X-Git-Url: https://git.auder.net/?p=vchess.git;a=blobdiff_plain;f=public%2Fjavascripts%2Fbase_rules.js;h=e405cbaa4e595da56210f09a7e0920c27c406be1;hp=26c744777c1b4a4b77f311363e372ce2dd63a3bb;hb=b6487fb9c41705187cf97215fc9e8f86a59057c7;hpb=3c09dc498791ac478679bf2f42f441342c4fa22c

diff --git a/public/javascripts/base_rules.js b/public/javascripts/base_rules.js
index 26c74477..e405cbaa 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,]}
@@ -27,48 +31,403 @@ 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;
 	}
 
-	/////////////////
+	// 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], [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],
+			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 == "position flags"
-	constructor(fen, moves)
+	// Fen string fully describes the game state
+	constructor(fen)
 	{
-		this.moves = moves;
-		// Use fen string to initialize variables, flags and board
-		this.board = VariantRules.GetBoard(fen);
-		this.setFlags(fen);
-		this.initVariables(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);
 	}
 
-	initVariables(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]}; //respective squares of white and black king
-		const fenParts = fen.split(" ");
-		const position = fenParts[0].split("/");
-		for (let i=0; i<position.length; i++)
+		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<position[i].length; j++)
+			for (let j=0; j<fenRows[i].length; j++)
 			{
-				switch (position[i].charAt(j))
+				switch (fenRows[i].charAt(j))
 				{
 					case 'k':
 						this.kingPos['b'] = [i,k];
@@ -91,70 +450,60 @@ class ChessRules
 							this.INIT_COL_ROOK['w'][1] = k;
 						break;
 					default:
-						let num = parseInt(position[i].charAt(j));
+						const num = parseInt(fenRows[i].charAt(j));
 						if (!isNaN(num))
 							k += (num-1);
 				}
 				k++;
 			}
 		}
-		const epSq = this.moves.length > 0 ? this.getEpSquare(this.lastMove) : undefined;
-		this.epSquares = [ epSq ];
 	}
 
-	// Turn diagram fen into double array ["wb","wp","bk",...]
-	static GetBoard(fen)
+	// Some additional variables from FEN (variant dependant)
+	setOtherVariables(fen)
 	{
-		let rows = fen.split(" ")[0].split("/");
-		const [sizeX,sizeY] = VariantRules.size;
-		let board = doubleArray(sizeX, sizeY, "");
-		for (let i=0; i<rows.length; i++)
+		// Set flags and enpassant:
+		const parsedFen = V.ParseFen(fen);
+		if (V.HasFlags)
+			this.setFlags(parsedFen.flags);
+		if (V.HasEnpassant)
 		{
-			let j = 0;
-			for (let indexInRow = 0; indexInRow < rows[i].length; indexInRow++)
-			{
-				let character = rows[i][indexInRow];
-				let num = parseInt(character);
-				if (!isNaN(num))
-					j += num; //just shift j
-				else //something at position i,j
-					board[i][j++] = VariantRules.fen2board(character);
-			}
+			const epSq = parsedFen.enpassant != "-"
+				? V.SquareToCoords(parsedFen.enpassant)
+				: undefined;
+			this.epSquares = [ epSq ];
 		}
-		return board;
+		// Search for king and rooks positions:
+		this.scanKingsRooks(fen);
 	}
 
-	// Overridable: flags can change a lot
-	setFlags(fen)
+	/////////////////////
+	// GETTERS & SETTERS
+
+	static get size()
 	{
-		// white a-castle, h-castle, black a-castle, h-castle
-		this.castleFlags = {'w': new Array(2), 'b': new Array(2)};
-		let flags = fen.split(" ")[1]; //flags right after position
-		for (let i=0; i<4; i++)
-			this.castleFlags[i < 2 ? 'w' : 'b'][i%2] = (flags.charAt(i) == '1');
+		return {x:8, y:8};
 	}
 
