From a8122cb27c53eabbd49772921c899dad11496962 Mon Sep 17 00:00:00 2001
From: Mark Spanbroek <mark@spanbroek.net>
Date: Tue, 26 Nov 2024 10:59:04 +0100
Subject: [PATCH] primary proposer for a round

---
 mysticeti.nim                                      |  1 +
 mysticeti/validator.nim                            |  3 +++
 mysticeti/validator/round.nim                      |  3 +++
 tests/mysticeti/validator/testRound.nim            | 13 +++++++++++++
 tests/mysticeti/validator/testValidatorNetwork.nim | 11 +++++++++++
 5 files changed, 31 insertions(+)

diff --git a/mysticeti.nim b/mysticeti.nim
index 224ece3..5022fb8 100644
--- a/mysticeti.nim
+++ b/mysticeti.nim
@@ -10,6 +10,7 @@ export validator.new
 export validator.identifier
 export validator.membership
 export validator.round
+export validator.primaryProposer
 export validator.nextRound
 export validator.propose
 export validator.check
diff --git a/mysticeti/validator.nim b/mysticeti/validator.nim
index dafba3e..14af208 100644
--- a/mysticeti/validator.nim
+++ b/mysticeti/validator.nim
@@ -33,6 +33,9 @@ func membership*(validator: Validator): CommitteeMember =
 func round*(validator: Validator): uint64 =
   validator.rounds.latest.number
 
+func primaryProposer*(validator: Validator): CommitteeMember =
+  validator.rounds.latest.primaryProposer
+
 func nextRound*(validator: Validator) =
   validator.rounds.addNewRound()
 
diff --git a/mysticeti/validator/round.nim b/mysticeti/validator/round.nim
index 8738375..d70d03b 100644
--- a/mysticeti/validator/round.nim
+++ b/mysticeti/validator/round.nim
@@ -32,6 +32,9 @@ func next*(round: Round): auto =
 func `[]`*(round: Round, member: CommitteeMember): auto =
   round.slots[int(member)]
 
+func primaryProposer*(round: Round): CommitteeMember =
+  CommitteeMember((round.number mod round.slots.len.uint64).int)
+
 iterator proposers*(round: Round): CommitteeMember =
   let length = round.slots.len
   let offset = (round.number mod length.uint64).int
diff --git a/tests/mysticeti/validator/testRound.nim b/tests/mysticeti/validator/testRound.nim
index 7b45124..05a1066 100644
--- a/tests/mysticeti/validator/testRound.nim
+++ b/tests/mysticeti/validator/testRound.nim
@@ -120,6 +120,19 @@ suite "Validator Round":
     check third.previous == none Round
     check third.next == none Round
 
+  test "primary proposer rotates on a round-robin schedule":
+    var round: Round
+    round = Round.new(0, 4)
+    check round.primaryProposer == CommitteeMember(0)
+    round = Round.new(1, 4)
+    check round.primaryProposer == CommitteeMember(1)
+    round = Round.new(2, 4)
+    check round.primaryProposer == CommitteeMember(2)
+    round = Round.new(3, 4)
+    check round.primaryProposer == CommitteeMember(3)
+    round = Round.new(4, 4)
+    check round.primaryProposer == CommitteeMember(0)
+
   test "proposers are ordered round-robin for each round":
     var round: Round
     round = Round.new(0, 4)
diff --git a/tests/mysticeti/validator/testValidatorNetwork.nim b/tests/mysticeti/validator/testValidatorNetwork.nim
index 6fdd05b..2f3bcca 100644
--- a/tests/mysticeti/validator/testValidatorNetwork.nim
+++ b/tests/mysticeti/validator/testValidatorNetwork.nim
@@ -19,6 +19,17 @@ suite "Validator Network":
   setup:
     simulator = NetworkSimulator.init()
 
+  test "primary proposer rotates on a round-robin schedule":
+    check simulator.validators.allIt(it.primaryProposer == CommitteeMember(0))
+    simulator.nextRound()
+    check simulator.validators.allIt(it.primaryProposer == CommitteeMember(1))
+    simulator.nextRound()
+    check simulator.validators.allIt(it.primaryProposer == CommitteeMember(2))
+    simulator.nextRound()
+    check simulator.validators.allIt(it.primaryProposer == CommitteeMember(3))
+    simulator.nextRound()
+    check simulator.validators.allIt(it.primaryProposer == CommitteeMember(0))
+
   test "validators include blocks from previous round as parents":
     let previous = !simulator.exchangeProposals()
     simulator.nextRound()