ckeditor/ckeditor5-heading

/**
 * @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 heading/headingediting
 */

import Plugin from '@ckeditor/ckeditor5-core/src/plugin';
import Paragraph from '@ckeditor/ckeditor5-paragraph/src/paragraph';
import HeadingCommand from './headingcommand';

import priorities from '@ckeditor/ckeditor5-utils/src/priorities';

const defaultModelElement = 'paragraph';

/**
 * The headings engine feature. It handles switching between block formats – headings and paragraph.
 * This class represents the engine part of the heading feature. See also {@link module:heading/heading~Heading}.
 * It introduces `heading1`-`headingN` commands which allow to convert paragraphs into headings.
 *
 * @extends module:core/plugin~Plugin
 */
export default class HeadingEditing extends Plugin {
    /**
     * @inheritDoc
     */
    static get pluginName() {
        return 'HeadingEditing';
    }

    /**
     * @inheritDoc
     */
    constructor( editor ) {
        super( editor );

        editor.config.define( 'heading', {
            options: [
                { model: 'paragraph', title: 'Paragraph', class: 'ck-heading_paragraph' },
                { model: 'heading1', view: 'h2', title: 'Heading 1', class: 'ck-heading_heading1' },
                { model: 'heading2', view: 'h3', title: 'Heading 2', class: 'ck-heading_heading2' },
                { model: 'heading3', view: 'h4', title: 'Heading 3', class: 'ck-heading_heading3' }
            ]
        } );
    }

    /**
     * @inheritDoc
     */
    static get requires() {
        return [ Paragraph ];
    }

    /**
     * @inheritDoc
     */
    init() {
        const editor = this.editor;
        const options = editor.config.get( 'heading.options' );

        const modelElements = [];

        for ( const option of options ) {
            // Skip paragraph - it is defined in required Paragraph feature.
            if ( option.model !== defaultModelElement ) {
                // Schema.
                editor.model.schema.register( option.model, {
                    inheritAllFrom: '$block'
                } );

                editor.conversion.elementToElement( option );

                modelElements.push( option.model );
            }
        }

        this._addDefaultH1Conversion( editor );

        // Register the heading command for this option.
        editor.commands.add( 'heading', new HeadingCommand( editor, modelElements ) );
    }

    /**
     * @inheritDoc
     */
    afterInit() {
        // If the enter command is added to the editor, alter its behavior.
        // Enter at the end of a heading element should create a paragraph.
        const editor = this.editor;
        const enterCommand = editor.commands.get( 'enter' );
        const options = editor.config.get( 'heading.options' );

        if ( enterCommand ) {
            this.listenTo( enterCommand, 'afterExecute', ( evt, data ) => {
                const positionParent = editor.model.document.selection.getFirstPosition().parent;
                const isHeading = options.some( option => positionParent.is( option.model ) );

                if ( isHeading && !positionParent.is( defaultModelElement ) && positionParent.childCount === 0 ) {
                    data.writer.rename( positionParent, defaultModelElement );
                }
            } );
        }
    }

    /**
     * Adds default conversion for `h1` -> `heading1` with a low priority.
     *
     * @private
     * @param {module:core/editor/editor~Editor} editor Editor instance on which to add the `h1` conversion.
     */
    _addDefaultH1Conversion( editor ) {
        editor.conversion.for( 'upcast' ).elementToElement( {
            model: 'heading1',
            view: 'h1',
            // With a `low` priority, `paragraph` plugin autoparagraphing mechanism is executed. Make sure
            // this listener is called before it. If not, `h1` will be transformed into a paragraph.
            converterPriority: priorities.get( 'low' ) + 1
        } );
    }
}