/*!
 * Chai - overwriteProperty utility
 * Copyright(c) 2012-2013 Jake Luer <jake@alogicalparadox.com>
 * MIT Licensed
 */

/**
 * ### overwriteProperty (ctx, name, fn)
 *
 * Overwites an already existing property getter and provides
 * access to previous value. Must return function to use as getter.
 *
 *     utils.overwriteProperty(chai.Assertion.prototype, 'ok', function (_super) {
 *       return function () {
 *         var obj = utils.flag(this, 'object');
 *         if (obj instanceof Foo) {
 *           new chai.Assertion(obj.name).to.equal('bar');
 *         } else {
 *           _super.call(this);
 *         }
 *       }
 *     });
 *
 *
 * Can also be accessed directly from `chai.Assertion`.
 *
 *     chai.Assertion.overwriteProperty('foo', fn);
 *
 * Then can be used as any other assertion.
 *
 *     expect(myFoo).to.be.ok;
 *
 * @param {Object} ctx object whose property is to be overwritten
 * @param {String} name of property to overwrite
 * @param {Function} getter function that returns a getter function to be used for name
 * @name overwriteProperty
 * @api public
 */

module.exports = function (ctx, name, getter) {
  var _get = Object.getOwnPropertyDescriptor(ctx, name)
    , _super = function () {};

  if (_get && 'function' === typeof _get.get)
    _super = _get.get

  Object.defineProperty(ctx, name,
    { get: function () {
        var result = getter(_super).call(this);
        return result === undefined ? this : result;
      }
    , configurable: true
  });
};
