Upgrade to 4.5.7 and add some plugin

[perso/Immae/Projets/packagist/connexionswing-ckeditor-component.git] / sources / plugins / undo / plugin.js

/**
 * @license Copyright (c) 2003-2016, CKSource - Frederico Knabben. All rights reserved.
 * For licensing, see LICENSE.md or http://ckeditor.com/license
 */

/**
 * @fileOverview Undo/Redo system for saving a shapshot for document modification
 *              and other recordable changes.
 */

'use strict';

( function() {
        var keystrokes = [
                        CKEDITOR.CTRL + 90 /*Z*/,
                        CKEDITOR.CTRL + 89 /*Y*/,
                        CKEDITOR.CTRL + CKEDITOR.SHIFT + 90 /*Z*/
                ],
                backspaceOrDelete = { 8: 1, 46: 1 };

        CKEDITOR.plugins.add( 'undo', {
                // jscs:disable maximumLineLength
                lang: 'af,ar,bg,bn,bs,ca,cs,cy,da,de,de-ch,el,en,en-au,en-ca,en-gb,eo,es,et,eu,fa,fi,fo,fr,fr-ca,gl,gu,he,hi,hr,hu,id,is,it,ja,ka,km,ko,ku,lt,lv,mk,mn,ms,nb,nl,no,pl,pt,pt-br,ro,ru,si,sk,sl,sq,sr,sr-latn,sv,th,tr,tt,ug,uk,vi,zh,zh-cn', // %REMOVE_LINE_CORE%
                // jscs:enable maximumLineLength
                icons: 'redo,redo-rtl,undo,undo-rtl', // %REMOVE_LINE_CORE%
                hidpi: true, // %REMOVE_LINE_CORE%
                init: function( editor ) {
                        var undoManager = editor.undoManager = new UndoManager( editor ),
                                editingHandler = undoManager.editingHandler = new NativeEditingHandler( undoManager );

                        var undoCommand = editor.addCommand( 'undo', {
                                exec: function() {
                                        if ( undoManager.undo() ) {
                                                editor.selectionChange();
                                                this.fire( 'afterUndo' );
                                        }
                                },
                                startDisabled: true,
                                canUndo: false
                        } );

                        var redoCommand = editor.addCommand( 'redo', {
                                exec: function() {
                                        if ( undoManager.redo() ) {
                                                editor.selectionChange();
                                                this.fire( 'afterRedo' );
                                        }
                                },
                                startDisabled: true,
                                canUndo: false
                        } );

                        editor.setKeystroke( [
                                [ keystrokes[ 0 ], 'undo' ],
                                [ keystrokes[ 1 ], 'redo' ],
                                [ keystrokes[ 2 ], 'redo' ]
                        ] );

                        undoManager.onChange = function() {
                                undoCommand.setState( undoManager.undoable() ? CKEDITOR.TRISTATE_OFF : CKEDITOR.TRISTATE_DISABLED );
                                redoCommand.setState( undoManager.redoable() ? CKEDITOR.TRISTATE_OFF : CKEDITOR.TRISTATE_DISABLED );
                        };

                        function recordCommand( event ) {
                                // If the command hasn't been marked to not support undo.
                                if ( undoManager.enabled && event.data.command.canUndo !== false )
                                        undoManager.save();
                        }

                        // We'll save snapshots before and after executing a command.
                        editor.on( 'beforeCommandExec', recordCommand );
                        editor.on( 'afterCommandExec', recordCommand );

                        // Save snapshots before doing custom changes.
                        editor.on( 'saveSnapshot', function( evt ) {
                                undoManager.save( evt.data && evt.data.contentOnly );
                        } );

                        // Event manager listeners should be attached on contentDom.
                        editor.on( 'contentDom', editingHandler.attachListeners, editingHandler );

                        editor.on( 'instanceReady', function() {
                                // Saves initial snapshot.
                                editor.fire( 'saveSnapshot' );
                        } );

                        // Always save an undo snapshot - the previous mode might have
                        // changed editor contents.
                        editor.on( 'beforeModeUnload', function() {
                                editor.mode == 'wysiwyg' && undoManager.save( true );
                        } );

                        function toggleUndoManager() {
                                undoManager.enabled = editor.readOnly ? false : editor.mode == 'wysiwyg';
                                undoManager.onChange();
                        }

                        // Make the undo manager available only in wysiwyg mode.
                        editor.on( 'mode', toggleUndoManager );

                        // Disable undo manager when in read-only mode.
                        editor.on( 'readOnly', toggleUndoManager );

                        if ( editor.ui.addButton ) {
                                editor.ui.addButton( 'Undo', {
                                        label: editor.lang.undo.undo,
                                        command: 'undo',
                                        toolbar: 'undo,10'
                                } );

                                editor.ui.addButton( 'Redo', {
                                        label: editor.lang.undo.redo,
                                        command: 'redo',
                                        toolbar: 'undo,20'
                                } );
                        }

                        /**
                         * Resets the undo stack.
                         *
                         * @member CKEDITOR.editor
                         */
                        editor.resetUndo = function() {
                                // Reset the undo stack.
                                undoManager.reset();

                                // Create the first image.
                                editor.fire( 'saveSnapshot' );
                        };

                        /**
                         * Amends the top of the undo stack (last undo image) with the current DOM changes.
                         *
                         *              function() {
                         *                      editor.fire( 'saveSnapshot' );
                         *                      editor.document.body.append(...);
                         *                      // Makes new changes following the last undo snapshot a part of it.
                         *                      editor.fire( 'updateSnapshot' );
                         *                      ..
                         *              }
                         *
                         * @event updateSnapshot
                         * @member CKEDITOR.editor
                         * @param {CKEDITOR.editor} editor This editor instance.
                         */
                        editor.on( 'updateSnapshot', function() {
                                if ( undoManager.currentImage )
                                        undoManager.update();
                        } );

