import 'dart:async';
import 'package:flutter/material.dart';
import 'package:camera/camera.dart';

List<CameraDescription> cameras;

void main() {
  runApp(MaterialApp(home: MyApp()));
}

class MyApp extends StatefulWidget {
  const MyApp({
    Key key,
  }) : super(key: key);

  @override
  State<StatefulWidget> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp>
    with WidgetsBindingObserver, TickerProviderStateMixin {
  final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

  CameraController controller;

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
    Future.microtask(() {
      availableCameras().then((value) {
        cameras = value;
        if (controller == null) {
          final camera = _selectDefaultCamera(cameras);
          onNewCameraSelected(camera);
        }
      });
    });
  }

  @override
  void dispose() {
    WidgetsBinding.instance.removeObserver(this);
    super.dispose();
  }

  @override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    // App state changed before we got the chance to initialize.
    if (controller == null || !controller.value.isInitialized) {
      return;
    }
    if (state == AppLifecycleState.inactive) {
      controller?.dispose();
    } else if (state == AppLifecycleState.resumed) {
      if (controller != null) {
        onNewCameraSelected(controller.description);
      }
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      appBar: AppBar(
        title: const Text('Camera example'),
      ),
      body: Column(
        children: <Widget>[
          Expanded(
            child: Container(
              color: Colors.black,
              padding: const EdgeInsets.all(1.0),
              child: Center(
                child: _cameraPreviewWidget(),
              ),
            ),
          ),
        ],
      ),
    );
  }

  Widget _cameraPreviewWidget() {
    if (controller == null) {
      return const CircularProgressIndicator();
    }else if (!controller.value.isInitialized) {
      return const CircularProgressIndicator();
    } else {
      return CameraPreview(controller);
    }
  }

  void showInSnackBar(String message) {
    // ignore: deprecated_member_use
    _scaffoldKey.currentState.showSnackBar(SnackBar(content: Text(message)));
  }

  Future<void> onNewCameraSelected(CameraDescription cameraDescription) async {
    if (controller != null) {
      final ctrl = controller;
      setState(() {
        controller = null;
      });
      await ctrl.dispose();
    }

    controller = CameraController(
      cameraDescription,
      ResolutionPreset.medium,
      enableAudio: false,
    );

    // If the controller is updated then update the UI.
    controller.addListener(() {
      if (mounted) {
        setState(() {});
      }
      if (controller.value.hasError) {
        showInSnackBar('Camera error ${controller.value.errorDescription}');
      }
    });

    try {
      await controller.initialize();
    } on CameraException catch (e) {
      print(e);
    }

    if (mounted) {
      setState(() {});
    }
  }
}

CameraDescription _selectDefaultCamera(List<CameraDescription> cameras) {
  for (final camera in cameras) {
    if (camera.lensDirection == CameraLensDirection.front) {
      return camera;
    }
  }
  return cameras[0];
}