-	///////////////////
-	// GETTERS, SETTERS
-
-	// Simple useful getters
-	static get size() { return [8,8]; }
-	// 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"; }
+	// Color of thing on suqare (i,j). 'undefined' if square is empty
+	getColor(i,j)
+	{
+		return this.board[i][j].charAt(0);
+	}
 
-	get lastMove() {
-		const L = this.moves.length;
-		return L>0 ? this.moves[L-1] : null;
+	// Piece type on square (i,j). 'undefined' if square is empty
+	getPiece(i,j)
+	{
+		return this.board[i][j].charAt(1);
 	}
-	get turn() {
-		return this.moves.length%2==0 ? 'w' : 'b';
+
+	// Get opponent color
+	getOppCol(color)
+	{
+		return (color=="w" ? "b" : "w");
 	}
 
-	// Pieces codes
+	// Pieces codes (for a clearer code)
 	static get PAWN() { return 'p'; }
 	static get ROOK() { return 'r'; }
 	static get KNIGHT() { return 'n'; }
@@ -162,11 +511,18 @@ 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 ''; }
+	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] ],
@@ -174,38 +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(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)
-		{
-			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)
@@ -213,22 +538,23 @@ 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]);
 		}
 	}
 
-	// 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({
@@ -251,7 +577,7 @@ 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({
@@ -265,18 +591,18 @@ class ChessRules
 		return mv;
 	}
 
-	// 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);
 		let moves = [];
-		const [sizeX,sizeY] = VariantRules.size;
 		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)
@@ -284,74 +610,78 @@ 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.turn;
 		let moves = [];
-		const V = VariantRules;
-		const [sizeX,sizeY] = VariantRules.size;
-		const shift = (color == "w" ? -1 : 1);
-		const firstRank = (color == 'w' ? sizeY-1 : 0);
-		const startRank = (color == "w" ? sizeY-2 : 1);
-		const lastRank = (color == "w" ? 0 : sizeY-1);
-
-		if (x+shift >= 0 && x+shift < sizeX && x+shift != lastRank)
+		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)
 		{
-			// 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 generally 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.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]));
-			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]));
-		}
-
-		if (x+shift == lastRank)
-		{
-			// Promotion
-			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}));
-				// 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}));
-			});
+			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}));
+					}
+				}
+			}
 		}
 
-		// 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)
 		{
-			let epStep = epSquare.y - y;
-			var 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;
@@ -360,32 +690,31 @@ 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)
 	{
-		const V = VariantRules;
-		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 ?
 	getPotentialKingMoves(sq)
 	{
-		const V = VariantRules;
 		// Initialize with normal moves
 		let moves = this.getSlideNJumpMoves(sq,
 			V.steps[V.ROOK].concat(V.steps[V.BISHOP]), "oneStep");
@@ -395,17 +724,14 @@ class ChessRules
 	getCastleMoves([x,y])
 	{
 		const c = this.getColor(x,y);
-		const [sizeX,sizeY] = VariantRules.size;
-		if (x != (c=="w" ? sizeX-1 : 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], [sizeY-2,sizeY-3] ]; //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
 		{
@@ -413,13 +739,15 @@ 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 &&
+				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;
 				}
@@ -462,47 +790,48 @@ class ChessRules
 		return moves;
 	}
 
-	///////////////////
+	////////////////////
 	// MOVES VALIDATION
 
-	canIplay(side, [x,y])
-	{
-		return ((side=='w' && this.moves.length%2==0) || (side=='b' && this.moves.length%2==1))
-			&& 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) );
 	}
 
-	// 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 [];
-		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;
 		const oppCol = this.getOppCol(color);
 		let potentialMoves = [];
-		const [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++)
 			{
-				// Next condition ... != oppCol is a little HACK to work with checkered variant
-				if (this.board[i][j] != VariantRules.EMPTY && this.getColor(i,j) != oppCol)
-					Array.prototype.push.apply(potentialMoves, this.getPotentialMovesFrom([i,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]));
+				}
 			}
 		}
-		// 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);
 	}
 
