Step 7 - Add client interfaces and callback wrapper

mpp-library/domain/src/commonMain/kotlin/org/example/library/domain/repository/HelloWorldClient.kt

@@ -0,0 +1,50 @@
+
+/*
+ * Copyright 2020 IceRock MAG Inc. Use of this source code is governed by the Apache 2.0 license.
+ */
+package org.example.library.domain.repository
+
+import io.grpc.examples.helloworld.HelloReply
+import io.grpc.examples.helloworld.HelloRequest
+import kotlin.coroutines.suspendCoroutine
+
+interface HelloWorldSuspendClient {
+    suspend fun sendHello(message: HelloRequest): HelloReply
+}
+
+interface HelloWorldCallbackClient {
+    fun sendHello(message: HelloRequest, callback: (HelloReply?, Exception?) -> Unit)
+}
+
+class HelloWorldSuspendClientImpl(
+    private val callbackClientCalls: HelloWorldCallbackClient
+): HelloWorldSuspendClient {
+
+    private suspend fun <In, Out> convertCallbackCallToSuspend(
+        input: In,
+        callbackClosure: ((In, ((Out?, Throwable?) -> Unit)) -> Unit),
+    ): Out {
+        return suspendCoroutine { continuation ->
+            callbackClosure(input) { result, error ->
+                Unit
+                when {
+                    error != null -> {
+                        continuation.resumeWith(Result.failure(error))
+                    }
+                    result != null -> {
+                        continuation.resumeWith(Result.success(result))
+                    }
+                    else -> {
+                        continuation.resumeWith(Result.failure(IllegalStateException("Incorrect grpc call processing")))
+                    }
+                }
+            }
+        }
+    }
+
+    override suspend fun sendHello(message: HelloRequest): HelloReply {
+        return convertCallbackCallToSuspend(message, callbackClosure = { input, callback ->
+            callbackClientCalls.sendHello(input, callback)
+        })
+    }
+}