X-Git-Url: https://git.auder.net/?a=blobdiff_plain;f=client%2Fclient_OLD%2Fjavascripts%2Fbase_rules.js;fp=client%2Fclient_OLD%2Fjavascripts%2Fbase_rules.js;h=9f6ec9ecbb2b2e7ff3d197422d37462cb50cb9a7;hb=625022fdcf750f0aff8fcd699f7e9b89730e1d10;hp=0000000000000000000000000000000000000000;hpb=b955c65b942d09d24b5c3bed0d755d4f2f8f71f1;p=vchess.git

diff --git a/client/client_OLD/javascripts/base_rules.js b/client/client_OLD/javascripts/base_rules.js
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+// (Orthodox) Chess rules are defined in ChessRules class.
+// Variants generally inherit from it, and modify some parts.
+
+class PiPo //Piece+Position
+{
+	// o: {piece[p], color[c], posX[x], posY[y]}
+	constructor(o)
+	{
+		this.p = o.p;
+		this.c = o.c;
+		this.x = o.x;
+		this.y = o.y;
+	}
+}
+
+// TODO: for animation, moves should contains "moving" and "fading" maybe...
+class Move
+{
+	// o: {appear, vanish, [start,] [end,]}
+	// appear,vanish = arrays of PiPo
+	// start,end = coordinates to apply to trigger move visually (think castle)
+	constructor(o)
+	{
+		this.appear = o.appear;
+		this.vanish = o.vanish;
+		this.start = !!o.start ? o.start : {x:o.vanish[0].x, y:o.vanish[0].y};
+		this.end = !!o.end ? o.end : {x:o.appear[0].x, y:o.appear[0].y};
+	}
+}
+
+// NOTE: x coords = top to bottom; y = left to right (from white player perspective)
+class ChessRules
+{
+	//////////////
+	// MISC UTILS
+
+	static get HasFlags() { return true; } //some variants don't have flags
+
+	static get HasEnpassant() { return true; } //some variants don't have ep.
+
+	// Path to pieces
+	static getPpath(b)
+	{
+		return b; //usual pieces in pieces/ folder
+	}
+
+	// Turn "wb" into "B" (for FEN)
+	static board2fen(b)
+	{
+		return b[0]=='w' ? b[1].toUpperCase() : b[1];
+	}
+
+	// Turn "p" into "bp" (for board)
+	static fen2board(f)
+	{
+		return f.charCodeAt()<=90 ? "w"+f.toLowerCase() : "b"+f;
+	}
+
+	// Check if FEN describe a position
+	static IsGoodFen(fen)
+	{
+		const fenParsed = V.ParseFen(fen);
+		// 1) Check position
+		if (!V.IsGoodPosition(fenParsed.position))
+			return false;
+		// 2) Check turn
+		if (!fenParsed.turn || !V.IsGoodTurn(fenParsed.turn))
+			return false;
+		// 3) Check moves count
+		if (!fenParsed.movesCount || !(parseInt(fenParsed.movesCount) >= 0))
+			return false;
+		// 4) Check flags
+		if (V.HasFlags && (!fenParsed.flags || !V.IsGoodFlags(fenParsed.flags)))
+			return false;
+		// 5) Check enpassant
+		if (V.HasEnpassant &&
+			(!fenParsed.enpassant || !V.IsGoodEnpassant(fenParsed.enpassant)))
+		{
+			return false;
+		}
+		return true;
+	}
+
+	// Is position part of the FEN a priori correct?
+	static IsGoodPosition(position)
+	{
+		if (position.length == 0)
+			return false;
+		const rows = position.split("/");
+		if (rows.length != V.size.x)
+			return false;
+		for (let row of rows)
+		{
+			let sumElts = 0;
+			for (let i=0; i<row.length; i++)
+			{
+				if (V.PIECES.includes(row[i].toLowerCase()))
+					sumElts++;
+				else
+				{
+					const num = parseInt(row[i]);
+					if (isNaN(num))
+						return false;
+					sumElts += num;
+				}
+			}
+			if (sumElts != V.size.y)
+				return false;
+		}
+		return true;
+	}
+
+	// For FEN checking
+	static IsGoodTurn(turn)
+	{
+		return ["w","b"].includes(turn);
+	}
+
+	// For FEN checking
+	static IsGoodFlags(flags)
+	{
+		return !!flags.match(/^[01]{4,4}$/);
+	}
+
+	static IsGoodEnpassant(enpassant)
+	{
+		if (enpassant != "-")
+		{
+			const ep = V.SquareToCoords(fenParsed.enpassant);
+			if (isNaN(ep.x) || !V.OnBoard(ep))
+				return false;
+		}
+		return true;
+	}
+
+	// 3 --> d (column number to letter)
+	static CoordToColumn(colnum)
+	{
+		return String.fromCharCode(97 + colnum);
+	}
+
+	// d --> 3 (column letter to number)
+	static ColumnToCoord(column)
+	{
+		return column.charCodeAt(0) - 97;
+	}
+
+	// a4 --> {x:3,y:0}
+	static SquareToCoords(sq)
+	{
+		return {
+			// NOTE: column is always one char => max 26 columns
+			// row is counted from black side => subtraction
+			x: V.size.x - parseInt(sq.substr(1)),
+			y: sq[0].charCodeAt() - 97
+		};
+	}
+
+	// {x:0,y:4} --> e8
+	static CoordsToSquare(coords)
+	{
+		return V.CoordToColumn(coords.y) + (V.size.x - coords.x);
+	}
+
+	// Aggregates flags into one object
+	aggregateFlags()
+	{
+		return this.castleFlags;
+	}
+
+	// Reverse operation
+	disaggregateFlags(flags)
+	{
+		this.castleFlags = flags;
+	}
+
+	// En-passant square, if any
+	getEpSquare(moveOrSquare)
+	{
+		if (!moveOrSquare)
+			return undefined;
+		if (typeof moveOrSquare === "string")
+		{
+			const square = moveOrSquare;
+			if (square == "-")
+				return undefined;
+			return V.SquareToCoords(square);
+		}
+		// Argument is a move:
+		const move = moveOrSquare;
+		const [sx,sy,ex] = [move.start.x,move.start.y,move.end.x];
+		// TODO: next conditions are first for Atomic, and third for Checkered
+		if (move.appear.length > 0 && move.appear[0].p == V.PAWN && ["w","b"].includes(move.appear[0].c) && Math.abs(sx - ex) == 2)
+		{
+			return {
+				x: (sx + ex)/2,
+				y: sy
+			};
+		}
+		return undefined; //default
+	}
+
+	// Can thing on square1 take thing on square2
+	canTake([x1,y1], [x2,y2])
+	{
+		return this.getColor(x1,y1) !== this.getColor(x2,y2);
+	}
+
+	// Is (x,y) on the chessboard?
