michael@0: /* -*- Mode: Javascript; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* vim: set ft=javascript ts=2 et sw=2 tw=80: */
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:  * A simple undo stack manager.
michael@0:  *
michael@0:  * Actions are added along with the necessary code to
michael@0:  * reverse the action.
michael@0:  *
michael@0:  * @param function aChange Called whenever the size or position
michael@0:  *   of the undo stack changes, to use for updating undo-related
michael@0:  *   UI.
michael@0:  * @param integer aMaxUndo Maximum number of undo steps.
michael@0:  *   defaults to 50.
michael@0:  */
michael@0: function UndoStack(aMaxUndo)
michael@0: {
michael@0:   this.maxUndo = aMaxUndo || 50;
michael@0:   this._stack = [];
michael@0: }
michael@0: 
michael@0: exports.UndoStack = UndoStack;
michael@0: 
michael@0: UndoStack.prototype = {
michael@0:   // Current index into the undo stack.  Is positioned after the last
michael@0:   // currently-applied change.
michael@0:   _index: 0,
michael@0: 
michael@0:   // The current batch depth (see startBatch() for details)
michael@0:   _batchDepth: 0,
michael@0: 
michael@0:   destroy: function Undo_destroy()
michael@0:   {
michael@0:     this.uninstallController();
michael@0:     delete this._stack;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Start a collection of related changes.  Changes will be batched
michael@0:    * together into one undo/redo item until endBatch() is called.
michael@0:    *
michael@0:    * Batches can be nested, in which case the outer batch will contain
michael@0:    * all items from the inner batches.  This allows larger user
michael@0:    * actions made up of a collection of smaller actions to be
michael@0:    * undone as a single action.
michael@0:    */
michael@0:   startBatch: function Undo_startBatch()
michael@0:   {
michael@0:     if (this._batchDepth++ === 0) {
michael@0:       this._batch = [];
michael@0:     }
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * End a batch of related changes, performing its action and adding
michael@0:    * it to the undo stack.
michael@0:    */
michael@0:   endBatch: function Undo_endBatch()
michael@0:   {
michael@0:     if (--this._batchDepth > 0) {
michael@0:       return;
michael@0:     }
michael@0: 
michael@0:     // Cut off the end of the undo stack at the current index,
michael@0:     // and the beginning to prevent a stack larger than maxUndo.
michael@0:     let start = Math.max((this._index + 1) - this.maxUndo, 0);
michael@0:     this._stack = this._stack.slice(start, this._index);
michael@0: 
michael@0:     let batch = this._batch;
michael@0:     delete this._batch;
michael@0:     let entry = {
michael@0:       do: function() {
michael@0:         for (let item of batch) {
michael@0:           item.do();
michael@0:         }
michael@0:       },
michael@0:       undo: function() {
michael@0:         for (let i = batch.length - 1; i >= 0; i--) {
michael@0:           batch[i].undo();
michael@0:         }
michael@0:       }
michael@0:     };
michael@0:     this._stack.push(entry);
michael@0:     this._index = this._stack.length;
michael@0:     entry.do();
michael@0:     this._change();
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Perform an action, adding it to the undo stack.
michael@0:    *
michael@0:    * @param function aDo Called to perform the action.
michael@0:    * @param function aUndo Called to reverse the action.
michael@0:    */
michael@0:   do: function Undo_do(aDo, aUndo) {
michael@0:     this.startBatch();
michael@0:     this._batch.push({ do: aDo, undo: aUndo });
michael@0:     this.endBatch();
michael@0:   },
michael@0: 
michael@0:   /*
michael@0:    * Returns true if undo() will do anything.
michael@0:    */
michael@0:   canUndo: function Undo_canUndo()
michael@0:   {
michael@0:     return this._index > 0;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Undo the top of the undo stack.
michael@0:    *
michael@0:    * @return true if an action was undone.
michael@0:    */
michael@0:   undo: function Undo_canUndo()
michael@0:   {
michael@0:     if (!this.canUndo()) {
michael@0:       return false;
michael@0:     }
michael@0:     this._stack[--this._index].undo();
michael@0:     this._change();
michael@0:     return true;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Returns true if redo() will do anything.
michael@0:    */
michael@0:   canRedo: function Undo_canRedo()
michael@0:   {
michael@0:     return this._stack.length > this._index;
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Redo the most recently undone action.
michael@0:    *
michael@0:    * @return true if an action was redone.
michael@0:    */
michael@0:   redo: function Undo_canRedo()
michael@0:   {
michael@0:     if (!this.canRedo()) {
michael@0:       return false;
michael@0:     }
michael@0:     this._stack[this._index++].do();
michael@0:     this._change();
michael@0:     return true;
michael@0:   },
michael@0: 
michael@0:   _change: function Undo__change()
michael@0:   {
michael@0:     if (this._controllerWindow) {
michael@0:       this._controllerWindow.goUpdateCommand("cmd_undo");
michael@0:       this._controllerWindow.goUpdateCommand("cmd_redo");
michael@0:     }
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * ViewController implementation for undo/redo.
michael@0:    */
michael@0: 
michael@0:   /**
michael@0:    * Install this object as a command controller.
michael@0:    */
michael@0:   installController: function Undo_installController(aControllerWindow)
michael@0:   {
michael@0:     this._controllerWindow = aControllerWindow;
michael@0:     aControllerWindow.controllers.appendController(this);
michael@0:   },
michael@0: 
michael@0:   /**
michael@0:    * Uninstall this object from the command controller.
michael@0:    */
michael@0:   uninstallController: function Undo_uninstallController()
michael@0:   {
michael@0:     if (!this._controllerWindow) {
michael@0:       return;
michael@0:     }
michael@0:     this._controllerWindow.controllers.removeController(this);
michael@0:   },
michael@0: 
michael@0:   supportsCommand: function Undo_supportsCommand(aCommand)
michael@0:   {
michael@0:     return (aCommand == "cmd_undo" ||
michael@0:             aCommand == "cmd_redo");
michael@0:   },
michael@0: 
michael@0:   isCommandEnabled: function Undo_isCommandEnabled(aCommand)
michael@0:   {
michael@0:     switch(aCommand) {
michael@0:       case "cmd_undo": return this.canUndo();
michael@0:       case "cmd_redo": return this.canRedo();
michael@0:     };
michael@0:     return false;
michael@0:   },
michael@0: 
michael@0:   doCommand: function Undo_doCommand(aCommand)
michael@0:   {
michael@0:     switch(aCommand) {
michael@0:       case "cmd_undo": return this.undo();
michael@0:       case "cmd_redo": return this.redo();
michael@0:     }
michael@0:   },
michael@0: 
michael@0:   onEvent: function Undo_onEvent(aEvent) {},
michael@0: }