Service worker building (but not quite right yet)

lib/sw-plugin.js

@@ -0,0 +1,67 @@
+/**
+ * Copyright 2020 Google Inc. 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.
+ */
+import { createHash } from 'crypto';
+import { posix } from 'path';
+
+const importPrefix = 'service-worker:';
+
+export default function serviceWorkerPlugin({
+  output = 'sw.js',
+  filterAssets = () => true,
+} = {}) {
+  return {
+    name: 'service-worker',
+    async resolveId(id, importer) {
+      if (!id.startsWith(importPrefix)) return;
+
+      const plainId = id.slice(importPrefix.length);
+      const result = await this.resolve(plainId, importer);
+      if (!result) return;
+
+      return importPrefix + result.id;
+    },
+    load(id) {
+      if (!id.startsWith(importPrefix)) return;
+      const fileId = this.emitFile({
+        type: 'chunk',
+        id: id.slice(importPrefix.length),
+        fileName: output,
+      });
+
+      return `export default import.meta.ROLLUP_FILE_URL_${fileId};`;
+    },
+    generateBundle(options, bundle) {
+      const swChunk = bundle[output];
+      const toCacheInSW = Object.values(bundle).filter(
+        (item) => item !== swChunk && filterAssets(item),
+      );
+      const urls = toCacheInSW.map(
+        (item) =>
+          posix
+            .relative(posix.dirname(output), item.fileName)
+            .replace(/((?<=^|\/)index)?\.html?$/, '') || '.',
+      );
+
+      const versionHash = createHash('sha1');
+      for (const item of toCacheInSW) {
+        versionHash.update(item.code || item.source);
+      }
+      const version = versionHash.digest('hex');
+
+      swChunk.code =
+        `const ASSETS = ${JSON.stringify(urls)};\n` +
+        `const VERSION = ${JSON.stringify(version)};\n` +
+        swChunk.code;
+    },
+  };
+}