Pre-construct frontend index.html (#609)

* Pre-construct frontend index.html

* Only preload things that matter

* Fix entry point in dev mode

* Template Service worker url

* Update referenced service worker

gulp/tasks/gen-index-html.js

@@ -0,0 +1,44 @@
+const gulp = require('gulp');
+const replace = require('gulp-batch-replace');
+const path = require('path');
+const url = require('url');
+const config = require('../config');
+const md5 = require('../common/md5.js');
+
+const buildReplaces = {
+  '/home-assistant-polymer/build/core.js': 'core.js',
+  '/home-assistant-polymer/src/home-assistant.html': 'frontend.html',
+};
+
+function generateIndex(es6) {
+  const targetPath = es6 ? config.output : config.output_es5;
+  const targetUrl = es6 ? '/frontend_latest/' : '/frontend_es5/';
+
+  const toReplace = [
+    ['/home-assistant-polymer/hass_frontend/mdi.html',
+      `/static/mdi-${md5(path.resolve(config.output, 'mdi.html'))}.html`],
+    ['/home-assistant-polymer/build-temp/compatibility.js',
+      `/static/compatibility-${md5(path.resolve(config.output_es5, 'compatibility.js'))}.js`],
+  ];
+
+  if (!es6) {
+    toReplace.push([
+      '/service_worker.js', '/service_worker_es5.js'
+    ]);
+  }
+
+  for (const [replaceSearch, filename] of Object.entries(buildReplaces)) {
+    const parsed = path.parse(filename);
+    const hash = md5(path.resolve(targetPath, filename));
+    toReplace.push([
+      replaceSearch,
+      url.resolve(targetUrl, `${parsed.name}-${hash}${parsed.ext}`)]);
+  }
+
+  gulp.src(path.resolve(config.polymer_dir, 'index.html'))
+    .pipe(replace(toReplace))
+    .pipe(gulp.dest(targetPath));
+}
+
+gulp.task('gen-index-html-es5', generateIndex.bind(null, /* es6= */ false));
+gulp.task('gen-index-html', generateIndex.bind(null, /* es6= */ true));