public class MainActivity extends AppCompatActivity {

    private final int REQUEST_CAMERA_PERMISSION = 0;
    private TextureView mTextureView;
    private ImageButton mCaptureBtn;
    private CameraManager mCameraManager;
    private CameraDevice mCameraDevice;
    private String mCameraId;
    private Size mPreviewSize;
    private int mWidth;
    private int mHeight;
    private CameraDevice.StateCallback mCameraDeviceStateCallback = new CameraDevice.StateCallback() {
        @Override
        public void onOpened(CameraDevice cameraDevice) {
            mCameraDevice = cameraDevice;
            createCameraPreview();
        }

        @Override
        public void onDisconnected(CameraDevice cameraDevice) {
            mCameraDevice.close();
            mCameraDevice = null;
        }

        @Override
        public void onError(CameraDevice cameraDevice, int i) {
            mCameraDevice.close();
            mCameraDevice = null;
        }
    };
    private HandlerThread mBackgroundThread;
    private Handler mBackgroundHandler;
    private static SparseIntArray ORIENTATIONS = new SparseIntArray();

    static {
        ORIENTATIONS.append(Surface.ROTATION_0, 0);
        ORIENTATIONS.append(Surface.ROTATION_90, 90);
        ORIENTATIONS.append(Surface.ROTATION_180, 180);
        ORIENTATIONS.append(Surface.ROTATION_270, 270);
    }

    private CameraCaptureSession mSession;
    private CaptureRequest.Builder mBuilder;
    private CameraCaptureSession.CaptureCallback mSessionCaptureCallback = new CameraCaptureSession.CaptureCallback() {
        @Override
        public void onCaptureStarted(CameraCaptureSession session, CaptureRequest request, long timestamp, long frameNumber) {
            super.onCaptureStarted(session, request, timestamp, frameNumber);
        }
    };

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mCameraManager = (CameraManager) getSystemService(CAMERA_SERVICE);
        mTextureView = (TextureView) findViewById(R.id.camera_texture_view);
        mCaptureBtn = (ImageButton) findViewById(R.id.capture_btn);
        mTextureView.setSurfaceTextureListener(new TextureView.SurfaceTextureListener() {
            @Override
            public void onSurfaceTextureAvailable(SurfaceTexture surfaceTexture, int width, int height) {
                mWidth = width;
                mHeight = height;
                getCameraId();
                openCamera();
            }

            @Override
            public void onSurfaceTextureSizeChanged(SurfaceTexture surfaceTexture, int i, int i1) {

            }

            @Override
            public boolean onSurfaceTextureDestroyed(SurfaceTexture surfaceTexture) {
                return false;
            }

            @Override
            public void onSurfaceTextureUpdated(SurfaceTexture surfaceTexture) {

            }
        });
    }

    private void getCameraId() {
        try {
            for (String cameraId : mCameraManager.getCameraIdList()) {
                CameraCharacteristics characteristics = mCameraManager.getCameraCharacteristics(cameraId);
                if (characteristics.get(CameraCharacteristics.LENS_FACING) == CameraCharacteristics.LENS_FACING_FRONT) {
                    continue;
                }
                mCameraId = cameraId;
                return;
            }
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private Size getPreferredPreviewSize(Size[] sizes, int width, int height) {
        List<Size> collectorSizes = new ArrayList<>();
        for (Size option : sizes) {
            if (width > height) {
                if (option.getWidth() > width && option.getHeight() > height) {
                    collectorSizes.add(option);
                }
            } else {
                if (option.getHeight() > width && option.getWidth() > height) {
                    collectorSizes.add(option);
                }
            }
        }
        if (collectorSizes.size() > 0) {
            return Collections.min(collectorSizes, new Comparator<Size>() {
                @Override
                public int compare(Size s1, Size s2) {
                    return Long.signum(s1.getWidth() * s1.getHeight() - s2.getWidth() * s2.getHeight());
                }
            });
        }
        return sizes[0];
    }

