refactor: simplify restore point

apps/server/src/services/restore-service/restore.service.ts

@@ -0,0 +1,106 @@
+import { JSONFile } from 'lowdb/node';
+import { deepEqual } from 'fast-equals';
+
+import { publicFiles } from '../../setup/index.js';
+
+import { isRestorePoint } from './restore.parser.js';
+import type { RestorePoint } from './restore.type.js';
+
+let failedCreateAttempts = 0;
+let savedState: RestorePoint | null = null;
+let fileRef: JSONFile<RestorePoint | null> | null = null;
+
+/**
+ * Service manages saving snapshot of application state
+ * that can then be restored when reopening
+ */
+export const restoreService = {
+  save,
+  load,
+  clear,
+};
+
+/**
+ * Saves a restore point
+ * @param [writeFn=write] - allows overriding the write function for testing
+ * @public
+ */
+async function save(data: RestorePoint, writeFn = write) {
+  // after three failed attempts, mark the service as unavailable
+  if (failedCreateAttempts > 3) {
+    return;
+  }
+
+  if (deepEqual(data, savedState)) {
+    return;
+  }
+
+  try {
+    await writeFn(data);
+    savedState = { ...data };
+    failedCreateAttempts = 0;
+  } catch (_error) {
+    failedCreateAttempts += 1;
+  }
+}
+
+/**
+ * Attempts reading a restore point from a given file path
+ * Returns null if none found, restore point otherwise
+ * @param [readFn=read] - allows overriding the read function for testing
+ * @public
+ */
+async function load(readFn = read): Promise<RestorePoint | null> {
+  try {
+    const maybeRestorePoint = await readFn();
+    if (isRestorePoint(maybeRestorePoint)) {
+      return maybeRestorePoint;
+    }
+  } catch (_error) {
+    // no need to notify the user
+  }
+  return null;
+}
+
+/**
+ * Clears the restore file
+ * @param [writeFn=write] - allows overriding the write function for testing
+ * @public
+ */
+async function clear(writeFn = write) {
+  try {
+    await writeFn(null);
+  } catch (_error) {
+    // nothing to do
+  }
+}
+
+/**
+ * Initialised file reference
+ * @private
+ */
+async function init(): Promise<JSONFile<RestorePoint | null>> {
+  if (fileRef) return fileRef;
+
+  fileRef = new JSONFile<RestorePoint | null>(publicFiles.restoreFile);
+  return fileRef;
+}
+
+/**
+ * Reads from an intialized file reference
+ * @private
+ */
+async function read(): Promise<RestorePoint | null> {
+  const file = await init();
+  return file.read();
+}
+
+/**
+ * Writes to an intialized file reference
+ * @throws - if writing fails
+ * @private
+ */
+async function write(data: RestorePoint | null) {
+  const file = await init();
+  return file.write(data);
+}