X-Git-Url: https://git.auder.net/?a=blobdiff_plain;f=public%2Fjavascripts%2Fbase_rules.js;h=5763af7e1d0f86e40789ff7c9467ce66a3bd1334;hb=7931e479adf93c87771ded1892a0873af72ae46d;hp=cdd75727f08b77e0dc8c306f42c7a425cd814281;hpb=6037f1d82232e62b669018b548845baf480f9e64;p=vchess.git

diff --git a/public/javascripts/base_rules.js b/public/javascripts/base_rules.js
index cdd75727..5763af7e 100644
--- a/public/javascripts/base_rules.js
+++ b/public/javascripts/base_rules.js
@@ -1,3 +1,6 @@
+// (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]}
@@ -10,6 +13,7 @@ class PiPo //Piece+Position
 	}
 }
 
+// TODO: for animation, moves should contains "moving" and "fading" maybe...
 class Move
 {
 	// o: {appear, vanish, [start,] [end,]}
@@ -50,17 +54,20 @@ class ChessRules
 	constructor(fen, moves)
 	{
 		this.moves = moves;
-		// Use fen string to initialize variables, flags and board
-		this.board = VariantRules.GetBoard(fen);
-		this.flags = VariantRules.GetFlags(fen);
+		// 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)
 	{
 		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]}; //respective squares of white and black king
+		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++)
@@ -91,68 +98,120 @@ class ChessRules
 							this.INIT_COL_ROOK['w'][1] = k;
 						break;
 					default:
-						let num = parseInt(position[i].charAt(j));
+						const num = parseInt(position[i].charAt(j));
 						if (!isNaN(num))
 							k += (num-1);
 				}
 				k++;
 			}
 		}
-		const epSq = this.moves.length > 0 ? this.getEpSquare(this.lastMove) : undefined;
+		const epSq = (this.moves.length > 0 ? this.getEpSquare(this.lastMove) : undefined);
 		this.epSquares = [ epSq ];
 	}
 
+	// Check if FEN describe a position
+	static IsGoodFen(fen)
+	{
+		const fenParts = fen.split(" ");
+		if (fenParts.length== 0 || fenParts.length > 3)
+			return false;
+		// 1) Check position
+		const position = fenParts[0];
+		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;
+		}
+		// 2) Check flags (if present)
+		if (fenParts.length >= 2)
+		{
+			if (!V.IsGoodFlags(fenParts[1]))
+				return false;
+		}
+		// 3) Check turn (if present)
+		if (fenParts.length == 3)
+		{
+			if (!["w","b"].includes(fenParts[2]))
+				return false;
+		}
+		return true;
+	}
+
+	// For FEN checking
+	static IsGoodFlags(flags)
+	{
+		return !!flags.match(/^[01]{4,4}$/);
+	}
+
 	// Turn diagram fen into double array ["wb","wp","bk",...]
 	static GetBoard(fen)
 	{
-		let rows = fen.split(" ")[0].split("/");
-		const [sizeX,sizeY] = VariantRules.size;
-		let board = doubleArray(sizeX, sizeY, "");
+		const rows = fen.split(" ")[0].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++)
 			{
-				let character = rows[i][indexInRow];
-				let num = parseInt(character);
+				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++] = VariantRules.fen2board(character);
+					board[i][j++] = V.fen2board(character);
 			}
 		}
 		return board;
 	}
 
-	// Overridable: flags can change a lot
-	static GetFlags(fen)
+	// Extract (relevant) flags from fen
+	setFlags(fenflags)
 	{
 		// white a-castle, h-castle, black a-castle, h-castle
-		let flags = {'w': new Array(2), 'b': new Array(2)};
-		let fenFlags = fen.split(" ")[1]; //flags right after position
+		this.castleFlags = {'w': [true,true], 'b': [true,true]};
+		if (!fenflags)
+			return;
 		for (let i=0; i<4; i++)
-			flags[i < 2 ? 'w' : 'b'][i%2] = (fenFlags.charAt(i) == '1');
-		return flags;
+			this.castleFlags[i < 2 ? 'w' : 'b'][i%2] = (fenflags.charAt(i) == '1');
+	}
+
+	// Initialize turn (white or black)
+	setTurn(turnflag)
+	{
+		this.turn = turnflag || "w";
 	}
 
 	///////////////////
 	// GETTERS, SETTERS
 
-	// Simple useful getters
-	static get size() { return [8,8]; }
+	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
-	getOppCol(color) { return color=="w" ? "b" : "w"; }
+	getOppCol(color) { return (color=="w" ? "b" : "w"); }
 
 	get lastMove() {
 		const L = this.moves.length;
-		return L>0 ? this.moves[L-1] : null;
-	}
-	get turn() {
-		return this.moves.length%2==0 ? 'w' : 'b';
+		return (L>0 ? this.moves[L-1] : null);
 	}
 
