ckeditor/ckeditor5-engine

/**
 * @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 engine/view/observer/fakeselectionobserver
 */

import Observer from './observer';
import ViewSelection from '../selection';
import { keyCodes } from '@ckeditor/ckeditor5-utils/src/keyboard';
import { debounce } from 'lodash-es';

/**
 * Fake selection observer class. If view selection is fake it is placed in dummy DOM container. This observer listens
 * on {@link module:engine/view/document~Document#event:keydown keydown} events and handles moving fake view selection to the correct place
 * if arrow keys are pressed.
 * Fires {@link module:engine/view/document~Document#event:selectionChange selectionChange event} simulating natural behaviour of
 * {@link module:engine/view/observer/selectionobserver~SelectionObserver SelectionObserver}.
 *
 * @extends module:engine/view/observer/observer~Observer
 */
export default class FakeSelectionObserver extends Observer {
    /**
     * Creates new FakeSelectionObserver instance.
     *
     * @param {module:engine/view/view~View} view
     */
    constructor( view ) {
        super( view );

        /**
         * Fires debounced event `selectionChangeDone`. It uses `lodash#debounce` method to delay function call.
         *
         * @private
         * @param {Object} data Selection change data.
         * @method #_fireSelectionChangeDoneDebounced
         */
        this._fireSelectionChangeDoneDebounced = debounce( data => this.document.fire( 'selectionChangeDone', data ), 200 );
    }

    /**
     * @inheritDoc
     */
    observe() {
        const document = this.document;

        document.on( 'keydown', ( eventInfo, data ) => {
            const selection = document.selection;

            if ( selection.isFake && _isArrowKeyCode( data.keyCode ) && this.isEnabled ) {
                // Prevents default key down handling - no selection change will occur.
                data.preventDefault();

                this._handleSelectionMove( data.keyCode );
            }
        }, { priority: 'lowest' } );
    }

    /**
     * @inheritDoc
     */
    destroy() {
        super.destroy();

        this._fireSelectionChangeDoneDebounced.cancel();
    }

    /**
     * Handles collapsing view selection according to given key code. If left or up key is provided - new selection will be
     * collapsed to left. If right or down key is pressed - new selection will be collapsed to right.
     *
     * This method fires {@link module:engine/view/document~Document#event:selectionChange} and
     * {@link module:engine/view/document~Document#event:selectionChangeDone} events imitating behaviour of
     * {@link module:engine/view/observer/selectionobserver~SelectionObserver}.
     *
     * @private
     * @param {Number} keyCode
     * @fires module:engine/view/document~Document#event:selectionChange
     * @fires module:engine/view/document~Document#event:selectionChangeDone
     */
    _handleSelectionMove( keyCode ) {
        const selection = this.document.selection;
        const newSelection = new ViewSelection( selection.getRanges(), { backward: selection.isBackward, fake: false } );

        // Left or up arrow pressed - move selection to start.
        if ( keyCode == keyCodes.arrowleft || keyCode == keyCodes.arrowup ) {
            newSelection.setTo( newSelection.getFirstPosition() );
        }

        // Right or down arrow pressed - move selection to end.
        if ( keyCode == keyCodes.arrowright || keyCode == keyCodes.arrowdown ) {
            newSelection.setTo( newSelection.getLastPosition() );
        }

        const data = {
            oldSelection: selection,
            newSelection,
            domSelection: null
        };

        // Fire dummy selection change event.
        this.document.fire( 'selectionChange', data );

        // Call` #_fireSelectionChangeDoneDebounced` every time when `selectionChange` event is fired.
        // This function is debounced what means that `selectionChangeDone` event will be fired only when
        // defined int the function time will elapse since the last time the function was called.
        // So `selectionChangeDone` will be fired when selection will stop changing.
        this._fireSelectionChangeDoneDebounced( data );
    }
}

// Checks if one of the arrow keys is pressed.
//
// @private
// @param {Number} keyCode
// @returns {Boolean}
function _isArrowKeyCode( keyCode ) {
    return keyCode == keyCodes.arrowright ||
        keyCode == keyCodes.arrowleft ||
        keyCode == keyCodes.arrowup ||
        keyCode == keyCodes.arrowdown;
}