X-Git-Url: https://git.auder.net/?a=blobdiff_plain;f=public%2Fjavascripts%2Fbase_rules.js;h=ba77d7187538a7d98749c257c5ff10a39ab416c2;hb=6e62b1c7d177585003e923d423025dff280a7525;hp=2a962a964c726181c2a480a86cdad7a969137cb4;hpb=8ddc00a072c5a4aa679e5a420a7f9664d18e03f3;p=vchess.git

diff --git a/public/javascripts/base_rules.js b/public/javascripts/base_rules.js
index 2a962a96..ba77d718 100644
--- a/public/javascripts/base_rules.js
+++ b/public/javascripts/base_rules.js
@@ -31,91 +31,58 @@ class Move
 // 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;
 	}
 
-	/////////////////
-	// INITIALIZATION
-
-	// fen == "position [flags [turn]]"
-	constructor(fen, moves)
-	{
-		this.moves = moves;
-		// Use fen string to initialize variables, flags, turn and board
-		const fenParts = fen.split(" ");
-		this.board = V.GetBoard(fenParts[0]);
-		this.setFlags(fenParts[1]); //NOTE: fenParts[1] might be undefined
-		this.setTurn(fenParts[2]); //Same note
-		this.initVariables(fen);
-	}
-
-	// Some additional variables from FEN (variant dependant)
-	initVariables(fen)
+	// Check if FEN describe a position
+	static IsGoodFen(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 fenParts = fen.split(" ");
-		const position = fenParts[0].split("/");
-		for (let i=0; i<position.length; i++)
+		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 flags
+		if (V.HasFlags && (!fenParsed.flags || !V.IsGoodFlags(fenParsed.flags)))
+			return false;
+		// 4) Check enpassant
+		if (V.HasEnpassant &&
+			(!fenParsed.enpassant || !V.IsGoodEnpassant(fenParsed.enpassant)))
 		{
-			let k = 0; //column index on board
-			for (let j=0; j<position[i].length; j++)
-			{
-				switch (position[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(position[i].charAt(j));
-						if (!isNaN(num))
-							k += (num-1);
-				}
-				k++;
-			}
+			return false;
 		}
-		this.epSquares = [ this.getEpSquare(this.lastMove || fenParts[3]) ];
+		return true;
 	}
 
-	// Check if FEN describe a position
-	static IsGoodFen(fen)
+	// Is position part of the FEN a priori correct?
+	static IsGoodPosition(position)
 	{
-		const fenParts = fen.split(" ");
-		if (fenParts.length== 0)
+		if (position.length == 0)
 			return false;
-		// 1) Check position
-		const position = fenParts[0];
 		const rows = position.split("/");
 		if (rows.length != V.size.x)
 			return false;
@@ -137,31 +104,270 @@ class ChessRules
 			if (sumElts != V.size.y)
 				return false;
 		}
-		// 2) Check flags (if present)
-		if (fenParts.length >= 2)
+		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 != "-")
 		{
-			if (!V.IsGoodFlags(fenParts[1]))
+			const ep = V.SquareToCoords(fenParsed.enpassant);
+			if (isNaN(ep.x) || !V.OnBoard(ep))
 				return false;
 		}
-		// 3) Check turn (if present)
-		if (fenParts.length >= 3)
+		return true;
+	}
+
+	// 3 --> d (column number to letter)
+	static CoordToColumn(colnum)
+	{
+		return String.fromCharCode(97 + colnum);
+	}
+
+	// d --> 3 (column letter to number)
+	static ColumnToCoord(colnum)
+	{
+		return String.fromCharCode(97 + colnum);
+	}
+
+	// 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];
+		if (this.getPiece(sx,sy) == V.PAWN && Math.abs(sx - ex) == 2)
 		{
-			if (!["w","b"].includes(fenParts[2]))
-				return false;
+			return {
+				x: (sx + ex)/2,
+				y: sy
+			};
 		}
-		return true;
+		return undefined; //default
 	}
 
-	// For FEN checking
-	static IsGoodFlags(flags)
+	// Can thing on square1 take thing on square2
+	canTake([x1,y1], [x2,y2])
 	{
-		return !!flags.match(/^[01]{4,4}$/);
+		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], [this.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 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],
+		};
+		let nextIdx = 2;
+		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() +
+			(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;
 	}
 
