import 'dart:math' as math;

import 'package:flutter/cupertino.dart';

class DashedProgressPainter extends CustomPainter {
  final double progress;      // 0..1
  final double thickness;
  final double dash;
  final double gap;
  final Color baseColor;
  final Color progressColor;
  final double radius;

  DashedProgressPainter({
    required this.progress,
    required this.thickness,
    required this.dash,
    required this.gap,
    required this.baseColor,
    required this.progressColor,
    required this.radius,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final y = size.height / 2;
    final dashPaintBase = Paint()..color = baseColor..style = PaintingStyle.fill;
    final dashPaintProg = Paint()..color = progressColor..style = PaintingStyle.fill;

    final total = size.width;
    final cutoff = total * progress; // everything left of this is colored

    double x = 0;
    while (x < total) {
      final dashEnd = (x + dash).clamp(0.0, total);
      final rrect = RRect.fromRectAndRadius(
        Rect.fromLTWH(x, y - thickness / 2, dashEnd - x, thickness),
        Radius.circular(radius),
      );
      // base (grey) dash
      canvas.drawRRect(rrect, dashPaintBase);

      // overlap the colored part inside this dash (if any)
      final colorEnd = math.min(dashEnd, cutoff);
      if (colorEnd > x) {
        final coloredRect = RRect.fromRectAndRadius(
          Rect.fromLTWH(x, y - thickness / 2, colorEnd - x, thickness),
          Radius.circular(radius),
        );
        canvas.drawRRect(coloredRect, dashPaintProg);
      }

      x += dash + gap;
    }
  }

  @override
  bool shouldRepaint(covariant DashedProgressPainter old) {
    return old.progress != progress ||
        old.thickness != thickness ||
        old.dash != dash ||
        old.gap != gap ||
        old.baseColor != baseColor ||
        old.progressColor != progressColor ||
        old.radius != radius;
  }
}