mobile_nebula/lib/screens/siteConfig/ScanQRScreen.dart

import 'package:flutter/material.dart';
import 'package:mobile_scanner/mobile_scanner.dart';

class ScanQRScreen extends StatefulWidget {
  @override
  State<ScanQRScreen> createState() => _ScanQRScreenState();
}

class _ScanQRScreenState extends State<ScanQRScreen> {
  final MobileScannerController cameraController = MobileScannerController(
    autoStart: true,
    formats: [BarcodeFormat.qrCode],
  );

  @override
  Widget build(BuildContext context) {
    final scanWindow = Rect.fromCenter(
      center: MediaQuery.sizeOf(context).center(Offset.zero),
      width: 250,
      height: 250,
    );

    return Scaffold(
        appBar: AppBar(title: const Text('Scan QR')),
        backgroundColor: Colors.black,
        body: Stack(fit: StackFit.expand, children: [
          Center(
            child: MobileScanner(
                fit: BoxFit.contain,
                controller: cameraController,
                scanWindow: scanWindow,
                onDetect: (BarcodeCapture barcodes) {
                  var barcode = barcodes.barcodes.firstOrNull;
                  if (barcode != null && mounted) {
                    cameraController.stop().then((_) {
                      Navigator.pop(context, barcode.rawValue);
                    });
                  }
                }),
          ),
          ValueListenableBuilder(
            valueListenable: cameraController,
            builder: (context, value, child) {
              if (!value.isInitialized || !value.isRunning || value.error != null) {
                return const SizedBox();
              }

              return CustomPaint(
                painter: ScannerOverlay(scanWindow: scanWindow),
              );
            },
          ),
          Align(
            alignment: Alignment.bottomCenter,
            child: Padding(
              padding: const EdgeInsets.all(16.0),
              child: Row(
                mainAxisAlignment: MainAxisAlignment.spaceEvenly,
                children: [
                  ToggleFlashlightButton(controller: cameraController),
                  SwitchCameraButton(controller: cameraController),
                ],
              ),
            ),
          ),
        ]));
  }
}

class ScannerOverlay extends CustomPainter {
  const ScannerOverlay({
    required this.scanWindow,
    this.borderRadius = 12.0,
  });

  final Rect scanWindow;
  final double borderRadius;

  @override
  void paint(Canvas canvas, Size size) {
    // we need to pass the size to the custom paint widget
    final backgroundPath = Path()..addRect(Rect.largest);

    final cutoutPath = Path()
      ..addRRect(
        RRect.fromRectAndCorners(
          scanWindow,
          topLeft: Radius.circular(borderRadius),
          topRight: Radius.circular(borderRadius),
          bottomLeft: Radius.circular(borderRadius),
          bottomRight: Radius.circular(borderRadius),
        ),
      );

    final backgroundPaint = Paint()
      ..color = Colors.black.withOpacity(0.5)
      ..style = PaintingStyle.fill
      ..blendMode = BlendMode.dstOut;

    final backgroundWithCutout = Path.combine(
      PathOperation.difference,
      backgroundPath,
      cutoutPath,
    );

    final borderPaint = Paint()
      ..color = Colors.white
      ..style = PaintingStyle.stroke
      ..strokeWidth = 4.0;

    final borderRect = RRect.fromRectAndCorners(
      scanWindow,
      topLeft: Radius.circular(borderRadius),
      topRight: Radius.circular(borderRadius),
      bottomLeft: Radius.circular(borderRadius),
      bottomRight: Radius.circular(borderRadius),
    );

    // First, draw the background,
    // with a cutout area that is a bit larger than the scan window.
    // Finally, draw the scan window itself.
    canvas.drawPath(backgroundWithCutout, backgroundPaint);
    canvas.drawRRect(borderRect, borderPaint);
  }

  @override
  bool shouldRepaint(ScannerOverlay oldDelegate) {
    return scanWindow != oldDelegate.scanWindow || borderRadius != oldDelegate.borderRadius;
  }
}

class SwitchCameraButton extends StatelessWidget {
  const SwitchCameraButton({required this.controller, super.key});

  final MobileScannerController controller;

  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder(
      valueListenable: controller,
      builder: (context, state, child) {
        if (!state.isInitialized || !state.isRunning) {
          return const SizedBox.shrink();
        }

        final int? availableCameras = state.availableCameras;

        if (availableCameras != null && availableCameras < 2) {
          return const SizedBox.shrink();
        }

        final Widget icon;

        switch (state.cameraDirection) {
          case CameraFacing.front:
            icon = const Icon(Icons.camera_front);
          case CameraFacing.back:
            icon = const Icon(Icons.camera_rear);
        }

        return IconButton(
          iconSize: 32.0,
          color: Colors.white,
          icon: icon,
          onPressed: () async {
            await controller.switchCamera();
          },
        );
      },
    );
  }
}

class ToggleFlashlightButton extends StatelessWidget {
  const ToggleFlashlightButton({required this.controller, super.key});

  final MobileScannerController controller;

  @override
  Widget build(BuildContext context) {
    return ValueListenableBuilder(
      valueListenable: controller,
      builder: (context, controllerState, child) {
        if (!controllerState.isInitialized || !controllerState.isRunning) {
          return const SizedBox.shrink();
        }

        switch (controllerState.torchState) {
          case TorchState.auto:
            return IconButton(
              color: Colors.white,
              iconSize: 32.0,
              icon: const Icon(Icons.flash_auto),
              onPressed: () async {
                await controller.toggleTorch();
              },
            );
          case TorchState.off:
            return IconButton(
              color: Colors.white,
              iconSize: 32.0,
              icon: const Icon(Icons.flash_off),
              onPressed: () async {
                await controller.toggleTorch();
              },
            );
          case TorchState.on:
            return IconButton(
              color: Colors.white,
              iconSize: 32.0,
              icon: const Icon(Icons.flash_on),
              onPressed: () async {
                await controller.toggleTorch();
              },
            );
          case TorchState.unavailable:
            return const SizedBox.square(
              dimension: 48.0,
              child: Icon(
                Icons.no_flash,
                size: 32.0,
                color: Colors.grey,
              ),
            );
        }
      },
    );
  }
}