HORIZON PROJECT

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;