                        /**
                         * Locks the undo manager to prevent any save/update operations.
                         *
                         * It is convenient to lock the undo manager before performing DOM operations
                         * that should not be recored (e.g. auto paragraphing).
                         *
                         * See {@link CKEDITOR.plugins.undo.UndoManager#lock} for more details.
                         *
                         * **Note:** In order to unlock the undo manager, {@link #unlockSnapshot} has to be fired
                         * the same number of times that `lockSnapshot` has been fired.
                         *
                         * @since 4.0
                         * @event lockSnapshot
                         * @member CKEDITOR.editor
                         * @param {CKEDITOR.editor} editor This editor instance.
                         * @param data
                         * @param {Boolean} [data.dontUpdate] When set to `true`, the last snapshot will not be updated
                         * with the current content and selection. Read more in the {@link CKEDITOR.plugins.undo.UndoManager#lock} method.
                         * @param {Boolean} [data.forceUpdate] When set to `true`, the last snapshot will always be updated
                         * with the current content and selection. Read more in the {@link CKEDITOR.plugins.undo.UndoManager#lock} method.
                         */
                        editor.on( 'lockSnapshot', function( evt ) {
                                var data = evt.data;
                                undoManager.lock( data && data.dontUpdate, data && data.forceUpdate );
                        } );

                        /**
                         * Unlocks the undo manager and updates the latest snapshot.
                         *
                         * @since 4.0
                         * @event unlockSnapshot
                         * @member CKEDITOR.editor
                         * @param {CKEDITOR.editor} editor This editor instance.
                         */
                        editor.on( 'unlockSnapshot', undoManager.unlock, undoManager );
                }
        } );

        CKEDITOR.plugins.undo = {};

        /**
         * Main logic for the Redo/Undo feature.
         *
         * @private
         * @class CKEDITOR.plugins.undo.UndoManager
         * @constructor Creates an UndoManager class instance.
         * @param {CKEDITOR.editor} editor
         */
        var UndoManager = CKEDITOR.plugins.undo.UndoManager = function( editor ) {
                /**
                 * An array storing the number of key presses, count in a row. Use {@link #keyGroups} members as index.
                 *
                 * **Note:** The keystroke count will be reset after reaching the limit of characters per snapshot.
                 *
                 * @since 4.4.4
                 */
                this.strokesRecorded = [ 0, 0 ];

                /**
                 * When the `locked` property is not `null`, the undo manager is locked, so
                 * operations like `save` or `update` are forbidden.
                 *
                 * The manager can be locked and unlocked by the {@link #lock} and {@link #unlock}
                 * methods, respectively.
                 *
                 * @readonly
                 * @property {Object} [locked=null]
                 */
                this.locked = null;

                /**
                 * Contains the previously processed key group, based on {@link #keyGroups}.
                 * `-1` means an unknown group.
                 *
                 * @since 4.4.4
                 * @readonly
                 * @property {Number} [previousKeyGroup=-1]
                 */
                this.previousKeyGroup = -1;

                /**
                 * The maximum number of snapshots in the stack. Configurable via {@link CKEDITOR.config#undoStackSize}.
                 *
                 * @readonly
                 * @property {Number} [limit]
                 */
                this.limit = editor.config.undoStackSize || 20;

                /**
                 * The maximum number of characters typed/deleted in one undo step.
                 *
                 * @since 4.4.5
                 * @readonly
                 */
                this.strokesLimit = 25;

                this.editor = editor;

                // Reset the undo stack.
                this.reset();
        };

        UndoManager.prototype = {
                /**
                 * Handles keystroke support for the undo manager. It is called on `keyup` event for
                 * keystrokes that can change the editor content.
                 *
                 * @param {Number} keyCode The key code.
                 * @param {Boolean} [strokesPerSnapshotExceeded] When set to `true`, the method will
                 * behave as if the strokes limit was exceeded regardless of the {@link #strokesRecorded} value.
                 */
                type: function( keyCode, strokesPerSnapshotExceeded ) {
                        var keyGroup = UndoManager.getKeyGroup( keyCode ),
                                // Count of keystrokes in current a row.
                                // Note if strokesPerSnapshotExceeded will be exceeded, it'll be restarted.
                                strokesRecorded = this.strokesRecorded[ keyGroup ] + 1;

                        strokesPerSnapshotExceeded =
                                ( strokesPerSnapshotExceeded || strokesRecorded >= this.strokesLimit );

                        if ( !this.typing )
                                onTypingStart( this );

                        if ( strokesPerSnapshotExceeded ) {
                                // Reset the count of strokes, so it'll be later assigned to this.strokesRecorded.
                                strokesRecorded = 0;

                                this.editor.fire( 'saveSnapshot' );
                        } else {
                                // Fire change event.
                                this.editor.fire( 'change' );
                        }

                        // Store recorded strokes count.
                        this.strokesRecorded[ keyGroup ] = strokesRecorded;
                        // This prop will tell in next itaration what kind of group was processed previously.
                        this.previousKeyGroup = keyGroup;
                },

                /**
                 * Whether the new `keyCode` belongs to a different group than the previous one ({@link #previousKeyGroup}).
                 *
                 * @since 4.4.5
                 * @param {Number} keyCode
                 * @returns {Boolean}
                 */
                keyGroupChanged: function( keyCode ) {
                        return UndoManager.getKeyGroup( keyCode ) != this.previousKeyGroup;
                },

