ckeditor5-image-upload-base64
Version:
The development environment of CKEditor 5 – the best browser-based rich text editor.
120 lines (115 loc) • 5.39 kB
JavaScript
/**
* @license Copyright (c) 2003-2020, CKSource - Frederico Knabben. All rights reserved.
* For licensing, see LICENSE.md or https://ckeditor.com/legal/ckeditor-oss-license
*/
/**
* @module undo/undo
*/
import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
import UndoEditing from './undoediting';
import UndoUI from './undoui';
/**
* The undo feature.
*
* This is a "glue" plugin which loads the {@link module:undo/undoediting~UndoEditing undo editing feature}
* and {@link module:undo/undoui~UndoUI undo UI feature}.
*
* Below is the explanation of the undo mechanism working together with {@link module:engine/model/history~History History}:
*
* Whenever a {@link module:engine/model/operation/operation~Operation operation} is applied to the
* {@link module:engine/model/document~Document document}, it is saved to `History` as is.
* The {@link module:engine/model/batch~Batch batch} that owns that operation is also saved, in
* {@link module:undo/undocommand~UndoCommand}, together with the selection that was present in the document before the
* operation was applied. A batch is saved instead of the operation because changes are undone batch-by-batch, not operation-by-operation
* and a batch is seen as one undo step.
*
* After some changes happen to the document, the `History` and `UndoCommand` stack can be represented as follows:
*
* History Undo stack
* ============== ==================================
* [operation A1] [batch A]
* [operation B1] [batch B]
* [operation B2] [batch C]
* [operation C1]
* [operation C2]
* [operation B3]
* [operation C3]
*
* Where operations starting with the same letter are from same batch.
*
* Undoing a batch means that a set of operations which will reverse the effects of that batch needs to be generated.
* For example, if a batch added several letters, undoing the batch should remove them. It is important to apply undoing
* operations in the reversed order, so if a batch has operation `X`, `Y`, `Z`, reversed operations `Zr`, `Yr` and `Xr`
* need to be applied. Otherwise reversed operation `Xr` would operate on a wrong document state, because operation `X`
* does not know that operations `Y` and `Z` happened.
*
* After operations from an undone batch got {@link module:engine/model/operation/operation~Operation#getReversed reversed},
* one needs to make sure if they are ready to be applied. In the scenario above, operation `C3` is the last operation and `C3r`
* bases on up-to-date document state, so it can be applied to the document.
*
* History Undo stack
* ================= ==================================
* [ operation A1 ] [ batch A ]
* [ operation B1 ] [ batch B ]
* [ operation B2 ] [ processing undoing batch C ]
* [ operation C1 ]
* [ operation C2 ]
* [ operation B3 ]
* [ operation C3 ]
* [ operation C3r ]
*
* Next is operation `C2`, reversed to `C2r`. `C2r` bases on `C2`, so it bases on the wrong document state. It needs to be
* transformed by operations from history that happened after it, so it "knows" about them. Let us assume that `C2' = C2r * B3 * C3 * C3r`,
* where `*` means "transformed by". Rest of operations from that batch are processed in the same fashion.
*
* History Undo stack Redo stack
* ================= ================================== ==================================
* [ operation A1 ] [ batch A ] [ batch Cr ]
* [ operation B1 ] [ batch B ]
* [ operation B2 ]
* [ operation C1 ]
* [ operation C2 ]
* [ operation B3 ]
* [ operation C3 ]
* [ operation C3r ]
* [ operation C2' ]
* [ operation C1' ]
*
* Selective undo works on the same basis, however, instead of undoing the last batch in the undo stack, any batch can be undone.
* The same algorithm applies: operations from a batch (i.e. `A1`) are reversed and then transformed by operations stored in history.
*
* Redo also is very similar to undo. It has its own stack that is filled with undoing (reversed batches). Operations from
* batch that is re-done are reversed-back, transformed in proper order and applied to the document.
*
* History Undo stack Redo stack
* ================= ================================== ==================================
* [ operation A1 ] [ batch A ]
* [ operation B1 ] [ batch B ]
* [ operation B2 ] [ batch Crr ]
* [ operation C1 ]
* [ operation C2 ]
* [ operation B3 ]
* [ operation C3 ]
* [ operation C3r ]
* [ operation C2' ]
* [ operation C1' ]
* [ operation C1'r]
* [ operation C2'r]
* [ operation C3rr]
*
* @extends module:core/plugin~Plugin
*/
export default class Undo extends Plugin {
/**
* @inheritDoc
*/
static get requires() {
return [ UndoEditing, UndoUI ];
}
/**
* @inheritDoc
*/
static get pluginName() {
return 'Undo';
}
}