From b84a995a05fecb9ef90c9184959f285f324e7411 Mon Sep 17 00:00:00 2001
From: Fabian Mastenbroek <mail.fabianm@gmail.com>
Date: Fri, 16 Feb 2018 14:39:53 +0100
Subject: refactor(#18): Provide access to latest sender

This change adds a `sender` property to the `Context` interface to
provide processes access to the sender of the latest received message.

Please note that methods like `hold()` and `interrupt()` may change the value
of this property.
---
 .../kotlin/com/atlarge/opendc/simulator/Context.kt |  8 ++++++++
 .../com/atlarge/opendc/omega/OmegaSimulation.kt    | 22 ++++++++++++++--------
 2 files changed, 22 insertions(+), 8 deletions(-)

diff --git a/opendc-core/src/main/kotlin/com/atlarge/opendc/simulator/Context.kt b/opendc-core/src/main/kotlin/com/atlarge/opendc/simulator/Context.kt
index c89bdb59..13170256 100644
--- a/opendc-core/src/main/kotlin/com/atlarge/opendc/simulator/Context.kt
+++ b/opendc-core/src/main/kotlin/com/atlarge/opendc/simulator/Context.kt
@@ -50,6 +50,14 @@ interface Context<S, out M> {
      */
     val delta: Duration
 
+    /**
+     * The sender of the last received message or `null` in case the process has not received any messages yet.
+     *
+     * Note that this property is only guaranteed to be correct when accessing after a single suspending call. Methods
+     * like `hold()` and `interrupt()` may change the value of this property.
+     */
+    val sender: Entity<*, *>?
+
     /**
      * The observable state of the entity bound to this scope.
      */
diff --git a/opendc-kernel-omega/src/main/kotlin/com/atlarge/opendc/omega/OmegaSimulation.kt b/opendc-kernel-omega/src/main/kotlin/com/atlarge/opendc/omega/OmegaSimulation.kt
index 9c6d4ab3..bd3f4529 100644
--- a/opendc-kernel-omega/src/main/kotlin/com/atlarge/opendc/omega/OmegaSimulation.kt
+++ b/opendc-kernel-omega/src/main/kotlin/com/atlarge/opendc/omega/OmegaSimulation.kt
@@ -249,11 +249,6 @@ internal class OmegaSimulation<M>(bootstrap: Bootstrap<M>) : Simulation<M>, Boot
         override val model: M
             get() = this@OmegaSimulation.model
 
-        /**
-         * The state of the entity.
-         */
-        override var state: S = process.initialState
-
         /**
          * The current point in simulation time.
          */
@@ -268,9 +263,9 @@ internal class OmegaSimulation<M>(bootstrap: Bootstrap<M>) : Simulation<M>, Boot
             get() = maxOf(time - last, 0)
 
         /**
-         * The [CoroutineContext] for a [Context].
+         * The state of the entity.
          */
-        override val context: CoroutineContext = EmptyCoroutineContext
+        override var state: S = process.initialState
 
         /**
          * The observable state of an [Entity] within the simulation is provided by the context of the simulation.
@@ -278,6 +273,16 @@ internal class OmegaSimulation<M>(bootstrap: Bootstrap<M>) : Simulation<M>, Boot
         override val <T : Entity<S, *>, S> T.state: S
             get() = context?.state ?: initialState
 
+        /**
+         * The sender of the last received message or `null` in case the process has not received any messages yet.
+         */
+        override var sender: Entity<*, *>? = null
+
+        /**
+         * The [CoroutineContext] for a [Context].
+         */
+        override val context: CoroutineContext = EmptyCoroutineContext
+
         /**
          * The continuation to resume the execution of the process.
          */
@@ -359,7 +364,8 @@ internal class OmegaSimulation<M>(bootstrap: Bootstrap<M>) : Simulation<M>, Boot
          *
          * @return The envelope containing the message.
          */
-        suspend fun receiveEnvelope(): Envelope<*> = suspendCoroutine { continuation = it }
+        suspend fun receiveEnvelope() = suspendCoroutine<Envelope<*>> { continuation = it }
+            .also { sender = it.sender }
 
         // Completion continuation implementation
         /**
-- 
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