                /**
                 * Resets the undo stack.
                 */
                reset: function() {
                        // Stack for all the undo and redo snapshots, they're always created/removed
                        // in consistency.
                        this.snapshots = [];

                        // Current snapshot history index.
                        this.index = -1;

                        this.currentImage = null;

                        this.hasUndo = false;
                        this.hasRedo = false;
                        this.locked = null;

                        this.resetType();
                },

                /**
                 * Resets all typing variables.
                 *
                 * @see #type
                 */
                resetType: function() {
                        this.strokesRecorded = [ 0, 0 ];
                        this.typing = false;
                        this.previousKeyGroup = -1;
                },

                /**
                 * Refreshes the state of the {@link CKEDITOR.plugins.undo.UndoManager undo manager}
                 * as well as the state of the `undo` and `redo` commands.
                 */
                refreshState: function() {
                        // These lines can be handled within onChange() too.
                        this.hasUndo = !!this.getNextImage( true );
                        this.hasRedo = !!this.getNextImage( false );
                        // Reset typing
                        this.resetType();
                        this.onChange();
                },

                /**
                 * Saves a snapshot of the document image for later retrieval.
                 *
                 * @param {Boolean} onContentOnly If set to `true`, the snapshot will be saved only if the content has changed.
                 * @param {CKEDITOR.plugins.undo.Image} image An optional image to save. If skipped, current editor will be used.
                 * @param {Boolean} [autoFireChange=true] If set to `false`, will not trigger the {@link CKEDITOR.editor#change} event to editor.
                 */
                save: function( onContentOnly, image, autoFireChange ) {
                        var editor = this.editor;
                        // Do not change snapshots stack when locked, editor is not ready,
                        // editable is not ready or when editor is in mode difference than 'wysiwyg'.
                        if ( this.locked || editor.status != 'ready' || editor.mode != 'wysiwyg' )
                                return false;

                        var editable = editor.editable();
                        if ( !editable || editable.status != 'ready' )
                                return false;

                        var snapshots = this.snapshots;

                        // Get a content image.
                        if ( !image )
                                image = new Image( editor );

                        // Do nothing if it was not possible to retrieve an image.
                        if ( image.contents === false )
                                return false;

                        // Check if this is a duplicate. In such case, do nothing.
                        if ( this.currentImage ) {
                                if ( image.equalsContent( this.currentImage ) ) {
                                        if ( onContentOnly )
                                                return false;

                                        if ( image.equalsSelection( this.currentImage ) )
                                                return false;
                                } else if ( autoFireChange !== false ) {
                                        editor.fire( 'change' );
                                }
                        }

                        // Drop future snapshots.
                        snapshots.splice( this.index + 1, snapshots.length - this.index - 1 );

                        // If we have reached the limit, remove the oldest one.
                        if ( snapshots.length == this.limit )
                                snapshots.shift();

                        // Add the new image, updating the current index.
                        this.index = snapshots.push( image ) - 1;

                        this.currentImage = image;

                        if ( autoFireChange !== false )
                                this.refreshState();
                        return true;
                },

                /**
                 * Sets editor content/selection to the one stored in `image`.
                 *
                 * @param {CKEDITOR.plugins.undo.Image} image
                 */
                restoreImage: function( image ) {
                        // Bring editor focused to restore selection.
                        var editor = this.editor,
                                sel;

                        if ( image.bookmarks ) {
                                editor.focus();
                                // Retrieve the selection beforehand. (#8324)
                                sel = editor.getSelection();
                        }

                        // Start transaction - do not allow any mutations to the
                        // snapshots stack done when selecting bookmarks (much probably
                        // by selectionChange listener).
                        this.locked = { level: 999 };

                        this.editor.loadSnapshot( image.contents );

                        if ( image.bookmarks )
                                sel.selectBookmarks( image.bookmarks );
                        else if ( CKEDITOR.env.ie ) {
                                // IE BUG: If I don't set the selection to *somewhere* after setting
                                // document contents, then IE would create an empty paragraph at the bottom
                                // the next time the document is modified.
                                var $range = this.editor.document.getBody().$.createTextRange();
                                $range.collapse( true );
                                $range.select();
                        }

                        this.locked = null;

                        this.index = image.index;
                        this.currentImage = this.snapshots[ this.index ];

                        // Update current image with the actual editor
                        // content, since actualy content may differ from
                        // the original snapshot due to dom change. (#4622)
                        this.update();
                        this.refreshState();

                        editor.fire( 'change' );
                },

                /**
                 * Gets the closest available image.
                 *
                 * @param {Boolean} isUndo If `true`, it will return the previous image.
                 * @returns {CKEDITOR.plugins.undo.Image} Next image or `null`.
                 */
                getNextImage: function( isUndo ) {
                        var snapshots = this.snapshots,
                                currentImage = this.currentImage,
                                image, i;

                        if ( currentImage ) {
                                if ( isUndo ) {
                                        for ( i = this.index - 1; i >= 0; i-- ) {
                                                image = snapshots[ i ];
                                                if ( !currentImage.equalsContent( image ) ) {
                                                        image.index = i;
                                                        return image;
                                                }
                                        }
                                } else {
                                        for ( i = this.index + 1; i < snapshots.length; i++ ) {
                                                image = snapshots[ i ];
                                                if ( !currentImage.equalsContent( image ) ) {
                                                        image.index = i;
                                                        return image;
                                                }
                                        }
                                }
                        }

                        return null;
                },

                /**
                 * Checks the current redo state.
                 *
                 * @returns {Boolean} Whether the document has a previous state to retrieve.
                 */
                redoable: function() {
                        return this.enabled && this.hasRedo;
                },

