function CellSet(definition) {
	definition = definition || {};
	this.cells = {};
	if(definition.type == 'rectangle') {
		this.fromRectangle(definition);
	} else if(definition.type == 'isochrome') {
		this.fromIsochrome(definition);
	}
}

CellSet.prototype.fromRectangle = function(definition) {
	var xMax = definition.x + definition.width;
	var yMax = definition.y + definition.height;
	for(var i = definition.x; i < xMax; i++) {
		for(var j = definition.y; j < yMax; j++) {
			this.add(i, j);
		}
	}
};

CellSet.prototype.fromIsochrome = function(definition) {
	var originColor = definition.data[definition.x][definition.y];
	var queue = [{i: definition.x, j: definition.y}];
	while(queue.length > 0) {
		var p = queue[0];
		this.add(p.i, p.j);
		for(var d = -1; d < 2; d += 2) {
			[{i: p.i + d, j: p.j}, {i: p.i, j: p.j + d}].forEach(
				gateKeeper(this, definition.data, queue, originColor)
			);
		}
		queue.shift();
	}
};

CellSet.prototype.add = function(i, j) {
	this.cells[id(i, j)] = true;
};

CellSet.prototype.remove = function(i, j) {
	delete this.cells[id(i, j)];
};

CellSet.prototype.contains = function(i, j) {
	return !!this.cells[id(i, j)];
};

CellSet.prototype.isEmpty = function() {
	return Object.keys(this.cells).length < 1;
};

CellSet.prototype.iter = function(f) {
	for(var key in this.cells) {
		var coordinates = key.split(':');
		f(coordinates[0], coordinates[1]);
	}
}

return {
	make: function(definition) {return new CellSet(definition);},
};

function id(i, j) {
	return i + ':' + j;
}

function gateKeeper(cellSet, data, queue, originColor) {
	return function(p1) {
		if(p1.i >= 0 && p1.i < data.length && p1.j >= 0 && p1.j < data.length
			&& !cellSet.contains(p1.i, p1.j)
			&& data[p1.i][p1.j] == originColor) {
			queue.push(p1);
		}
	}
}