gulpfile.js

/**
 * Copyright 2015 The AMP HTML Authors. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS-IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

checkMinVersion();

var $$ = require('gulp-load-plugins')();
var babel = require('babelify');
var browserify = require('browserify');
var buffer = require('vinyl-buffer');
var closureCompile = require('./build-system/tasks/compile').closureCompile;
var cleanupBuildDir = require('./build-system/tasks/compile').cleanupBuildDir;
var jsifyCssAsync = require('./build-system/tasks/jsify-css').jsifyCssAsync;
var fs = require('fs-extra');
var gulp = $$.help(require('gulp'));
var lazypipe = require('lazypipe');
var minimatch = require('minimatch');
var minimist = require('minimist');
var source = require('vinyl-source-stream');
var touch = require('touch');
var watchify = require('watchify');
var windowConfig = require('./build-system/window-config');
var internalRuntimeVersion = require('./build-system/internal-version').VERSION;
var internalRuntimeToken = require('./build-system/internal-version').TOKEN;

var argv = minimist(process.argv.slice(2), { boolean: ['strictBabelTransform'] });

require('./build-system/tasks');


/**
 * Build all the AMP extensions
 *
 * @param {!Object} options
 */
function buildExtensions(options) {
  // We pass watch further in to have browserify watch the built file
  // and update it if any of its required deps changed.
  // Each extension and version must be listed individually here.
  buildExtension('amp-access', '0.1', true, options);
  buildExtension('amp-accordion', '0.1', true, options);
  buildExtension('amp-ad', '0.1', false, options);
  buildExtension('amp-analytics', '0.1', false, options);
  buildExtension('amp-anim', '0.1', false, options);
  buildExtension('amp-audio', '0.1', false, options);
  buildExtension('amp-brid-player', '0.1', false, options);
  buildExtension('amp-brightcove', '0.1', false, options);
  buildExtension('amp-kaltura-player', '0.1', false, options);
  buildExtension('amp-carousel', '0.1', true, options);
  buildExtension('amp-dailymotion', '0.1', false, options);
  buildExtension('amp-dynamic-css-classes', '0.1', false, options);
  buildExtension('amp-facebook', '0.1', false, options);
  buildExtension('amp-fit-text', '0.1', true, options);
  buildExtension('amp-fx-flying-carpet', '0.1', true, options);
  buildExtension('amp-font', '0.1', false, options);
  buildExtension('amp-form', '0.1', false, options);
  buildExtension('amp-iframe', '0.1', false, options);
  buildExtension('amp-image-lightbox', '0.1', true, options);
  buildExtension('amp-instagram', '0.1', false, options);
  buildExtension('amp-jwplayer', '0.1', false, options);
  buildExtension('amp-lightbox', '0.1', false, options);
  buildExtension('amp-list', '0.1', false, options);
  buildExtension('amp-live-list', '0.1', true, options);
  buildExtension('amp-mustache', '0.1', false, options);
  buildExtension('amp-pinterest', '0.1', true, options);
  buildExtension('amp-reach-player', '0.1', false, options);
  buildExtension('amp-sidebar', '0.1', true, options);
  buildExtension('amp-soundcloud', '0.1', false, options);
  buildExtension('amp-springboard-player', '0.1', false, options);
  buildExtension('amp-sticky-ad', '0.1', true, options);
  buildExtension('amp-install-serviceworker', '0.1', false, options);
  /**
   * @deprecated `amp-slides` is deprecated and will be deleted before 1.0.
   * Please see {@link AmpCarousel} with `type=slides` attribute instead.
   */
  buildExtension('amp-slides', '0.1', false, options);
  buildExtension('amp-social-share', '0.1', true, options);
  buildExtension('amp-twitter', '0.1', false, options);
  buildExtension('amp-user-notification', '0.1', true, options);
  buildExtension('amp-vimeo', '0.1', false, options);
  buildExtension('amp-vine', '0.1', false, options);
  buildExtension('amp-youtube', '0.1', false, options);
}


/**
 * Compile the polyfills script and drop it in the build folder
 */
function polyfillsForTests() {
  compileJs('./src/', 'polyfills.js', './build/');
}

