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/* 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() {
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() {
if (this._batchDepth++ === 0) {
this._batch = [];
}
},
/**
* End a batch of related changes, performing its action and adding
* it to the undo stack.
*/
endBatch() {
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.
const start = Math.max(this._index + 1 - this.maxUndo, 0);
this._stack = this._stack.slice(start, this._index);
const batch = this._batch;
delete this._batch;
const entry = {
do() {
for (const item of batch) {
item.do();
}
},
undo() {
for (let i = batch.length - 1; i >= 0; i--) {
batch[i].undo();
}
},
};
this._stack.push(entry);
this._index = this._stack.length;
entry.do();
},
/**
* 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(toDo, undo) {
this.startBatch();
this._batch.push({ do: toDo, undo });
this.endBatch();
},
/*
* Returns true if undo() will do anything.
*/
canUndo() {
return this._index > 0;
},
/**
* Undo the top of the undo stack.
*
* @return true if an action was undone.
*/
undo() {
if (!this.canUndo()) {
return false;
}
this._stack[--this._index].undo();
return true;
},
/**
* Returns true if redo() will do anything.
*/
canRedo() {
return this._stack.length > this._index;
},
/**
* Redo the most recently undone action.
*
* @return true if an action was redone.
*/
redo() {
if (!this.canRedo()) {
return false;
}
this._stack[this._index++].do();
return true;
},
/**
* ViewController implementation for undo/redo.
*/
/**
* Install this object as a command controller.
*/
installController(controllerWindow) {
const controllers = controllerWindow.controllers;
// Only available when running in a Firefox panel.
if (!controllers || !controllers.appendController) {
return;
}
this._controllerWindow = controllerWindow;
controllers.appendController(this);
},
/**
* Uninstall this object from the command controller.
*/
uninstallController() {
if (!this._controllerWindow) {
return;
}
this._controllerWindow.controllers.removeController(this);
},
supportsCommand(command) {
return command == "cmd_undo" || command == "cmd_redo";
},
isCommandEnabled(command) {
switch (command) {
case "cmd_undo":
return this.canUndo();
case "cmd_redo":
return this.canRedo();
}
return false;
},
doCommand(command) {
switch (command) {
case "cmd_undo":
return this.undo();
case "cmd_redo":
return this.redo();
default:
return null;
}
},
onEvent() {},
};
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