Meshtastic-Android/app/src/main/java/com/geeksville/mesh/SafeBluetooth.kt

package com.geeksville.mesh

import android.bluetooth.*
import android.content.Context
import com.geeksville.android.Logging
import com.geeksville.concurrent.CallbackContinuation
import com.geeksville.concurrent.Continuation
import com.geeksville.concurrent.SyncContinuation
import java.io.IOException


/**
 * Uses coroutines to safely access a bluetooth GATT device with a synchronous API
 *
 * The BTLE API on android is dumb.  You can only have one outstanding operation in flight to
 * the device.  If you try to do something when something is pending, the operation just returns
 * false.  You are expected to chain your operations from the results callbacks.
 *
 * This class fixes the API by using coroutines to let you safely do a series of BTLE operations.
 */
class SafeBluetooth(private val context: Context, private val device: BluetoothDevice) :
    Logging {

    /// Timeout before we declare a bluetooth operation failed
    var timeoutMsec = 5 * 1000L

    /// Users can access the GATT directly as needed
    lateinit var gatt: BluetoothGatt

    var state = BluetoothProfile.STATE_DISCONNECTED
    private var currentWork: BluetoothContinuation? = null
    private val workQueue = mutableListOf<BluetoothContinuation>()

    /**
     * a schedulable bit of bluetooth work, includes both the closure to call to start the operation
     * and the completion (either async or sync) to call when it completes
     */
    private class BluetoothContinuation(
        val tag: String,
        val completion: com.geeksville.concurrent.Continuation<*>,
        val startWorkFn: () -> Boolean
    ) : Logging {

        /// Start running a queued bit of work, return true for success or false for fatal bluetooth error
        fun startWork(): Boolean {
            debug("Starting work: $tag")
            return startWorkFn()
        }
    }

    private val gattCallback = object : BluetoothGattCallback() {

        override fun onConnectionStateChange(
            gatt: BluetoothGatt,
            status: Int,
            newState: Int
        ) {
            info("new bluetooth connection state $newState")
            state = newState
            when (newState) {
                BluetoothProfile.STATE_CONNECTED -> {
                    //logAssert(workQueue.isNotEmpty())
                    //val work = workQueue.removeAt(0)
                    completeWork(status, Unit)
                }
                BluetoothProfile.STATE_DISCONNECTED -> {
                    // cancel any queued ops?  for now I think it is best to keep them around
                    // failAllWork(IOException("Lost connection"))
                }
            }
        }

        override fun onServicesDiscovered(gatt: BluetoothGatt, status: Int) {
            completeWork(status, Unit)
        }

        override fun onCharacteristicRead(
            gatt: BluetoothGatt,
            characteristic: BluetoothGattCharacteristic,
            status: Int
        ) {
            completeWork(status, characteristic)
        }

        override fun onCharacteristicWrite(
            gatt: BluetoothGatt,
            characteristic: BluetoothGattCharacteristic,
            status: Int
        ) {
            completeWork(status, characteristic)
        }

        override fun onMtuChanged(gatt: BluetoothGatt, mtu: Int, status: Int) {
            completeWork(status, mtu)
        }
    }


    /// If we have work we can do, start doing it.
    private fun startNewWork() {
        logAssert(currentWork == null)

        if (workQueue.isNotEmpty()) {
            val newWork = workQueue.removeAt(0)
            currentWork = newWork
            logAssert(newWork.startWork())
        }
    }

    private fun <T> queueWork(tag: String, cont: Continuation<T>, initFn: () -> Boolean) {
        val btCont = BluetoothContinuation(tag, cont, initFn)

        synchronized(workQueue) {
            debug("Enqueuing work: ${btCont.tag}")
            workQueue.add(btCont)

            // if we don't have any outstanding operations, run first item in queue
            if (currentWork == null)
                startNewWork()
        }
    }

    /**
     * Called from our big GATT callback, completes the current job and then schedules a new one
     */
    private fun <T : Any> completeWork(status: Int, res: T) {

        // startup next job in queue before calling the completion handler
        val work =
            synchronized(workQueue) {
                val w = currentWork!! // will throw if null, which is helpful
                currentWork = null // We are now no longer working on anything

                startNewWork()
                w
            }

        if (status != 0)
            work.completion.resumeWithException(IOException("Bluetooth status=$status"))
        else
            work.completion.resume(Result.success(res) as Result<Nothing>)
    }