 	// Pieces codes
@@ -163,6 +222,11 @@ class ChessRules
 	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 ''; }
 
@@ -172,15 +236,25 @@ class ChessRules
 			'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] ],
-			'q': [ [-1,0],[1,0],[0,-1],[0,1],[-1,-1],[-1,1],[1,-1],[1,1] ]
 		};
 	}
 
+	// Aggregates flags into one object
+	get flags() {
+		return this.castleFlags;
+	}
+
+	// Reverse operation
+	parseFlags(flags)
+	{
+		this.castleFlags = flags;
+	}
+
 	// En-passant square, if any
 	getEpSquare(move)
 	{
 		const [sx,sy,ex] = [move.start.x,move.start.y,move.end.x];
-		if (this.getPiece(sx,sy) == VariantRules.PAWN && Math.abs(sx - ex) == 2)
+		if (this.getPiece(sx,sy) == V.PAWN && Math.abs(sx - ex) == 2)
 		{
 			return {
 				x: (sx + ex)/2,
@@ -190,10 +264,10 @@ class ChessRules
 		return undefined; //default
 	}
 
-	// can thing on square1 take thing on square2
+	// Can thing on square1 take thing on square2
 	canTake([x1,y1], [x2,y2])
 	{
-		return this.getColor(x1,y1) != this.getColor(x2,y2);
+		return this.getColor(x1,y1) !== this.getColor(x2,y2);
 	}
 
 	///////////////////
@@ -204,17 +278,17 @@ class ChessRules
 	{
 		switch (this.getPiece(x,y))
 		{
-			case VariantRules.PAWN:
+			case V.PAWN:
 				return this.getPotentialPawnMoves([x,y]);
-			case VariantRules.ROOK:
+			case V.ROOK:
 				return this.getPotentialRookMoves([x,y]);
-			case VariantRules.KNIGHT:
+			case V.KNIGHT:
 				return this.getPotentialKnightMoves([x,y]);
-			case VariantRules.BISHOP:
+			case V.BISHOP:
 				return this.getPotentialBishopMoves([x,y]);
-			case VariantRules.QUEEN:
+			case V.QUEEN:
 				return this.getPotentialQueenMoves([x,y]);
-			case VariantRules.KING:
+			case V.KING:
 				return this.getPotentialKingMoves([x,y]);
 		}
 	}
@@ -222,7 +296,7 @@ class ChessRules
 	// Build a regular move from its initial and destination squares; tr: transformation
 	getBasicMove([sx,sy], [ex,ey], tr)
 	{
-		var mv = new Move({
+		let mv = new Move({
 			appear: [
 				new PiPo({
 					x: ex,
@@ -242,7 +316,7 @@ class ChessRules
 		});
 
 		// The opponent piece disappears if we take it
-		if (this.board[ex][ey] != VariantRules.EMPTY)
+		if (this.board[ex][ey] != V.EMPTY)
 		{
 			mv.vanish.push(
 				new PiPo({
@@ -256,18 +330,23 @@ 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")
 	getSlideNJumpMoves([x,y], steps, oneStep)
 	{
 		const color = this.getColor(x,y);
-		var moves = [];
-		const [sizeX,sizeY] = VariantRules.size;
+		let moves = [];
 		outerLoop:
 		for (let step of steps)
 		{
 			let i = x + step[0];
 			let j = y + step[1];
-			while (i>=0 && i<sizeX && j>=0 && j<sizeY && this.board[i][j] == VariantRules.EMPTY)
+			while (V.OnBoard(i,j) && this.board[i][j] == V.EMPTY)
 			{
 				moves.push(this.getBasicMove([x,y], [i,j]));
 				if (oneStep !== undefined)
@@ -275,22 +354,22 @@ class ChessRules
 				i += step[0];
 				j += step[1];
 			}
-			if (i>=0 && i<8 && j>=0 && j<8 && this.canTake([x,y], [i,j]))
+			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 considering color "color" ?
+	// What are the pawn moves from square x,y ?
 	getPotentialPawnMoves([x,y])
 	{
-		const color = this.getColor(x,y);
-		var moves = [];
-		var V = VariantRules;
-		const [sizeX,sizeY] = VariantRules.size;
-		let shift = (color == "w" ? -1 : 1);
-		let startRank = (color == "w" ? sizeY-2 : 1);
-		let lastRank = (color == "w" ? 0 : sizeY-1);
+		const color = this.turn;
+		let moves = [];
+		const [sizeX,sizeY] = [V.size.x,V.size.y];
+		const shift = (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);
 