/**
 * Compile and optionally minify the stylesheets and the scripts
 * and drop them in the dist folder
 *
 * @param {boolean} watch
 * @param {boolean} shouldMinify
 * @param {boolean=} opt_preventRemoveAndMakeDir
 * @param {boolean=} opt_checkTypes
 */
function compile(watch, shouldMinify, opt_preventRemoveAndMakeDir,
    opt_checkTypes) {
  compileCss();
  compileJs('./3p/', 'integration.js', './dist.3p/' + internalRuntimeVersion, {
    minifiedName: 'f.js',
    checkTypes: opt_checkTypes,
    watch: watch,
    minify: shouldMinify,
    preventRemoveAndMakeDir: opt_preventRemoveAndMakeDir,
  });
  // The main binary does not yet compile successfully with type checking
  // turned on. Skip for now.
  if (opt_checkTypes && !argv.more) {
    return;
  }
  // For compilation with babel we start with the amp-babel entry point,
  // but then rename to the amp.js which we've been using all along.
  compileJs('./src/', 'amp-babel.js', './dist', {
    toName: 'amp.js',
    minifiedName: 'v0.js',
    includePolyfills: true,
    checkTypes: opt_checkTypes,
    watch: watch,
    preventRemoveAndMakeDir: opt_preventRemoveAndMakeDir,
    minify: shouldMinify,
    // If there is a sync JS error during initial load,
    // at least try to unhide the body.
    wrapper: windowConfig.getTemplate() +
        'try{(function(){<%= contents %>})()}catch(e){' +
        'setTimeout(function(){' +
        'var s=document.body.style;' +
        's.opacity=1;' +
        's.visibility="visible";' +
        's.animation="none";' +
        's.WebkitAnimation="none;"},1000);throw e};'
  });
  thirdPartyBootstrap(watch, shouldMinify);
}

/**
 * Compile all the css and drop in the build folder
 *
 * @return {!Promise} containing a Readable	Stream
 */
function compileCss() {
  console.info('Recompiling CSS.');
  return jsifyCssAsync('css/amp.css').then(function(css) {
    return gulp.src('css/**.css')
        .pipe($$.file('css.js', 'export const cssText = ' + css))
        .pipe(gulp.dest('build'));
  });
}

/**
 * Enables watching for file changes in css, extensions, and examples.
 */
function watch() {
  $$.watch('css/**/*.css', function() {
    compileCss();
  });
  buildAlp({
    watch: true,
  });
  buildExtensions({
    watch: true,
  });
  buildExamples(true);
  compile(true);
}

/**
 * Copies extensions from
 * extensions/$name/$version/$name.js
 * to
 * dist/v0/$name-$version.js
 *
 * Optionally copies the CSS at extensions/$name/$version/$name.css into
 * a generated JS file that can be required from the extensions as
 * `import {CSS} from '../../../build/$name-0.1.css';`
 *
 * @param {string} name Name of the extension. Must be the sub directory in
 *     the extensions directory and the name of the JS and optional CSS file.
 * @param {string} version Version of the extension. Must be identical to
 *     the sub directory inside the extension directory
 * @param {boolean} hasCss Whether there is a CSS file for this extension.
 * @param {?Object} options
 * @return {!Stream} Gulp object
 */
function buildExtension(name, version, hasCss, options) {
  options = options || {};
  var path = 'extensions/' + name + '/' + version;
  var jsPath = path + '/' + name + '.js';
  var jsTestPath = path + '/test/' + 'test-' + name + '.js';
  if (argv.files && options.bundleOnlyIfListedInFiles) {
    const passedFiles = Array.isArray(argv.files) ? argv.files : [argv.files];
    const shouldBundle = passedFiles.some(glob => {
      return minimatch(jsPath, glob) || minimatch(jsTestPath, glob);
    });
    if (!shouldBundle) {
      return;
    }
  }
  console.log('Bundling ' + name);
  // Building extensions is a 2 step process because of the renaming
  // and CSS inlining. This watcher watches the original file, copies
  // it to the destination and adds the CSS.
  if (options.watch) {
    // Do not set watchers again when we get called by the watcher.
    var copy = Object.create(options);
    copy.watch = false;
    $$.watch(path + '/*', function() {
      buildExtension(name, version, hasCss, copy);
    });
  }
  if (hasCss) {
    mkdirSync('build');
    return jsifyCssAsync(path + '/' + name + '.css').then(function(css) {
      var jsCss = 'export const CSS = ' + css + ';\n';
      var builtName = 'build/' + name + '-' + version + '.css.js';
      fs.writeFileSync(builtName, jsCss, 'utf-8');
      return buildExtensionJs(path, name, version, options);
    });
  } else {
    return buildExtensionJs(path, name, version, options);
  }
}