+	static OnBoard(x,y)
+	{
+		return (x>=0 && x<V.size.x && y>=0 && y<V.size.y);
+	}
+
+	// Used in interface: 'side' arg == player color
+	canIplay(side, [x,y])
+	{
+		return (this.turn == side && this.getColor(x,y) == side);
+	}
+
+	// On which squares is color under check ? (for interface)
+	getCheckSquares(color)
+	{
+		return this.isAttacked(this.kingPos[color], [V.GetOppCol(color)])
+			? [JSON.parse(JSON.stringify(this.kingPos[color]))] //need to duplicate!
+			: [];
+	}
+
+	/////////////
+	// FEN UTILS
+
+	// Setup the initial random (assymetric) position
+	static GenRandInitFen()
+	{
+		let pieces = { "w": new Array(8), "b": new Array(8) };
+		// Shuffle pieces on first and last rank
+		for (let c of ["w","b"])
+		{
+			let positions = _.range(8);
+
+			// Get random squares for bishops
+			let randIndex = 2 * _.random(3);
+			const bishop1Pos = positions[randIndex];
+			// The second bishop must be on a square of different color
+			let randIndex_tmp = 2 * _.random(3) + 1;
+			const bishop2Pos = positions[randIndex_tmp];
+			// Remove chosen squares
+			positions.splice(Math.max(randIndex,randIndex_tmp), 1);
+			positions.splice(Math.min(randIndex,randIndex_tmp), 1);
+
+			// Get random squares for knights
+			randIndex = _.random(5);
+			const knight1Pos = positions[randIndex];
+			positions.splice(randIndex, 1);
+			randIndex = _.random(4);
+			const knight2Pos = positions[randIndex];
+			positions.splice(randIndex, 1);
+
+			// Get random square for queen
+			randIndex = _.random(3);
+			const queenPos = positions[randIndex];
+			positions.splice(randIndex, 1);
+
+			// Rooks and king positions are now fixed,
+			// because of the ordering rook-king-rook
+			const rook1Pos = positions[0];
+			const kingPos = positions[1];
+			const rook2Pos = positions[2];
+
+			// Finally put the shuffled pieces in the board array
+			pieces[c][rook1Pos] = 'r';
+			pieces[c][knight1Pos] = 'n';
+			pieces[c][bishop1Pos] = 'b';
+			pieces[c][queenPos] = 'q';
+			pieces[c][kingPos] = 'k';
+			pieces[c][bishop2Pos] = 'b';
+			pieces[c][knight2Pos] = 'n';
+			pieces[c][rook2Pos] = 'r';
+		}
+		return pieces["b"].join("") +
+			"/pppppppp/8/8/8/8/PPPPPPPP/" +
+			pieces["w"].join("").toUpperCase() +
+			" w 0 1111 -"; //add turn + flags + enpassant
+	}
+
+	// "Parse" FEN: just return untransformed string data
+	static ParseFen(fen)
+	{
+		const fenParts = fen.split(" ");
+		let res =
+		{
+			position: fenParts[0],
+			turn: fenParts[1],
+			movesCount: fenParts[2],
+		};
+		let nextIdx = 3;
+		if (V.HasFlags)
+			Object.assign(res, {flags: fenParts[nextIdx++]});
+		if (V.HasEnpassant)
+			Object.assign(res, {enpassant: fenParts[nextIdx]});
+		return res;
+	}
+
+	// Return current fen (game state)
+	getFen()
+	{
+		return this.getBaseFen() + " " +
+			this.getTurnFen() + " " + this.movesCount +
+			(V.HasFlags ? (" " + this.getFlagsFen()) : "") +
+			(V.HasEnpassant ? (" " + this.getEnpassantFen()) : "");
+	}
+
+	// Position part of the FEN string
+	getBaseFen()
+	{
+		let position = "";
+		for (let i=0; i<V.size.x; i++)
+		{
+			let emptyCount = 0;
+			for (let j=0; j<V.size.y; j++)
+			{
+				if (this.board[i][j] == V.EMPTY)
+					emptyCount++;
+				else
+				{
+					if (emptyCount > 0)
+					{
+						// Add empty squares in-between
+						position += emptyCount;
+						emptyCount = 0;
+					}
+					position += V.board2fen(this.board[i][j]);
+				}
+			}
+			if (emptyCount > 0)
+			{
+				// "Flush remainder"
+				position += emptyCount;
+			}
+			if (i < V.size.x - 1)
+				position += "/"; //separate rows
+		}
+		return position;
+	}
+
+	getTurnFen()
+	{
+		return this.turn;
+	}
+
+	// Flags part of the FEN string
+	getFlagsFen()
+	{
+		let flags = "";
+		// Add castling flags
+		for (let i of ['w','b'])
+		{
+			for (let j=0; j<2; j++)
+				flags += (this.castleFlags[i][j] ? '1' : '0');
+		}
+		return flags;
+	}
+
+	// Enpassant part of the FEN string
+	getEnpassantFen()
+	{
+		const L = this.epSquares.length;
+		if (!this.epSquares[L-1])
+			return "-"; //no en-passant
+		return V.CoordsToSquare(this.epSquares[L-1]);
+	}
+
+	// Turn position fen into double array ["wb","wp","bk",...]
