Gruntfile.js

module.exports = function(grunt) {
  require('jit-grunt')(grunt); // Just in time library loading

  var fs = require('fs');

  /**
   * @param  {string} file
   * @return {Array}  retval - path to file as Array
   */
  function getLoadPaths(file) {
    var config;
    var parts = file.split('/');
    parts.pop(); // eliminate filename

    // initialize search path with directory containing LESS file
    var retVal = [];
    retVal.push(parts.join('/'));

    // Iterate through theme.config.php files collecting parent themes in search path:
    while (config = fs.readFileSync("themes/" + parts[1] + "/theme.config.php", "UTF-8")) {
      // First identify mixins:
      var mixinMatches = config.match(/["']mixins["']\s*=>\s*\[([^\]]+)\]/);
      if (mixinMatches !== null) {
        var mixinParts = mixinMatches[1].split(',');
        for (var i = 0; i < mixinParts.length; i++) {
          parts[1] = mixinParts[i].trim().replace(/['"]/g, '');
          retVal.push(parts.join('/') + '/');
        }
      }

      // Now move up to parent theme:
      var matches = config.match(/["']extends["']\s*=>\s*['"](\w+)['"]/);

      // "extends" set to "false" or missing entirely? We've hit the end of the line:
      if (matches === null || matches[1] === 'false') {
        break;
      }

      parts[1] = matches[1];
      retVal.push(parts.join('/') + '/');
    }
    return retVal;
  }

  var fontAwesomePath = '"../../bootstrap3/css/fonts"';
  var lessFileSettings = [{
    expand: true,
    src: "themes/*/less/compiled.less",
    rename: function (dest, src) {
      return src.replace('/less/', '/css/').replace('.less', '.css');
    }
  }];

  grunt.initConfig({
    // LESS compilation
    less: {
      compile: {
        files: lessFileSettings,
        options: {
          paths: getLoadPaths,
          compress: true,
          modifyVars: {
            'fa-font-path': fontAwesomePath
          }
        }
      }
    },
    // Less with maps
    lessdev: {
      less: {
      }
    },
    // SASS compilation
    scss: {
      sass: {
        options: {
          style: 'compress'
        }
      }
    },

    // Convert LESS to SASS, mostly for development team use
    lessToSass: {
      convert: {
        files: [
          {
            expand: true,
            cwd: 'themes/bootstrap3/less',
            src: ['*.less', 'components/*.less'],
            ext: '.scss',
            dest: 'themes/bootstrap3/scss'
          },
          {
            expand: true,
            cwd: 'themes/bootprint3/less',
            src: ['*.less'],
            ext: '.scss',
            dest: 'themes/bootprint3/scss'
          },
          {
            expand: true,
            cwd: 'themes/sandal/less',
            src: ['*.less'],
            ext: '.scss',
            dest: 'themes/sandal/scss'
          }
        ],
        options: {
          replacements: [
            // Activate SCSS
            {
              pattern: /\/\* #SCSS>/gi,
              replacement: "/* #SCSS> */",
              order: -1 // Do before anything else
            },
            {
              pattern: /<#SCSS \*\//gi,
              replacement: "/* <#SCSS */",
              order: -1
            },
            // Deactivate LESS
            {
              pattern: /\/\* #LESS> \*\//gi,
              replacement: "/* #LESS>",
              order: -1
            },
            {
              pattern: /\/\* <#LESS \*\//gi,
              replacement: "<#LESS */",
              order: -1
            },
            { // Change separator in @include statements
              pattern: /@include ([^\(]+)\(([^\)]+)\);/gi,
              replacement: function mixinCommas(match, $1, $2) {
                return '@include ' + $1 + '(' + $2.replace(/;/g, ',') + ');';
              },
              order: 4 // after defaults included in less-to-sass
            },
            { // Remove unquote
              pattern: /unquote\("([^"]+)"\)/gi,
              replacement: function ununquote(match, $1) {
                return $1;
              },
              order: 4
            },
            { // Inline &:extends converted
              pattern: /&:extend\(([^\)]+)\)/gi,
              replacement: '@extend $1',
              order: 4
            },
            { // Wrap variables in calcs with #{}
              pattern: /calc\([^;]+/gi,
              replacement: function calcVariables(match) {
                return match.replace(/(\$[^ ]+)/gi, '#{$1}');
              },
              order: 4
            },
            { // Remove !default from extends (icons.scss)
              pattern: /@extend ([^;}]+) !default;/gi,
              replacement: '@extend $1;',
              order: 5
            }
          ]
        }
      }
    },

    watch: {
      options: {
        atBegin: true
      },
      less: {
        files: 'themes/*/less/**/*.less',
        tasks: ['less']
      },
      lessdev: {
        files: 'themes/*/less/**/*.less',
        tasks: ['lessdev']
      },
      scss: {
        files: 'themes/*/scss/**/*.scss',
        tasks: ['scss']
      }
    }
  });

  grunt.registerMultiTask('lessdev', function lessWithMaps() {
    grunt.config.set('less', {
      dev: {
        files: lessFileSettings,
        options: {
          paths: getLoadPaths,
          sourceMap: true,
          sourceMapFileInline: true,
          modifyVars: {
            'fa-font-path': fontAwesomePath
          }
        }
      }
    });
    grunt.task.run('less');
  });

  grunt.registerMultiTask('scss', function sassScan() {
    var sassConfig = {},
      path = require('path'),
      themeList = fs.readdirSync(path.resolve('themes')).filter(function (theme) {
        return fs.existsSync(path.resolve('themes/' + theme + '/scss/compiled.scss'))
            || fs.existsSync(path.resolve('themes/' + theme + '/scss/print.scss'));
      });

    /**
     * Define mapping of input (scss) to output files (css) for following sass task
     */
    for (var i in themeList) {
      var config = {
        options: {
          outputStyle: 'compressed'
        },
        files: [{
          expand: true,
          cwd: path.join('themes', themeList[i], 'scss'),
          src: ['compiled.scss', 'print.scss'],
          dest: path.join('themes', themeList[i], 'css'),
          ext: '.css'
        }]
      };
      for (var key in this.data.options) {
        config.options[key] = this.data.options[key] + '';
      }

      /* get Array of unique input paths */
      config.options.includePaths = Array.from(
          new Set(
              getLoadPaths('themes/' + themeList[i] + '/scss/compiled.scss')
                  .concat(getLoadPaths('themes/' + themeList[i] + '/scss/print.scss'))
          )
      );

      sassConfig[themeList[i]] = config;
    }

    grunt.config.set('sass', sassConfig);
    grunt.task.run('sass');
  });
  grunt.registerTask('default', ['scss']);
};