Kovenant utility: Promise queue

PromiseQueue.kt

package com.ydangleapps.bluetooth

import nl.komponents.kovenant.*
import nl.komponents.kovenant.functional.bind

/** Queue operations */
class PromiseQueue {

    // Pending operations
    val pendingOperations = mutableListOf<() -> Promise<Unit, Exception>>()
    var isRunning = false

    // Add queued operation
    fun<V> add(callback : () -> Promise<V, Exception>) : Promise<V, Exception> {

        // Create pending promise
        val pending = deferred<V, Exception>()

        // Add to list
        pendingOperations.add {

            // Wait for promise to complete
            task {} bind { callback() } success {
                pending.resolve(it)
            } fail {
                pending.reject(it)
            } then {}

        }

        // Start if this is the first one
        if (!isRunning) {
            isRunning = true
            runNextOperation()
        }

        // Done, wait for promise
        return pending.promise

    }

    private fun runNextOperation() {

        // Get next op
        val next = pendingOperations.firstOrNull()
        if (next == null) {
            isRunning = false
            return
        }

        // Remove it
        pendingOperations.removeAt(0)

        // Run it, wait for promise
        next() always {

            // Run next in the chain
            runNextOperation()

        }

    }

}