Use pwa-starter-kit style gulpfile for post-build transformations

gulpfile.js

@@ -0,0 +1,43 @@
+/**
+@license
+Copyright (c) 2018 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+*/
+
+const gulp = require('gulp');
+const rename = require('gulp-rename');
+const replace = require('gulp-replace');
+const del = require('del');
+
+/**
+ * Cleans the prpl-server build in the server directory.
+ */
+gulp.task('prpl-server:clean', () => {
+  return del('server/build');
+});
+
+/**
+ * Copies the prpl-server build to the server directory while renaming the
+ * node_modules directory so services like App Engine will upload it.
+ */
+gulp.task('prpl-server:build', () => {
+  const pattern = 'node_modules';
+  const replacement = 'node_assets';
+
+  return gulp.src('build/**')
+    .pipe(rename(((path) => {
+      path.basename = path.basename.replace(pattern, replacement);
+      path.dirname = path.dirname.replace(pattern, replacement);
+    })))
+    .pipe(replace(pattern, replacement))
+    .pipe(gulp.dest('server/build'));
+});
+
+gulp.task('prpl-server', gulp.series(
+  'prpl-server:clean',
+  'prpl-server:build'
+));