/**
9) Facebook On-site Question (45mins) - Implement JavaScript's Generator#Next()
Implement a class called Enumerator, which has a method next().
The Enumerator will be initialized with a flat array (e.g. [1,6,8]).
Calling Enumerator.next() will return the subsequent value in the array, until the array is empty and it will return -1.

e = new Enumerator([1,6])
e.next()  // returns 1
e.next()  // returns 6
e.next()  // returns -1


Implement a class called SuperEnumerator, which has a method next().
The SuperEnumerator will be initialized with an array with nested arrays (e.g. [1,6,[3,4],1,[2,[8,3,[4]]]1])
Calling SuperEnumerator.next() will return the subsequent value in the nested array, as though it was flattened, until the array is empty and it will return -1.

e = new Enumerator([1,[3,[3,4],4],[1]])
e.next()  // returns 1
e.next()  // returns 3
e.next()  // returns 3
e.next()  // returns 4
e.next()  // returns 4
e.next()  // returns 1
e.next()  // returns -1

Note: The constructor and next() should have a complexity of O(1).


*/


function Generator(input) {
  const arr = input;
  let recurse = null;

  const getNext = () => {
    let nextVal = null;
    if (recurse) {
      nextVal = recurse.next();
      if (nextVal) {
        return nextVal
      } else {
        recurse = null; // recursive generator is done...
      }
    }
    nextVal = arr.shift();
    if (typeof nextVal === 'object') {
      recurse = new Generator(nextVal);
      return recurse.next();
    } else {
      return nextVal;
    }
  }

  return {
    next: function() {
      return getNext();
    }
  }
}

const test = new Generator([1,[3,[3,4],4],[1]]);
console.log(test.next());
console.log(test.next());
console.log(test.next());
console.log(test.next());
console.log(test.next());
console.log(test.next());
console.log(test.next());
console.log(test.next());
console.log(test.next());