graph_widget.dart

class MyApp extends StatefulWidget {
  const MyApp({Key? key, required this.repository}) : super(key: key);

  final Repository repository;

  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  final _data = {
    '1HR': [
      const FlSpot(0, 120),
      const FlSpot(30, 100),
      const FlSpot(40, 150),
      const FlSpot(50, 200),
      const FlSpot(60, 140),
      const FlSpot(70, 240),
      const FlSpot(80, 145),
    ],
    '1DAY': [
      const FlSpot(0, 620),
      const FlSpot(30, 500),
      const FlSpot(40, 350),
      const FlSpot(50, 700),
      const FlSpot(60, 140),
      const FlSpot(70, 40),
      const FlSpot(80, 145),
    ],
    '1WK': [
      const FlSpot(0, 1720),
      const FlSpot(30, 4100),
      const FlSpot(40, 3150),
      const FlSpot(50, 1200),
      const FlSpot(60, 1140),
      const FlSpot(70, 240),
      const FlSpot(80, 145),
    ],
  };

  String _selected = '1HR';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: Center(
          child: Padding(
            padding: const EdgeInsets.symmetric(vertical: 24),
            child: LineChart(
              LineChartData(
                minX: 0,
                maxX: getMaxX(_data[_selected]!),
                minY: 0,
                maxY: getMaxY(_data[_selected]!),
                borderData: FlBorderData(show: false),
                titlesData: FlTitlesData(
                  show: true,
                  bottomTitles: AxisTitles(
                    axisNameWidget: Row(
                      mainAxisAlignment: MainAxisAlignment.center,
                      crossAxisAlignment: CrossAxisAlignment.center,
                      mainAxisSize: MainAxisSize.max,
                      children: ['1HR', '1DAY', '1WK', '1MTH', '1YR']
                          .map((e) => bottomTitleWidget(e, _selected == e))
                          .toList(),
                    ),
                  ),
                  leftTitles: AxisTitles(
                    sideTitles: SideTitles(
                      showTitles: false,
                    ),
                  ),
                  topTitles: AxisTitles(
                    sideTitles: SideTitles(showTitles: false),
                  ),
                  rightTitles: AxisTitles(
                    sideTitles: SideTitles(showTitles: false),
                  ),
                ),
                gridData: FlGridData(show: false),
                lineBarsData: [
                  LineChartBarData(
                    barWidth: 2,
                    isStrokeCapRound: true,
                    belowBarData: BarAreaData(
                      show: true,
                      cutOffY: 1500,
                      applyCutOffY: false,
                      gradient: LinearGradient(
                        colors: [Colors.deepPurple, Colors.white]
                            .map((color) => color.withOpacity(0.3))
                            .toList(),
                        begin: Alignment.topCenter,
                        end: Alignment.bottomCenter,
                      ),
                    ),
                    color: Colors.deepPurple,
                    isCurved: true,
                    dotData: FlDotData(show: false),
                    spots: _data[_selected],
                  )
                ],
              ),
            ),
          ),
        ),
      ),
    );
  }

  Widget bottomTitleWidget(String text, bool isSelected) {
    final style = TextStyle(
      color: isSelected ? Colors.deepPurple : const Color(0xff68737d),
      fontWeight: FontWeight.bold,
      fontSize: 16,
    );

    return GestureDetector(
      onTap: () {
        setState(() {
          _selected = text;
        });
      },
      child: Padding(
        padding: const EdgeInsets.symmetric(horizontal: 16),
        child: Text(text, style: style),
      ),
    );
  }

  double getMaxX(List<FlSpot> data) {
    final xData = data.map((e) => e.x).toList();

    return xData.reduce(max);
  }

  double getMaxY(List<FlSpot> data) {
    final yData = data.map((e) => e.y).toList();

    return yData.reduce(max);
  }
}

God bless you Boss