feat(subtitles): add local Japanese subtitle generation (#240)

src/core/services/subtitle-generation-files.ts

@@ -0,0 +1,32 @@
+import { constants } from 'node:fs';
+import { copyFile, link } from 'node:fs/promises';
+import { homedir } from 'node:os';
+import path from 'node:path';
+
+export function expandSubtitleGenerationPath(value: string): string {
+  if (value === '~') return homedir();
+  if (value.startsWith('~/') || value.startsWith('~\\'))
+    return path.join(homedir(), value.slice(2));
+  return value;
+}
+
+// Prefer atomic publication. Filesystems without hard links still get exclusive creation.
+export async function publishSubtitleGenerationFile(
+  source: string,
+  destination: string,
+): Promise<void> {
+  try {
+    await link(source, destination);
+  } catch (error) {
+    if (
+      !(error instanceof Error) ||
+      !('code' in error) ||
+      (error.code !== 'ENOTSUP' &&
+        error.code !== 'EOPNOTSUPP' &&
+        error.code !== 'EPERM' &&
+        error.code !== 'EXDEV')
+    )
+      throw error;
+    await copyFile(source, destination, constants.COPYFILE_EXCL);
+  }
+}