 		if (x+shift >= 0 && x+shift < sizeX && x+shift != lastRank)
 		{
@@ -298,42 +377,56 @@ class ChessRules
 			if (this.board[x+shift][y] == V.EMPTY)
 			{
 				moves.push(this.getBasicMove([x,y], [x+shift,y]));
-				if (x==startRank && this.board[x+2*shift][y] == V.EMPTY)
+				// 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)
 				{
 					// Two squares jump
 					moves.push(this.getBasicMove([x,y], [x+2*shift,y]));
 				}
 			}
 			// Captures
-			if (y>0 && this.canTake([x,y], [x+shift,y-1]) && this.board[x+shift][y-1] != V.EMPTY)
+			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.canTake([x,y], [x+shift,y+1]) && this.board[x+shift][y+1] != V.EMPTY)
+			}
+			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]));
+			}
 		}
 
 		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:color,p:p}));
+					moves.push(this.getBasicMove([x,y], [x+shift,y], {c:pawnColor,p:p}));
 				// Captures
-				if (y>0 && this.canTake([x,y], [x+shift,y-1]) && this.board[x+shift][y-1] != V.EMPTY)
-					moves.push(this.getBasicMove([x,y], [x+shift,y-1], {c:color,p:p}));
-				if (y<sizeY-1 && this.canTake([x,y], [x+shift,y+1]) && this.board[x+shift][y+1] != V.EMPTY)
-					moves.push(this.getBasicMove([x,y], [x+shift,y+1], {c:color,p:p}));
+				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], {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}));
+				}
 			});
 		}
 
 		// En passant
 		const Lep = this.epSquares.length;
-		const epSquare = Lep>0 ? this.epSquares[Lep-1] : undefined;
+		const epSquare = (Lep>0 ? this.epSquares[Lep-1] : undefined);
 		if (!!epSquare && epSquare.x == x+shift && Math.abs(epSquare.y - y) == 1)
 		{
-			let epStep = epSquare.y - y;
-			var enpassantMove = this.getBasicMove([x,y], [x+shift,y+epStep]);
+			const epStep = epSquare.y - y;
+			let enpassantMove = this.getBasicMove([x,y], [x+shift,y+epStep]);
 			enpassantMove.vanish.push({
 				x: x,
 				y: y+epStep,
@@ -349,52 +442,51 @@ class ChessRules
 	// What are the rook moves from square x,y ?
 	getPotentialRookMoves(sq)
 	{
-		return this.getSlideNJumpMoves(sq, VariantRules.steps[VariantRules.ROOK]);
+		return this.getSlideNJumpMoves(sq, V.steps[V.ROOK]);
 	}
 
 	// What are the knight moves from square x,y ?
 	getPotentialKnightMoves(sq)
 	{
-		return this.getSlideNJumpMoves(sq, VariantRules.steps[VariantRules.KNIGHT], "oneStep");
+		return this.getSlideNJumpMoves(sq, V.steps[V.KNIGHT], "oneStep");
 	}
 
 	// What are the bishop moves from square x,y ?
 	getPotentialBishopMoves(sq)
 	{
-		return this.getSlideNJumpMoves(sq, VariantRules.steps[VariantRules.BISHOP]);
+		return this.getSlideNJumpMoves(sq, V.steps[V.BISHOP]);
 	}
 
 	// What are the queen moves from square x,y ?
 	getPotentialQueenMoves(sq)
 	{
-		return this.getSlideNJumpMoves(sq, VariantRules.steps[VariantRules.QUEEN]);
+		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, VariantRules.steps[VariantRules.QUEEN], "oneStep");
+		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" ? 7 : 0) || y != this.INIT_COL_KING[c])
+		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)
 
-		const V = VariantRules;
-
 		// Castling ?
 		const oppCol = this.getOppCol(c);
 		let moves = [];
 		let i = 0;
-		const finalSquares = [ [2,3], [6,5] ]; //king, then rook
+		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.flags[c][castleSide])
+			if (!this.castleFlags[c][castleSide])
 				continue;
 			// If this code is reached, rooks and king are on initial position
 
@@ -402,7 +494,7 @@ class ChessRules
 			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 &&
+				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)))))
 				{
@@ -452,8 +544,7 @@ class ChessRules
 
 	canIplay(side, [x,y])
 	{
-		return ((side=='w' && this.moves.length%2==0) || (side=='b' && this.moves.length%2==1))
-			&& this.getColor(x,y) == side;
+		return (this.turn == side && this.getColor(x,y) == side);
 	}
 
 	getPossibleMovesFrom(sq)
@@ -462,13 +553,12 @@ class ChessRules
 		return this.filterValid( this.getPotentialMovesFrom(sq) );
 	}
 
