Row(
  children: [
    // Left pane: task names and assignees (fixed width)
    SizedBox(width: 300, child: TaskListPane()),
    // Right pane: timeline bars (horizontally scrollable)
    Expanded(child: TimelinePane()),
  ],
)

class _GanttChartPageState extends State<GanttChartPage> {
  final _leftVertical = ScrollController();
  final _rightVertical = ScrollController();

  @override
  void initState() {
    super.initState();
    _leftVertical.addListener(() {
      if (_rightVertical.offset != _leftVertical.offset) {
        _rightVertical.jumpTo(_leftVertical.offset);
      }
    });
    _rightVertical.addListener(() {
      if (_leftVertical.offset != _rightVertical.offset) {
        _leftVertical.jumpTo(_rightVertical.offset);
      }
    });
  }
}

class GanttBarPainter extends CustomPainter {
  final List<WbsTask> tasks;
  final DateTime startDate;
  final double dayWidth;

  @override
  void paint(Canvas canvas, Size size) {
    final paint = Paint();

    for (int i = 0; i < tasks.length; i++) {
      final task = tasks[i];
      final y = i * 40.0 + 8;
      final startX = task.startDate.difference(startDate).inDays * dayWidth;
      final barWidth = task.duration.inDays * dayWidth;

      // Background bar
      paint.color = _progressColor(task.progressRate).withAlpha(80);
      canvas.drawRRect(
        RRect.fromRectAndRadius(
          Rect.fromLTWH(startX, y, barWidth, 24),
          const Radius.circular(4),
        ),
        paint,
      );

      // Progress fill
      paint.color = _progressColor(task.progressRate);
      canvas.drawRRect(
        RRect.fromRectAndRadius(
          Rect.fromLTWH(startX, y, barWidth * task.progressRate / 100, 24),
          const Radius.circular(4),
        ),
        paint,
      );
    }
  }

  Color _progressColor(int progress) {
    if (progress >= 100) return const Color(0xFF4CAF50); // done: green
    if (progress >= 50) return const Color(0xFFFF9800);  // in progress: orange
    return const Color(0xFFFF5722);                       // behind: red
  }

  @override
  bool shouldRepaint(GanttBarPainter old) =>
      old.tasks != tasks || old.startDate != startDate;
}

class WbsTask {
  final String id;
  final String title;
  final String? assignee;
  final DateTime startDate;
  final Duration duration;
  final int progressRate; // 0-100
  final List<String> dependencies;
}

CREATE TABLE wbs_tasks (
  id uuid PRIMARY KEY DEFAULT gen_random_uuid(),
  title text NOT NULL,
  start_date date NOT NULL,
  end_date date NOT NULL,
  progress_rate int DEFAULT 0 CHECK (progress_rate BETWEEN 0 AND 100),
  dependencies uuid[],
  user_id uuid REFERENCES auth.users(id)
);

@override
bool shouldRepaint(GanttBarPainter old) =>
    old.tasks != tasks || old.startDate != startDate;