parser.js

const importRegexp = /^:import\((.+)\)$/;

export default class Parser {
  constructor( pathFetcher, trace ) {
    this.pathFetcher = pathFetcher;
    this.plugin = this.plugin.bind( this );
    this.exportTokens = {};
    this.translations = {};
    this.trace = trace;
  }

  plugin( css ) {
    return Promise.all( this.fetchAllImports( css ) )
      .then( () => this.linkImportedSymbols( css ) )
      .then( () => this.extractExports( css ) );
  }

  fetchAllImports( css ) {
    let imports = [];
    css.each( node => {
      if ( node.type === 'rule' && node.selector.match( importRegexp ) ) {
        imports.push( this.fetchImport( node, css.source.input.from, imports.length ) );
      }
    } );
    return imports;
  }

  linkImportedSymbols( css ) {
    css.eachDecl( decl => {
      Object.keys( this.translations ).forEach( translation => {
        decl.value = decl.value.replace( translation, this.translations[translation] );
      } );
    } );
  }

  extractExports( css ) {
    css.each( node => {
      if ( node.type === 'rule' && node.selector === ':export' ) {
        this.handleExport( node );
      }
    } );
  }

  handleExport( exportNode ) {
    exportNode.each( decl => {
      if ( decl.type === 'decl' ) {
        Object.keys( this.translations ).forEach( translation => {
          decl.value = decl.value.replace( translation, this.translations[translation] );
        } );
        this.exportTokens[decl.prop] = decl.value;
      }
    } );
    exportNode.removeSelf();
  }

  fetchImport( importNode, relativeTo, depNr ) {
    let file = importNode.selector.match( importRegexp )[1],
      depTrace = this.trace + String.fromCharCode( depNr );
    return this.pathFetcher( file, relativeTo, depTrace ).then( exports => {
      importNode.each( decl => {
        if ( decl.type === 'decl' ) {
          this.translations[decl.prop] = exports[decl.value];
        }
      } );
      importNode.removeSelf();
    }, err => console.log( err ) );
  }
}