function cartesianProduct(input, current) {
if (!input || !input.length) { return []; }
var head = input[0];
var tail = input.slice(1);
var output = [];
for (var key in head) {
for (var i = 0; i < head[key].length; i++) {
var newCurrent = copy(current);
newCurrent[key] = head[key][i];
if (tail.length) {
var productOfTail =
cartesianProduct(tail, newCurrent);
output = output.concat(productOfTail);
} else output.push(newCurrent);
}
}
return output;
}