+	static GetBoard(position)
+	{
+		const rows = position.split("/");
+		let board = doubleArray(V.size.x, V.size.y, "");
+		for (let i=0; i<rows.length; i++)
+		{
+			let j = 0;
+			for (let indexInRow = 0; indexInRow < rows[i].length; indexInRow++)
+			{
+				const character = rows[i][indexInRow];
+				const num = parseInt(character);
+				if (!isNaN(num))
+					j += num; //just shift j
+				else //something at position i,j
+					board[i][j++] = V.fen2board(character);
+			}
+		}
+		return board;
+	}
+
+	// Extract (relevant) flags from fen
+	setFlags(fenflags)
+	{
+		// white a-castle, h-castle, black a-castle, h-castle
+		this.castleFlags = {'w': [true,true], 'b': [true,true]};
+		if (!fenflags)
+			return;
+		for (let i=0; i<4; i++)
+			this.castleFlags[i < 2 ? 'w' : 'b'][i%2] = (fenflags.charAt(i) == '1');
+	}
+
+	//////////////////
+	// INITIALIZATION
+
+	// Fen string fully describes the game state
+	constructor(fen)
+	{
+		const fenParsed = V.ParseFen(fen);
+		this.board = V.GetBoard(fenParsed.position);
+		this.turn = fenParsed.turn[0]; //[0] to work with MarseilleRules
+		this.movesCount = parseInt(fenParsed.movesCount);
+		this.setOtherVariables(fen);
+	}
+
+	// Scan board for kings and rooks positions
+	scanKingsRooks(fen)
+	{
+		this.INIT_COL_KING = {'w':-1, 'b':-1};
+		this.INIT_COL_ROOK = {'w':[-1,-1], 'b':[-1,-1]};
+		this.kingPos = {'w':[-1,-1], 'b':[-1,-1]}; //squares of white and black king
+		const fenRows = V.ParseFen(fen).position.split("/");
+		for (let i=0; i<fenRows.length; i++)
+		{
+			let k = 0; //column index on board
+			for (let j=0; j<fenRows[i].length; j++)
+			{
+				switch (fenRows[i].charAt(j))
+				{
+					case 'k':
+						this.kingPos['b'] = [i,k];
+						this.INIT_COL_KING['b'] = k;
+						break;
+					case 'K':
+						this.kingPos['w'] = [i,k];
+						this.INIT_COL_KING['w'] = k;
+						break;
+					case 'r':
+						if (this.INIT_COL_ROOK['b'][0] < 0)
+							this.INIT_COL_ROOK['b'][0] = k;
+						else
+							this.INIT_COL_ROOK['b'][1] = k;
+						break;
+					case 'R':
+						if (this.INIT_COL_ROOK['w'][0] < 0)
+							this.INIT_COL_ROOK['w'][0] = k;
+						else
+							this.INIT_COL_ROOK['w'][1] = k;
+						break;
+					default:
+						const num = parseInt(fenRows[i].charAt(j));
+						if (!isNaN(num))
+							k += (num-1);
+				}
+				k++;
+			}
+		}
+	}
+
+	// Some additional variables from FEN (variant dependant)
+	setOtherVariables(fen)
+	{
+		// Set flags and enpassant:
+		const parsedFen = V.ParseFen(fen);
+		if (V.HasFlags)
+			this.setFlags(parsedFen.flags);
+		if (V.HasEnpassant)
+		{
+			const epSq = parsedFen.enpassant != "-"
+				? V.SquareToCoords(parsedFen.enpassant)
+				: undefined;
+			this.epSquares = [ epSq ];
+		}
+		// Search for king and rooks positions:
+		this.scanKingsRooks(fen);
+	}
+
+	/////////////////////
+	// GETTERS & SETTERS
+
+	static get size()
+	{
+		return {x:8, y:8};
+	}
+
+	// Color of thing on suqare (i,j). 'undefined' if square is empty
+	getColor(i,j)
+	{
+		return this.board[i][j].charAt(0);
+	}
+
+	// Piece type on square (i,j). 'undefined' if square is empty
+	getPiece(i,j)
+	{
+		return this.board[i][j].charAt(1);
+	}
+
+	// Get opponent color
+	static GetOppCol(color)
+	{
+		return (color=="w" ? "b" : "w");
+	}
+
+	// Get next color (for compatibility with 3 and 4 players games)
+	static GetNextCol(color)
+	{
+		return V.GetOppCol(color);
+	}
+
+	// Pieces codes (for a clearer code)
+	static get PAWN() { return 'p'; }
+	static get ROOK() { return 'r'; }
+	static get KNIGHT() { return 'n'; }
+	static get BISHOP() { return 'b'; }
+	static get QUEEN() { return 'q'; }
+	static get KING() { return 'k'; }
+
+	// For FEN checking:
+	static get PIECES()
+	{
+		return [V.PAWN,V.ROOK,V.KNIGHT,V.BISHOP,V.QUEEN,V.KING];
+	}
+
+	// Empty square
+	static get EMPTY() { return ""; }
+
+	// Some pieces movements
+	static get steps()
+	{
+		return {
+			'r': [ [-1,0],[1,0],[0,-1],[0,1] ],
+			'n': [ [-1,-2],[-1,2],[1,-2],[1,2],[-2,-1],[-2,1],[2,-1],[2,1] ],
+			'b': [ [-1,-1],[-1,1],[1,-1],[1,1] ],
+		};
+	}
+
+	////////////////////
+	// MOVES GENERATION
+
+	// All possible moves from selected square (assumption: color is OK)
+	getPotentialMovesFrom([x,y])
+	{
+		switch (this.getPiece(x,y))
+		{
+			case V.PAWN:
+				return this.getPotentialPawnMoves([x,y]);
+			case V.ROOK:
+				return this.getPotentialRookMoves([x,y]);
+			case V.KNIGHT:
+				return this.getPotentialKnightMoves([x,y]);
+			case V.BISHOP:
+				return this.getPotentialBishopMoves([x,y]);
+			case V.QUEEN:
+				return this.getPotentialQueenMoves([x,y]);
+			case V.KING:
+				return this.getPotentialKingMoves([x,y]);
+		}
+	}
+
+	// Build a regular move from its initial and destination squares.