                /**
                 * Checks the current undo state.
                 *
                 * @returns {Boolean} Whether the document has a future state to restore.
                 */
                undoable: function() {
                        return this.enabled && this.hasUndo;
                },

                /**
                 * Performs an undo operation on current index.
                 */
                undo: function() {
                        if ( this.undoable() ) {
                                this.save( true );

                                var image = this.getNextImage( true );
                                if ( image )
                                        return this.restoreImage( image ), true;
                        }

                        return false;
                },

                /**
                 * Performs a redo operation on current index.
                 */
                redo: function() {
                        if ( this.redoable() ) {
                                // Try to save. If no changes have been made, the redo stack
                                // will not change, so it will still be redoable.
                                this.save( true );

                                // If instead we had changes, we can't redo anymore.
                                if ( this.redoable() ) {
                                        var image = this.getNextImage( false );
                                        if ( image )
                                                return this.restoreImage( image ), true;
                                }
                        }

                        return false;
                },

                /**
                 * Updates the last snapshot of the undo stack with the current editor content.
                 *
                 * @param {CKEDITOR.plugins.undo.Image} [newImage] The image which will replace the current one.
                 * If it is not set, it defaults to the image taken from the editor.
                 */
                update: function( newImage ) {
                        // Do not change snapshots stack is locked.
                        if ( this.locked )
                                return;

                        if ( !newImage )
                                newImage = new Image( this.editor );

                        var i = this.index,
                                snapshots = this.snapshots;

                        // Find all previous snapshots made for the same content (which differ
                        // only by selection) and replace all of them with the current image.
                        while ( i > 0 && this.currentImage.equalsContent( snapshots[ i - 1 ] ) )
                                i -= 1;

                        snapshots.splice( i, this.index - i + 1, newImage );
                        this.index = i;
                        this.currentImage = newImage;
                },

                /**
                 * Amends the last snapshot and changes its selection (only in case when content
                 * is equal between these two).
                 *
                 * @since 4.4.4
                 * @param {CKEDITOR.plugins.undo.Image} newSnapshot New snapshot with new selection.
                 * @returns {Boolean} Returns `true` if selection was amended.
                 */
                updateSelection: function( newSnapshot ) {
                        if ( !this.snapshots.length )
                                return false;

                        var snapshots = this.snapshots,
                                lastImage = snapshots[ snapshots.length - 1 ];

                        if ( lastImage.equalsContent( newSnapshot ) ) {
                                if ( !lastImage.equalsSelection( newSnapshot ) ) {
                                        snapshots[ snapshots.length - 1 ] = newSnapshot;
                                        this.currentImage = newSnapshot;
                                        return true;
                                }
                        }

                        return false;
                },

                /**
                 * Locks the snapshot stack to prevent any save/update operations and when necessary,
                 * updates the tip of the snapshot stack with the DOM changes introduced during the
                 * locked period, after the {@link #unlock} method is called.
                 *
                 * It is mainly used to ensure any DOM operations that should not be recorded
                 * (e.g. auto paragraphing) are not added to the stack.
                 *
                 * **Note:** For every `lock` call you must call {@link #unlock} once to unlock the undo manager.
                 *
                 * @since 4.0
                 * @param {Boolean} [dontUpdate] When set to `true`, the last snapshot will not be updated
                 * with current content and selection. By default, if undo manager was up to date when the lock started,
                 * the last snapshot will be updated to the current state when unlocking. This means that all changes
                 * done during the lock will be merged into the previous snapshot or the next one. Use this option to gain
                 * more control over this behavior. For example, it is possible to group changes done during the lock into
                 * a separate snapshot.
                 * @param {Boolean} [forceUpdate] When set to `true`, the last snapshot will always be updated with the
                 * current content and selection regardless of the current state of the undo manager.
                 * When not set, the last snapshot will be updated only if the undo manager was up to date when locking.
                 * Additionally, this option makes it possible to lock the snapshot when the editor is not in the `wysiwyg` mode,
                 * because when it is passed, the snapshots will not need to be compared.
                 */
                lock: function( dontUpdate, forceUpdate ) {
                        if ( !this.locked ) {
                                if ( dontUpdate )
                                        this.locked = { level: 1 };
                                else {
                                        var update = null;

                                        if ( forceUpdate )
                                                update = true;
                                        else {
                                                // Make a contents image. Don't include bookmarks, because:
                                                // * we don't compare them,
                                                // * there's a chance that DOM has been changed since
                                                // locked (e.g. fake) selection was made, so createBookmark2 could fail.
                                                // http://dev.ckeditor.com/ticket/11027#comment:3
                                                var imageBefore = new Image( this.editor, true );

                                                // If current editor content matches the tip of snapshot stack,
                                                // the stack tip must be updated by unlock, to include any changes made
                                                // during this period.
                                                if ( this.currentImage && this.currentImage.equalsContent( imageBefore ) )
                                                        update = imageBefore;
                                        }

                                        this.locked = { update: update, level: 1 };
                                }

                        // Increase the level of lock.
                        } else {
                                this.locked.level++;
                        }
                },

                /**
                 * Unlocks the snapshot stack and checks to amend the last snapshot.
                 *
                 * See {@link #lock} for more details.
                 *
                 * @since 4.0
                 */
                unlock: function() {
                        if ( this.locked ) {
                                // Decrease level of lock and check if equals 0, what means that undoM is completely unlocked.
                                if ( !--this.locked.level ) {
                                        var update = this.locked.update;

                                        this.locked = null;

                                        // forceUpdate was passed to lock().
                                        if ( update === true )
                                                this.update();
                                        // update is instance of Image.
                                        else if ( update ) {
                                                var newImage = new Image( this.editor, true );

