Function startFileWatch

examples/pdf-server/server.ts:455–510

(viewUUID: string, filePath: string)

const FILE_WATCH_DEBOUNCE_MS = 150;

export function startFileWatch(viewUUID: string, filePath: string): void {
  const resolved = path.resolve(filePath);
  let stat: fs.Stats;
  try {
    stat = fs.statSync(resolved);
  } catch {
    return; // vanished between validation and here
  }

  // Replace any existing watcher for this view
  stopFileWatch(viewUUID);

  const entry: ViewFileWatch = {
    filePath: resolved,
    watcher: null as unknown as fs.FSWatcher,
    lastMtimeMs: stat.mtimeMs,
    debounce: null,
  };

  const onEvent = (eventType: string): void => {
    if (entry.debounce) clearTimeout(entry.debounce);
    entry.debounce = setTimeout(() => {
      entry.debounce = null;
      let s: fs.Stats;
      try {
        s = fs.statSync(resolved);
      } catch {
        return; // gone mid-atomic-write; next rename will re-attach
      }
      if (s.mtimeMs === entry.lastMtimeMs) return; // spurious / already sent
      entry.lastMtimeMs = s.mtimeMs;
      enqueueCommand(viewUUID, { type: "file_changed", mtimeMs: s.mtimeMs });
    }, FILE_WATCH_DEBOUNCE_MS);

    // Atomic saves replace the inode — old watcher stops firing. Re-attach.
    if (eventType === "rename") {
      try {
        entry.watcher.close();
      } catch {
        /* already closed */
      }
      try {
        entry.watcher = fs.watch(resolved, onEvent);
      } catch {
        // File removed, not replaced. Leave closed; pruneStaleQueues cleans up.
      }
    }
  };

  try {
    entry.watcher = fs.watch(resolved, onEvent);
  } catch {
    return; // fs.watch unsupported (e.g. some network filesystems)
  }
  viewFileWatches.set(viewUUID, entry);
}

export function stopFileWatch(viewUUID: string): void {