-	// Turn diagram fen into double array ["wb","wp","bk",...]
-	static GetBoard(fen)
+	// Flags part of the FEN string
+	getFlagsFen()
 	{
-		const rows = fen.split(" ")[0].split("/");
+		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++)
 		{
@@ -190,30 +396,114 @@ class ChessRules
 			this.castleFlags[i < 2 ? 'w' : 'b'][i%2] = (fenflags.charAt(i) == '1');
 	}
 
-	// Initialize turn (white or black)
-	setTurn(turnflag)
+	//////////////////
+	// INITIALIZATION
+
+	// Fen string fully describes the game state
+	constructor(fen, moves)
+	{
+		this.moves = moves;
+		const fenParsed = V.ParseFen(fen);
+		this.board = V.GetBoard(fenParsed.position);
+		this.turn = fenParsed.turn[0]; //[0] to work with MarseilleRules
+		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)
 	{
-		this.turn = turnflag || "w";
+		// 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
+	/////////////////////
+	// GETTERS & SETTERS
 
-	static get size() { return {x:8, y:8}; }
+	static get size()
+	{
+		return {x:8, y:8};
+	}
 
-	// Two next functions return 'undefined' if called on empty square
-	getColor(i,j) { return this.board[i][j].charAt(0); }
-	getPiece(i,j) { return this.board[i][j].charAt(1); }
+	// Color of thing on suqare (i,j). 'undefined' if square is empty
+	getColor(i,j)
+	{
+		return this.board[i][j].charAt(0);
+	}
 
-	// Color
-	getOppCol(color) { return (color=="w" ? "b" : "w"); }
+	// Piece type on square (i,j). 'undefined' if square is empty
+	getPiece(i,j)
+	{
+		return this.board[i][j].charAt(1);
+	}
 
-	get lastMove() {
+	// Get opponent color
+	getOppCol(color)
+	{
+		return (color=="w" ? "b" : "w");
+	}
+
+	get lastMove()
+	{
 		const L = this.moves.length;
 		return (L>0 ? this.moves[L-1] : null);
 	}
 
-	// Pieces codes
+	// Pieces codes (for a clearer code)
 	static get PAWN() { return 'p'; }
 	static get ROOK() { return 'r'; }
 	static get KNIGHT() { return 'n'; }
@@ -222,15 +512,17 @@ class ChessRules
 	static get KING() { return 'k'; }
 
 	// For FEN checking:
-	static get PIECES() {
+	static get PIECES()
+	{
 		return [V.PAWN,V.ROOK,V.KNIGHT,V.BISHOP,V.QUEEN,V.KING];
 	}
 
 	// Empty square
-	static get EMPTY() { return ''; }
+	static get EMPTY() { return ""; }
 
 	// Some pieces movements
-	static get steps() {
+	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] ],
@@ -238,50 +530,7 @@ class ChessRules
 		};
 	}
 
-	// Aggregates flags into one object
-	get flags() {
-		return this.castleFlags;
-	}
-
-	// Reverse operation
-	parseFlags(flags)
-	{
-		this.castleFlags = flags;
-	}
-
-	// En-passant square, if any
-	getEpSquare(moveOrSquare)
-	{
-		if (typeof moveOrSquare === "string")
-		{
-			const square = moveOrSquare;
-			if (square == "-")
-				return undefined;
-			return {
-				x: square[0].charCodeAt()-97,
-				y: V.size.x-parseInt(square[1])
-			};
-		}
-		// Argument is a move:
-		const move = moveOrSquare;
-		const [sx,sy,ex] = [move.start.x,move.start.y,move.end.x];
-		if (this.getPiece(sx,sy) == V.PAWN && 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);
-	}
-
-	///////////////////
+	////////////////////
 	// MOVES GENERATION
 
 	// All possible moves from selected square (assumption: color is OK)
@@ -304,7 +553,8 @@ class ChessRules
 		}
 	}
 
-	// Build a regular move from its initial and destination squares; tr: transformation
+	// Build a regular move from its initial and destination squares.
+	// tr: transformation
 	getBasicMove([sx,sy], [ex,ey], tr)
 	{
 		let mv = new Move({
@@ -341,13 +591,8 @@ class ChessRules
 		return mv;
 	}
 
-	// Is (x,y) on the chessboard?
-	static OnBoard(x,y)
-	{
-		return (x>=0 && x<V.size.x && y>=0 && y<V.size.y);
-	}
-
-	// Generic method to find possible moves of non-pawn pieces ("sliding or jumping")
+	// Generic method to find possible moves of non-pawn pieces:
+	// "sliding or jumping"
 	getSlideNJumpMoves([x,y], steps, oneStep)
 	{
 		const color = this.getColor(x,y);
@@ -377,74 +622,65 @@ class ChessRules
 		const color = this.turn;
 		let moves = [];
 		const [sizeX,sizeY] = [V.size.x,V.size.y];
-		const shift = (color == "w" ? -1 : 1);
+		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
 
