index.js

var path = require('path');
var Promise = require('bluebird');
var uniq = require('uniq');
var fs = Promise.promisifyAll(require('fs'));

var SERVER_APP_PATH = 'src/server/app/publish';
var PREAMBLE_PATH = path.join(SERVER_APP_PATH, 'preamble.js');
var CAPSULE_BUILD_PATH = path.join(SERVER_APP_PATH, 'capsule.build.js');
var SAMPLE_CAPSULE_PATH = path.join(SERVER_APP_PATH, 'sample-capsule.json');

fs.readFileAsync(PREAMBLE_PATH)
  .then(function(preamble) {
    return fs.writeFileAsync(CAPSULE_BUILD_PATH, preamble);
  })
  .then(function() {
    return fs.readFileAsync(SAMPLE_CAPSULE_PATH);
  })
  .then(JSON.parse)
  .then(function(capsule) {
    var widgets = uniq(capsule.widgets.map(function(w) {
      return w.referenceId;
    }));

    var importStatements = '';
    widgets.forEach(function(w) {
      importStatements += 'import \'' + w + '\'\n';
    });

    return importStatements;
  })
  .then(function(importStatements) {
    return fs.appendFileAsync(CAPSULE_BUILD_PATH, importStatements, function(err) {
      console.log('done!');
    });
  });