followCursor function

Future<void> followCursor({ required Future<int?> read(int? since), int? since, Duration interval = const Duration(seconds: 1), Future<void> delay(Duration) = _wait, bool shouldStop() = _never, })

Polls a cursor-paged source until told to stop; the loop behind --follow.

Pure Dart: it imports no Flutter library, so a command that runs under dart run can use it through package:crumbs/cli.dart.

Each round calls read with the cursor the previous round returned (since on the first round), then asks shouldStop, then waits interval through delay. read returns the next cursor; a null keeps the cursor of the last round that returned one, so an empty poll never rewinds. delay and shouldStop exist so a test can run the loop without a clock or a Ctrl-C; by default the loop waits on the real clock and ends only when the process does.

Implementation

Future<void> followCursor({
  required Future<int?> Function(int? since) read,
  int? since,
  Duration interval = const Duration(seconds: 1),
  Future<void> Function(Duration) delay = _wait,
  bool Function() shouldStop = _never,
}) async {
  var cursor = since;
  while (true) {
    cursor = await read(cursor) ?? cursor;
    if (shouldStop()) return;

    await delay(interval);
  }
}