-		if (x+shift >= 0 && x+shift < sizeX && x+shift != lastRank)
+		if (x+shiftX >= 0 && x+shiftX < sizeX) //TODO: always true
 		{
-			// Normal moves
-			if (this.board[x+shift][y] == V.EMPTY)
+			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)
 			{
-				moves.push(this.getBasicMove([x,y], [x+shift,y]));
-				// Next condition because variants with pawns on 1st rank allow them to jump
-				if ([startRank,firstRank].includes(x) && this.board[x+2*shift][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*shift,y]));
+					moves.push(this.getBasicMove([x,y], [x+2*shiftX,y]));
 				}
 			}
 			// Captures
-			if (y>0 && this.board[x+shift][y-1] != V.EMPTY
-				&& this.canTake([x,y], [x+shift,y-1]))
-			{
-				moves.push(this.getBasicMove([x,y], [x+shift,y-1]));
-			}
-			if (y<sizeY-1 && this.board[x+shift][y+1] != V.EMPTY
-				&& this.canTake([x,y], [x+shift,y+1]))
+			for (let shiftY of [-1,1])
 			{
-				moves.push(this.getBasicMove([x,y], [x+shift,y+1]));
-			}
-		}
-
-		if (x+shift == lastRank)
-		{
-			// Promotion
-			const pawnColor = this.getColor(x,y); //can be different for checkered
-			let promotionPieces = [V.ROOK,V.KNIGHT,V.BISHOP,V.QUEEN];
-			promotionPieces.forEach(p => {
-				// Normal move
-				if (this.board[x+shift][y] == V.EMPTY)
-					moves.push(this.getBasicMove([x,y], [x+shift,y], {c:pawnColor,p:p}));
-				// Captures
-				if (y>0 && this.board[x+shift][y-1] != V.EMPTY
-					&& this.canTake([x,y], [x+shift,y-1]))
+				if (y + shiftY >= 0 && y + shiftY < sizeY
+					&& this.board[x+shiftX][y+shiftY] != V.EMPTY
+					&& this.canTake([x,y], [x+shiftX,y+shiftY]))
 				{
-					moves.push(this.getBasicMove([x,y], [x+shift,y-1], {c:pawnColor,p:p}));
-				}
-				if (y<sizeY-1 && this.board[x+shift][y+1] != V.EMPTY
-					&& this.canTake([x,y], [x+shift,y+1]))
-				{
-					moves.push(this.getBasicMove([x,y], [x+shift,y+1], {c:pawnColor,p:p}));
+					for (let piece of finalPieces)
+					{
+						moves.push(this.getBasicMove([x,y], [x+shiftX,y+shiftY],
+							{c:pawnColor,p:piece}));
+					}
 				}
-			});
+			}
 		}
 
-		// En passant
-		const Lep = this.epSquares.length;
-		const epSquare = (Lep>0 ? this.epSquares[Lep-1] : undefined);
-		if (!!epSquare && epSquare.x == x+shift && Math.abs(epSquare.y - y) == 1)
+		if (V.HasEnpassant)
 		{
-			const epStep = epSquare.y - y;
-			let enpassantMove = this.getBasicMove([x,y], [x+shift,y+epStep]);
-			enpassantMove.vanish.push({
-				x: x,
-				y: y+epStep,
-				p: 'p',
-				c: this.getColor(x,y+epStep)
-			});
-			moves.push(enpassantMove);
+			// 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;
@@ -471,7 +707,8 @@ class ChessRules
 	// What are the queen moves from square x,y ?
 	getPotentialQueenMoves(sq)
 	{
-		return this.getSlideNJumpMoves(sq, V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
+		return this.getSlideNJumpMoves(sq,
+			V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
 	}
 
 	// What are the king moves from square x,y ?
@@ -501,13 +738,15 @@ class ChessRules
 				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)?
+			// 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)))))
+					(this.getColor(x,i) != c
+						|| ![V.KING,V.ROOK].includes(this.getPiece(x,i)))))
 				{
 					continue castlingCheck;
 				}
@@ -550,17 +789,12 @@ class ChessRules
 		return moves;
 	}
 