-	// TODO: once a promotion is filtered, the others results are same: useless computations
+	// TODO: promotions (into R,B,N,Q) should be filtered only once
 	filterValid(moves)
 	{
 		if (moves.length == 0)
 			return [];
-		let color = this.turn;
-		return moves.filter(m => { return !this.underCheck(m, color); });
+		return moves.filter(m => { return !this.underCheck(m); });
 	}
 
 	// Search for all valid moves considering current turn (for engine and game end)
@@ -476,14 +566,13 @@ class ChessRules
 	{
 		const color = this.turn;
 		const oppCol = this.getOppCol(color);
-		var potentialMoves = [];
-		let [sizeX,sizeY] = VariantRules.size;
-		for (var i=0; i<sizeX; i++)
+		let potentialMoves = [];
+		for (let i=0; i<V.size.x; i++)
 		{
-			for (var j=0; j<sizeY; j++)
+			for (let j=0; j<V.size.y; j++)
 			{
-				// Next condition ... != oppCol is a little HACK to work with checkered variant
-				if (this.board[i][j] != VariantRules.EMPTY && this.getColor(i,j) != oppCol)
+				// Next condition "!= oppCol" = harmless hack 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]));
 			}
 		}
@@ -491,25 +580,24 @@ class ChessRules
 		// No: if happen on last 1/2 move, could lead to forbidden moves, wrong evals
 		return this.filterValid(potentialMoves);
 	}
-	
+
 	// Stop at the first move found
 	atLeastOneMove()
 	{
 		const color = this.turn;
 		const oppCol = this.getOppCol(color);
-		let [sizeX,sizeY] = VariantRules.size;
-		for (var i=0; i<sizeX; i++)
+		for (let i=0; i<V.size.x; i++)
 		{
-			for (var j=0; j<sizeY; j++)
+			for (let j=0; j<V.size.y; j++)
 			{
-				if (this.board[i][j] != VariantRules.EMPTY && this.getColor(i,j) != oppCol)
+				if (this.board[i][j] != V.EMPTY && this.getColor(i,j) != oppCol)
 				{
 					const moves = this.getPotentialMovesFrom([i,j]);
 					if (moves.length > 0)
 					{
-						for (let i=0; i<moves.length; i++)
+						for (let k=0; k<moves.length; k++)
 						{
-							if (this.filterValid([moves[i]]).length > 0)
+							if (this.filterValid([moves[k]]).length > 0)
 								return true;
 						}
 					}
@@ -519,7 +607,7 @@ class ChessRules
 		return false;
 	}
 
-	// Check if pieces of color 'colors' are attacking square x,y
+	// Check if pieces of color in array 'colors' are attacking square x,y
 	isAttacked(sq, colors)
 	{
 		return (this.isAttackedByPawn(sq, colors)
@@ -530,17 +618,17 @@ class ChessRules
 			|| this.isAttackedByKing(sq, colors));
 	}
 
-	// Is square x,y attacked by pawns of color c ?
+	// 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<8)
+			if (x+pawnShift>=0 && x+pawnShift<V.size.x)
 			{
 				for (let i of [-1,1])
 				{
-					if (y+i>=0 && y+i<8 && this.getPiece(x+pawnShift,y+i)==VariantRules.PAWN
+					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;
@@ -551,55 +639,53 @@ class ChessRules
 		return false;
 	}
 
-	// Is square x,y attacked by rooks of color c ?
+	// Is square x,y attacked by 'colors' rooks ?
 	isAttackedByRook(sq, colors)
 	{
-		return this.isAttackedBySlideNJump(sq, colors,
-			VariantRules.ROOK, VariantRules.steps[VariantRules.ROOK]);
+		return this.isAttackedBySlideNJump(sq, colors, V.ROOK, V.steps[V.ROOK]);
 	}
 
-	// Is square x,y attacked by knights of color c ?
+	// Is square x,y attacked by 'colors' knights ?
 	isAttackedByKnight(sq, colors)
 	{
 		return this.isAttackedBySlideNJump(sq, colors,
-			VariantRules.KNIGHT, VariantRules.steps[VariantRules.KNIGHT], "oneStep");
+			V.KNIGHT, V.steps[V.KNIGHT], "oneStep");
 	}
 
-	// Is square x,y attacked by bishops of color c ?
+	// Is square x,y attacked by 'colors' bishops ?
 	isAttackedByBishop(sq, colors)
 	{
-		return this.isAttackedBySlideNJump(sq, colors,
-			VariantRules.BISHOP, VariantRules.steps[VariantRules.BISHOP]);
+		return this.isAttackedBySlideNJump(sq, colors, V.BISHOP, V.steps[V.BISHOP]);
 	}
 
