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val cameraManager: CameraManager = ...

// Get the two output targets from the activity / fragment
val surface1 = ...  // from SurfaceView
val surface2 = ...  // from SurfaceView

val dualCamera = findShortLongCameraPair(manager)!!
val outputTargets = DualCameraOutputs(
        null, mutableListOf(surface1), mutableListOf(surface2))

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fun openDualCamera(cameraManager: CameraManager,
                   dualCamera: DualCamera,
                   executor: Executor = AsyncTask.SERIAL_EXECUTOR,
                   callback: (CameraDevice) -> Unit) {

    cameraManager.openCamera(
            dualCamera.logicalId, executor, object : CameraDevice.StateCallback() {
        override fun onOpened(device: CameraDevice) = callback(device)
        // Omitting for brevity...
        override fun onError(device: CameraDevice, error: Int) = onDisconnected(device)

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/**
* Helper class used to encapsulate a logical camera and two underlying
* physical cameras
*/
data class DualCamera(val logicalId: String, val physicalId1: String, val physicalId2: String)

fun findDualCameras(manager: CameraManager, facing: Int? = null): Array<DualCamera> {
    val dualCameras = ArrayList<DualCamera>()

    // Iterate over all the available camera characteristics

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imageReader.setOnImageAvailableListener({
        val frame =  it.acquireNextImage()
        // Do something with `frame` here
        it.close()
}, null)

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val frameBufferCount = 3  // just an example, depends on your usage of ImageReader
val imageReader = ImageReader.newInstance(
        imageReaderSize.width, imageReaderSize.height, ImageFormat.YUV_420_888
        frameBufferCount)

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val surfaceView = findViewById<SurfaceView>(...)
surfaceView.holder.addCallback(object : SurfaceHolder.Callback {
    override fun surfaceCreated(holder: SurfaceHolder) {
        // We do not need to specify image format, and it will be considered of type PRIV
        // Surface is now ready and we could use it as an output target for CameraSession
    }
    ...
})

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val characteristics: CameraCharacteristics = ...

// Hardware level will be one of:
// - CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LEGACY,
// - CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_EXTERNAL,
// - CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_LIMITED,
// - CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_FULL,
// - CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL_3
val hardwareLevel = characteristics.get(
        CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL)

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fun <T>getMaximumOutputSize(
        characteristics: CameraCharacteristics, targetClass: Class<T>, format: Int? = null):
        Size {
    val config = characteristics.get(
            CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP)

    // If image format is provided, use it to determine supported sizes; else use target class
    val allSizes = if (format == null)
        config.getOutputSizes(targetClass) else config.getOutputSizes(format)
    return allSizes.sortedWith(compareBy { it.height * it.width }).reversed()[0]

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val characteristics: CameraCharacteristics = ...
val targetClass: Class<T> = ...  // e.g. SurfaceView::class.java
val sizes = characteristics.get(
        CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP)
        .getOutputSizes(targetClass)

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val characteristics: CameraCharacteristics = ...
val outputFormat: Int = ...  // e.g. ImageFormat.JPEG
val sizes = characteristics.get(
        CameraCharacteristics.SCALER_STREAM_CONFIGURATION_MAP)
        .getOutputSizes(outputFormat)