                                                if ( !update.equalsContent( newImage ) )
                                                        this.update();
                                        }
                                }
                        }
                }
        };

        /**
         * Codes for navigation keys like *Arrows*, *Page Up/Down*, etc.
         * Used by the {@link #isNavigationKey} method.
         *
         * @since 4.4.5
         * @readonly
         * @static
         */
        UndoManager.navigationKeyCodes = {
                37: 1, 38: 1, 39: 1, 40: 1, // Arrows.
                36: 1, 35: 1, // Home, End.
                33: 1, 34: 1 // PgUp, PgDn.
        };

        /**
         * Key groups identifier mapping. Used for accessing members in
         * {@link #strokesRecorded}.
         *
         * * `FUNCTIONAL` &ndash; identifier for the *Backspace* / *Delete* key.
         * * `PRINTABLE` &ndash; identifier for printable keys.
         *
         * Example usage:
         *
         *              undoManager.strokesRecorded[ undoManager.keyGroups.FUNCTIONAL ];
         *
         * @since 4.4.5
         * @readonly
         * @static
         */
        UndoManager.keyGroups = {
                PRINTABLE: 0,
                FUNCTIONAL: 1
        };

        /**
         * Checks whether a key is one of navigation keys (*Arrows*, *Page Up/Down*, etc.).
         * See also the {@link #navigationKeyCodes} property.
         *
         * @since 4.4.5
         * @static
         * @param {Number} keyCode
         * @returns {Boolean}
         */
        UndoManager.isNavigationKey = function( keyCode ) {
                return !!UndoManager.navigationKeyCodes[ keyCode ];
        };

        /**
         * Returns the group to which the passed `keyCode` belongs.
         *
         * @since 4.4.5
         * @static
         * @param {Number} keyCode
         * @returns {Number}
         */
        UndoManager.getKeyGroup = function( keyCode ) {
                var keyGroups = UndoManager.keyGroups;

                return backspaceOrDelete[ keyCode ] ? keyGroups.FUNCTIONAL : keyGroups.PRINTABLE;
        };

        /**
         * @since 4.4.5
         * @static
         * @param {Number} keyGroup
         * @returns {Number}
         */
        UndoManager.getOppositeKeyGroup = function( keyGroup ) {
                var keyGroups = UndoManager.keyGroups;
                return ( keyGroup == keyGroups.FUNCTIONAL ? keyGroups.PRINTABLE : keyGroups.FUNCTIONAL );
        };

        /**
         * Whether we need to use a workaround for functional (*Backspace*, *Delete*) keys not firing
         * the `keypress` event in Internet Explorer in this environment and for the specified `keyCode`.
         *
         * @since 4.4.5
         * @static
         * @param {Number} keyCode
         * @returns {Boolean}
         */
        UndoManager.ieFunctionalKeysBug = function( keyCode ) {
                return CKEDITOR.env.ie && UndoManager.getKeyGroup( keyCode ) == UndoManager.keyGroups.FUNCTIONAL;
        };

        // Helper method called when undoManager.typing val was changed to true.
        function onTypingStart( undoManager ) {
                // It's safe to now indicate typing state.
                undoManager.typing = true;

                // Manually mark snapshot as available.
                undoManager.hasUndo = true;
                undoManager.hasRedo = false;

                undoManager.onChange();
        }

        /**
         * Contains a snapshot of the editor content and selection at a given point in time.
         *
         * @private
         * @class CKEDITOR.plugins.undo.Image
         * @constructor Creates an Image class instance.
         * @param {CKEDITOR.editor} editor The editor instance on which the image is created.
         * @param {Boolean} [contentsOnly] If set to `true`, the image will only contain content without the selection.
         */
        var Image = CKEDITOR.plugins.undo.Image = function( editor, contentsOnly ) {
                        this.editor = editor;

                        editor.fire( 'beforeUndoImage' );

                        var contents = editor.getSnapshot();

                        // In IE, we need to remove the expando attributes.
                        if ( CKEDITOR.env.ie && contents )
                                contents = contents.replace( /\s+data-cke-expando=".*?"/g, '' );

                        this.contents = contents;

                        if ( !contentsOnly ) {
                                var selection = contents && editor.getSelection();
                                this.bookmarks = selection && selection.createBookmarks2( true );
                        }

                        editor.fire( 'afterUndoImage' );
                };

        // Attributes that browser may changing them when setting via innerHTML.
        var protectedAttrs = /\b(?:href|src|name)="[^"]*?"/gi;

        Image.prototype = {
                /**
                 * @param {CKEDITOR.plugins.undo.Image} otherImage Image to compare to.
                 * @returns {Boolean} Returns `true` if content in `otherImage` is the same.
                 */
                equalsContent: function( otherImage ) {
                        var thisContents = this.contents,
                                otherContents = otherImage.contents;

                        // For IE7 and IE QM: Comparing only the protected attribute values but not the original ones.(#4522)
                        if ( CKEDITOR.env.ie && ( CKEDITOR.env.ie7Compat || CKEDITOR.env.quirks ) ) {
                                thisContents = thisContents.replace( protectedAttrs, '' );
                                otherContents = otherContents.replace( protectedAttrs, '' );
                        }

                        if ( thisContents != otherContents )
                                return false;

                        return true;
                },

                /**
                 * @param {CKEDITOR.plugins.undo.Image} otherImage Image to compare to.
                 * @returns {Boolean} Returns `true` if selection in `otherImage` is the same.
                 */
                equalsSelection: function( otherImage ) {
                        var bookmarksA = this.bookmarks,
                                bookmarksB = otherImage.bookmarks;

