public class MainActivity extends AppCompatActivity  implements ActivityCompat.OnRequestPermissionsResultCallback,
        AdapterView.OnItemSelectedListener,
        CompoundButton.OnCheckedChangeListener {
    private static final String ON_DEVICE_LABELLING = "On-device labeling";
    private static final String CLOUD_LABELLING = "Cloud labeling";
    private static final String TAG = "LivePreviewActivity";
    private static final int PERMISSION_REQUESTS = 1;

    private CameraSource cameraSource = null;
    private CameraSourcePreview preview;
    private GraphicOverlay graphicOverlay;
    private String selectedModel = ON_DEVICE_LABELLING;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        Log.d(TAG, "onCreate");

        setContentView(R.layout.activity_main);

        preview = (CameraSourcePreview) findViewById(R.id.firePreview);
        if (preview == null) {
            Log.d(TAG, "Preview is null");
        }
        graphicOverlay = (GraphicOverlay) findViewById(R.id.fireFaceOverlay);
        if (graphicOverlay == null) {
            Log.d(TAG, "graphicOverlay is null");
        }

        Spinner spinner = (Spinner) findViewById(R.id.spinner);
        List options = new ArrayList<>();
        options.add(ON_DEVICE_LABELLING);
        options.add(CLOUD_LABELLING);
        // Creating adapter for spinner
        ArrayAdapter dataAdapter = new ArrayAdapter<>(this, R.layout.spinner_style, options);
        // Drop down layout style - list view with radio button
        dataAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        // attaching data adapter to spinner
        spinner.setAdapter(dataAdapter);
        spinner.setOnItemSelectedListener(this);

        ToggleButton facingSwitch = (ToggleButton) findViewById(R.id.facingswitch);
        facingSwitch.setOnCheckedChangeListener(this);

        if (allPermissionsGranted()) {
            createCameraSource(selectedModel);
        } else {
            getRuntimePermissions();
        }
    }

    @Override
    public synchronized void onItemSelected(AdapterView parent, View view, int pos, long id) {
        // An item was selected. You can retrieve the selected item using
        // parent.getItemAtPosition(pos)
        selectedModel = parent.getItemAtPosition(pos).toString();
        Log.d(TAG, "Selected model: " + selectedModel);
        preview.stop();
        if (allPermissionsGranted()) {
            createCameraSource(selectedModel);
            startCameraSource();
        } else {
            getRuntimePermissions();
        }
    }

    @Override
    public void onNothingSelected(AdapterView parent) {
        // Do nothing.
    }

    @Override
    public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
        Log.d(TAG, "Set facing");
        if (cameraSource != null) {
            if (isChecked) {
                cameraSource.setFacing(CameraSource.CAMERA_FACING_FRONT);
            } else {
                cameraSource.setFacing(CameraSource.CAMERA_FACING_BACK);
            }
        }
        preview.stop();
        startCameraSource();
    }

    private void createCameraSource(String model) {
        // If there's no existing cameraSource, create one.
        if (cameraSource == null) {
            cameraSource = new CameraSource(this, graphicOverlay);
        }

        switch (model) {
            case ON_DEVICE_LABELLING:
                Log.i(TAG, "Using Image Label Detector Processor ondevice");
                cameraSource.setMachineLearningFrameProcessor(new ImageLabelingProcessor());
                break;
            case CLOUD_LABELLING:
                Log.i(TAG, "Using Image Label Detector Processor cloud");
                cameraSource.setMachineLearningFrameProcessor(new CloudImageLabelingProcessor());
                break;
            default:
                Log.e(TAG, "Unknown model: " + model);
        }
    }

    /**
     * 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) {
                Log.e(TAG, "Unable to start camera source.", e);
                cameraSource.release();
                cameraSource = null;
            }
        }
    }

    @Override
    public void onResume() {
        super.onResume();
        Log.d(TAG, "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 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];
        }
    }

    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);
        }
    }

    @Override
    public void onRequestPermissionsResult(
            int requestCode, String[] permissions, int[] grantResults) {
        Log.i(TAG, "Permission granted!");
        if (allPermissionsGranted()) {
            createCameraSource(selectedModel);
        }
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    }

    private static boolean isPermissionGranted(Context context, String permission) {
        if (ContextCompat.checkSelfPermission(context, permission)
                == PackageManager.PERMISSION_GRANTED) {
            Log.i(TAG, "Permission granted: " + permission);
            return true;
        }
        Log.i(TAG, "Permission NOT granted: " + permission);
        return false;
    }
}