How to get the middle point of custom path in dart?

class PathPainter extends CustomPainter {
  PathPainter({required this.progress});

  final double progress;

  @override
  void paint(Canvas canvas, Size size) {
    var path = createPath(size);
    try {
      PathMetric pathMetric = path.computeMetrics().first;
      Path extractPath =
          pathMetric.extractPath(0.0, pathMetric.length * progress);

      // drawing circle at the start of path

      canvas.drawCircle(
          Offset(0, size.height), 8.0, Paint()..color = Colors.green);

      canvas.drawPath(extractPath, myPaint);

      var metric = extractPath.computeMetrics().first;
      final offset = metric.getTangentForOffset(metric.length)!.position;
      print(offset);

       //if (offset == const Offset(30.5, 275.8)) {
         //   print("i am matched");
           // canvas.drawCircle(Offset(30.5, 275.8), 8.0, Paint()..color = Colors.green);
 }

      canvas.drawCircle(offset, 8.0, Paint()..color = Colors.green);
    } catch (e) {}
  }

  @override
  bool shouldRepaint(covariant CustomPainter oldDelegate) {
    // TODO: implement shouldRepaint
    return true;
  }
}

This is the code I am using to build my path. I am trying to figure out the middle point of this path or how to get the middle point of any custom path.

Why do I need it?

I am trying to add a circle in the middle of path as the path progresses (animates).

What I've tried

 if (offset == const Offset(30.5, 275.8)) {
            print("i am matched");
            canvas.drawCircle(Offset(30.5, 275.8), 8.0, Paint()..color = Colors.green);
  }

I've tried this code sample just to put a circle on a static offset from the path, but it didn't work.

Also tried

  var length = pathMetric.length / 2;

  if (extractPath.computeMetrics().length == length) {
    canvas.drawCircle(offset, 8.0,  Paint()..color = Colors.green);
  }

Any help would be appreciated.

All of this hustle is because I am trying to build the path in this .gif.

https://cdn-images-1.medium.com/max/800/1*OH8yRHjfJhBvRxLlUAqT4Q.gif