+	// tr: transformation
+	getBasicMove([sx,sy], [ex,ey], tr)
+	{
+		let mv = new Move({
+			appear: [
+				new PiPo({
+					x: ex,
+					y: ey,
+					c: !!tr ? tr.c : this.getColor(sx,sy),
+					p: !!tr ? tr.p : this.getPiece(sx,sy)
+				})
+			],
+			vanish: [
+				new PiPo({
+					x: sx,
+					y: sy,
+					c: this.getColor(sx,sy),
+					p: this.getPiece(sx,sy)
+				})
+			]
+		});
+
+		// The opponent piece disappears if we take it
+		if (this.board[ex][ey] != V.EMPTY)
+		{
+			mv.vanish.push(
+				new PiPo({
+					x: ex,
+					y: ey,
+					c: this.getColor(ex,ey),
+					p: this.getPiece(ex,ey)
+				})
+			);
+		}
+		return mv;
+	}
+
+	// Generic method to find possible moves of non-pawn pieces:
+	// "sliding or jumping"
+	getSlideNJumpMoves([x,y], steps, oneStep)
+	{
+		const color = this.getColor(x,y);
+		let moves = [];
+		outerLoop:
+		for (let step of steps)
+		{
+			let i = x + step[0];
+			let j = y + step[1];
+			while (V.OnBoard(i,j) && this.board[i][j] == V.EMPTY)
+			{
+				moves.push(this.getBasicMove([x,y], [i,j]));
+				if (oneStep !== undefined)
+					continue outerLoop;
+				i += step[0];
+				j += step[1];
+			}
+			if (V.OnBoard(i,j) && this.canTake([x,y], [i,j]))
+				moves.push(this.getBasicMove([x,y], [i,j]));
+		}
+		return moves;
+	}
+
+	// What are the pawn moves from square x,y ?
+	getPotentialPawnMoves([x,y])
+	{
+		const color = this.turn;
+		let moves = [];
+		const [sizeX,sizeY] = [V.size.x,V.size.y];
+		const shiftX = (color == "w" ? -1 : 1);
+		const firstRank = (color == 'w' ? sizeX-1 : 0);
+		const startRank = (color == "w" ? sizeX-2 : 1);
+		const lastRank = (color == "w" ? 0 : sizeX-1);
+		const pawnColor = this.getColor(x,y); //can be different for checkered
+
+		// NOTE: next condition is generally true (no pawn on last rank)
+		if (x+shiftX >= 0 && x+shiftX < sizeX)
+		{
+			const finalPieces = x + shiftX == lastRank
+				? [V.ROOK,V.KNIGHT,V.BISHOP,V.QUEEN]
+				: [V.PAWN]
+			// One square forward
+			if (this.board[x+shiftX][y] == V.EMPTY)
+			{
+				for (let piece of finalPieces)
+				{
+					moves.push(this.getBasicMove([x,y], [x+shiftX,y],
+						{c:pawnColor,p:piece}));
+				}
+				// Next condition because pawns on 1st rank can generally jump
+				if ([startRank,firstRank].includes(x)
+					&& this.board[x+2*shiftX][y] == V.EMPTY)
+				{
+					// Two squares jump
+					moves.push(this.getBasicMove([x,y], [x+2*shiftX,y]));
+				}
+			}
+			// Captures
+			for (let shiftY of [-1,1])
+			{
+				if (y + shiftY >= 0 && y + shiftY < sizeY
+					&& this.board[x+shiftX][y+shiftY] != V.EMPTY
+					&& this.canTake([x,y], [x+shiftX,y+shiftY]))
+				{
+					for (let piece of finalPieces)
+					{
+						moves.push(this.getBasicMove([x,y], [x+shiftX,y+shiftY],
+							{c:pawnColor,p:piece}));
+					}
+				}
+			}
+		}
+
+		if (V.HasEnpassant)
+		{
+			// En passant
+			const Lep = this.epSquares.length;
+			const epSquare = this.epSquares[Lep-1]; //always at least one element
+			if (!!epSquare && epSquare.x == x+shiftX && Math.abs(epSquare.y - y) == 1)
+			{
+				let enpassantMove = this.getBasicMove([x,y], [epSquare.x,epSquare.y]);
+				enpassantMove.vanish.push({
+					x: x,
+					y: epSquare.y,
+					p: 'p',
+					c: this.getColor(x,epSquare.y)
+				});
+				moves.push(enpassantMove);
+			}
+		}
+
+		return moves;
+	}
+
+	// What are the rook moves from square x,y ?
