/**
 * @class Simplified Dijkstra's algorithm: all edges have a value of 1
 * @augments ROT.Path
 * @see ROT.Path
 */
ROT.Path.Dijkstra = function(toX, toY, passableCallback, options) {
	ROT.Path.call(this, toX, toY, passableCallback, options);

	this._computed = {};
	this._todo = [];
	this._add(toX, toY, null);
}
ROT.Path.Dijkstra.extend(ROT.Path);

/**
 * Compute a path from a given point
 * @see ROT.Path#compute
 */
ROT.Path.Dijkstra.prototype.compute = function(fromX, fromY, callback) {
	var key = fromX+","+fromY;
	if (!(key in this._computed)) { this._compute(fromX, fromY); }
	if (!(key in this._computed)) { return; }
	
	var item = this._computed[key];
	while (item) {
		callback(item.x, item.y);
		item = item.prev;
	}
}

/**
 * Compute a non-cached value
 */
ROT.Path.Dijkstra.prototype._compute = function(fromX, fromY) {
	while (this._todo.length) {
		var item = this._todo.shift();
		if (item.x == fromX && item.y == fromY) { return; }
		
		var neighbors = this._getNeighbors(item.x, item.y);
		
		for (var i=0;i<neighbors.length;i++) {
			var neighbor = neighbors[i];
			var x = neighbor[0];
			var y = neighbor[1];
			var id = x+","+y;
			if (id in this._computed) { continue; } /* already done */	
			this._add(x, y, item); 
		}
	}
}

ROT.Path.Dijkstra.prototype._add = function(x, y, prev) {
	var obj = {
		x: x,
		y: y,
		prev: prev
	}
	this._computed[x+","+y] = obj;
	this._todo.push(obj);
}