Transfer Source

data class MyTransferData(
    val id: String,
    val token: String
)

class MySampleSource {

    val source: WPTSource

    val config = WPTConfig(
        ParcelUuid.fromString("21f8190c-e4bc-11ed-b5ea-0242ac120001"), 
        WPTCoder.aes(
            "MyApplicationDemoSalt!".toByteArray(), // static data
            "7x9ZEvEVf4IqlBxuYmzKhw==".decodeBase64()!!.toByteArray() // 16 bytes encoded in Base64
        )
    )

    constructor(appContext: Context) {
        source = WPTSource(appContext, config)
        source.listener = object : WPTScannerListener {
            override fun devicesChanged(devices: WPTTargetDevices) {
                val candidate = devices.bestCandidate()
                if (candidate != null) {
                    // device found
                    val dataToTransfer = MyTransferData("123", "10a82fe8d1c4df")
                    val json = Gson().toJson(dataToTransfer)
                    val jsonData = json.toByteArray()
                    val encoded = candidate.encode(jsonData)
                    val base64 = Base64.getEncoder().encodeToString(encoded)
                    // QR code with the base64 string
                    
                } else if (devices.isProcessingDevice()) {
                    // device is processing
                } else {
                    // waiting for a device to be found
                }
            }
        }

        source.start { result ->
            result.onSuccess {
                // waiting for a device to be found
            }.onFailure { error ->
                // process error
                if (error is WPTSourceError) {
                    // process WPTSourceError
                }
            }
        }
    }
}

class WPTSource {

    /** Listener that will be notified when a target device changes */
    var listener: WPTSourceListener?

    /** Starts the source (in Bluetooth terms - starts scanning for Bluetooth devices) */
    fun start(completion: (Result<Unit>) -> Unit)

    /** Stops the source */
    fun stop(completion: (Result<Unit>) -> Unit)
}

interface WPTSourceListener {

    /**
     * When possible target device was found or was changed.
     *
     * @param devices Devices available for the transfer
     */ 
    fun devicesChanged(devices: WPTTargetDevices)
}

class WPTTargetDevices {

    /** All found devices. */
    val allDevices: List<WPTTargetDevice>

    /** The best candidate for the target. */
    fun bestCandidate(): WPTTargetDevice?
    
    /** Returns true if there is at least one device that is in the [WPTTargetDevice.State.DISCOVERED] state. */
    fun isProcessingDevice()
}

class WPTTargetDevice {

    /** The state of the device. */
    val state: State

    /** Name of the device */
    val name: String

    /** The time when the device was found. */
    val created: Long

    /**
     * When the device is found, encrypted data needs to be transferred via a generated/scanned QR code.
     * Use this method for a particular device to encode your data.
     *
     * @param data Data to be encoded.
     * @return Encoded data.
     */
    @Throws fun encode(data: ByteArray): ByteArray
}

class WPTSourceError: Throwable {

    /** The reason of the error. */
    val reason: Reason
    /** The permission that is missing in case of the [Reason.BLUETOOTH_PERMISSION_NOT_GRANTED]. */
    val permission: String?

    /**
     * The reason of the error.
     */
    enum class Reason {
        /** The scanner is already running/already stopped.*/
        WRONG_STATE,
        /** Bluetooth permission not granted. Use WPTPermissions to ask for permissions. */
        BLUETOOTH_PERMISSION_NOT_GRANTED,
        /** Bluetooth is turned off. */
        BLUETOOTH_NOT_ENABLED,
        /** Bluetooth is not supported by this device. */
        BLUETOOTH_MISSING,
        /**
         * Location is disabled in the system settings. You can navigate the user to the
         * system settings with startActivity(Intent(android.provider.Settings.ACTION_LOCATION_SOURCE_SETTINGS)).
         *
         * This might happened only if you're supporting Android 11 or lower.
         */
        LOCATION_NOT_ENABLED,
        /** Unknown error */
        UNKNOWN
    }
}