/**
 * Build the JavaScript for the extension specified
 *
 * @param {string} path Path to the extensions directory
 * @param {string} name Name of the extension. Must be the sub directory in
 *     the extensions directory and the name of the JS and optional CSS file.
 * @param {string} version Version of the extension. Must be identical to
 *     the sub directory inside the extension directory
 * @param {!Object} options
 * @return {!Stream} Gulp object
 */
function buildExtensionJs(path, name, version, options) {
  compileJs(path + '/', name + '.js', './dist/v0', {
    watch: options.watch,
    preventRemoveAndMakeDir: options.preventRemoveAndMakeDir,
    minify: options.minify,
    toName:  name + '-' + version + '.max.js',
    minifiedName: name + '-' + version + '.js',
    latestName: name + '-latest.js',
    wrapper: '(window.AMP = window.AMP || [])' +
        '.push(function(AMP) {<%= contents %>\n});',
  });
}

/**
 * Main Build
 */
function build() {
  process.env.NODE_ENV = 'development';
  polyfillsForTests();
  buildAlp();
  buildExtensions({bundleOnlyIfListedInFiles: true});
  buildExamples(false);
  compile();
}

/**
 * Dist Build
 */
function dist() {
  process.env.NODE_ENV = 'production';
  cleanupBuildDir();
  compile(false, true, true);
  buildAlp({minify: true, watch: false, preventRemoveAndMakeDir: true});
  buildExtensions({minify: true, preventRemoveAndMakeDir: true});
  buildExperiments({minify: true, watch: false, preventRemoveAndMakeDir: true});
  buildLoginDone({minify: true, watch: false, preventRemoveAndMakeDir: true});
}

/**
 * Dedicated type check path.
 */
function checkTypes() {
  process.env.NODE_ENV = 'production';
  cleanupBuildDir();
  buildAlp({
    minify: true,
    checkTypes: true,
    preventRemoveAndMakeDir: true,
  });
  buildExperiments({
    minify: true,
    checkTypes: true,
    preventRemoveAndMakeDir: true,
  });
  compile(false, true, /* opt_preventRemoveAndMakeDir*/ true,
      /* check types */ true);
  // These are not turned on on Travis.
}

/**
 * Build the examples
 *
 * @param {boolean} watch
 */
function buildExamples(watch) {
  if (watch) {
    $$.watch('examples/*.html', function() {
      buildExamples(false);
    });
  }

  fs.copy('examples/', 'examples.build/', {clobber: true},
      function(err) {
        if (err) {
          return $$.util.log($$.util.colors.red('copy error: ', err));
        }
        $$.util.log($$.util.colors.green('copied examples to examples.build'));
      });

  // Also update test-example-validation.js
  buildExample('ads.amp.html');
  buildExample('ads.with.script.amp.html');
  buildExample('alp.amp.html');
  buildExample('analytics-notification.amp.html');
  buildExample('analytics.amp.html');
  buildExample('article.amp.html');
  buildExample('brid-player.amp.html');
  buildExample('brightcove.amp.html');
  buildExample('kaltura.amp.html');
  buildExample('responsive.amp.html');
  buildExample('article-access.amp.html');
  buildExample('dailymotion.amp.html');
  buildExample('carousel.amp.html');
  buildExample('csp.amp.html');
  buildExample('layout-flex-item.amp.html');
  buildExample('live-list.amp.html');
  buildExample('live-list-update.amp.html');
  buildExample('metadata-examples/article-json-ld.amp.html');
  buildExample('metadata-examples/article-microdata.amp.html');
  buildExample('metadata-examples/recipe-json-ld.amp.html');
  buildExample('metadata-examples/recipe-microdata.amp.html');
  buildExample('metadata-examples/review-json-ld.amp.html');
  buildExample('metadata-examples/review-microdata.amp.html');
  buildExample('metadata-examples/video-json-ld.amp.html');
  buildExample('metadata-examples/video-microdata.amp.html');
  buildExample('everything.amp.html');
  buildExample('font.amp.html');
  buildExample('forms.amp.html');
  buildExample('facebook.amp.html');
  buildExample('instagram.amp.html');
  buildExample('jwplayer.amp.html');
  buildExample('pinterest.amp.html');
  buildExample('reach-player.amp.html');
  buildExample('released.amp.html');
  buildExample('social-share.amp.html');
  buildExample('twitter.amp.html');
  buildExample('soundcloud.amp.html');
  buildExample('springboard-player.amp.html');
  buildExample('sticky.ads.amp.html');
  buildExample('user-notification.amp.html');
  buildExample('vimeo.amp.html');
  buildExample('vine.amp.html');
  buildExample('multiple-docs.html');
  buildExample('youtube.amp.html');
  buildExample('openx.amp.html');