-	///////////////////
+	////////////////////
 	// MOVES VALIDATION
 
-	canIplay(side, [x,y])
-	{
-		return (this.turn == side && this.getColor(x,y) == side);
-	}
-
+	// For the interface: possible moves for the current turn from square sq
 	getPossibleMovesFrom(sq)
 	{
-		// Assuming color is right (already checked)
 		return this.filterValid( this.getPotentialMovesFrom(sq) );
 	}
 
@@ -569,10 +803,17 @@ class ChessRules
 	{
 		if (moves.length == 0)
 			return [];
-		return moves.filter(m => { return !this.underCheck(m); });
+		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)
+	// Search for all valid moves considering current turn
+	// (for engine and game end)
 	getAllValidMoves()
 	{
 		const color = this.turn;
@@ -582,13 +823,14 @@ class ChessRules
 		{
 			for (let j=0; j<V.size.y; j++)
 			{
-				// Next condition "!= oppCol" = harmless hack to work with checkered variant
+				// 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]));
+				{
+					Array.prototype.push.apply(potentialMoves,
+						this.getPotentialMovesFrom([i,j]));
+				}
 			}
 		}
-		// NOTE: prefer lazy undercheck tests, letting the king being taken?
-		// No: if happen on last 1/2 move, could lead to forbidden moves, wrong evals
 		return this.filterValid(potentialMoves);
 	}
 
@@ -618,7 +860,7 @@ class ChessRules
 		return false;
 	}
 
-	// Check if pieces of color in array 'colors' are attacking square x,y
+	// Check if pieces of color in 'colors' are attacking (king) on square x,y
 	isAttacked(sq, colors)
 	{
 		return (this.isAttackedByPawn(sq, colors)
@@ -704,27 +946,14 @@ class ChessRules
 		return false;
 	}
 
-	// Is current player under check after his move ?
-	underCheck(move)
+	// Is color under check after his move ?
+	underCheck(color)
 	{
-		const color = this.turn;
-		this.play(move);
-		let res = this.isAttacked(this.kingPos[color], [this.getOppCol(color)]);
-		this.undo(move);
-		return res;
+		return this.isAttacked(this.kingPos[color], [this.getOppCol(color)]);
 	}
 
-	// On which squares is opponent under check after our move ?
-	getCheckSquares(move)
-	{
-		this.play(move);
-		const color = this.turn; //opponent
-		let res = this.isAttacked(this.kingPos[color], [this.getOppCol(color)])
-			? [ JSON.parse(JSON.stringify(this.kingPos[color])) ] //need to duplicate!
-			: [ ];
-		this.undo(move);
-		return res;
-	}
+	/////////////////
+	// MOVES PLAYING
 
 	// Apply a move on board
 	static PlayOnBoard(board, move)
@@ -743,11 +972,16 @@ class ChessRules
 			board[psq.x][psq.y] = psq.c + psq.p;
 	}
 
-	// Before move is played, update variables + flags
+	// After move is played, update variables + flags
 	updateVariables(move)
 	{
-		const piece = this.getPiece(move.start.x,move.start.y);
-		const c = this.turn;
+		const piece = move.vanish[0].p;
+		let c = move.vanish[0].c;
+		if (c == "c") //if (!["w","b"].includes(c))
+		{
+			// 'c = move.vanish[0].c' doesn't work for Checkered
+			c = this.getOppCol(this.turn);
+		}
 		const firstRank = (c == "w" ? V.size.x-1 : 0);
 
 		// Update king position + flags
@@ -774,8 +1008,8 @@ class ChessRules
 		}
 	}
 
-	// After move is undo-ed, un-update variables (flags are reset)
-	// TODO: more symmetry, by storing flags increment in move...
+	// 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
@@ -784,48 +1018,49 @@ class ChessRules
 			this.kingPos[c] = [move.start.x, move.start.y];
 	}
 
-	// Hash of position+flags+turn after a move is played (to detect repetitions)
-	getHashState()
-	{
-		return hex_md5(this.getFen());
-	}
-
 	play(move, ingame)
 	{
 		// DEBUG:
 //		if (!this.states) this.states = [];
-//		if (!ingame) this.states.push(JSON.stringify(this.board));
+//		if (!ingame) this.states.push(this.getFen());
 
 		if (!!ingame)
 			move.notation = [this.getNotation(move), this.getLongNotation(move)];
 