+	getPotentialRookMoves(sq)
+	{
+		return this.getSlideNJumpMoves(sq, V.steps[V.ROOK]);
+	}
+
+	// What are the knight moves from square x,y ?
+	getPotentialKnightMoves(sq)
+	{
+		return this.getSlideNJumpMoves(sq, V.steps[V.KNIGHT], "oneStep");
+	}
+
+	// What are the bishop moves from square x,y ?
+	getPotentialBishopMoves(sq)
+	{
+		return this.getSlideNJumpMoves(sq, V.steps[V.BISHOP]);
+	}
+
+	// What are the queen moves from square x,y ?
+	getPotentialQueenMoves(sq)
+	{
+		return this.getSlideNJumpMoves(sq,
+			V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
+	}
+
+	// What are the king moves from square x,y ?
+	getPotentialKingMoves(sq)
+	{
+		// Initialize with normal moves
+		let moves = this.getSlideNJumpMoves(sq,
+			V.steps[V.ROOK].concat(V.steps[V.BISHOP]), "oneStep");
+		return moves.concat(this.getCastleMoves(sq));
+	}
+
+	getCastleMoves([x,y])
+	{
+		const c = this.getColor(x,y);
+		if (x != (c=="w" ? V.size.x-1 : 0) || y != this.INIT_COL_KING[c])
+			return []; //x isn't first rank, or king has moved (shortcut)
+
+		// Castling ?
+		const oppCol = V.GetOppCol(c);
+		let moves = [];
+		let i = 0;
+		const finalSquares = [ [2,3], [V.size.y-2,V.size.y-3] ]; //king, then rook
+		castlingCheck:
+		for (let castleSide=0; castleSide < 2; castleSide++) //large, then small
+		{
+			if (!this.castleFlags[c][castleSide])
+				continue;
+			// If this code is reached, rooks and king are on initial position
+
+			// Nothing on the path of the king ?
+			// (And no checks; OK also if y==finalSquare)
+			let step = finalSquares[castleSide][0] < y ? -1 : 1;
+			for (i=y; i!=finalSquares[castleSide][0]; i+=step)
+			{
+				if (this.isAttacked([x,i], [oppCol]) || (this.board[x][i] != V.EMPTY &&
+					// NOTE: next check is enough, because of chessboard constraints
+					(this.getColor(x,i) != c
+						|| ![V.KING,V.ROOK].includes(this.getPiece(x,i)))))
+				{
+					continue castlingCheck;
+				}
+			}
+
+			// Nothing on the path to the rook?
+			step = castleSide == 0 ? -1 : 1;
+			for (i = y + step; i != this.INIT_COL_ROOK[c][castleSide]; i += step)
+			{
+				if (this.board[x][i] != V.EMPTY)
+					continue castlingCheck;
+			}
+			const rookPos = this.INIT_COL_ROOK[c][castleSide];
+
+			// Nothing on final squares, except maybe king and castling rook?
+			for (i=0; i<2; i++)
+			{
+				if (this.board[x][finalSquares[castleSide][i]] != V.EMPTY &&
+					this.getPiece(x,finalSquares[castleSide][i]) != V.KING &&
+					finalSquares[castleSide][i] != rookPos)
+				{
+					continue castlingCheck;
+				}
+			}
+
+			// If this code is reached, castle is valid
+			moves.push( new Move({
+				appear: [
+					new PiPo({x:x,y:finalSquares[castleSide][0],p:V.KING,c:c}),
+					new PiPo({x:x,y:finalSquares[castleSide][1],p:V.ROOK,c:c})],
+				vanish: [
+					new PiPo({x:x,y:y,p:V.KING,c:c}),
+					new PiPo({x:x,y:rookPos,p:V.ROOK,c:c})],
+				end: Math.abs(y - rookPos) <= 2
+					? {x:x, y:rookPos}
+					: {x:x, y:y + 2 * (castleSide==0 ? -1 : 1)}
+			}) );
+		}
+
+		return moves;
+	}
+
+	////////////////////
+	// MOVES VALIDATION
+
+	// For the interface: possible moves for the current turn from square sq
+	getPossibleMovesFrom(sq)
+	{
+		return this.filterValid( this.getPotentialMovesFrom(sq) );
+	}
+
+	// TODO: promotions (into R,B,N,Q) should be filtered only once
+	filterValid(moves)
+	{
+		if (moves.length == 0)
+			return [];
+		const color = this.turn;
+		return moves.filter(m => {
+			this.play(m);
+			const res = !this.underCheck(color);
+			this.undo(m);
+			return res;
+		});
+	}
+
+	// Search for all valid moves considering current turn
+	// (for engine and game end)
+	getAllValidMoves()
+	{
+		const color = this.turn;
+		const oppCol = V.GetOppCol(color);
+		let potentialMoves = [];
+		for (let i=0; i<V.size.x; i++)
+		{
+			for (let j=0; j<V.size.y; j++)
+			{
+				// Next condition "!= oppCol" to work with checkered variant
+				if (this.board[i][j] != V.EMPTY && this.getColor(i,j) != oppCol)
+				{
+					Array.prototype.push.apply(potentialMoves,
+						this.getPotentialMovesFrom([i,j]));
+				}
+			}
+		}
+		return this.filterValid(potentialMoves);
+	}
+
+	// Stop at the first move found
+	atLeastOneMove()
+	{
+		const color = this.turn;
+		const oppCol = V.GetOppCol(color);
+		for (let i=0; i<V.size.x; i++)
+		{
+			for (let j=0; j<V.size.y; j++)
+			{
+				if (this.board[i][j] != V.EMPTY && this.getColor(i,j) != oppCol)
+				{
+					const moves = this.getPotentialMovesFrom([i,j]);
+					if (moves.length > 0)
+					{
+						for (let k=0; k<moves.length; k++)
+						{
+							if (this.filterValid([moves[k]]).length > 0)
+								return true;
+						}
+					}
+				}
+			}
+		}
+		return false;
+	}
+
+	// Check if pieces of color in 'colors' are attacking (king) on square x,y
+	isAttacked(sq, colors)
+	{
+		return (this.isAttackedByPawn(sq, colors)
+			|| this.isAttackedByRook(sq, colors)
+			|| this.isAttackedByKnight(sq, colors)
+			|| this.isAttackedByBishop(sq, colors)
+			|| this.isAttackedByQueen(sq, colors)
+			|| this.isAttackedByKing(sq, colors));
+	}
+
+	// Is square x,y attacked by 'colors' pawns ?