  // TODO(dvoytenko, #1393): Enable for proxy-testing.
  // // Examples are also copied into `c/` directory for AMP-proxy testing.
  // fs.copy('examples.build/', 'c/', {clobber: true},
  //     copyHandler.bind(null, 'examples.build to c folder'));
}

/**
 * Copies an examples file to examples.build folder and changes all
 * JS references to local / minified copies.
 *
 * @param {string} name HTML file in examples/
 */
function buildExample(name) {
  var input = 'examples/' + name;
  console.log('Processing ' + name);
  var html = fs.readFileSync(input, 'utf8');
  var max = html;
  max = max.replace(/(https:\/\/cdn.ampproject.org\/.+?).js/g, '$1.max.js');
  max = max.replace('https://cdn.ampproject.org/v0.max.js', '../dist/amp.js');
  max = max.replace(/https:\/\/cdn.ampproject.org\/v0\//g, '../dist/v0/');
  gulp.src(input)
      .pipe($$.file(name.replace('.html', '.max.html'),max))
      .pipe(gulp.dest('examples.build/'));

  var min = max;
  min = min.replace(/\.max\.js/g, '.js');
  min = min.replace('../dist/amp.js', '../dist/v0.js');
  gulp.src(input)
      .pipe($$.file(name.replace('.html', '.min.html'), min))
      .pipe(gulp.dest('examples.build/'));
}

/**
 * Copies frame.html to output folder, replaces js references to minified
 * copies, and generates symlink to it.
 *
 * @param {boolean} watch
 * @param {boolean} shouldMinify
 */
function thirdPartyBootstrap(watch, shouldMinify) {
  var input = '3p/frame.max.html';
  if (watch) {
    $$.watch(input, function() {
      thirdPartyBootstrap(false);
    });
  }
  console.log('Processing ' + input);
  var html = fs.readFileSync(input, 'utf8');
  var min = html;
  // By default we use an absolute URL, that is independent of the
  // actual frame host for the JS inside the frame.
  var jsPrefix = 'https://3p.ampproject.net/' + internalRuntimeVersion;
  // But during testing we need a relative reference because the
  // version is not available on the absolute path.
  if (argv.fortesting) {
    jsPrefix = '.';
  }
  // Convert default relative URL to absolute min URL.
  min = min.replace(/\.\/integration\.js/g, jsPrefix + '/f.js');
  gulp.src(input)
      .pipe($$.file('frame.html', min))
      .pipe(gulp.dest('dist.3p/' + internalRuntimeVersion))
      .on('end', function() {
        var aliasToLatestBuild = 'dist.3p/current';
        if (shouldMinify) {
          aliasToLatestBuild += '-min';
        }
        if (fs.existsSync(aliasToLatestBuild)) {
          fs.unlinkSync(aliasToLatestBuild);
        }
        fs.symlinkSync(
            './' + internalRuntimeVersion,
            aliasToLatestBuild,
            'dir');
      });
}

var activeBundleOperationCount = 0;

/**
 * Compile a javascript file
 *
 * @param {string} srcDir Path to the src directory
 * @param {string} srcFilename Name of the JS source file
 * @param {string} destDir Destination folder for output script
 * @param {?Object} options
 */
function compileJs(srcDir, srcFilename, destDir, options) {
  options = options || {};
  var bundler = browserify(srcDir + srcFilename, {debug: true})
      .transform(babel, { loose: argv.strictBabelTransform ? undefined : 'all' });
  if (options.watch) {
    bundler = watchify(bundler);
  }

  var wrapper = options.wrapper || '<%= contents %>';

  var lazybuild = lazypipe()
      .pipe(source, srcFilename)
      .pipe(buffer)
      .pipe($$.replace, /\$internalRuntimeVersion\$/g, internalRuntimeVersion)
      .pipe($$.replace, /\$internalRuntimeToken\$/g, internalRuntimeToken)
      .pipe($$.wrap, wrapper)
      .pipe($$.sourcemaps.init.bind($$.sourcemaps), {loadMaps: true});

