Function applySnapshot

src/utils/fileHistory.ts:537–591

* Applies the given file snapshot state to the tracked files (writes/deletes * on disk), returning the list of changed file paths. Async IO only.

(
  state: FileHistoryState,
  targetSnapshot: FileHistorySnapshot,
)

 * on disk), returning the list of changed file paths. Async IO only.
 */
async function applySnapshot(
  state: FileHistoryState,
  targetSnapshot: FileHistorySnapshot,
): Promise<string[]> {
  const filesChanged: string[] = []
  for (const trackingPath of state.trackedFiles) {
    try {
      const filePath = maybeExpandFilePath(trackingPath)
      const targetBackup = targetSnapshot.trackedFileBackups[trackingPath]

      const backupFileName: BackupFileName | undefined = targetBackup
        ? targetBackup.backupFileName
        : getBackupFileNameFirstVersion(trackingPath, state)

      if (backupFileName === undefined) {
        // Error resolving the backup, so don't touch the file
        logError(
          new Error('FileHistory: Error finding the backup file to apply'),
        )
        logEvent('tengu_file_history_rewind_restore_file_failed', {
          dryRun: false,
        })
        continue
      }

      if (backupFileName === null) {
        // File did not exist at the target version; delete it if present.
        try {
          await unlink(filePath)
          logForDebugging(`FileHistory: [Rewind] Deleted ${filePath}`)
          filesChanged.push(filePath)
        } catch (e: unknown) {
          if (!isENOENT(e)) throw e
          // Already absent; nothing to do.
        }
        continue
      }

      // File should exist at a specific version. Restore only if it differs.
      if (await checkOriginFileChanged(filePath, backupFileName)) {
        await restoreBackup(filePath, backupFileName)
        logForDebugging(
          `FileHistory: [Rewind] Restored ${filePath} from ${backupFileName}`,
        )
        filesChanged.push(filePath)
      }
    } catch (error) {
      logError(error)
      logEvent('tengu_file_history_rewind_restore_file_failed', {
        dryRun: false,
      })
    }
  }
  return filesChanged
}

/**
 * Checks if the original file has been changed compared to the backup file.