import 'package:flutter/material.dart';

class FlowSegment {
  final Offset from;
  final Offset to;
  final Color color;
  final double powerW;
  final bool dashed;

  const FlowSegment({
    required this.from,
    required this.to,
    required this.color,
    required this.powerW,
    this.dashed = false,
  });
}

class FlowPainter extends CustomPainter {
  final List<FlowSegment> segments;
  final double animValue;
  final Color lineColor;

  const FlowPainter({
    required this.segments,
    required this.animValue,
    required this.lineColor,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final linePaint = Paint()
      ..color = lineColor
      ..strokeWidth = 1.5
      ..style = PaintingStyle.stroke
      ..strokeCap = StrokeCap.round;

    for (final seg in segments) {
      final src = Offset(seg.from.dx * size.width, seg.from.dy * size.height);
      final dst = Offset(seg.to.dx * size.width, seg.to.dy * size.height);

      if (seg.dashed) {
        _drawDashed(canvas, src, dst, linePaint);
      } else {
        canvas.drawLine(src, dst, linePaint);
      }

      if (seg.powerW > 30) {
        final n = (seg.powerW / 600).clamp(1, 5).round();
        final r = seg.powerW > 1500 ? 3.5 : 2.5;
        final particlePaint = Paint()
          ..color = seg.color
          ..style = PaintingStyle.fill;

        for (int i = 0; i < n; i++) {
          final t = (animValue + i / n) % 1.0;
          final pos = Offset.lerp(src, dst, t)!;
          canvas.drawCircle(pos, r, particlePaint);
        }
      }
    }
  }

  void _drawDashed(Canvas canvas, Offset src, Offset dst, Paint paint) {
    final dir = dst - src;
    final length = dir.distance;
    if (length == 0) return;
    final unit = dir / length;
    const dashLen = 5.0;
    const gapLen  = 4.0;
    double pos = 0;
    while (pos < length) {
      final end = (pos + dashLen).clamp(0.0, length);
      canvas.drawLine(src + unit * pos, src + unit * end, paint);
      pos += dashLen + gapLen;
    }
  }

  @override
  bool shouldRepaint(FlowPainter old) =>
      old.animValue != animValue ||
      old.lineColor != lineColor ||
      old.segments.length != segments.length;
}