  var lazywrite = lazypipe()
      .pipe($$.sourcemaps.write.bind($$.sourcemaps), './')
      .pipe(gulp.dest.bind(gulp), destDir);

  function rebundle() {
    activeBundleOperationCount++;
    bundler.bundle()
      .on('error', function(err) {
        activeBundleOperationCount--;
        if (err instanceof SyntaxError) {
          console.error($$.util.colors.red('Syntax error:', err.message));
        } else {
          console.error($$.util.colors.red(err.message));
        }
      })
      .pipe(lazybuild())
      .pipe($$.rename(options.toName || srcFilename))
      .pipe(lazywrite())
      .on('end', function() {
        activeBundleOperationCount--;
        if (activeBundleOperationCount == 0) {
          console.info($$.util.colors.green('All current JS updates done.'));
        }
      });
  }

  if (options.watch) {
    bundler.on('update', function() {
      console.log('-> bundling ' + srcDir + '...');
      rebundle();
      // Touch file in unit test set. This triggers rebundling of tests because
      // karma only considers changes to tests files themselves re-bundle
      // worthy.
      touch('test/_init_tests.js');
    });
  }

  function minify() {
    console.log('Minifying ' + srcFilename);
    closureCompile(srcDir + srcFilename, destDir, options.minifiedName,
        options)
        .then(function() {
          fs.writeFileSync(destDir + '/version.txt', internalRuntimeVersion);
          if (options.latestName) {
            fs.copySync(
                destDir + '/' + options.minifiedName,
                destDir + '/' + options.latestName);
          }
        });
  }

  /*
  Pre closure compiler minification. Add this back, should we have problems
  with closure.
  function minify() {
    console.log('Minifying ' + srcFilename);
    bundler.bundle()
      .on('error', function(err) { console.error(err); this.emit('end'); })
      .pipe(lazybuild())
      .pipe($$.uglify({
        preserveComments: 'some'
      }))
      .pipe($$.rename(options.minifiedName))
      .pipe(lazywrite())
      .on('end', function() {
        fs.writeFileSync(destDir + '/version.txt', internalRuntimeVersion);
        if (options.latestName) {
          fs.copySync(
              destDir + '/' + options.minifiedName,
              destDir + '/' + options.latestName);
        }
      });
  }
  */

  if (options.minify) {
    minify();
  } else {
    rebundle();
  }
}

/**
 * Build all the AMP experiments.html/js.
 *
 * @param {!Object} options
 */
function buildExperiments(options) {
  options = options || {};
  console.log('Bundling experiments.html/js');

  function copyHandler(name, err) {
    if (err) {
      return $$.util.log($$.util.colors.red('copy error: ', err));
    }
    $$.util.log($$.util.colors.green('copied ' + name));
  }

  var path = 'tools/experiments';
  var htmlPath = path + '/experiments.html';
  var jsPath = path + '/experiments.js';
  var watch = options.watch;
  if (watch === undefined) {
    watch = argv.watch || argv.w;
  }

  // Building extensions is a 2 step process because of the renaming
  // and CSS inlining. This watcher watches the original file, copies
  // it to the destination and adds the CSS.
  if (watch) {
    // Do not set watchers again when we get called by the watcher.
    var copy = Object.create(options);
    copy.watch = false;
    $$.watch(path + '/*', function() {
      buildExperiments(copy);
    });
  }

  // Build HTML.
  console.log('Processing ' + htmlPath);
  var html = fs.readFileSync(htmlPath, 'utf8');
  var minHtml = html.replace('../../dist.tools/experiments/experiments.max.js',
      'https://cdn.ampproject.org/v0/experiments.js');
  gulp.src(htmlPath)
      .pipe($$.file('experiments.cdn.html', minHtml))
      .pipe(gulp.dest('dist.tools/experiments/'));

  // Build JS.
  var js = fs.readFileSync(jsPath, 'utf8');
  var builtName = 'experiments.max.js';
  var minifiedName = 'experiments.js';
  return gulp.src(path + '/*.js')
      .pipe($$.file(builtName, js))
      .pipe(gulp.dest('build/experiments/'))
      .on('end', function() {
        compileJs('./build/experiments/', builtName, './dist.tools/experiments/', {
          watch: false,
          minify: options.minify || argv.minify,
          includePolyfills: true,
          minifiedName: minifiedName,
          preventRemoveAndMakeDir: options.preventRemoveAndMakeDir,
          checkTypes: options.checkTypes,
        });
      });
}


