/** Absolute on POSIX (`/…`), Windows (`C:\…`, `C:/…`) or a UNC share (`\\…`). */
function isAbsolute(path: string): boolean {
  return path.startsWith("/") || path.startsWith("\\") || /^[A-Za-z]:[\\/]/.test(path);
}

/**
 * The on-disk path of a row in the `downloads` store.
 *
 * `downloads.file_path` is stored relative to the storage root while a download
 * is queued, but the worker rewrites it to the absolute path it actually wrote
 * once the transfer completes — so a *completed* row is already rooted. Joining
 * it onto the storage root a second time produced
 * `/data/user/0/app//data/user/0/app/videos/x.mp4`; the asset protocol could not
 * open that, so offline video failed with `MEDIA_ERR_SRC_NOT_SUPPORTED` while
 * audio, which resolves the same column through Rust, played fine.
 *
 * TRACES: UR-071 | DR-133 | UT-124
 */
export function downloadedFilePath(storageRoot: string, filePath: string): string {
  return isAbsolute(filePath) ? filePath : `${storageRoot}/${filePath}`;
}