/**
 * @class Abstract FOV algorithm
 * @param {function} lightPassesCallback Does the light pass through x,y?
 * @param {object} [options]
 * @param {int} [options.topology=8] 4/6/8
 */
ROT.FOV = function(lightPassesCallback, options) {
	this._lightPasses = lightPassesCallback;
	this._options = {
		topology: 8
	}
	for (var p in options) { this._options[p] = options[p]; }
};

/**
 * Compute visibility
 * @param {int} x
 * @param {int} y
 * @param {int} R Maximum visibility radius
 * @param {function} callback
 */
ROT.FOV.prototype.compute = function(x, y, R, callback) {}

/**
 * Return all neighbors in a concentric ring
 * @param {int} cx center-x
 * @param {int} cy center-y
 * @param {int} r range
 */
ROT.FOV.prototype._getCircle = function(cx, cy, r) {
	var result = [];
	var dirs, countFactor, startOffset;

	switch (this._options.topology) {
		case 4:
			countFactor = 1;
			startOffset = [0, 1];
			dirs = [
				ROT.DIRS[8][7],
				ROT.DIRS[8][1],
				ROT.DIRS[8][3],
				ROT.DIRS[8][5]
			]
		break;

		case 6:
			dirs = ROT.DIRS[6];
			countFactor = 1;
			startOffset = [-1, 1];
		break;

		case 8:
			dirs = ROT.DIRS[4];
			countFactor = 2;
			startOffset = [-1, 1];
		break;
	}

	/* starting neighbor */
	var x = cx + startOffset[0]*r;
	var y = cy + startOffset[1]*r;

	/* circle */
	for (var i=0;i<dirs.length;i++) {
		for (var j=0;j<r*countFactor;j++) {
			result.push([x, y]);
			x += dirs[i][0];
			y += dirs[i][1];

		}
	}

	return result;
}