+	isAttackedByPawn([x,y], colors)
+	{
+		for (let c of colors)
+		{
+			let pawnShift = (c=="w" ? 1 : -1);
+			if (x+pawnShift>=0 && x+pawnShift<V.size.x)
+			{
+				for (let i of [-1,1])
+				{
+					if (y+i>=0 && y+i<V.size.y && this.getPiece(x+pawnShift,y+i)==V.PAWN
+						&& this.getColor(x+pawnShift,y+i)==c)
+					{
+						return true;
+					}
+				}
+			}
+		}
+		return false;
+	}
+
+	// Is square x,y attacked by 'colors' rooks ?
+	isAttackedByRook(sq, colors)
+	{
+		return this.isAttackedBySlideNJump(sq, colors, V.ROOK, V.steps[V.ROOK]);
+	}
+
+	// Is square x,y attacked by 'colors' knights ?
+	isAttackedByKnight(sq, colors)
+	{
+		return this.isAttackedBySlideNJump(sq, colors,
+			V.KNIGHT, V.steps[V.KNIGHT], "oneStep");
+	}
+
+	// Is square x,y attacked by 'colors' bishops ?
+	isAttackedByBishop(sq, colors)
+	{
+		return this.isAttackedBySlideNJump(sq, colors, V.BISHOP, V.steps[V.BISHOP]);
+	}
+
+	// Is square x,y attacked by 'colors' queens ?
+	isAttackedByQueen(sq, colors)
+	{
+		return this.isAttackedBySlideNJump(sq, colors, V.QUEEN,
+			V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
+	}
+
+	// Is square x,y attacked by 'colors' king(s) ?
+	isAttackedByKing(sq, colors)
+	{
+		return this.isAttackedBySlideNJump(sq, colors, V.KING,
+			V.steps[V.ROOK].concat(V.steps[V.BISHOP]), "oneStep");
+	}
+
+	// Generic method for non-pawn pieces ("sliding or jumping"):
+	// is x,y attacked by a piece of color in array 'colors' ?
+	isAttackedBySlideNJump([x,y], colors, piece, steps, oneStep)
+	{
+		for (let step of steps)
+		{
+			let rx = x+step[0], ry = y+step[1];
+			while (V.OnBoard(rx,ry) && this.board[rx][ry] == V.EMPTY && !oneStep)
+			{
+				rx += step[0];
+				ry += step[1];
+			}
+			if (V.OnBoard(rx,ry) && this.getPiece(rx,ry) === piece
+				&& colors.includes(this.getColor(rx,ry)))
+			{
+				return true;
+			}
+		}
+		return false;
+	}
+
+	// Is color under check after his move ?
+	underCheck(color)
+	{
+		return this.isAttacked(this.kingPos[color], [V.GetOppCol(color)]);
+	}
+
+	/////////////////
+	// MOVES PLAYING
+
+	// Apply a move on board
+	static PlayOnBoard(board, move)
+	{
+		for (let psq of move.vanish)
+			board[psq.x][psq.y] = V.EMPTY;
+		for (let psq of move.appear)
+			board[psq.x][psq.y] = psq.c + psq.p;
+	}
+	// Un-apply the played move
+	static UndoOnBoard(board, move)
+	{
+		for (let psq of move.appear)
+			board[psq.x][psq.y] = V.EMPTY;
+		for (let psq of move.vanish)
+			board[psq.x][psq.y] = psq.c + psq.p;
+	}
+
+	// After move is played, update variables + flags
+	updateVariables(move)
+	{
+		let piece = undefined;
+		let c = undefined;
+		if (move.vanish.length >= 1)
+		{
+			// Usual case, something is moved
+			piece = move.vanish[0].p;
+			c = move.vanish[0].c;
+		}
+		else
+		{
+			// Crazyhouse-like variants
+			piece = move.appear[0].p;
+			c = move.appear[0].c;
+		}
+		if (c == "c") //if (!["w","b"].includes(c))
+		{
+			// 'c = move.vanish[0].c' doesn't work for Checkered
+			c = V.GetOppCol(this.turn);
+		}
+		const firstRank = (c == "w" ? V.size.x-1 : 0);
+
+		// Update king position + flags
+		if (piece == V.KING && move.appear.length > 0)
+		{
+			this.kingPos[c][0] = move.appear[0].x;
+			this.kingPos[c][1] = move.appear[0].y;
+			if (V.HasFlags)
+				this.castleFlags[c] = [false,false];
+			return;
+		}
+		if (V.HasFlags)
+		{
+			// Update castling flags if rooks are moved
+			const oppCol = V.GetOppCol(c);
+			const oppFirstRank = (V.size.x-1) - firstRank;
+			if (move.start.x == firstRank //our rook moves?
