/**
 * @class Maze generator - Eller's algorithm
 * See http://homepages.cwi.nl/~tromp/maze.html for explanation
 * @augments ROT.Map
 */
ROT.Map.EllerMaze = function(width, height) {
	ROT.Map.call(this, width, height);
}
ROT.Map.EllerMaze.extend(ROT.Map);

ROT.Map.EllerMaze.prototype.create = function(callback) {
	var map = this._fillMap(1);
	var w = Math.ceil((this._width-2)/2);
	
	var rand = 9/24;
	
	var L = [];
	var R = [];
	
	for (var i=0;i<w;i++) {
		L.push(i);
		R.push(i);
	}
	L.push(w-1); /* fake stop-block at the right side */

	for (var j=1;j+3<this._height;j+=2) {
		/* one row */
		for (var i=0;i<w;i++) {
			/* cell coords (will be always empty) */
			var x = 2*i+1;
			var y = j;
			map[x][y] = 0;
			
			/* right connection */
			if (i != L[i+1] && ROT.RNG.getUniform() > rand) {
				this._addToList(i, L, R);
				map[x+1][y] = 0;
			}
			
			/* bottom connection */
			if (i != L[i] && ROT.RNG.getUniform() > rand) {
				/* remove connection */
				this._removeFromList(i, L, R);
			} else {
				/* create connection */
				map[x][y+1] = 0;
			}
		}
	}

	/* last row */
	for (var i=0;i<w;i++) {
		/* cell coords (will be always empty) */
		var x = 2*i+1;
		var y = j;
		map[x][y] = 0;
		
		/* right connection */
		if (i != L[i+1] && (i == L[i] || ROT.RNG.getUniform() > rand)) {
			/* dig right also if the cell is separated, so it gets connected to the rest of maze */
			this._addToList(i, L, R);
			map[x+1][y] = 0;
		}
		
		this._removeFromList(i, L, R);
	}
	
	for (var i=0;i<this._width;i++) {
		for (var j=0;j<this._height;j++) {
			callback(i, j, map[i][j]);
		}
	}
	
	return this;
}

/**
 * Remove "i" from its list
 */
ROT.Map.EllerMaze.prototype._removeFromList = function(i, L, R) {
	R[L[i]] = R[i];
	L[R[i]] = L[i];
	R[i] = i;
	L[i] = i;
}

/**
 * Join lists with "i" and "i+1"
 */
ROT.Map.EllerMaze.prototype._addToList = function(i, L, R) {
	R[L[i+1]] = R[i];
	L[R[i]] = L[i+1];
	R[i] = i+1;
	L[i+1] = i;
}