/**
 * Build "Login Done" page.
 *
 * @param {!Object} options
 */
function buildLoginDone(options) {
  return buildLoginDoneVersion('0.1', options);
}

/**
 * Build "Login Done" page for the specified version.
 *
 * @param {!Object} options
 */
function buildLoginDoneVersion(version, options) {
  options = options || {};
  console.log('Bundling amp-login-done.html/js');

  function copyHandler(name, err) {
    if (err) {
      return $$.util.log($$.util.colors.red('copy error: ', err));
    }
    $$.util.log($$.util.colors.green('copied ' + name));
  }

  var path = 'extensions/amp-access/' + version + '/';
  var htmlPath = path + 'amp-login-done.html';
  var jsPath = path + 'amp-login-done.js';
  var watch = options.watch;
  if (watch === undefined) {
    watch = argv.watch || argv.w;
  }

  // Building extensions is a 2 step process because of the renaming
  // and CSS inlining. This watcher watches the original file, copies
  // it to the destination and adds the CSS.
  if (watch) {
    // Do not set watchers again when we get called by the watcher.
    var copy = Object.create(options);
    copy.watch = false;
    $$.watch(path + '/*', function() {
      buildLoginDoneVersion(version, copy);
    });
  }

  // Build HTML.
  console.log('Processing ' + htmlPath);
  var html = fs.readFileSync(htmlPath, 'utf8');
  var minHtml = html.replace(
      '../../../dist/v0/amp-login-done-' + version + '.max.js',
      'https://cdn.ampproject.org/v0/amp-login-done-' + version + '.js');

  mkdirSync('dist');
  mkdirSync('dist/v0');

  fs.writeFileSync('dist/v0/amp-login-done-' + version + '.html',
      minHtml);

  // Build JS.
  var js = fs.readFileSync(jsPath, 'utf8');
  var builtName = 'amp-login-done-' + version + '.max.js';
  var minifiedName = 'amp-login-done-' + version + '.js';
  var latestName = 'amp-login-done-latest.js';
  return gulp.src(path + '/*.js')
      .pipe($$.file(builtName, js))
      .pipe(gulp.dest('build/all/v0/'))
      .on('end', function() {
        compileJs('./build/all/v0/', builtName, './dist/v0/', {
          watch: false,
          includePolyfills: true,
          minify: options.minify || argv.minify,
          minifiedName: minifiedName,
          preventRemoveAndMakeDir: options.preventRemoveAndMakeDir,
          latestName: latestName,
        });
      });
}

/**
 * Build ALP JS
 *
 * @param {!Object} options
 */
function buildAlp(options) {
  options = options || {};
  console.log('Bundling alp.js');

  compileJs('./ads/alp/', 'install-alp.js', './dist/', {
    toName: 'alp.max.js',
    watch: options.watch,
    minify: options.minify || argv.minify,
    includeWindowConfig: true,
    includePolyfills: true,
    minifiedName: 'alp.js',
    preventRemoveAndMakeDir: options.preventRemoveAndMakeDir,
  });
}

/**
 * Exits the process if gulp is running with a node version lower than
 * the required version. This has to run very early to avoid parse
 * errors from modules that e.g. use let.
 */
function checkMinVersion() {
  var majorVersion = Number(process.version.replace(/v/, '').split('.')[0]);
  if (majorVersion < 4) {
    console.log('Please run AMP with node.js version 4 or newer.');
    console.log('Your version is', process.version);
    process.exit(1);
  }
}

function mkdirSync(path) {
  try {
    fs.mkdirSync(path);
  } catch(e) {
    if (e.code != 'EEXIST') {
      throw e;
    }
  }
}


/**
 * Gulp tasks
 */
gulp.task('build', 'Builds the AMP library', build);
gulp.task('check-types', 'Check JS types', checkTypes);
gulp.task('css', 'Recompile css to build directory', compileCss);
gulp.task('default', 'Same as "watch"', ['watch', 'serve']);
gulp.task('dist', 'Build production binaries', dist);
gulp.task('extensions', 'Build AMP Extensions', buildExtensions);
gulp.task('watch', 'Watches for changes in files, re-build', watch);
gulp.task('build-experiments', 'Builds experiments.html/js', buildExperiments);
gulp.task('build-login-done', 'Builds login-done.html/js', buildLoginDone);