poststylus/index.js

'use strict';

var postcss = require('postcss'),
    path = require('path'),
    map = require('multi-stage-sourcemap');

module.exports = function (plugins, warnFn) {

  plugins = plugins || [];

  var processPlugin = function(plugin) {

    // If plugin is a string, require the package that we assume it points to
    if (typeof plugin === 'string') {
      return require(plugin)();
    }

    return plugin;
  };

  // Either process each if its an array, or directly if singular
  if (typeof plugins.map !== 'undefined') {
    plugins = plugins.map(processPlugin);
  } else {
    plugins = processPlugin(plugins);
  }

  // Return stylus function after postcss processing
  return function(style) {
    style = this || style;
    var filename = style.options.filename;

    // Grab stylus' ouput css before it's compiled to file
    style.on('end', function(err, css) {

      // Exit on error
      if (err){
        return err;
      }

      // Postcss options
      var processOptions = {
        from: filename,
        to: path.join(
          path.dirname(filename),
          path.basename(filename, path.extname(filename))
        ) + '.css'
      };

      // If stylus has a sourcemap, ensure postcss also generates one
      if (style.sourcemap) {
        processOptions.map = { annotation: false };
      }

      // Run postcss with user plugins
      var processed = postcss(plugins).process(css, processOptions);

      // If sourcemaps generated, combine them
      if (processed.map && style.sourcemap) {

        var comboMap = map.transfer({
          fromSourceMap: processed.map.toString(),
          toSourceMap: style.sourcemap
        });

        style.sourcemap = JSON.parse(comboMap);

      }

      // Pipe postcss errors to console
      if (!warnFn || typeof warnFn !== 'function'){
        warnFn = console.error;
      }

      processed.warnings().forEach(warnFn);

      return processed.css;

    });

  };
};