michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: /**
michael@0:  * Allows registering a mock XPCOM component, that temporarily replaces the
michael@0:  *  original one when an object implementing a given ContractID is requested
michael@0:  *  using createInstance.
michael@0:  *
michael@0:  * @param aContractID
michael@0:  *        The ContractID of the component to replace, for example
michael@0:  *        "@mozilla.org/filepicker;1".
michael@0:  *
michael@0:  * @param aReplacementCtor
michael@0:  *        The constructor function for the JavaScript object that will be
michael@0:  *        created every time createInstance is called. This object must
michael@0:  *        implement QueryInterface and provide the XPCOM interfaces required by
michael@0:  *        the specified ContractID (for example
michael@0:  *        Components.interfaces.nsIFilePicker).
michael@0:  */
michael@0: 
michael@0: function MockObjectRegisterer(aContractID, aReplacementCtor) {
michael@0:   this._contractID = aContractID;
michael@0:   this._replacementCtor = aReplacementCtor;
michael@0: }
michael@0: 
michael@0: MockObjectRegisterer.prototype = {
michael@0:   /**
michael@0:    * Replaces the current factory with one that returns a new mock object.
michael@0:    *
michael@0:    * After register() has been called, it is mandatory to call unregister() to
michael@0:    * restore the original component. Usually, you should use a try-catch block
michael@0:    * to ensure that unregister() is called.
michael@0:    */
michael@0:   register: function MOR_register() {
michael@0:     if (this._originalFactory)
michael@0:       throw new Exception("Invalid object state when calling register()");
michael@0: 
michael@0:     // Define a factory that creates a new object using the given constructor.
michael@0:     var providedConstructor = this._replacementCtor;
michael@0:     this._mockFactory = {
michael@0:       createInstance: function MF_createInstance(aOuter, aIid) {
michael@0:         if (aOuter != null)
michael@0:           throw SpecialPowers.Cr.NS_ERROR_NO_AGGREGATION;
michael@0:         return new providedConstructor().QueryInterface(aIid);
michael@0:       }
michael@0:     };
michael@0: 
michael@0:     var retVal = SpecialPowers.swapFactoryRegistration(this._cid, this._contractID, this._mockFactory, this._originalFactory);
michael@0:     if ('error' in retVal) {
michael@0:       throw new Exception("ERROR: " + retVal.error);
michael@0:     } else {
michael@0:       this._cid = retVal.cid;
michael@0:       this._originalFactory = retVal.originalFactory;
michael@0:     }
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Restores the original factory.
michael@0:    */
michael@0:   unregister: function MOR_unregister() {
michael@0:     if (!this._originalFactory)
michael@0:       throw new Exception("Invalid object state when calling unregister()");
michael@0: 
michael@0:     // Free references to the mock factory.
michael@0:     SpecialPowers.swapFactoryRegistration(this._cid, this._contractID, this._mockFactory, this._originalFactory);
michael@0: 
michael@0:     // Allow registering a mock factory again later.
michael@0:     this._cid = null;
michael@0:     this._originalFactory = null;
michael@0:     this._mockFactory = null;
michael@0:   },
michael@0: 
michael@0:   // --- Private methods and properties ---
michael@0: 
michael@0:   /**
michael@0:    * The factory of the component being replaced.
michael@0:    */
michael@0:   _originalFactory: null,
michael@0: 
michael@0:   /**
michael@0:    * The CID under which the mock contractID was registered.
michael@0:    */
michael@0:   _cid: null,
michael@0: 
michael@0:   /**
michael@0:    * The nsIFactory that was automatically generated by this object.
michael@0:    */
michael@0:   _mockFactory: null
michael@0: }