                        if ( bookmarksA || bookmarksB ) {
                                if ( !bookmarksA || !bookmarksB || bookmarksA.length != bookmarksB.length )
                                        return false;

                                for ( var i = 0; i < bookmarksA.length; i++ ) {
                                        var bookmarkA = bookmarksA[ i ],
                                                bookmarkB = bookmarksB[ i ];

                                        if ( bookmarkA.startOffset != bookmarkB.startOffset || bookmarkA.endOffset != bookmarkB.endOffset ||
                                                !CKEDITOR.tools.arrayCompare( bookmarkA.start, bookmarkB.start ) ||
                                                !CKEDITOR.tools.arrayCompare( bookmarkA.end, bookmarkB.end ) ) {
                                                return false;
                                        }
                                }
                        }

                        return true;
                }

                /**
                 * Editor content.
                 *
                 * @readonly
                 * @property {String} contents
                 */

                /**
                 * Bookmarks representing the selection in an image.
                 *
                 * @readonly
                 * @property {Object[]} bookmarks Array of bookmark2 objects, see {@link CKEDITOR.dom.range#createBookmark2} for definition.
                 */
        };

        /**
         * A class encapsulating all native event listeners which have to be used in
         * order to handle undo manager integration for native editing actions (excluding drag and drop and paste support
         * handled by the Clipboard plugin).
         *
         * @since 4.4.4
         * @private
         * @class CKEDITOR.plugins.undo.NativeEditingHandler
         * @member CKEDITOR.plugins.undo Undo manager owning the handler.
         * @constructor
         * @param {CKEDITOR.plugins.undo.UndoManager} undoManager
         */
        var NativeEditingHandler = CKEDITOR.plugins.undo.NativeEditingHandler = function( undoManager ) {
                // We'll use keyboard + input events to determine if snapshot should be created.
                // Since `input` event is fired before `keyup`. We can tell in `keyup` event if input occured.
                // That will tell us if any printable data was inserted.
                // On `input` event we'll increase input fired counter for proper key code.
                // Eventually it might be canceled by paste/drop using `ignoreInputEvent` flag.
                // Order of events can be found in http://www.w3.org/TR/DOM-Level-3-Events/

                /**
                 * An undo manager instance owning the editing handler.
                 *
                 * @property {CKEDITOR.plugins.undo.UndoManager} undoManager
                 */
                this.undoManager = undoManager;

                /**
                 * See {@link #ignoreInputEventListener}.
                 *
                 * @since 4.4.5
                 * @private
                 */
                this.ignoreInputEvent = false;

                /**
                 * A stack of pressed keys.
                 *
                 * @since 4.4.5
                 * @property {CKEDITOR.plugins.undo.KeyEventsStack} keyEventsStack
                 */
                this.keyEventsStack = new KeyEventsStack();

                /**
                 * An image of the editor during the `keydown` event (therefore without DOM modification).
                 *
                 * @property {CKEDITOR.plugins.undo.Image} lastKeydownImage
                 */
                this.lastKeydownImage = null;
        };

        NativeEditingHandler.prototype = {
                /**
                 * The `keydown` event listener.
                 *
                 * @param {CKEDITOR.dom.event} evt
                 */
                onKeydown: function( evt ) {
                        var keyCode = evt.data.getKey();

                        // The composition is in progress - ignore the key. (#12597)
                        if ( keyCode === 229 ) {
                                return;
                        }

                        // Block undo/redo keystrokes when at the bottom/top of the undo stack (#11126 and #11677).
                        if ( CKEDITOR.tools.indexOf( keystrokes, evt.data.getKeystroke() ) > -1 ) {
                                evt.data.preventDefault();
                                return;
                        }

                        // Cleaning tab functional keys.
                        this.keyEventsStack.cleanUp( evt );

                        var undoManager = this.undoManager;

                        // Gets last record for provided keyCode. If not found will create one.
                        var last = this.keyEventsStack.getLast( keyCode );
                        if ( !last ) {
                                this.keyEventsStack.push( keyCode );
                        }

                        // We need to store an image which will be used in case of key group
                        // change.
                        this.lastKeydownImage = new Image( undoManager.editor );

                        if ( UndoManager.isNavigationKey( keyCode ) || this.undoManager.keyGroupChanged( keyCode ) ) {
                                if ( undoManager.strokesRecorded[ 0 ] || undoManager.strokesRecorded[ 1 ] ) {
                                        // We already have image, so we'd like to reuse it.

                                        // #12300
                                        undoManager.save( false, this.lastKeydownImage, false );
                                        undoManager.resetType();
                                }
                        }
                },

                /**
                 * The `input` event listener.
                 */
                onInput: function() {
                        // Input event is ignored if paste/drop event were fired before.
                        if ( this.ignoreInputEvent ) {
                                // Reset flag - ignore only once.
                                this.ignoreInputEvent = false;
                                return;
                        }

                        var lastInput = this.keyEventsStack.getLast();
                        // Nothing in key events stack, but input event called. Interesting...
                        // That's because on Android order of events is buggy and also keyCode is set to 0.
                        if ( !lastInput ) {
                                lastInput = this.keyEventsStack.push( 0 );
                        }

                        // Increment inputs counter for provided key code.
                        this.keyEventsStack.increment( lastInput.keyCode );

                        // Exceeded limit.
                        if ( this.keyEventsStack.getTotalInputs() >= this.undoManager.strokesLimit ) {
                                this.undoManager.type( lastInput.keyCode, true );
                                this.keyEventsStack.resetInputs();
                        }
                },