-	// Is square x,y attacked by queens of color c ?
+	// Is square x,y attacked by 'colors' queens ?
 	isAttackedByQueen(sq, colors)
 	{
-		return this.isAttackedBySlideNJump(sq, colors,
-			VariantRules.QUEEN, VariantRules.steps[VariantRules.QUEEN]);
+		return this.isAttackedBySlideNJump(sq, colors, V.QUEEN,
+			V.steps[V.ROOK].concat(V.steps[V.BISHOP]));
 	}
 
-	// Is square x,y attacked by king of color c ?
+	// Is square x,y attacked by 'colors' king(s) ?
 	isAttackedByKing(sq, colors)
 	{
-		return this.isAttackedBySlideNJump(sq, colors,
-			VariantRules.KING, VariantRules.steps[VariantRules.QUEEN], "oneStep");
+		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 piece != color ?
+	// 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 (rx>=0 && rx<8 && ry>=0 && ry<8 && this.board[rx][ry] == VariantRules.EMPTY
-				&& !oneStep)
+			while (V.OnBoard(rx,ry) && this.board[rx][ry] == V.EMPTY && !oneStep)
 			{
 				rx += step[0];
 				ry += step[1];
 			}
-			if (rx>=0 && rx<8 && ry>=0 && ry<8 && this.board[rx][ry] != VariantRules.EMPTY
-				&& this.getPiece(rx,ry) == piece && colors.includes(this.getColor(rx,ry)))
+			if (V.OnBoard(rx,ry) && this.getPiece(rx,ry) === piece
+				&& colors.includes(this.getColor(rx,ry)))
 			{
 				return true;
 			}
@@ -607,22 +693,22 @@ class ChessRules
 		return false;
 	}
 
-	// Is color c under check after move ?
+	// Is current player under check after his move ?
 	underCheck(move)
 	{
 		const color = this.turn;
 		this.play(move);
-		let res = this.isAttacked(this.kingPos[color], this.getOppCol(color));
+		let res = this.isAttacked(this.kingPos[color], [this.getOppCol(color)]);
 		this.undo(move);
 		return res;
 	}
 
-	// On which squares is color c under check (after move) ?
+	// 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))
+		let res = this.isAttacked(this.kingPos[color], [this.getOppCol(color)])
 			? [ JSON.parse(JSON.stringify(this.kingPos[color])) ] //need to duplicate!
 			: [ ];
 		this.undo(move);
@@ -633,7 +719,7 @@ class ChessRules
 	static PlayOnBoard(board, move)
 	{
 		for (let psq of move.vanish)
-			board[psq.x][psq.y] = VariantRules.EMPTY;
+			board[psq.x][psq.y] = V.EMPTY;
 		for (let psq of move.appear)
 			board[psq.x][psq.y] = psq.c + psq.p;
 	}
@@ -641,7 +727,7 @@ class ChessRules
 	static UndoOnBoard(board, move)
 	{
 		for (let psq of move.appear)
-			board[psq.x][psq.y] = VariantRules.EMPTY;
+			board[psq.x][psq.y] = V.EMPTY;
 		for (let psq of move.vanish)
 			board[psq.x][psq.y] = psq.c + psq.p;
 	}
@@ -650,87 +736,113 @@ class ChessRules
 	updateVariables(move)
 	{
 		const piece = this.getPiece(move.start.x,move.start.y);
-		const c = this.getColor(move.start.x,move.start.y);
-		const firstRank = (c == "w" ? 7 : 0);
+		const c = this.turn;
+		const firstRank = (c == "w" ? V.size.x-1 : 0);
 
 		// Update king position + flags
-		if (piece == VariantRules.KING && move.appear.length > 0)
+		if (piece == V.KING && move.appear.length > 0)
 		{
 			this.kingPos[c][0] = move.appear[0].x;
 			this.kingPos[c][1] = move.appear[0].y;
-			this.flags[c] = [false,false];
+			this.castleFlags[c] = [false,false];
 			return;
 		}
 		const oppCol = this.getOppCol(c);
-		const oppFirstRank = 7 - firstRank;
+		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.flags[c][flagIdx] = false;
+			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[c].includes(move.end.y))
+			&& this.INIT_COL_ROOK[oppCol].includes(move.end.y))
 		{
-			const flagIdx = move.end.y == this.INIT_COL_ROOK[oppCol][0] ? 0 : 1;
-			this.flags[oppCol][flagIdx] = false;
+			const flagIdx = (move.end.y == this.INIT_COL_ROOK[oppCol][0] ? 0 : 1);
+			this.castleFlags[oppCol][flagIdx] = false;
 		}
 	}
 
+	// After move is undo-ed, un-update variables (flags are reset)
+	// 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) == VariantRules.KING)
+		if (this.getPiece(move.start.x,move.start.y) == V.KING)
 			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)
-			move.notation = this.getNotation(move);
+			move.notation = [this.getNotation(move), this.getLongNotation(move)];
 
