(function (exports) {
  'use strict';

  function id (val) { return val; }
  function get (key) { return function (val) { return val[key]; }; }

  /**
   * Searches for specific element in a given array using
   * the binary search algorithm.<br><br>
   * Time complexity: O(log N).
   *
   * @example
   *
   * var search = require('path-to-algorithms/src/searching/'+
   * 'binarysearch').binarySearch;
   * console.log(search([1, 2, 3, 4, 5], 4)); // 3
   *
   * @public
   * @module searching/binarysearch
   * @param {Array} array Input array.
   * @param {Number} value Value of the element which index should be found.
   * @returns {Number} Index of the element or -1 if not found.
   */
  function binarySearch(array, value, key) {
    key = !key ? id : typeof key === 'string' ? get(key) : key;
    value = key(value);
    var middle = Math.floor(array.length / 2);
    var left = 0;
    var right = array.length;
    while (right >= left) {
      var middleValue = key(array[middle]);
      if (middleValue === value) {
        return middle;
      } else if (middleValue > value) {
        right = middle - 1;
      } else {
        left = middle + 1;
      }
      middle = Math.floor((left + right) / 2);
    }
    return -1;
  }

  exports.binarySearch = binarySearch;

})(typeof window === 'undefined' ? module.exports : window);