                /**
                 * The `keyup` event listener.
                 *
                 * @param {CKEDITOR.dom.event} evt
                 */
                onKeyup: function( evt ) {
                        var undoManager = this.undoManager,
                                keyCode = evt.data.getKey(),
                                totalInputs = this.keyEventsStack.getTotalInputs();

                        // Remove record from stack for provided key code.
                        this.keyEventsStack.remove( keyCode );

                        // Second part of the workaround for IEs functional keys bug. We need to check whether something has really
                        // changed because we blindly mocked the keypress event.
                        // Also we need to be aware that lastKeydownImage might not be available (#12327).
                        if ( UndoManager.ieFunctionalKeysBug( keyCode ) && this.lastKeydownImage &&
                                this.lastKeydownImage.equalsContent( new Image( undoManager.editor, true ) ) ) {
                                return;
                        }

                        if ( totalInputs > 0 ) {
                                undoManager.type( keyCode );
                        } else if ( UndoManager.isNavigationKey( keyCode ) ) {
                                // Note content snapshot has been checked in keydown.
                                this.onNavigationKey( true );
                        }
                },

                /**
                 * Method called for navigation change. At first it will check if current content does not differ
                 * from the last saved snapshot.
                 *
                 * * If the content is different, the method creates a standard, extra snapshot.
                 * * If the content is not different, the method will compare the selection, and will
                 * amend the last snapshot selection if it changed.
                 *
                 * @param {Boolean} skipContentCompare If set to `true`, it will not compare content, and only do a selection check.
                 */
                onNavigationKey: function( skipContentCompare ) {
                        var undoManager = this.undoManager;

                        // We attempt to save content snapshot, if content didn't change, we'll
                        // only amend selection.
                        if ( skipContentCompare || !undoManager.save( true, null, false ) )
                                undoManager.updateSelection( new Image( undoManager.editor ) );

                        undoManager.resetType();
                },

                /**
                 * Makes the next `input` event to be ignored.
                 */
                ignoreInputEventListener: function() {
                        this.ignoreInputEvent = true;
                },

                /**
                 * Attaches editable listeners required to provide the undo functionality.
                 */
                attachListeners: function() {
                        var editor = this.undoManager.editor,
                                editable = editor.editable(),
                                that = this;

                        // We'll create a snapshot here (before DOM modification), because we'll
                        // need unmodified content when we got keygroup toggled in keyup.
                        editable.attachListener( editable, 'keydown', function( evt ) {
                                that.onKeydown( evt );

                                // On IE keypress isn't fired for functional (backspace/delete) keys.
                                // Let's pretend that something's changed.
                                if ( UndoManager.ieFunctionalKeysBug( evt.data.getKey() ) ) {
                                        that.onInput();
                                }
                        }, null, null, 999 );

                        // Only IE can't use input event, because it's not fired in contenteditable.
                        editable.attachListener( editable, ( CKEDITOR.env.ie ? 'keypress' : 'input' ), that.onInput, that, null, 999 );

                        // Keyup executes main snapshot logic.
                        editable.attachListener( editable, 'keyup', that.onKeyup, that, null, 999 );

                        // On paste and drop we need to ignore input event.
                        // It would result with calling undoManager.type() on any following key.
                        editable.attachListener( editable, 'paste', that.ignoreInputEventListener, that, null, 999 );
                        editable.attachListener( editable, 'drop', that.ignoreInputEventListener, that, null, 999 );

                        // Click should create a snapshot if needed, but shouldn't cause change event.
                        // Don't pass onNavigationKey directly as a listener because it accepts one argument which
                        // will conflict with evt passed to listener.
                        // #12324 comment:4
                        editable.attachListener( editable.isInline() ? editable : editor.document.getDocumentElement(), 'click', function() {
                                that.onNavigationKey();
                        }, null, null, 999 );

                        // When pressing `Tab` key while editable is focused, `keyup` event is not fired.
                        // Which means that record for `tab` key stays in key events stack.
                        // We assume that when editor is blurred `tab` key is already up.
                        editable.attachListener( this.undoManager.editor, 'blur', function() {
                                that.keyEventsStack.remove( 9 /*Tab*/ );
                        }, null, null, 999 );
                }
        };

        /**
         * This class represents a stack of pressed keys and stores information
         * about how many `input` events each key press has caused.
         *
         * @since 4.4.5
         * @private
         * @class CKEDITOR.plugins.undo.KeyEventsStack
         * @constructor
         */
        var KeyEventsStack = CKEDITOR.plugins.undo.KeyEventsStack = function() {
                /**
                 * @readonly
                 */
                this.stack = [];
        };

        KeyEventsStack.prototype = {
                /**
                 * Pushes a literal object with two keys: `keyCode` and `inputs` (whose initial value is set to `0`) to stack.
                 * It is intended to be called on the `keydown` event.
                 *
                 * @param {Number} keyCode
                 */
                push: function( keyCode ) {
                        var length = this.stack.push( { keyCode: keyCode, inputs: 0 } );
                        return this.stack[ length - 1 ];
                },

                /**
                 * Returns the index of the last registered `keyCode` in the stack.
                 * If no `keyCode` is provided, then the function will return the index of the last item.
                 * If an item is not found, it will return `-1`.
                 *
                 * @param {Number} [keyCode]
                 * @returns {Number}
                 */
                getLastIndex: function( keyCode ) {
                        if ( typeof keyCode != 'number' ) {
                                return this.stack.length - 1; // Last index or -1.
                        } else {
                                var i = this.stack.length;
                                while ( i-- ) {
                                        if ( this.stack[ i ].keyCode == keyCode ) {
                                                return i;
                                        }
                                }
                                return -1;
                        }
                },

