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- /**
- * @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';
- }
- }
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