(function (root) {
  var localStorageMemory = {}
  var cache = {}

  /**
   * number of stored items.
   */
  localStorageMemory.length = 0

  /**
   * returns item for passed key, or null
   *
   * @para {String} key
   *       name of item to be returned
   * @returns {String|null}
   */
  localStorageMemory.getItem = function (key) {
    if (key in cache) {
      return cache[key]
    }

    return null
  }

  /**
   * sets item for key to passed value, as String
   *
   * @para {String} key
   *       name of item to be set
   * @para {String} value
   *       value, will always be turned into a String
   * @returns {undefined}
   */
  localStorageMemory.setItem = function (key, value) {
    if (typeof value === 'undefined') {
      localStorageMemory.removeItem(key)
    } else {
      if (!(cache.hasOwnProperty(key))) {
        localStorageMemory.length++
      }

      cache[key] = '' + value
    }
  }

  /**
   * removes item for passed key
   *
   * @para {String} key
   *       name of item to be removed
   * @returns {undefined}
   */
  localStorageMemory.removeItem = function (key) {
    if (cache.hasOwnProperty(key)) {
      delete cache[key]
      localStorageMemory.length--
    }
  }

  /**
   * returns name of key at passed index
   *
   * @para {Number} index
   *       Position for key to be returned (starts at 0)
   * @returns {String|null}
   */
  localStorageMemory.key = function (index) {
    return Object.keys(cache)[index] || null
  }

  /**
   * removes all stored items and sets length to 0
   *
   * @returns {undefined}
   */
  localStorageMemory.clear = function () {
    cache = {}
    localStorageMemory.length = 0
  }

  if (typeof exports === 'object') {
    module.exports = localStorageMemory
  } else {
    root.localStorageMemory = localStorageMemory
  }
})(this)