A PostCSS theme loader for CKEditor 5

cke5-postcss-theme-loader.js

const fs = require( 'fs' );
const path = require( 'path' );
const postcss = require( 'postcss' );
const postcssImport = require( 'postcss-import' );
const postcssCssnext = require( 'postcss-cssnext' );

module.exports = postcss.plugin( 'postcss-ck-theme-importer', ( options ) => {
	const themeName = options.themePath.split( '/' ).slice( -1 );
	console.log( `Using theme "${ themeName }".` );

	return ( root, result ) => {
		const fileName = path.basename( root.source.input.file );
		const relativeFilePath = path.relative( __dirname, root.source.input.file );
		const themeFile = path.resolve( __dirname, options.themePath, fileName );

		if ( fs.existsSync( themeFile ) ) {
			const relativeThemeFilePath = path.relative( __dirname, themeFile );

			console.log( `Found a corresponding theme file for ${ relativeFilePath }: ${ relativeThemeFilePath }.` );

			return new Promise( ( resolve, reject ) => {
				fs.readFile( themeFile, 'utf8', ( err, data ) => {
					const processor = postcss( {
						plugins: [
							postcssImport()
						]
					} );

					return processor.process( data, { from: themeFile } )
						.then( result => {
							root.append( result.css );
							root.append( '\n' );

							resolve();
						} );
				} );
			} );
		} else {
			console.log( `Theme file for ${ relativeFilePath } not found.` );
		}
	};
} );