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+/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set ft=javascript ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/**
+ * A simple undo stack manager.
+ *
+ * Actions are added along with the necessary code to
+ * reverse the action.
+ *
+ * @param integer maxUndo Maximum number of undo steps.
+ * defaults to 50.
+ */
+function UndoStack(maxUndo) {
+ this.maxUndo = maxUndo || 50;
+ this._stack = [];
+}
+
+exports.UndoStack = UndoStack;
+
+UndoStack.prototype = {
+ // Current index into the undo stack. Is positioned after the last
+ // currently-applied change.
+ _index: 0,
+
+ // The current batch depth (see startBatch() for details)
+ _batchDepth: 0,
+
+ destroy: function () {
+ this.uninstallController();
+ delete this._stack;
+ },
+
+ /**
+ * Start a collection of related changes. Changes will be batched
+ * together into one undo/redo item until endBatch() is called.
+ *
+ * Batches can be nested, in which case the outer batch will contain
+ * all items from the inner batches. This allows larger user
+ * actions made up of a collection of smaller actions to be
+ * undone as a single action.
+ */
+ startBatch: function () {
+ if (this._batchDepth++ === 0) {
+ this._batch = [];
+ }
+ },
+
+ /**
+ * End a batch of related changes, performing its action and adding
+ * it to the undo stack.
+ */
+ endBatch: function () {
+ if (--this._batchDepth > 0) {
+ return;
+ }
+
+ // Cut off the end of the undo stack at the current index,
+ // and the beginning to prevent a stack larger than maxUndo.
+ let start = Math.max((this._index + 1) - this.maxUndo, 0);
+ this._stack = this._stack.slice(start, this._index);
+
+ let batch = this._batch;
+ delete this._batch;
+ let entry = {
+ do: function () {
+ for (let item of batch) {
+ item.do();
+ }
+ },
+ undo: function () {
+ for (let i = batch.length - 1; i >= 0; i--) {
+ batch[i].undo();
+ }
+ }
+ };
+ this._stack.push(entry);
+ this._index = this._stack.length;
+ entry.do();
+ this._change();
+ },
+
+ /**
+ * Perform an action, adding it to the undo stack.
+ *
+ * @param function toDo Called to perform the action.
+ * @param function undo Called to reverse the action.
+ */
+ do: function (toDo, undo) {
+ this.startBatch();
+ this._batch.push({ do: toDo, undo });
+ this.endBatch();
+ },
+
+ /*
+ * Returns true if undo() will do anything.
+ */
+ canUndo: function () {
+ return this._index > 0;
+ },
+
+ /**
+ * Undo the top of the undo stack.
+ *
+ * @return true if an action was undone.
+ */
+ undo: function () {
+ if (!this.canUndo()) {
+ return false;
+ }
+ this._stack[--this._index].undo();
+ this._change();
+ return true;
+ },
+
+ /**
+ * Returns true if redo() will do anything.
+ */
+ canRedo: function () {
+ return this._stack.length > this._index;
+ },
+
+ /**
+ * Redo the most recently undone action.
+ *
+ * @return true if an action was redone.
+ */
+ redo: function () {
+ if (!this.canRedo()) {
+ return false;
+ }
+ this._stack[this._index++].do();
+ this._change();
+ return true;
+ },
+
+ _change: function () {
+ if (this._controllerWindow) {
+ this._controllerWindow.goUpdateCommand("cmd_undo");
+ this._controllerWindow.goUpdateCommand("cmd_redo");
+ }
+ },
+
+ /**
+ * ViewController implementation for undo/redo.
+ */
+
+ /**
+ * Install this object as a command controller.
+ */
+ installController: function (controllerWindow) {
+ this._controllerWindow = controllerWindow;
+ controllerWindow.controllers.appendController(this);
+ },
+
+ /**
+ * Uninstall this object from the command controller.
+ */
+ uninstallController: function () {
+ if (!this._controllerWindow) {
+ return;
+ }
+ this._controllerWindow.controllers.removeController(this);
+ },
+
+ supportsCommand: function (command) {
+ return (command == "cmd_undo" ||
+ command == "cmd_redo");
+ },
+
+ isCommandEnabled: function (command) {
+ switch (command) {
+ case "cmd_undo": return this.canUndo();
+ case "cmd_redo": return this.canRedo();
+ }
+ return false;
+ },
+
+ doCommand: function (command) {
+ switch (command) {
+ case "cmd_undo": return this.undo();
+ case "cmd_redo": return this.redo();
+ default: return null;
+ }
+ },
+
+ onEvent: function (event) {},
+};