var MapCache = require('./_MapCache');
  
  /** Error message constants. */
  var FUNC_ERROR_TEXT = 'Expected a function';
  
  /**
   * Creates a function that memoizes the result of `func`. If `resolver` is
   * provided, it determines the cache key for storing the result based on the
   * arguments provided to the memoized function. By default, the first argument
   * provided to the memoized function is used as the map cache key. The `func`
   * is invoked with the `this` binding of the memoized function.
   *
   * **Note:** The cache is exposed as the `cache` property on the memoized
   * function. Its creation may be customized by replacing the `_.memoize.Cache`
   * constructor with one whose instances implement the
   * [`Map`](http://ecma-international.org/ecma-262/7.0/#sec-properties-of-the-map-prototype-object)
   * method interface of `clear`, `delete`, `get`, `has`, and `set`.
   *
   * @static
   * @memberOf _
   * @since 0.1.0
   * @category Function
   * @param {Function} func The function to have its output memoized.
   * @param {Function} [resolver] The function to resolve the cache key.
   * @returns {Function} Returns the new memoized function.
   * @example
   *
   * var object = { 'a': 1, 'b': 2 };
   * var other = { 'c': 3, 'd': 4 };
   *
   * var values = _.memoize(_.values);
   * values(object);
   * // => [1, 2]
   *
   * values(other);
   * // => [3, 4]
   *
   * object.a = 2;
   * values(object);
   * // => [1, 2]
   *
   * // Modify the result cache.
   * values.cache.set(object, ['a', 'b']);
   * values(object);
   * // => ['a', 'b']
   *
   * // Replace `_.memoize.Cache`.
   * _.memoize.Cache = WeakMap;
   */
  function memoize(func, resolver) {
    if (typeof func != 'function' || (resolver != null && typeof resolver != 'function')) {
      throw new TypeError(FUNC_ERROR_TEXT);
    }
    var memoized = function() {
      var args = arguments,
          key = resolver ? resolver.apply(this, args) : args[0],
          cache = memoized.cache;
  
      if (cache.has(key)) {
        return cache.get(key);
      }
      var result = func.apply(this, args);
      memoized.cache = cache.set(key, result) || cache;
      return result;
    };
    memoized.cache = new (memoize.Cache || MapCache);
    return memoized;
  }
  
  // Expose `MapCache`.
  memoize.Cache = MapCache;
  
  module.exports = memoize;