+				&& this.INIT_COL_ROOK[c].includes(move.start.y))
+			{
+				const flagIdx = (move.start.y == this.INIT_COL_ROOK[c][0] ? 0 : 1);
+				this.castleFlags[c][flagIdx] = false;
+			}
+			else if (move.end.x == oppFirstRank //we took opponent rook?
+				&& this.INIT_COL_ROOK[oppCol].includes(move.end.y))
+			{
+				const flagIdx = (move.end.y == this.INIT_COL_ROOK[oppCol][0] ? 0 : 1);
+				this.castleFlags[oppCol][flagIdx] = false;
+			}
+		}
+	}
+
+	// After move is undo-ed *and flags resetted*, un-update other variables
+	// TODO: more symmetry, by storing flags increment in move (?!)
+	unupdateVariables(move)
+	{
+		// (Potentially) Reset king position
+		const c = this.getColor(move.start.x,move.start.y);
+		if (this.getPiece(move.start.x,move.start.y) == V.KING)
+			this.kingPos[c] = [move.start.x, move.start.y];
+	}
+
+	play(move)
+	{
+		// DEBUG:
+//		if (!this.states) this.states = [];
+//		const stateFen = this.getBaseFen() + this.getTurnFen() + this.getFlagsFen();
+//		this.states.push(stateFen);
+
+		if (V.HasFlags)
+			move.flags = JSON.stringify(this.aggregateFlags()); //save flags (for undo)
+		if (V.HasEnpassant)
+			this.epSquares.push( this.getEpSquare(move) );
+		if (!move.color)
+			move.color = this.turn; //for interface
+		V.PlayOnBoard(this.board, move);
+		this.turn = V.GetOppCol(this.turn);
+		this.movesCount++;
+		this.updateVariables(move);
+	}
+
+	undo(move)
+	{
+		if (V.HasEnpassant)
+			this.epSquares.pop();
+		if (V.HasFlags)
+			this.disaggregateFlags(JSON.parse(move.flags));
+		V.UndoOnBoard(this.board, move);
+		this.turn = V.GetOppCol(this.turn);
+		this.movesCount--;
+		this.unupdateVariables(move);
+
+		// DEBUG:
+//		const stateFen = this.getBaseFen() + this.getTurnFen() + this.getFlagsFen();
+//		if (stateFen != this.states[this.states.length-1]) debugger;
+//		this.states.pop();
+	}
+
+	///////////////
+	// END OF GAME
+
+	// What is the score ? (Interesting if game is over)
+	getCurrentScore()
+	{
+		if (this.atLeastOneMove()) // game not over
+			return "*";
+
+		// Game over
+		const color = this.turn;
+		// No valid move: stalemate or checkmate?
+		if (!this.isAttacked(this.kingPos[color], [V.GetOppCol(color)]))
+			return "1/2";
+		// OK, checkmate
+		return (color == "w" ? "0-1" : "1-0");
+	}
+
+	///////////////
+	// ENGINE PLAY
+
+	// Pieces values
+	static get VALUES()
+	{
+		return {
+			'p': 1,
+			'r': 5,
+			'n': 3,
+			'b': 3,
+			'q': 9,
+			'k': 1000
+		};
+	}
+
+	// "Checkmate" (unreachable eval)
+	static get INFINITY() { return 9999; }
+
+	// At this value or above, the game is over
+	static get THRESHOLD_MATE() { return V.INFINITY; }
+
+	// Search depth: 2 for high branching factor, 4 for small (Loser chess, eg.)
+	static get SEARCH_DEPTH() { return 3; }
+
+	// Assumption: at least one legal move
+	// NOTE: works also for extinction chess because depth is 3...