                /**
                 * Returns the last key recorded in the stack. If `keyCode` is provided, then it will return
                 * the  last record for this `keyCode`.
                 *
                 * @param {Number} [keyCode]
                 * @returns {Object} Last matching record or `null`.
                 */
                getLast: function( keyCode ) {
                        var index = this.getLastIndex( keyCode );
                        if ( index != -1 ) {
                                return this.stack[ index ];
                        } else {
                                return null;
                        }
                },

                /**
                 * Increments registered input events for stack record for a given `keyCode`.
                 *
                 * @param {Number} keyCode
                 */
                increment: function( keyCode ) {
                        var found = this.getLast( keyCode );
                        if ( !found ) { // %REMOVE_LINE%
                                throw new Error( 'Trying to increment, but could not found by keyCode: ' + keyCode + '.' ); // %REMOVE_LINE%
                        } // %REMOVE_LINE%

                        found.inputs++;
                },

                /**
                 * Removes the last record from the stack for the provided `keyCode`.
                 *
                 * @param {Number} keyCode
                 */
                remove: function( keyCode ) {
                        var index = this.getLastIndex( keyCode );

                        if ( index != -1 ) {
                                this.stack.splice( index, 1 );
                        }
                },

                /**
                 * Resets the `inputs` value to `0` for a given `keyCode` or in entire stack if a
                 * `keyCode` is not specified.
                 *
                 * @param {Number} [keyCode]
                 */
                resetInputs: function( keyCode ) {
                        if ( typeof keyCode == 'number' ) {
                                var last = this.getLast( keyCode );

                                if ( !last ) { // %REMOVE_LINE%
                                        throw new Error( 'Trying to reset inputs count, but could not found by keyCode: ' + keyCode + '.' ); // %REMOVE_LINE%
                                } // %REMOVE_LINE%

                                last.inputs = 0;
                        } else {
                                var i = this.stack.length;
                                while ( i-- ) {
                                        this.stack[ i ].inputs = 0;
                                }
                        }
                },

                /**
                 * Sums up inputs number for each key code and returns it.
                 *
                 * @returns {Number}
                 */
                getTotalInputs: function() {
                        var i = this.stack.length,
                                total = 0;

                        while ( i-- ) {
                                total += this.stack[ i ].inputs;
                        }
                        return total;
                },

                /**
                 * Cleans the stack based on a provided `keydown` event object. The rationale behind this method
                 * is that some keystrokes cause the `keydown` event to be fired in the editor, but not the `keyup` event.
                 * For instance, *Alt+Tab* will fire `keydown`, but since the editor is blurred by it, then there is
                 * no `keyup`, so the keystroke is not removed from the stack.
                 *
                 * @param {CKEDITOR.dom.event} event
                 */
                cleanUp: function( event ) {
                        var nativeEvent = event.data.$;

                        if ( !( nativeEvent.ctrlKey || nativeEvent.metaKey ) ) {
                                this.remove( 17 );
                        }
                        if ( !nativeEvent.shiftKey ) {
                                this.remove( 16 );
                        }
                        if ( !nativeEvent.altKey ) {
                                this.remove( 18 );
                        }
                }
        };
} )();

/**
 * The number of undo steps to be saved. The higher value is set, the more
 * memory is used for it.
 *
 *              config.undoStackSize = 50;
 *
 * @cfg {Number} [undoStackSize=20]
 * @member CKEDITOR.config
 */

/**
 * Fired when the editor is about to save an undo snapshot. This event can be
 * fired by plugins and customizations to make the editor save undo snapshots.
 *
 * @event saveSnapshot
 * @member CKEDITOR.editor
 * @param {CKEDITOR.editor} editor This editor instance.
 */

/**
 * Fired before an undo image is to be created. An *undo image* represents the
 * editor state at some point. It is saved into the undo store, so the editor is
 * able to recover the editor state on undo and redo operations.
 *
 * @since 3.5.3
 * @event beforeUndoImage
 * @member CKEDITOR.editor
 * @param {CKEDITOR.editor} editor This editor instance.
 * @see CKEDITOR.editor#afterUndoImage
 */

/**
 * Fired after an undo image is created. An *undo image* represents the
 * editor state at some point. It is saved into the undo store, so the editor is
 * able to recover the editor state on undo and redo operations.
 *
 * @since 3.5.3
 * @event afterUndoImage
 * @member CKEDITOR.editor
 * @param {CKEDITOR.editor} editor This editor instance.
 * @see CKEDITOR.editor#beforeUndoImage
 */

/**
 * Fired when the content of the editor is changed.
 *
 * Due to performance reasons, it is not verified if the content really changed.
 * The editor instead watches several editing actions that usually result in
 * changes. This event may thus in some cases be fired when no changes happen
 * or may even get fired twice.
 *
 * If it is important not to get the `change` event fired too often, you should compare the
 * previous and the current editor content inside the event listener. It is
 * not recommended to do that on every `change` event.
 *
 * Please note that the `change` event is only fired in the {@link #property-mode wysiwyg mode}.
 * In order to implement similar functionality in the source mode, you can listen for example to the {@link #key}
 * event or the native [`input`](https://developer.mozilla.org/en-US/docs/Web/Reference/Events/input)
 * event (not supported by Internet Explorer 8).
 *
 *              editor.on( 'mode', function() {
 *                      if ( this.mode == 'source' ) {
 *                              var editable = editor.editable();
 *                              editable.attachListener( editable, 'input', function() {
 *                                      // Handle changes made in the source mode.
 *                              } );
 *                      }
 *              } );
 *
 * @since 4.2
 * @event change
 * @member CKEDITOR.editor
 * @param {CKEDITOR.editor} editor This editor instance.
 */