@@ -511,12 +840,11 @@ class ChessRules
 	{
 		const color = this.turn;
 		const oppCol = this.getOppCol(color);
-		const [sizeX,sizeY] = VariantRules.size;
-		for (let i=0; i<sizeX; i++)
+		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 && 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)
@@ -533,7 +861,7 @@ class ChessRules
 		return false;
 	}
 
-	// Check if pieces of color '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)
@@ -544,17 +872,17 @@ 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;
@@ -565,57 +893,53 @@ 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)
 	{
-		const V = VariantRules;
 		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)
 	{
-		const V = VariantRules;
 		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;
 			}
@@ -623,33 +947,20 @@ class ChessRules
 		return false;
 	}
 
-	// Is color c under check after 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 color c under check (after 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)
 	{
 		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;
 	}
@@ -657,48 +968,71 @@ 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;
 	}
 
-	// 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.getColor(move.start.x,move.start.y);
-		const [sizeX,sizeY] = VariantRules.size;
-		const firstRank = (c == "w" ? sizeX-1 : 0);
+		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 = this.getOppCol(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.castleFlags[c] = [false,false];
+			if (V.HasFlags)
+				this.castleFlags[c] = [false,false];
 			return;
 		}
-		const oppCol = this.getOppCol(c);
-		const oppFirstRank = (sizeX-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))
+		if (V.HasFlags)
 		{
-			const flagIdx = (move.end.y == this.INIT_COL_ROOK[oppCol][0] ? 0 : 1);
-			this.castleFlags[oppCol][flagIdx] = false;
+			// Update castling flags if rooks are moved
+			const oppCol = this.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) == VariantRules.KING)
+		if (this.getPiece(move.start.x,move.start.y) == V.KING)
 			this.kingPos[c] = [move.start.x, move.start.y];
 	}
 
@@ -706,58 +1040,50 @@ class ChessRules
 	{
 		// 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);
 
-		move.flags = JSON.stringify(this.flags); //save flags (for undo)
+		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.movesCount++;
 		this.updateVariables(move);
-		this.moves.push(move);
-		this.epSquares.push( this.getEpSquare(move) );
-		VariantRules.PlayOnBoard(this.board, move);
+
+		if (!!ingame)
+		{
+			// Hash of current game state *after move*, to detect repetitions
+			move.hash = hex_md5(this.getFen());
+		}
 	}
 
 	undo(move)
 	{
-		VariantRules.UndoOnBoard(this.board, move);
-		this.epSquares.pop();
-		this.moves.pop();
+		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.movesCount--;
 		this.unupdateVariables(move);
-		this.parseFlags(JSON.parse(move.flags));
 
 		// DEBUG:
-//		let state = this.states.pop();
-//		if (JSON.stringify(this.board) != state)
+//		if (this.getFen() != this.states[this.states.length-1])
 //			debugger;
+//		this.states.pop();
 	}
 
-	//////////////
+	///////////////
 	// END OF GAME
 
-	checkRepetition()
-	{
-		// Check for 3 repetitions
-		if (this.moves.length >= 8)
-		{
-			// 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 true;
-			}
-		}
-		return false;
-	}
-
+	// Is game over ? And if yes, what is the score ?
 	checkGameOver()
 	{
-		if (this.checkRepetition())
-			return "1/2";
-
 		if (this.atLeastOneMove()) // game not over
 			return "*";
 
@@ -770,17 +1096,18 @@ 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";
+		return (color == "w" ? "0-1" : "1-0");
 	}
 