-		move.flags = JSON.stringify(this.flags); //save flags (for undo)
-		this.updateVariables(move);
-		this.moves.push(move);
-		this.epSquares.push( this.getEpSquare(move) );
-		this.turn = this.getOppCol(this.turn);
+		if (V.HasFlags)
+			move.flags = JSON.stringify(this.aggregateFlags()); //save flags (for undo)
+		if (V.HasEnpassant)
+			this.epSquares.push( this.getEpSquare(move) );
 		V.PlayOnBoard(this.board, move);
+		this.turn = this.getOppCol(this.turn);
+		this.moves.push(move);
+		this.updateVariables(move);
 
 		if (!!ingame)
-			move.hash = this.getHashState();
+		{
+			// Hash of current game state *after move*, to detect repetitions
+			move.hash = hex_md5(this.getFen());
+		}
 	}
 
 	undo(move)
 	{
+		if (V.HasEnpassant)
+			this.epSquares.pop();
+		if (V.HasFlags)
+			this.disaggregateFlags(JSON.parse(move.flags));
 		V.UndoOnBoard(this.board, move);
 		this.turn = this.getOppCol(this.turn);
-		this.epSquares.pop();
 		this.moves.pop();
 		this.unupdateVariables(move);
-		this.parseFlags(JSON.parse(move.flags));
 
 		// DEBUG:
-//		if (JSON.stringify(this.board) != this.states[this.states.length-1])
+//		if (this.getFen() != this.states[this.states.length-1])
 //			debugger;
 //		this.states.pop();
 	}
 
-	//////////////
+	///////////////
 	// END OF GAME
 
 	// Check for 3 repetitions (position + flags + turn)
@@ -869,14 +1104,15 @@ class ChessRules
 		if (!this.isAttacked(this.kingPos[color], [this.getOppCol(color)]))
 			return "1/2";
 		// OK, checkmate
-		return color == "w" ? "0-1" : "1-0";
+		return (color == "w" ? "0-1" : "1-0");
 	}
 
-	////////
-	//ENGINE
+	///////////////
+	// ENGINE PLAY
 
 	// Pieces values
-	static get VALUES() {
+	static get VALUES()
+	{
 		return {
 			'p': 1,
 			'r': 5,
@@ -887,18 +1123,14 @@ class ChessRules
 		};
 	}
 
-	static get INFINITY() {
-		return 9999; //"checkmate" (unreachable eval)
-	}
+	// "Checkmate" (unreachable eval)
+	static get INFINITY() { return 9999; }
 
-	static get THRESHOLD_MATE() {
-		// At this value or above, the game is over
-		return V.INFINITY;
-	}
+	// At this value or above, the game is over
+	static get THRESHOLD_MATE() { return V.INFINITY; }
 
-	static get SEARCH_DEPTH() {
-		return 3; //2 for high branching factor, 4 for small (Loser chess)
-	}
+	// 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...
@@ -917,7 +1149,7 @@ class ChessRules
 			let finish = (Math.abs(this.evalPosition()) >= V.THRESHOLD_MATE);
 			if (!finish && !this.atLeastOneMove())
 			{
-				// Try mate (for other variants)
+				// Test mate (for other variants)
 				const score = this.checkGameEnd();
 				if (score != "1/2")
 					finish = true;
@@ -930,12 +1162,14 @@ class ChessRules
 		// Rank moves using a min-max at depth 2
 		for (let i=0; i<moves1.length; i++)
 		{
-			moves1[i].eval = (color=="w" ? -1 : 1) * maxeval; //very low, I'm checkmated
+			// Initial self evaluation is very low: "I'm checkmated"
+			moves1[i].eval = (color=="w" ? -1 : 1) * maxeval;
 			this.play(moves1[i]);
 			let eval2 = undefined;
 			if (this.atLeastOneMove())
 			{
-				eval2 = (color=="w" ? 1 : -1) * maxeval; //initialized with checkmate value
+				// 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++)
@@ -946,12 +1180,15 @@ class ChessRules
 						evalPos = this.evalPosition()
 					else
 					{
-						// Work with scores for Loser variant
+						// Working with scores is more accurate (necessary for Loser variant)
 						const score = this.checkGameEnd();
 						evalPos = (score=="1/2" ? 0 : (score=="1-0" ? 1 : -1) * maxeval);
 					}
-					if ((color == "w" && evalPos < eval2) || (color=="b" && evalPos > eval2))
+					if ((color == "w" && evalPos < eval2)
+						|| (color=="b" && evalPos > eval2))
+					{
 						eval2 = evalPos;
+					}
 					this.undo(moves2[j]);
 				}
 			}
@@ -968,7 +1205,6 @@ class ChessRules
 			this.undo(moves1[i]);
 		}
 		moves1.sort( (a,b) => { return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
-		//console.log(moves1.map(m => { return [this.getNotation(m), m.eval]; }));
 