    private void openCamera() {
        if (ActivityCompat.checkSelfPermission(this, Manifest.permission.CAMERA)
                != PackageManager.PERMISSION_GRANTED && ActivityCompat.checkSelfPermission(this,
                Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
            Log.e("CameraNew", "Lacking privileges to access camera service, please request permission first.");
            ActivityCompat.requestPermissions(this, new String[]{
                    Manifest.permission.CAMERA, Manifest.permission.WRITE_EXTERNAL_STORAGE
            }, REQUEST_CAMERA_PERMISSION);
        }

        try {
            mCameraManager.openCamera(mCameraId, mCameraDeviceStateCallback, null);
            startBackgroundThread();
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    public void startBackgroundThread() {
        mBackgroundThread = new HandlerThread("Camera Background");
        mBackgroundThread.start();
        mBackgroundHandler = new Handler(mBackgroundThread.getLooper());
    }

    public void stopBackgroundThread() {
        if (mBackgroundThread != null) {
            mBackgroundThread.quitSafely();
            try {
                mBackgroundThread.join();
                mBackgroundThread = null;
                mBackgroundHandler = null;
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    private void createCameraPreview() {
        try {
            SurfaceTexture texture = mTextureView.getSurfaceTexture();
            assert texture != null;
            CameraCharacteristics characteristics = mCameraManager.getCameraCharacteristics(mCameraId);
            StreamConfigurationMap map = characteristics.get(CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP);
            int deviceOrientation = getWindowManager().getDefaultDisplay().getOrientation();
            int totalRotation = sensorToDeviceRotation(characteristics, deviceOrientation);
            boolean swapRotation = totalRotation == 90 || totalRotation == 270;
            int rotatedWidth = mWidth;
            int rotatedHeight = mHeight;
            if (swapRotation) {
                rotatedWidth = mHeight;
                rotatedHeight = mWidth;
            }
            mPreviewSize = getPreferredPreviewSize(map.getOutputSizes(SurfaceTexture.class), rotatedWidth, rotatedHeight);
            texture.setDefaultBufferSize(mPreviewSize.getWidth(), mPreviewSize.getHeight());
            Log.e("CameraActivity", "OptimalSize width: " + mPreviewSize.getWidth() + " height: " + mPreviewSize.getHeight());
            Surface surface = new Surface(texture);
            mBuilder = mCameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_PREVIEW);
            mBuilder.addTarget(surface);
            mCameraDevice.createCaptureSession(Arrays.asList(surface), new CameraCaptureSession.StateCallback() {
                @Override
                public void onConfigured(CameraCaptureSession cameraCaptureSession) {
                    if (null == mCameraDevice) {
                        return;
                    }
                    mSession = cameraCaptureSession;
                    mBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO);
                    try {
                        mSession.setRepeatingRequest(mBuilder.build(), mSessionCaptureCallback, mBackgroundHandler);
                    } catch (CameraAccessException e) {
                        e.printStackTrace();
                    }
                }

                @Override
                public void onConfigureFailed(CameraCaptureSession cameraCaptureSession) {
                    Toast.makeText(MainActivity.this, "Camera configuration change", Toast.LENGTH_SHORT).show();
                }
            }, null);
        } catch (CameraAccessException e) {
            e.printStackTrace();
        }
    }

    private static int sensorToDeviceRotation(CameraCharacteristics characteristics, int deviceOrientation) {
        int sensorOrientation = characteristics.get(CameraCharacteristics.SENSOR_ORIENTATION);
        deviceOrientation = ORIENTATIONS.get(deviceOrientation);
        return (sensorOrientation + deviceOrientation + 360) % 360;
    }


    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        if (requestCode == REQUEST_CAMERA_PERMISSION) {
            if (grantResults.length <= 0 || grantResults[0] == PackageManager.PERMISSION_DENIED) {
                // Permission denied
                Toast.makeText(this, "User denied permission, can't use take photo feature.",
                        Toast.LENGTH_SHORT).show();
            } else {

            }
        }
    }

    @Override
    protected void onResume() {
        super.onResume();
    }

    @Override
    protected void onPause() {
        super.onPause();
        if (mSession != null) {
            mSession.close();
            mSession = null;
        }
        if (mCameraDevice != null) {
            mCameraDevice.close();
            mCameraDevice = null;
        }

        stopBackgroundThread();
    }