fix(storage): protect Yomitan profiles across Electron runtime changes (#211)

src/shared/fs-utils.ts

@@ -1,5 +1,6 @@
 import fs from 'node:fs';
 import path from 'node:path';
+import { randomUUID } from 'node:crypto';
 
 export function ensureDir(dirPath: string): void {
   if (fs.existsSync(dirPath)) return;
@@ -12,3 +13,48 @@ export function ensureDirForFile(filePath: string): void {
     fs.mkdirSync(dir, { recursive: true });
   }
 }
+
+function syncDirectory(directoryPath: string): void {
+  // Node cannot open Windows directory handles for fsync. The atomic rename still prevents
+  // torn files there, while supported platforms also flush the directory entry below.
+  if (process.platform === 'win32') return;
+
+  const directory = fs.openSync(directoryPath, 'r');
+  try {
+    fs.fsyncSync(directory);
+  } finally {
+    fs.closeSync(directory);
+  }
+}
+
+/** Writes and flushes a sibling temporary file before atomically replacing the target. */
+export function writeTextFileAtomicallyDurable(filePath: string, content: string): void {
+  const directoryPath = path.dirname(filePath);
+  ensureDir(directoryPath);
+  const temporaryPath = path.join(directoryPath, `.${path.basename(filePath)}.${randomUUID()}.tmp`);
+  let temporaryFile: number | undefined;
+
+  try {
+    temporaryFile = fs.openSync(temporaryPath, 'wx', 0o600);
+    fs.writeFileSync(temporaryFile, content, 'utf8');
+    fs.fsyncSync(temporaryFile);
+    fs.closeSync(temporaryFile);
+    temporaryFile = undefined;
+    fs.renameSync(temporaryPath, filePath);
+    syncDirectory(directoryPath);
+  } catch (error) {
+    if (temporaryFile !== undefined) {
+      try {
+        fs.closeSync(temporaryFile);
+      } catch {
+        // Best effort cleanup preserves the original write failure.
+      }
+    }
+    try {
+      fs.rmSync(temporaryPath, { force: true });
+    } catch {
+      // The temporary file is disposable; the existing target stays untouched before rename.
+    }
+    throw error;
+  }
+}