add pwinner to find the winning outcome

agora/Agora/Governor/Scripts.hs

@@ -53,6 +53,7 @@ import Agora.Proposal (
   ProposalStatus (Draft, Locked),
   pemptyVotesFor,
   proposalDatumValid,
+  pwinner,
  )
 import Agora.Proposal.Scripts (
   proposalPolicy,
@@ -77,7 +78,6 @@ import Agora.Utils (
   mustFindDatum',
   pfindTxInByTxOutRef,
   pisDJust,
-  pisJust,
   pisUTXOSpent,
   psymbolValueOf,
   ptryFindDatum,
@@ -605,27 +605,7 @@ governorValidator gov =
           -- TODO: anything else to check here?
 
           -- Find the highest votes and the corresponding tag.
-          let highestVoteFolder =
+          winner <- tclet $ mustBePJust # "No winning outcome" #$ pwinner # proposalInputDatumF.votes
-                phoistAcyclic $
-                  plam
-                    ( \pair last' ->
-                        pif
-                          (pisJust # last')
-                          ( unTermCont $ do
-                              PJust last <- tcmatch last'
-                              let lastHighestVote = pfromData $ psndBuiltin # last
-                                  thisVote = pfromData $ psndBuiltin # pair
-                              pure $ pif (lastHighestVote #< thisVote) (pcon $ PJust pair) last'
-                          )
-                          (pcon $ PJust pair)
-                    )
-
-              votesList = pto $ pto $ pfromData proposalInputDatumF.votes
-
-              maybeWinner =
-                pfoldr # highestVoteFolder # pcon PNothing # votesList
-
-          winner <- tclet $ mustBePJust # "No winning outcome" # maybeWinner
 
           PDiscrete minimumVotes' <- pmatchC $ pfromData $ pfield @"execute" # proposalInputDatumF.thresholds
           let highestVote = pfromData $ psndBuiltin # winner

agora/Agora/Proposal.hs

@@ -31,6 +31,7 @@ module Agora.Proposal (
   -- * Plutarch helpers
   proposalDatumValid,
   pemptyVotesFor,
+  pwinner,
 ) where
 
 import GHC.Generics qualified as GHC
@@ -448,3 +449,37 @@ proposalDatumValid proposal =
           , ptraceIfFalse "Proposal has fewer cosigners than the limit" $ plength # (pfromData datum.cosigners) #<= pconstant proposal.maximumCosigners
           , ptraceIfFalse "Proposal votes and effects are compatible with each other" $ pkeysEqual # datum.effects # pto (pfromData datum.votes)
           ]
+
+{- | Find the winning outcome (and the corresponding vote count) given the votes.
+
+    FIXME: What if two or more outcomes have the exact same vote count?
+-}
+pwinner ::
+  Term
+    s
+    ( PProposalVotes
+        :--> PMaybe (PBuiltinPair (PAsData PResultTag) (PAsData PInteger))
+    )
+pwinner = phoistAcyclic $
+  plam $ \votes ->
+    let l :: Term _ (PBuiltinList _)
+        l = pto $ pto votes
+
+        f ::
+          Term
+            _
+            ( PBuiltinPair (PAsData PResultTag) (PAsData PInteger)
+                :--> PMaybe (PBuiltinPair (PAsData PResultTag) (PAsData PInteger))
+                :--> PMaybe (PBuiltinPair (PAsData PResultTag) (PAsData PInteger))
+            )
+        f = phoistAcyclic $
+          plam $ \this maybeLast -> pmatch maybeLast $ \case
+            PNothing -> pcon $ PJust this
+            PJust last ->
+              let lastVotes = pfromData $ psndBuiltin # last
+                  thisVotes = pfromData $ psndBuiltin # this
+               in pif
+                    (lastVotes #< thisVotes)
+                    (pcon $ PJust this)
+                    maybeLast
+     in pfoldr # f # pcon PNothing # l