN   , CpI.BB   , CpI.BQ   , CpI.BK   , CpI.BB   , CpI.BN   , CpI.BR   ,
    /* eslint-enable */
];


/**
 * Internal structure in `Position`, that encodes the state of the corresponding chess position.
 */
export interface PositionImpl {

    // Board state
    board: number[],

    // Flags
    turn: number,
    castling: number[],
    enPassant: number,
    variant: number,

    // Computed attributes
    legal: boolean | null,
    king: number[],
    effectiveCastling: number[] | null,
    effectiveEnPassant: number | null,
}


interface StartPositionInfo {
    board: number[],
    castling: number[],
    king: number[],
}


interface ScharnaglInfo {
    pieceScheme: number[],
    castling: number,
    kingFile: number,
}


const START_POSITION_INFO: (StartPositionInfo | null)[] = [

    { // Regular chess
        board: REGULAR_START_BOARD,
        castling: [ 129 /* (1 << A-file) | (1 << H-file) */, 129 /* (1 << A-file) | (1 << H-file) */ ],
        king: [ SquareImpl.E1, SquareImpl.E8 ],
    },

    null, // Chess960
    null, // no king
    null, // white king only
    null, // black king only

    { // Antichess
        board: REGULAR_START_BOARD,
        castling: [ 0, 0 ],
        king: [ -1, -1 ],
    },

    { // Horde
        board: HORDE_START_BOARD,
        castling: [ 0, 129 /* (1 << A-file) | (1 << H-file) */ ],
        king: [ -1, SquareImpl.E8 ],
    },
];


export function hasCanonicalStartPosition(variant: number) {
    return START_POSITION_INFO[variant] !== null;
}


export function makeEmpty(variant: number): PositionImpl {
    return {
        board: EMPTY_BOARD.slice(),
        turn: ColorImpl.WHITE,
        castling: [ 0, 0 ],
        enPassant: -1,
        variant: variant,
        legal: variant === GameVariantImpl.NO_KING,
        king: [ -1, -1 ],
        effectiveCastling: [ 0, 0 ],
        effectiveEnPassant: -1,
    };
}


/**
 * @param variant - Must be a variant with a canonical start position.
 */
export function makeInitial(variant: number): PositionImpl {
    const info = START_POSITION_INFO[variant]!; // WARNING: applicable only to variants with a canonical start position.
    return {
        board: info.board.slice(),
        turn: ColorImpl.WHITE,
        castling: info.castling.slice(),
        enPassant: -1,
        variant: variant,
        legal: true,
        king: info.king.slice(),
        effectiveCastling: info.castling.slice(),
        effectiveEnPassant: -1,
    };
}


/**
 * Chess960 initial position, following the numbering scheme proposed by Reinhard Scharnagl (see for instance https://chess960.net/start-positions/).
 *
 * @param scharnaglCode - Integer between 0 and 959 inclusive.
 */
export function make960FromScharnagl(scharnaglCode: number): PositionImpl {
    const info = decodeScharnagl(scharnaglCode);
    const rank1 = info.pieceScheme.map(piece => piece * 2 + ColorImpl.WHITE);
    const rank8 = info.pieceScheme.map(piece => piece * 2 + ColorImpl.BLACK);
    return {
        board: [
            /* eslint-disable @stylistic/comma-spacing, @stylistic/no-multi-spaces */
            rank1[0] , rank1[1] , rank1[2] , rank1[3] , rank1[4] , rank1[5] , rank1[6] , rank1[7] , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
            CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , CpI.WP   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
            SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
            SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
            SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
            SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.EMPTY, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
            CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , CpI.BP   , SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID, SpI.INVALID,
            rank8[0] , rank8[1] , rank8[2] , rank8[3] , rank8[4] , rank8[5] , rank8[6] , rank8[7] ,
            /* eslint-enable */
        ],
        turn: ColorImpl.WHITE,
        castling: [ info.castling, info.castling ],
        enPassant: -1,
        variant: GameVariantImpl.CHESS960,
        legal: true,
        king: [ SquareImpl.A1 + info.kingFile, SquareImpl.A8 + info.kingFile ],
        effectiveCastling: [ info.castling, info.castling ],
        effectiveEnPassant: -1,
    };
}


/**
 * @param scharnaglCode - Integer between 0 and 959 inclusive.
 */
function decodeScharnagl(scharnaglCode: number): ScharnaglInfo {
    const scheme = [ -1, -1, -1, -1, -1, -1, -1, -1 ];
    let castling = 0;
    let kingFile = -1;

    function forEachEmpty(fun: (file: number, emptyIndex: number) => void) {
        let emptyIndex = 0;
        for (let file = 0; file < 8; ++file) {
            if (scheme[file] >= 0) {
                continue;
            }
            fun(file, emptyIndex);
            ++emptyIndex;
        }
    }

    function setAt(piece: number, emptyIndexTarget1: number, emptyIndexTarget2: number) {
        forEachEmpty((file, emptyIndex) => {
            if (emptyIndex === emptyIndexTarget1 || emptyIndex === emptyIndexTarget2) {
                scheme[file] = piece;
            }
        });
    }

    // Light-square bishop
    scheme[(scharnaglCode % 4) * 2 + 1] = PieceImpl.BISHOP;
    scharnaglCode = Math.trunc(scharnaglCode / 4);

    // Dark-square bishop
    scheme[(scharnaglCode % 4) * 2] = PieceImpl.BISHOP;
    scharnaglCode = Math.trunc(scharnaglCode / 4);

    // Queen
    setAt(PieceImpl.QUEEN, scharnaglCode % 6, -1);
    scharnaglCode = Math.trunc(scharnaglCode / 6);

    // Knights
    switch (scharnaglCode) { // `scharnaglCode` is guaranteed here to be between 0 and 9 inclusive
        case 0: setAt(PieceImpl.KNIGHT, 0, 1); break;
        case 1: setAt(PieceImpl.KNIGHT, 0, 2); break;
        case 2: setAt(PieceImpl.KNIGHT, 0, 3); break;
        case 3: setAt(PieceImpl.KNIGHT, 0, 4); break;
        case 4: setAt(PieceImpl.KNIGHT, 1, 2); break;
        case 5: setAt(PieceImpl.KNIGHT, 1, 3); break;
        case 6: setAt(PieceImpl.KNIGHT, 1, 4); break;
        case 7: setAt(PieceImpl.KNIGHT, 2, 3); break;
        case 8: setAt(PieceImpl.KNIGHT, 2, 4); break;
        case 9: setAt(PieceImpl.KNIGHT, 3, 4); break;
    }

    // Rooks and king
    forEachEmpty((file, emptyIndex) => {
        if (emptyIndex === 1) {
            scheme[file] = PieceImpl.KING;
            kingFile = file;
        }
        else {
            scheme[file] = PieceImpl.ROOK;
            castling |= 1 << file;
        }
    });

    return {
        pieceScheme: scheme,
        castling: castling,
        kingFile: kingFile,
    };
}


export function makeCopy(position: PositionImpl): PositionImpl {
    return {
        board: position.board.slice(),
        turn: position.turn,
        castling: position.castling.slice(),
        enPassant: position.enPassant,
        variant: position.variant,
        legal: position.legal,
        king: position.king.slice(),
        effectiveCastling: position.effectiveCastling === null ? null : position.effectiveCastling.slice(),
        effectiveEnPassant: position.effectiveEnPassant,
    };
}