 		let candidates = [0]; //indices of candidates moves
 		for (let j=1; j<moves1.length && moves1[j].eval == moves1[0].eval; j++)
@@ -991,7 +1227,8 @@ class ChessRules
 					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); });
+			moves1.sort( (a,b) => {
+				return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
 		}
 		else
 			return currentBest;
@@ -1067,113 +1304,9 @@ class ChessRules
 		return evaluation;
 	}
 
-	////////////
-	// 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);
-			let bishop1Pos = positions[randIndex];
-			// The second bishop must be on a square of different color
-			let randIndex_tmp = 2 * _.random(3) + 1;
-			let 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);
-			let knight1Pos = positions[randIndex];
-			positions.splice(randIndex, 1);
-			randIndex = _.random(4);
-			let knight2Pos = positions[randIndex];
-			positions.splice(randIndex, 1);
-
-			// Get random square for queen
-			randIndex = _.random(3);
-			let queenPos = positions[randIndex];
-			positions.splice(randIndex, 1);
-
-			// Rooks and king positions are now fixed, because of the ordering rook-king-rook
-			let rook1Pos = positions[0];
-			let kingPos = positions[1];
-			let 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() +
-			" 1111 w"; //add flags + turn
-	}
-
-	// Return current fen according to pieces+colors state
-	getFen()
-	{
-		return this.getBaseFen() + " " + this.getFlagsFen() + " " + this.turn;
-	}
-
-	// Position part of the FEN string
-	getBaseFen()
-	{
-		let fen = "";
-		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
-						fen += emptyCount;
-						emptyCount = 0;
-					}
-					fen += V.board2fen(this.board[i][j]);
-				}
-			}
-			if (emptyCount > 0)
-			{
-				// "Flush remainder"
-				fen += emptyCount;
-			}
-			if (i < V.size.x - 1)
-				fen += "/"; //separate rows
-		}
-		return fen;
-	}
-
-	// Flags part of the FEN string
-	getFlagsFen()
-	{
-		let fen = "";
-		// Add castling flags
-		for (let i of ['w','b'])
-		{
-			for (let j=0; j<2; j++)
-				fen += (this.castleFlags[i][j] ? '1' : '0');
-		}
-		return fen;
-	}
+	/////////////////////////
+	// MOVES + GAME NOTATION
+	/////////////////////////
 
 	// Context: just before move is played, turn hasn't changed
 	getNotation(move)
@@ -1182,7 +1315,7 @@ class ChessRules
 			return (move.end.y < move.start.y ? "0-0-0" : "0-0");
 
 		// Translate final square
-		const finalSquare = String.fromCharCode(97 + move.end.y) + (V.size.x-move.end.x);
+		const finalSquare = V.CoordsToSquare(move.end);
 
 		const piece = this.getPiece(move.start.x, move.start.y);
 		if (piece == V.PAWN)
@@ -1192,12 +1325,12 @@ class ChessRules
 			if (move.vanish.length > move.appear.length)
 			{
 				// Capture
-				const startColumn = String.fromCharCode(97 + move.start.y);
+				const startColumn = V.CoordToColumn(move.start.y);
 				notation = startColumn + "x" + finalSquare;
 			}
 			else //no capture
 				notation = finalSquare;
-			if (move.appear.length > 0 && piece != move.appear[0].p) //promotion
+			if (move.appear.length > 0 && move.appear[0].p != V.PAWN) //promotion
 				notation += "=" + move.appear[0].p.toUpperCase();
 			return notation;
 		}
@@ -1213,10 +1346,8 @@ class ChessRules
 	// Complete the usual notation, may be required for de-ambiguification
 	getLongNotation(move)
 	{
-		const startSquare =
-			String.fromCharCode(97 + move.start.y) + (V.size.x-move.start.x);
-		const finalSquare = String.fromCharCode(97 + move.end.y) + (V.size.x-move.end.x);
-		return startSquare + finalSquare; //not encoding move. But short+long is enough
+		// Not encoding move. But short+long is enough
+		return V.CoordsToSquare(move.start) + V.CoordsToSquare(move.end);
 	}
 
 	// The score is already computed when calling this function