-		// Save flags (for undo)
-		move.flags = JSON.stringify(this.flags); //TODO: less costly?
+		move.flags = JSON.stringify(this.flags); //save flags (for undo)
 		this.updateVariables(move);
 		this.moves.push(move);
 		this.epSquares.push( this.getEpSquare(move) );
-		VariantRules.PlayOnBoard(this.board, move);
+		V.PlayOnBoard(this.board, move);
+
+		if (!!ingame)
+			move.hash = this.getHashState();
 	}
 
 	undo(move)
 	{
-		VariantRules.UndoOnBoard(this.board, move);
+		V.UndoOnBoard(this.board, move);
 		this.epSquares.pop();
 		this.moves.pop();
 		this.unupdateVariables(move);
-		this.flags = JSON.parse(move.flags);
+		this.parseFlags(JSON.parse(move.flags));
+
+		// DEBUG:
+//		if (JSON.stringify(this.board) != this.states[this.states.length-1])
+//			debugger;
+//		this.states.pop();
 	}
 
 	//////////////
 	// END OF GAME
 
-	checkGameOver()
+	// Check for 3 repetitions (position + flags + turn)
+	checkRepetition()
 	{
-		// Check for 3 repetitions
-		if (this.moves.length >= 8)
+		if (!this.hashStates)
+			this.hashStates = {};
+		const startIndex =
+			Object.values(this.hashStates).reduce((a,b) => { return a+b; }, 0)
+		// Update this.hashStates with last move (or all moves if continuation)
+		// NOTE: redundant storage, but faster and moderate size
+		for (let i=startIndex; i<this.moves.length; i++)
 		{
-			// NOTE: crude detection, only moves repetition
-			const L = this.moves.length;
-			if (_.isEqual(this.moves[L-1], this.moves[L-5]) &&
-				_.isEqual(this.moves[L-2], this.moves[L-6]) &&
-				_.isEqual(this.moves[L-3], this.moves[L-7]) &&
-				_.isEqual(this.moves[L-4], this.moves[L-8]))
-			{
-				return "1/2 (repetition)";
-			}
+			const move = this.moves[i];
+			if (!this.hashStates[move.hash])
+				this.hashStates[move.hash] = 1;
+			else
+				this.hashStates[move.hash]++;
 		}
+		return Object.values(this.hashStates).some(elt => { return (elt >= 3); });
+	}
 
-		if (this.atLeastOneMove())
-		{
-			// game not over
+	// Is game over ? And if yes, what is the score ?
+	checkGameOver()
+	{
+		if (this.checkRepetition())
+			return "1/2";
+
+		if (this.atLeastOneMove()) // game not over
 			return "*";
-		}
 
 		// Game over
 		return this.checkGameEnd();
@@ -741,7 +853,7 @@ class ChessRules
 	{
 		const color = this.turn;
 		// No valid move: stalemate or checkmate?
-		if (!this.isAttacked(this.kingPos[color], this.getOppCol(color)))
+		if (!this.isAttacked(this.kingPos[color], [this.getOppCol(color)]))
 			return "1/2";
 		// OK, checkmate
 		return color == "w" ? "0-1" : "1-0";
@@ -762,72 +874,141 @@ class ChessRules
 		};
 	}
 
+	static get INFINITY() {
+		return 9999; //"checkmate" (unreachable eval)
+	}
+
+	static get THRESHOLD_MATE() {
+		// At this value or above, the game is over
+		return V.INFINITY;
+	}
+
+	static get SEARCH_DEPTH() {
+		return 3; //2 for high branching factor, 4 for small (Loser chess)
+	}
+
 	// 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");
 
-		// Rank moves using a min-max at depth 2
-		let moves1 = this.getAllValidMoves();
-
-		for (let i=0; i<moves1.length; i++)
+		// Can I mate in 1 ? (for Magnetic & Extinction)
+		for (let i of _.shuffle(_.range(moves1.length)))
 		{
-			moves1[i].eval = (color=="w" ? -1 : 1) * 1000; //very low, I'm checkmated
-			let eval2 = (color=="w" ? 1 : -1) * 1000; //initialized with very high (checkmate) value
 			this.play(moves1[i]);
-			// Second half-move:
-			let moves2 = this.getAllValidMoves();
-			// If no possible moves AND underCheck, eval2 is correct.
-			// If !underCheck, eval2 is 0 (stalemate).
-			if (moves2.length == 0 && this.checkGameEnd() == "1/2")
-				eval2 = 0;
-			for (let j=0; j<moves2.length; j++)
+			let finish = (Math.abs(this.evalPosition()) >= V.THRESHOLD_MATE);
+			if (!finish && !this.atLeastOneMove())
 			{
-				this.play(moves2[j]);
-				let evalPos = this.evalPosition();
-				if ((color == "w" && evalPos < eval2) || (color=="b" && evalPos > eval2))
-					eval2 = evalPos;
-				this.undo(moves2[j]);
+				// Try mate (for other variants)
+				const score = this.checkGameEnd();
+				if (score != "1/2")
+					finish = true;
 			}
-			if ((color=="w" && eval2 > moves1[i].eval) || (color=="b" && eval2 < moves1[i].eval))
-				moves1[i].eval = eval2;
 			this.undo(moves1[i]);
+			if (finish)
+				return moves1[i];
 		}
-		moves1.sort( (a,b) => { return (color=="w" ? 1 : -1) * (b.eval - a.eval); });
 