-	////////
-	//ENGINE
+	///////////////
+	// ENGINE PLAY
 
 	// Pieces values
-	static get VALUES() {
+	static get VALUES()
+	{
 		return {
 			'p': 1,
 			'r': 5,
@@ -791,50 +1118,85 @@ 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 VariantRules.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
-	getComputerMove(moves1) //moves1 might be precomputed (Magnetic chess)
+	// NOTE: works also for extinction chess because depth is 3...
+	getComputerMove()
 	{
-		this.shouldReturn = false;
-		const maxeval = VariantRules.INFINITY;
+		const maxeval = V.INFINITY;
 		const color = this.turn;
-		if (!moves1)
-			moves1 = this.getAllValidMoves();
+		// 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 && !this.atLeastOneMove())
+			{
+				// Test mate (for other variants)
+				const score = this.checkGameEnd();
+				if (score != "1/2")
+					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++)
 		{
-			moves1[i].eval = (color=="w" ? -1 : 1) * maxeval; //very low, I'm checkmated
-			let eval2 = (color=="w" ? 1 : -1) * maxeval; //initialized with checkmate value
+			// Initial self evaluation is very low: "I'm checkmated"
+			moves1[i].eval = (color=="w" ? -1 : 1) * maxeval;
 			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 eval2 = undefined;
+			if (this.atLeastOneMove())
+			{
+				// 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]);
+					let evalPos = undefined;
+					if (this.atLeastOneMove())
+						evalPos = this.evalPosition()
+					else
+					{
+						// 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))
+					{
+						eval2 = evalPos;
+					}
+					this.undo(moves2[j]);
+				}
+			}
+			else
 			{
-				this.play(moves2[j]);
-				let evalPos = this.evalPosition();
-				if ((color == "w" && evalPos < eval2) || (color=="b" && evalPos > eval2))
-					eval2 = evalPos;
-				this.undo(moves2[j]);
+				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))
+			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); });
@@ -844,48 +1206,53 @@ class ChessRules
 			candidates.push(j);
 		let currentBest = moves1[_.sample(candidates, 1)];
 
-		// Skip depth 3 if we found a checkmate (or if we are checkmated in 1...)
-		if (VariantRules.SEARCH_DEPTH >= 3
-			&& Math.abs(moves1[0].eval) < VariantRules.THRESHOLD_MATE)
+		// 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)
 		{
-			// TODO: show current analyzed move for depth 3, allow stopping eval (return moves1[0])
 			for (let i=0; i<moves1.length; i++)
 			{
-				if (this.shouldReturn)
-					return currentBest; //depth-2, minimum
+				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(VariantRules.SEARCH_DEPTH-1, -maxeval, maxeval);
+					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;
+//		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);
-//		console.log(moves1.map(m => { return [this.getNotation(m), m.eval]; }));
 		return moves1[_.sample(candidates, 1)];
 	}
 
 	alphabeta(depth, alpha, beta)
   {
-		const maxeval = VariantRules.INFINITY;
+		const maxeval = V.INFINITY;
 		const color = this.turn;
 		if (!this.atLeastOneMove())
 		{
 			switch (this.checkGameEnd())
 			{
-				case "1/2": return 0;
-				default: return color=="w" ? -maxeval : maxeval;
+				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();
+		const moves = this.getAllValidMoves("computer");
     let v = color=="w" ? -maxeval : maxeval;
 		if (color == "w")
 		{
@@ -916,162 +1283,50 @@ 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)];
 				}
 			}
 		}
 		return evaluation;
 	}
 
