I am new to dart, and I came across the following code. This apparently updates the document in the firebase. Can someone explain in detail, what it really does?

abstract class FirestoreDocumentUpdater {
  static Future<void> update(

      // ignore: use_function_type_syntax_for_parameters

      DocumentReference<Map<String, dynamic>> documentRef,
      Map<String, dynamic> map) {
    debugPrint('update function called');
    return documentRef.update(
      Map.fromEntries(
        map.entries.map(
          (e) {
            return MapEntry(
                e.key,
                switch (e.value) {
                  DateTime t => toJsonDateTime(t),
                  Duration d => toJsonDuration(d),
                  Enum t => t.name,
                  _ => e.value,
                });
          },
        ),
      ),
    );
  }
}

Timestamp? toJsonDateTime(DateTime? dateTime) {
  if (dateTime == null) return null;
  return Timestamp.fromDate(dateTime);
}


int toJsonDuration(Duration duration) {
  return duration.inMicroseconds;
}