-		// TODO: show current analyzed move for depth 3, allow stopping eval (return moves1[0])
+		// 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
 			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(2, -1000, 1000);
+			let eval2 = undefined;
+			if (this.atLeastOneMove())
+			{
+				eval2 = (color=="w" ? 1 : -1) * maxeval; //initialized with checkmate value
+				// Second half-move:
+				let moves2 = this.getAllValidMoves("computer");
+				for (let j=0; j<moves2.length; j++)
+				{
+					this.play(moves2[j]);
+					let evalPos = undefined;
+					if (this.atLeastOneMove())
+						evalPos = this.evalPosition()
+					else
+					{
+						// Work with scores 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))
+						eval2 = evalPos;
+					this.undo(moves2[j]);
+				}
+			}
+			else
+			{
+				const score = this.checkGameEnd();
+				eval2 = (score=="1/2" ? 0 : (score=="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); });
+		//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++)
 			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;
 		if (!this.atLeastOneMove())
 		{
 			switch (this.checkGameEnd())
 			{
-				case "1/2": return 0;
-				default: return color=="w" ? -1000 : 1000;
+				case "1/2":
+					return 0;
+				default:
+					const score = this.checkGameEnd();
+					return (score=="1/2" ? 0 : (score=="1-0" ? 1 : -1) * maxeval);
 			}
 		}
 		if (depth == 0)
       return this.evalPosition();
-		const moves = this.getAllValidMoves();
-    let v = color=="w" ? -1000 : 1000;
+		const moves = this.getAllValidMoves("computer");
+    let v = color=="w" ? -maxeval : maxeval;
 		if (color == "w")
 		{
 			for (let i=0; i<moves.length; i++)
@@ -857,17 +1038,16 @@ class ChessRules
 
 	evalPosition()
 	{
-		const [sizeX,sizeY] = VariantRules.size;
 		let evaluation = 0;
-		//Just count material for now
-		for (let i=0; i<sizeX; i++)
+		// Just count material for now
+		for (let i=0; i<V.size.x; i++)
 		{
-			for (let j=0; j<sizeY; j++)
+			for (let j=0; j<V.size.y; j++)
 			{
-				if (this.board[i][j] != VariantRules.EMPTY)
+				if (this.board[i][j] != V.EMPTY)
 				{
 					const sign = this.getColor(i,j) == "w" ? 1 : -1;
-					evaluation += sign * VariantRules.VALUES[this.getPiece(i,j)];
+					evaluation += sign * V.VALUES[this.getPiece(i,j)];
 				}
 			}
 		}
@@ -877,12 +1057,12 @@ class ChessRules
 	////////////
 	// FEN utils
 
-	// Overridable..
+	// Setup the initial random (assymetric) position
 	static GenRandInitFen()
 	{
-		let pieces = [new Array(8), new Array(8)];
+		let pieces = { "w": new Array(8), "b": new Array(8) };
 		// Shuffle pieces on first and last rank
-		for (let c = 0; c <= 1; c++)
+		for (let c of ["w","b"])
 		{
 			let positions = _.range(8);
 
@@ -924,29 +1104,28 @@ class ChessRules
 			pieces[c][knight2Pos] = 'n';
 			pieces[c][rook2Pos] = 'r';
 		}
-		let fen = pieces[0].join("") +
+		return pieces["b"].join("") +
 			"/pppppppp/8/8/8/8/PPPPPPPP/" +
-			pieces[1].join("").toUpperCase() +
+			pieces["w"].join("").toUpperCase() +
 			" 1111"; //add flags
-		return fen;
 	}
 
 	// Return current fen according to pieces+colors state
 	getFen()
 	{
-		return this.getBaseFen() + " " + this.getFlagsFen();
+		return this.getBaseFen() + " " + this.getFlagsFen() + " " + this.turn;
 	}
 
