/**
 * @param {*[]} originalSet - Original set of elements we're forming power-set of.
 * @param {*[][]} allSubsets - All subsets that have been formed so far.
 * @param {*[]} currentSubSet - Current subset that we're forming at the moment.
 * @param {number} startAt - The position of in original set we're starting to form current subset.
 * @return {*[][]} - All subsets of original set.
 */
function btPowerSetRecursive(originalSet, allSubsets = [[]], currentSubSet = [], startAt = 0) {
  // Let's iterate over originalSet elements that may be added to the subset
  // without having duplicates. The value of startAt prevents adding the duplicates.
  for (let position = startAt; position < originalSet.length; position += 1) {
    // Let's push current element to the subset
    currentSubSet.push(originalSet[position]);

    // Current subset is already valid so let's memorize it.
    // We do array destruction here to save the clone of the currentSubSet.
    // We need to save a clone since the original currentSubSet is going to be
    // mutated in further recursive calls.
    allSubsets.push([...currentSubSet]);

    // Let's try to generate all other subsets for the current subset.
    // We're increasing the position by one to avoid duplicates in subset.
    btPowerSetRecursive(originalSet, allSubsets, currentSubSet, position + 1);

    // BACKTRACK. Exclude last element from the subset and try the next valid one.
    currentSubSet.pop();
  }

  // Return all subsets of a set.
  return allSubsets;
}

/**
 * Find power-set of a set using BACKTRACKING approach.
 *
 * @param {*[]} originalSet
 * @return {*[][]}
 */
export default function btPowerSet(originalSet) {
  return btPowerSetRecursive(originalSet);
}