import 'package:flutter/material.dart';

/// カメラ画面右端の露出スライダーを描画する CustomPainter。
///
/// - 縦トラック（白半透明）
/// - 中央基準線（0 EV を示すマーカー）
/// - 現在値を示すノブ（影付き白丸）
class ExposureSliderPainter extends CustomPainter {
  final double currentValue;
  final double minValue;
  final double maxValue;

  const ExposureSliderPainter({
    required this.currentValue,
    required this.minValue,
    required this.maxValue,
  });

  @override
  void paint(Canvas canvas, Size size) {
    final trackPaint = Paint()
      ..color = Colors.white.withValues(alpha: 0.3)
      ..strokeWidth = 4
      ..strokeCap = StrokeCap.round;

    final centerLinePaint = Paint()
      ..color = Colors.white54
      ..strokeWidth = 2;

    final knobPaint = Paint()
      ..color = Colors.white
      ..style = PaintingStyle.fill;

    final knobShadowPaint = Paint()
      ..color = Colors.black26
      ..maskFilter = const MaskFilter.blur(BlurStyle.normal, 4);

    // 縦トラック（中央線）
    final trackX = size.width / 2;
    canvas.drawLine(
      Offset(trackX, 10),
      Offset(trackX, size.height - 10),
      trackPaint,
    );

    // 0 EV マーカー
    canvas.drawLine(
      Offset(trackX - 6, size.height / 2),
      Offset(trackX + 6, size.height / 2),
      centerLinePaint,
    );

    // ノブ位置を算出
    final range = maxValue - minValue;
    if (range > 0) {
      // minValue(下端) → 0.0、maxValue(上端) → 1.0 に正規化してY座標に変換
      final normalized = (currentValue - minValue) / range;
      final knobY = (size.height - 20) * (1.0 - normalized) + 10;
      canvas.drawCircle(Offset(trackX, knobY), 7, knobShadowPaint);
      canvas.drawCircle(Offset(trackX, knobY), 6, knobPaint);
    }
  }

  @override
  bool shouldRepaint(ExposureSliderPainter oldDelegate) {
    return oldDelegate.currentValue != currentValue ||
        oldDelegate.minValue != minValue ||
        oldDelegate.maxValue != maxValue;
  }
}