    /**
     * Something went wrong, abort all queued
     */
    private fun failAllWork(ex: Exception) {
        synchronized(workQueue) {
            workQueue.forEach {
                it.completion.resumeWithException(ex)
            }
            workQueue.clear()
        }
    }

    /// helper glue to make sync continuations and then wait for the result
    private fun <T> makeSync(wrappedFn: (SyncContinuation<T>) -> Unit): T {
        val cont = SyncContinuation<T>()
        wrappedFn(cont)
        return cont.await(timeoutMsec)
    }

    // FIXME, pass in true for autoconnect - so we will autoconnect whenever the radio
    // comes in range (even if we made this connect call long ago when we got powered on)
    // see https://stackoverflow.com/questions/40156699/which-correct-flag-of-autoconnect-in-connectgatt-of-ble for
    // more info.
    // Otherwise if you pass in false, it will try to connect now and will timeout and fail in 30 seconds.
    private fun queueConnect(autoConnect: Boolean = false, cont: Continuation<Unit>) {
        queueWork("connect", cont) {
            val g = device.connectGatt(context, autoConnect, gattCallback)
            if (g != null)
                gatt = g
            g != null
        }
    }

    fun asyncConnect(autoConnect: Boolean = false, cb: (Result<Unit>) -> Unit) {
        logAssert(workQueue.isEmpty() && currentWork == null) // I don't think anything should be able to sneak in front
        queueConnect(autoConnect, CallbackContinuation(cb))
    }

    fun connect(autoConnect: Boolean = false) = makeSync<Unit> { queueConnect(autoConnect, it) }

    private fun queueReadCharacteristic(
        c: BluetoothGattCharacteristic,
        cont: Continuation<BluetoothGattCharacteristic>
    ) = queueWork("readc", cont) { gatt.readCharacteristic(c) }

    fun asyncReadCharacteristic(
        c: BluetoothGattCharacteristic,
        cb: (Result<BluetoothGattCharacteristic>) -> Unit
    ) = queueReadCharacteristic(c, CallbackContinuation(cb))

    fun readCharacteristic(c: BluetoothGattCharacteristic): BluetoothGattCharacteristic =
        makeSync { queueReadCharacteristic(c, it) }

    private fun queueDiscoverServices(cont: Continuation<Unit>) {
        queueWork("discover", cont) {
            gatt.discoverServices()
        }
    }

    fun asyncDiscoverServices(cb: (Result<Unit>) -> Unit) {
        logAssert(workQueue.isEmpty() && currentWork == null) // I don't think anything should be able to sneak in front
        queueDiscoverServices(CallbackContinuation(cb))
    }

    fun discoverServices() = makeSync<Unit> { queueDiscoverServices(it) }

    private fun queueRequestMtu(
        len: Int,
        cont: Continuation<Int>
    ) = queueWork("reqMtu", cont) { gatt.requestMtu(len) }

    fun asyncRequestMtu(
        len: Int,
        cb: (Result<Int>) -> Unit
    ) {
        logAssert(workQueue.isEmpty() && currentWork == null) // I don't think anything should be able to sneak in front
        queueRequestMtu(len, CallbackContinuation(cb))
    }

    fun requestMtu(len: Int): Int =
        makeSync { queueRequestMtu(len, it) }

    private fun queueWriteCharacteristic(
        c: BluetoothGattCharacteristic,
        cont: Continuation<BluetoothGattCharacteristic>
    ) = queueWork("writec", cont) { gatt.writeCharacteristic(c) }

    fun asyncWriteCharacteristic(
        c: BluetoothGattCharacteristic,
        cb: (Result<BluetoothGattCharacteristic>) -> Unit
    ) = queueWriteCharacteristic(c, CallbackContinuation(cb))

    fun writeCharacteristic(c: BluetoothGattCharacteristic): BluetoothGattCharacteristic =
        makeSync { queueWriteCharacteristic(c, it) }

    fun disconnect() {
        gatt.disconnect()
        failAllWork(Exception("SafeBluetooth disconnected"))
    }
}