Expose current pod assignments (#145)

* Expose current pod assignments

* Expose new public operations in the companion object

* Fix compilation for Scala 2.12

Author: yoohaemin

entities/src/main/scala/com/devsisters/shardcake/Sharding.scala

@@ -57,7 +57,7 @@ class Sharding private (
           shardManager.unregister(address).catchAllCause(ZIO.logErrorCause("Error during unregister", _))
     )
 
-  private def isSingletonNode: UIO[Boolean] =
+  val isSingletonNode: UIO[Boolean] =
     // Start singletons on the pod hosting shard 1.
     shardAssignments.get.map(_.get(1).contains(address))
 
@@ -127,7 +127,15 @@ class Sharding private (
       pod     = shards.get(shardId)
     } yield pod.contains(address)
 
-  def getPods: UIO[Set[PodAddress]] =
+  val getAssignments: UIO[Map[ShardId, PodAddress]] =
+    shardAssignments.get
+
+  val thisPodAssignments: UIO[Chunk[ShardId]] =
+    getAssignments.map(a =>
+      Chunk.fromIterable(a.view.collect { case (shardId, addr) if addr == this.address => shardId })
+    )
+
+  val getPods: UIO[Set[PodAddress]] =
     shardAssignments.get.map(_.values.toSet)
 
   private def updateAssignments(
@@ -622,6 +630,12 @@ object Sharding {
   def registerScoped: RIO[Sharding with Scope, Unit] =
     Sharding.register.withFinalizer(_ => Sharding.unregister)
 
+  /**
+   * Returns true if current node contains the singletons
+   */
+  def isSingletonNode: RIO[Sharding, Boolean] =
+    ZIO.serviceWithZIO[Sharding](_.isSingletonNode)
+
   /**
    * Start a computation that is guaranteed to run only on a single pod.
    * Each pod should call `registerSingleton` but only a single pod will actually run it at any given time.
@@ -676,6 +690,20 @@ object Sharding {
   ): URIO[Sharding, Broadcaster[Msg]] =
     ZIO.serviceWith[Sharding](_.broadcaster(topicType, sendTimeout))
 
+  /**
+   * Get the list of shards and the pod that holds them.
+   *
+   * Note: ShardId may not show up if the shard is not assigned to any pod.
+   */
+  def getAssignments: RIO[Sharding, Map[ShardId, PodAddress]] =
+    ZIO.serviceWithZIO[Sharding](_.getAssignments)
+
+  /**
+   * Get the list of shards currently assigned to the current pod
+   */
+  def thisPodAssignments: RIO[Sharding, Chunk[ShardId]] =
+    ZIO.serviceWithZIO[Sharding](_.thisPodAssignments)
+
   /**
    * Get the list of pods currently registered to the Shard Manager
    */