public class MainActivity extends AppCompatActivity implements
        CompoundButton.OnCheckedChangeListener{
    private static final int PERMISSION_REQUESTS = 1;
    private CameraSource cameraSource = null;
    private CameraSourcePreview preview;
    private GraphicOverlay graphicOverlay;
    private static final String TAG = "MainActivity";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        preview = findViewById(R.id.firePreview);
        graphicOverlay = findViewById(R.id.fireFaceOverlay);
        ToggleButton facingSwitch = findViewById(R.id.facingswitch);
        facingSwitch.setOnCheckedChangeListener(this);

        if (allPermissionsGranted()) {
            createCameraSource();
            startCameraSource();
        } else {
            getRuntimePermissions();
        }
    }
    @Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        if (cameraSource != null) {
            if (isChecked) {
                cameraSource.setFacing(CameraSource.CAMERA_FACING_FRONT);
            } else {
                cameraSource.setFacing(CameraSource.CAMERA_FACING_BACK);
            }
        }
        preview.stop();
        startCameraSource();
    }
    private void createCameraSource() {
        // If there's no existing cameraSource, create one.
        if (cameraSource == null) {
            cameraSource = new CameraSource(this, graphicOverlay);
        }
        cameraSource.setMachineLearningFrameProcessor(new FaceDetectionProcessor());
    }
    /**
     * Starts or restarts the camera source, if it exists. If the camera source doesn't exist yet
     * (e.g., because onResume was called before the camera source was created), this will be called
     * again when the camera source is created.
     */
    private void startCameraSource() {
        if (cameraSource != null) {
            try {
                if (preview == null) {
                    Log.d(TAG, "resume: Preview is null");
                }
                if (graphicOverlay == null) {
                    Log.d(TAG, "resume: graphOverlay is null");
                }
                preview.start(cameraSource, graphicOverlay);
            } catch (IOException e) {
                cameraSource.release();
                cameraSource = null;
            }
        }
    }

    @Override
    public void onResume() {
        super.onResume();
        startCameraSource();
    }

    /** Stops the camera. */
    @Override
    protected void onPause() {
        super.onPause();
        preview.stop();
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        if (cameraSource != null) {
            cameraSource.release();
        }
    }
    private boolean allPermissionsGranted() {
        for (String permission : getRequiredPermissions()) {
            if (!isPermissionGranted(this, permission)) {
                return false;
            }
        }
        return true;
    }
    private void getRuntimePermissions() {
        List allNeededPermissions = new ArrayList<>();
        for (String permission : getRequiredPermissions()) {
            if (!isPermissionGranted(this, permission)) {
                allNeededPermissions.add(permission);
            }
        }

        if (!allNeededPermissions.isEmpty()) {
            ActivityCompat.requestPermissions(
                    this, allNeededPermissions.toArray(new String[0]), PERMISSION_REQUESTS);
        }
    }
    private String[] getRequiredPermissions() {
        try {
            PackageInfo info =
                    this.getPackageManager()
                            .getPackageInfo(this.getPackageName(), PackageManager.GET_PERMISSIONS);
            String[] ps = info.requestedPermissions;
            if (ps != null && ps.length > 0) {
                return ps;
            } else {
                return new String[0];
            }
        } catch (Exception e) {
            return new String[0];
        }
    }

    @Override
    public void onRequestPermissionsResult(
            int requestCode, String[] permissions, int[] grantResults) {
        if (allPermissionsGranted()) {
            createCameraSource();
            startCameraSource();
        }
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    }

    private static boolean isPermissionGranted(Context context, String permission) {
        if (ContextCompat.checkSelfPermission(context, permission)
                == PackageManager.PERMISSION_GRANTED) {
            return true;
        }
        return false;
    }
}