add two phase commit protocol

Modules/RDTs/src/main/scala/rdts/datatypes/experiments/protocols/simplified/TwoPhaseCommit.scala

@@ -0,0 +1,49 @@
+package rdts.datatypes.experiments.protocols.simplified
+
+import rdts.base.LocalUid.replicaId
+import rdts.base.{LocalUid, Uid}
+import rdts.datatypes.experiments.protocols.Participants
+import rdts.datatypes.experiments.protocols.Participants.participants
+import rdts.datatypes.experiments.protocols.simplified.PrepareAbort.{Abort, Prepare}
+
+enum PrepareAbort:
+  case Prepare
+  case Abort
+
+case class Acknowledge()
+
+case class TwoPhaseCommit[A](
+    transaction: Option[A] = None,
+    voting: SimpleVoting[PrepareAbort] = SimpleVoting(),
+    acknowledgement: Set[Uid] = Set.empty
+):
+
+  // as the coordinator, propose a transaction
+  def commitRequest(transaction: A)(using LocalUid, Participants): TwoPhaseCommit[A] =
+    // check if there is a transaction ongoing
+    transaction match
+      case None => TwoPhaseCommit(Some(transaction), voting = voting.voteFor(Prepare))
+      case Some => TwoPhaseCommit()
+
+  // as a participant, vote for commit in the request phase
+  def prepare(using LocalUid, Participants): TwoPhaseCommit[A] =
+    transaction match
+      case Some(_) => TwoPhaseCommit(voting = voting.voteFor(Prepare))
+      case None    => TwoPhaseCommit()
+
+  // as a participant, vote for abort in the request phase
+  def abort(using LocalUid, Participants): TwoPhaseCommit[A] =
+    transaction match
+      case Some(_) => TwoPhaseCommit(voting = voting.voteFor(Abort))
+      case None    => TwoPhaseCommit()
+
+  // as a participant,
+  // check if request phase was accepted by everyone
+  // commit the transaction and send ack to the others
+  def acknowledge(using LocalUid, Participants): TwoPhaseCommit[A] =
+    // check if there is a transaction and everybody has voted
+    if transaction.isDefined && voting.votes.size == participants.size
+//      voting.votes.count(_.value == Prepare) == participants.size
+    then
+      TwoPhaseCommit(acknowledgement = Set(replicaId))
+    else TwoPhaseCommit()