package com.github.antweb.donkey

import android.bluetooth.BluetoothGatt
import android.bluetooth.BluetoothGattCharacteristic
import android.os.Environment
import java.io.BufferedInputStream
import java.io.File
import java.io.FileInputStream
import java.nio.ByteBuffer

class FileTransfer(
    private val gatt: BluetoothGatt,
    private val dataCharacteristic: BluetoothGattCharacteristic,
    private val mtu: Int
) {
    private val filePath = "/Download/SEND.txt"

    private val iterator = openFile().iterator()
    private var offset: Int = 0

    private fun openFile(): ByteArray {
        // TODO: Don't listen to Android Docs, use stuff that is not deprecated
        val file = File(
            Environment.getExternalStorageDirectory()
                .absolutePath, filePath
        )

        val size = file.length()
        val bytes = ByteArray(size.toInt())
        val buf = BufferedInputStream(FileInputStream(file))
        buf.read(bytes, 0, bytes.size)
        buf.close()

        return bytes
    }

    fun sendFile() {
        // Send first chunk
        sendNext()
    }

    fun sendNext() {
        if (!iterator.hasNext()) {
            return
        }

        gatt?.beginReliableWrite()



        val chunk = mutableListOf<Byte>()
        for (i in 0 until (mtu - 5)) {
            chunk.add(iterator.next())
        }

        // Our packet:
        // 4 byte header + chunk
        val header = offset
        offset += chunk.size

        val sendBuffer = ByteBuffer.allocate(chunk.size + 4)
        sendBuffer.putInt(header)
        sendBuffer.put(chunk.toByteArray())


        dataCharacteristic?.value = sendBuffer.array()
        gatt?.writeCharacteristic(dataCharacteristic)

        // This will trigger the onCharacteristicWrite callback once the other side ACKs
        // In there, we can call the actual gatt?.executeReliableWrite()
    }
}