FileSystemEvent? _canonicalEvent()

in lib/src/directory_watcher/mac_os.dart [237:299]
37 lines of code
16 McCabe index (conditional complexity)

  FileSystemEvent? _canonicalEvent(Set<FileSystemEvent> batch) {
    // An empty batch indicates that we've learned earlier that the batch is
    // contradictory (e.g. because of a move).
    if (batch.isEmpty) return null;

    var type = batch.first.type;
    var isDir = batch.first.isDirectory;
    var hadModifyEvent = false;

    for (var event in batch.skip(1)) {
      // If one event reports that the file is a directory and another event
      // doesn't, that's a contradiction.
      if (isDir != event.isDirectory) return null;

      // Modify events don't contradict either CREATE or REMOVE events. We can
      // safely assume the file was modified after a CREATE or before the
      // REMOVE; otherwise there will also be a REMOVE or CREATE event
      // (respectively) that will be contradictory.
      if (event is FileSystemModifyEvent) {
        hadModifyEvent = true;
        continue;
      }
      assert(event is FileSystemCreateEvent || event is FileSystemDeleteEvent);

      // If we previously thought this was a MODIFY, we now consider it to be a
      // CREATE or REMOVE event. This is safe for the same reason as above.
      if (type == FileSystemEvent.modify) {
        type = event.type;
        continue;
      }

      // A CREATE event contradicts a REMOVE event and vice versa.
      assert(type == FileSystemEvent.create || type == FileSystemEvent.delete);
      if (type != event.type) return null;
    }

    // If we got a CREATE event for a file we already knew about, that comes
    // from FSEvents reporting an add that happened prior to the watch
    // beginning. If we also received a MODIFY event, we want to report that,
    // but not the CREATE.
    if (type == FileSystemEvent.create &&
        hadModifyEvent &&
        _files.contains(batch.first.path)) {
      type = FileSystemEvent.modify;
    }

    switch (type) {
      case FileSystemEvent.create:
        // Issue 16003 means that a CREATE event for a directory can indicate
        // that the directory was moved and then re-created.
        // [_eventsBasedOnFileSystem] will handle this correctly by producing a
        // DELETE event followed by a CREATE event if the directory exists.
        if (isDir) return null;
        return ConstructableFileSystemCreateEvent(batch.first.path, false);
      case FileSystemEvent.delete:
        return ConstructableFileSystemDeleteEvent(batch.first.path, isDir);
      case FileSystemEvent.modify:
        return ConstructableFileSystemModifyEvent(
            batch.first.path, isDir, false);
      default:
        throw 'unreachable';
    }
  }