proxy.kt

import java.lang.reflect.InvocationHandler
import java.lang.reflect.Method
import java.lang.reflect.Proxy
import java.util.Timer
import kotlin.concurrent.timerTask
import kotlin.coroutines.Continuation
import kotlin.coroutines.intrinsics.COROUTINE_SUSPENDED
import kotlin.coroutines.resume
import kotlin.coroutines.resumeWithException
import kotlinx.coroutines.CancellationException
import kotlinx.coroutines.isActive
import kotlinx.coroutines.runBlocking

interface Service
{
    suspend fun duplicate(arg: String): String
}

class ProxyHandler : InvocationHandler
{
    override fun invoke(proxy: Any, method: Method, args: Array<out Any>?): Any {
        if (method.declaringClass == Object::class.java) {
            return method.invoke(proxy, args)
        }
        if (method.name == "duplicate") {
            val arg = args!![0] as String
            @Suppress("UNCHECKED_CAST")
            val continuation = args[1] as Continuation<String>
            val timer = Timer("background timer", true)
            timer.schedule(timerTask {
                if (!continuation.context.isActive) { // cancellation - is it right?
                    continuation.resumeWithException(CancellationException("Terminated"))
                    return@timerTask
                }
                if (arg.length == 1) {
                    continuation.resumeWithException(RuntimeException("Bad argument"))
                } else {
                    continuation.resume("$arg,$arg")
                }
            }, 1000L)
            return COROUTINE_SUSPENDED
        }
        error("Unknow method")
    }
}

fun main() {
    val iface = Service::class.java
    val proxy = Proxy.newProxyInstance(iface.classLoader, arrayOf(iface), ProxyHandler()) as Service
    runBlocking {
        try {
            val result1 = proxy.duplicate("A")
            println("result1 = $result1")
        } catch (e: Exception) {
            System.err.println("Error 1")
            e.printStackTrace()
        }
        try {
            val result2 = proxy.duplicate("BC")
            println("result2 = $result2")
        } catch (e: Exception) {
            System.err.println("Error 2")
            e.printStackTrace()
        }
    }
}