+	getComputerMove()
+	{
+		const maxeval = V.INFINITY;
+		const color = this.turn;
+		// Some variants may show a bigger moves list to the human (Switching),
+		// thus the argument "computer" below (which is generally ignored)
+		let moves1 = this.getAllValidMoves("computer");
+
+		// Can I mate in 1 ? (for Magnetic & Extinction)
+		for (let i of _.shuffle(_.range(moves1.length)))
+		{
+			this.play(moves1[i]);
+			let finish = (Math.abs(this.evalPosition()) >= V.THRESHOLD_MATE);
+			if (!finish)
+			{
+				const score = this.getCurrentScore();
+				if (["1-0","0-1"].includes(score))
+					finish = true;
+			}
+			this.undo(moves1[i]);
+			if (finish)
+				return moves1[i];
+		}
+
+		// Rank moves using a min-max at depth 2
+		for (let i=0; i<moves1.length; i++)
+		{
+			// Initial self evaluation is very low: "I'm checkmated"
+			moves1[i].eval = (color=="w" ? -1 : 1) * maxeval;
+			this.play(moves1[i]);
+			const score1 = this.getCurrentScore();
+			let eval2 = undefined;
+			if (score1 == "*")
+			{
+				// Initial enemy evaluation is very low too, for him
+				eval2 = (color=="w" ? 1 : -1) * maxeval;
+				// Second half-move:
+				let moves2 = this.getAllValidMoves("computer");
+				for (let j=0; j<moves2.length; j++)
+				{
+					this.play(moves2[j]);
+					const score2 = this.getCurrentScore();
+					const evalPos = score2 == "*"
+						? this.evalPosition()
+						: (score2=="1/2" ? 0 : (score2=="1-0" ? 1 : -1) * maxeval);
+					if ((color == "w" && evalPos < eval2)
+						|| (color=="b" && evalPos > eval2))
+					{
+						eval2 = evalPos;
+					}
+					this.undo(moves2[j]);
+				}
+			}
+			else
+				eval2 = (score1=="1/2" ? 0 : (score1=="1-0" ? 1 : -1) * maxeval);
+			if ((color=="w" && eval2 > moves1[i].eval)
+				|| (color=="b" && eval2 < moves1[i].eval))
+			{
+				moves1[i].eval = eval2;
+			}
+			this.undo(moves1[i]);
+		}
+		moves1.sort( (a,b) => { return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
+
+		let candidates = [0]; //indices of candidates moves
+		for (let j=1; j<moves1.length && moves1[j].eval == moves1[0].eval; j++)
+			candidates.push(j);
+		let currentBest = moves1[_.sample(candidates, 1)];
+
+		// From here, depth >= 3: may take a while, so we control time
+		const timeStart = Date.now();
+
+		// Skip depth 3+ if we found a checkmate (or if we are checkmated in 1...)
+		if (V.SEARCH_DEPTH >= 3 && Math.abs(moves1[0].eval) < V.THRESHOLD_MATE)
+		{
+			for (let i=0; i<moves1.length; i++)
+			{
+				if (Date.now()-timeStart >= 5000) //more than 5 seconds
+					return currentBest; //depth 2 at least
+				this.play(moves1[i]);
+				// 0.1 * oldEval : heuristic to avoid some bad moves (not all...)
+				moves1[i].eval = 0.1*moves1[i].eval +
+					this.alphabeta(V.SEARCH_DEPTH-1, -maxeval, maxeval);
+				this.undo(moves1[i]);
+			}
+			moves1.sort( (a,b) => {
+				return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
+		}
+		else
+			return currentBest;
+//		console.log(moves1.map(m => { return [this.getNotation(m), m.eval]; }));
+
+		candidates = [0];
+		for (let j=1; j<moves1.length && moves1[j].eval == moves1[0].eval; j++)
+			candidates.push(j);
+		return moves1[_.sample(candidates, 1)];
+	}
+
+	alphabeta(depth, alpha, beta)
+  {
+		const maxeval = V.INFINITY;
+		const color = this.turn;
+		const score = this.getCurrentScore();
+		if (score != "*")
+			return (score=="1/2" ? 0 : (score=="1-0" ? 1 : -1) * maxeval);
+		if (depth == 0)
+      return this.evalPosition();
+		const moves = this.getAllValidMoves("computer");
+    let v = color=="w" ? -maxeval : maxeval;
+		if (color == "w")
+		{
+			for (let i=0; i<moves.length; i++)
+      {
+				this.play(moves[i]);
+				v = Math.max(v, this.alphabeta(depth-1, alpha, beta));
+				this.undo(moves[i]);
+				alpha = Math.max(alpha, v);
+				if (alpha >= beta)
+					break; //beta cutoff
+			}
+		}
+		else //color=="b"
+		{
+			for (let i=0; i<moves.length; i++)
+			{
+				this.play(moves[i]);
+				v = Math.min(v, this.alphabeta(depth-1, alpha, beta));
+				this.undo(moves[i]);
+				beta = Math.min(beta, v);
+				if (alpha >= beta)
+					break; //alpha cutoff
+			}
+		}
+		return v;
+	}
+
+	evalPosition()
+	{
+		let evaluation = 0;
+		// Just count material for now
+		for (let i=0; i<V.size.x; i++)
+		{
+			for (let j=0; j<V.size.y; j++)
+			{
+				if (this.board[i][j] != V.EMPTY)
+				{
+					const sign = this.getColor(i,j) == "w" ? 1 : -1;
+					evaluation += sign * V.VALUES[this.getPiece(i,j)];
+				}
+			}
+		}
+		return evaluation;
+	}
+
+	/////////////////////////
+	// MOVES + GAME NOTATION
+	/////////////////////////
+
+	// Context: just before move is played, turn hasn't changed
+	// TODO: un-ambiguous notation (switch on piece type, check directions...)
+	getNotation(move)
+	{
+		if (move.appear.length == 2 && move.appear[0].p == V.KING) //castle
+			return (move.end.y < move.start.y ? "0-0-0" : "0-0");
+
+		// Translate final square
+		const finalSquare = V.CoordsToSquare(move.end);
+
+		const piece = this.getPiece(move.start.x, move.start.y);
+		if (piece == V.PAWN)
+		{
+			// Pawn move
+			let notation = "";
+			if (move.vanish.length > move.appear.length)
+			{
+				// Capture
+				const startColumn = V.CoordToColumn(move.start.y);
+				notation = startColumn + "x" + finalSquare;
+			}
+			else //no capture
+				notation = finalSquare;
+			if (move.appear.length > 0 && move.appear[0].p != V.PAWN) //promotion
+				notation += "=" + move.appear[0].p.toUpperCase();
+			return notation;
+		}
+
+		else
+		{
+			// Piece movement
+			return piece.toUpperCase() +
+				(move.vanish.length > move.appear.length ? "x" : "") + finalSquare;
+		}
+	}
+}