import LinkedList from '../dataStructures/linkedList';
/**
 * Refactored implementation of mergeSort (part of javascript-algorithms project) by Github users:
 * mgechev, AndriiHeonia and lekkas (part of javascript-algorithms project - all project contributors
 * at repository website)
 *
 * Link to repository: https://github.com/mgechev/javascript-algorithms
 */

/**
 * Specifies a function that defines the sort order. The array is sorted according to each
 * character's Unicode code point value, according to the string conversion of each element.
 *
 * @param a {*} first compared element.
 * @param b {*} second compared element.
 * @returns {Number}
 */

var defaultCompareFunction = function defaultCompareFunction(a, b) {
  // sort lexically
  var firstValue = a.toString();
  var secondValue = b.toString();

  if (firstValue === secondValue) {
    return 0;
  } else if (firstValue < secondValue) {
    return -1;
  }

  return 1;
};
/**
 * Mergesort method which is recursively called for sorting the input array.
 *
 * @param {Array} array The array which should be sorted.
 * @param {Function} compareFunction Compares two items in an array. If compareFunction is not supplied,
 * elements are sorted by converting them to strings and comparing strings in Unicode code point order.
 * @param {Number} startIndex Left side of the subarray.
 * @param {Number} endIndex Right side of the subarray.
 * @returns {Array} Array with sorted subarray.
 */


export default function mergeSort(array) {
  var compareFunction = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : defaultCompareFunction;
  var startIndex = arguments.length > 2 && arguments[2] !== undefined ? arguments[2] : 0;
  var endIndex = arguments.length > 3 && arguments[3] !== undefined ? arguments[3] : array.length;

  if (Math.abs(endIndex - startIndex) <= 1) {
    return [];
  }

  var middleIndex = Math.ceil((startIndex + endIndex) / 2);
  mergeSort(array, compareFunction, startIndex, middleIndex);
  mergeSort(array, compareFunction, middleIndex, endIndex);
  return merge(array, compareFunction, startIndex, middleIndex, endIndex);
}
/**
 * Devides and sort merges two subarrays of given array
 *
 * @param {Array} array The array which subarrays should be sorted.
 * @param {Number} startIndex The start of the first subarray.
 *   This subarray is with end middle - 1.
 * @param {Number} middleIndex The start of the second array.
 * @param {Number} endIndex end - 1 is the end of the second array.
 * @returns {Array} The array with sorted subarray.
 */

function merge(array, compareFunction, startIndex, middleIndex, endIndex) {
  var leftElements = new LinkedList();
  var rightElements = new LinkedList();
  var leftSize = middleIndex - startIndex;
  var rightSize = endIndex - middleIndex;
  var maxSize = Math.max(leftSize, rightSize);
  var size = endIndex - startIndex;

  for (var _i = 0; _i < maxSize; _i += 1) {
    if (_i < leftSize) {
      leftElements.push(array[startIndex + _i]);
    }

    if (_i < rightSize) {
      rightElements.push(array[middleIndex + _i]);
    }
  }

  var i = 0;

  while (i < size) {
    if (leftElements.first && rightElements.first) {
      if (compareFunction(leftElements.first.data, rightElements.first.data) > 0) {
        array[startIndex + i] = rightElements.shift().data;
      } else {
        array[startIndex + i] = leftElements.shift().data;
      }
    } else if (leftElements.first) {
      array[startIndex + i] = leftElements.shift().data;
    } else {
      array[startIndex + i] = rightElements.shift().data;
    }

    i += 1;
  }

  return array;
}