+	// Position part of the FEN string
 	getBaseFen()
 	{
 		let fen = "";
-		let [sizeX,sizeY] = VariantRules.size;
-		for (let i=0; i<sizeX; i++)
+		for (let i=0; i<V.size.x; i++)
 		{
 			let emptyCount = 0;
-			for (let j=0; j<sizeY; j++)
+			for (let j=0; j<V.size.y; j++)
 			{
-				if (this.board[i][j] == VariantRules.EMPTY)
+				if (this.board[i][j] == V.EMPTY)
 					emptyCount++;
 				else
 				{
@@ -956,7 +1135,7 @@ class ChessRules
 						fen += emptyCount;
 						emptyCount = 0;
 					}
-					fen += VariantRules.board2fen(this.board[i][j]);
+					fen += V.board2fen(this.board[i][j]);
 				}
 			}
 			if (emptyCount > 0)
@@ -964,13 +1143,13 @@ class ChessRules
 				// "Flush remainder"
 				fen += emptyCount;
 			}
-			if (i < sizeX - 1)
+			if (i < V.size.x - 1)
 				fen += "/"; //separate rows
 		}
 		return fen;
 	}
 
-	// Overridable..
+	// Flags part of the FEN string
 	getFlagsFen()
 	{
 		let fen = "";
@@ -978,7 +1157,7 @@ class ChessRules
 		for (let i of ['w','b'])
 		{
 			for (let j=0; j<2; j++)
-				fen += this.flags[i][j] ? '1' : '0';
+				fen += (this.castleFlags[i][j] ? '1' : '0');
 		}
 		return fen;
 	}
@@ -986,28 +1165,21 @@ class ChessRules
 	// Context: just before move is played, turn hasn't changed
 	getNotation(move)
 	{
-		if (move.appear.length == 2)
-		{
-			// Castle
-			if (move.end.y < move.start.y)
-				return "0-0-0";
-			else
-				return "0-0";
-		}
+		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
-		let finalSquare =
-			String.fromCharCode(97 + move.end.y) + (VariantRules.size[0]-move.end.x);
+		const finalSquare = String.fromCharCode(97 + move.end.y) + (V.size.x-move.end.x);
 
-		let piece = this.getPiece(move.start.x, move.start.y);
-		if (piece == VariantRules.PAWN)
+		const piece = this.getPiece(move.start.x, move.start.y);
+		if (piece == V.PAWN)
 		{
 			// Pawn move
 			let notation = "";
-			if (move.vanish.length > 1)
+			if (move.vanish.length > move.appear.length)
 			{
 				// Capture
-				let startColumn = String.fromCharCode(97 + move.start.y);
+				const startColumn = String.fromCharCode(97 + move.start.y);
 				notation = startColumn + "x" + finalSquare;
 			}
 			else //no capture
@@ -1020,31 +1192,54 @@ class ChessRules
 		else
 		{
 			// Piece movement
-			return piece.toUpperCase() + (move.vanish.length > 1 ? "x" : "") + finalSquare;
+			return piece.toUpperCase() +
+				(move.vanish.length > move.appear.length ? "x" : "") + finalSquare;
 		}
 	}
 
+	// 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
+	}
+
 	// The score is already computed when calling this function
 	getPGN(mycolor, score, fenStart, mode)
 	{
+		const zeroPad = x => { return (x<10 ? "0" : "") + x; };
 		let pgn = "";
 		pgn += '[Site "vchess.club"]<br>';
 		const d = new Date();
 		const opponent = mode=="human" ? "Anonymous" : "Computer";
-		pgn += '[Date "' + d.getFullYear() + '-' + (d.getMonth()+1) + '-' + d.getDate() + '"]<br>';
+		pgn += '[Variant "' + variant + '"]<br>';
+		pgn += '[Date "' + d.getFullYear() + '-' + (d.getMonth()+1) +
+			'-' + zeroPad(d.getDate()) + '"]<br>';
 		pgn += '[White "' + (mycolor=='w'?'Myself':opponent) + '"]<br>';
 		pgn += '[Black "' + (mycolor=='b'?'Myself':opponent) + '"]<br>';
-		pgn += '[Fen "' + fenStart + '"]<br>';
+		pgn += '[FenStart "' + fenStart + '"]<br>';
+		pgn += '[Fen "' + this.getFen() + '"]<br>';
 		pgn += '[Result "' + score + '"]<br><br>';
 
+		// Standard PGN
+		for (let i=0; i<this.moves.length; i++)
+		{
+			if (i % 2 == 0)
+				pgn += ((i/2)+1) + ".";
+			pgn += this.moves[i].notation[0] + " ";
+		}
+		pgn += "<br><br>";
+
+		// "Complete moves" PGN (helping in ambiguous cases)
 		for (let i=0; i<this.moves.length; i++)
 		{
 			if (i % 2 == 0)
 				pgn += ((i/2)+1) + ".";
-			pgn += this.moves[i].notation + " ";
+			pgn += this.moves[i].notation[1] + " ";
 		}
 
-		pgn += score;
 		return pgn;
 	}
 }