-	////////////
-	// FEN utils
-
-	// Overridable..
-	static GenRandInitFen()
-	{
-		let pieces = [new Array(8), new Array(8)];
-		// Shuffle pieces on first and last rank
-		for (let c = 0; c <= 1; c++)
-		{
-			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';
-		}
-		let fen = pieces[0].join("") +
-			"/pppppppp/8/8/8/8/PPPPPPPP/" +
-			pieces[1].join("").toUpperCase() +
-			" 1111"; //add flags
-		return fen;
-	}
-
-	// Return current fen according to pieces+colors state
-	getFen()
-	{
-		return this.getBaseFen() + " " + this.getFlagsFen();
-	}
-
-	getBaseFen()
-	{
-		let fen = "";
-		let [sizeX,sizeY] = VariantRules.size;
-		for (let i=0; i<sizeX; i++)
-		{
-			let emptyCount = 0;
-			for (let j=0; j<sizeY; j++)
-			{
-				if (this.board[i][j] == VariantRules.EMPTY)
-					emptyCount++;
-				else
-				{
-					if (emptyCount > 0)
-					{
-						// Add empty squares in-between
-						fen += emptyCount;
-						emptyCount = 0;
-					}
-					fen += VariantRules.board2fen(this.board[i][j]);
-				}
-			}
-			if (emptyCount > 0)
-			{
-				// "Flush remainder"
-				fen += emptyCount;
-			}
-			if (i < sizeX - 1)
-				fen += "/"; //separate rows
-		}
-		return fen;
-	}
-
-	// Overridable..
-	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
+	// TODO: un-ambiguous notation (switch on piece type, check directions...)
 	getNotation(move)
 	{
-		if (move.appear.length == 2 && move.appear[0].p == VariantRules.KING)
-		{
-			// 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
-		const finalSquare =
-			String.fromCharCode(97 + move.end.y) + (VariantRules.size[0]-move.end.x);
+		const finalSquare = V.CoordsToSquare(move.end);
 
 		const piece = this.getPiece(move.start.x, move.start.y);
-		if (piece == VariantRules.PAWN)
+		if (piece == V.PAWN)
 		{
 			// Pawn move
 			let notation = "";
 			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;
 		}
@@ -1084,28 +1339,41 @@ class ChessRules
 		}
 	}
 
+	// Complete the usual notation, may be required for de-ambiguification
+	getLongNotation(move)
+	{
+		// 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
-	getPGN(mycolor, score, fenStart, mode)
+	getPGN(moves, mycolor, score, fenStart, mode)
 	{
 		let pgn = "";
-		pgn += '[Site "vchess.club"]<br>';
-		const d = new Date();
+		pgn += '[Site "vchess.club"]\n';
 		const opponent = mode=="human" ? "Anonymous" : "Computer";
-		pgn += '[Variant "' + variant + '"]<br>';
-		pgn += '[Date "' + d.getFullYear() + '-' + (d.getMonth()+1) + '-' + d.getDate() + '"]<br>';
-		pgn += '[White "' + (mycolor=='w'?'Myself':opponent) + '"]<br>';
-		pgn += '[Black "' + (mycolor=='b'?'Myself':opponent) + '"]<br>';
-		pgn += '[Fen "' + fenStart + '"]<br>';
-		pgn += '[Result "' + score + '"]<br><br>';
-
-		for (let i=0; i<this.moves.length; i++)
+		pgn += '[Variant "' + variant + '"]\n';
+		pgn += '[Date "' + getDate(new Date()) + '"]\n';
+		// TODO: later when users are a bit less anonymous, use better names
+		const whiteName = ["human","computer"].includes(mode)
+			? (mycolor=='w'?'Myself':opponent)
+			: "analyze";
+		const blackName = ["human","computer"].includes(mode)
+			? (mycolor=='b'?'Myself':opponent)
+			: "analyze";
+		pgn += '[White "' + whiteName + '"]\n';
+		pgn += '[Black "' + blackName + '"]\n';
+		pgn += '[Fen "' + fenStart + '"]\n';
+		pgn += '[Result "' + score + '"]\n\n';
+
+		// Print moves
+		for (let i=0; i<moves.length; i++)
 		{
 			if (i % 2 == 0)
 				pgn += ((i/2)+1) + ".";
-			pgn += this.moves[i].notation + " ";
+			pgn += moves[i].notation + " ";
 		}
 
-		pgn += score;
-		return pgn;
+		return pgn + "\n";
 	}
 }