Implemented Best PreVote Candidate algorithm

src/main/java/com/limechain/grandpa/GrandpaService.java

@@ -4,7 +4,9 @@
 import com.limechain.exception.storage.BlockStorageGenericException;
 import com.limechain.grandpa.state.RoundState;
 import com.limechain.network.protocol.grandpa.messages.commit.Vote;
+import com.limechain.network.protocol.grandpa.messages.vote.SignedMessage;
 import com.limechain.network.protocol.grandpa.messages.vote.Subround;
+import com.limechain.network.protocol.grandpa.messages.vote.VoteMessage;
 import com.limechain.network.protocol.warp.dto.BlockHeader;
 import com.limechain.storage.block.BlockState;
 import io.emeraldpay.polkaj.types.Hash256;
@@ -111,6 +113,27 @@ public Vote getGrandpaGhost() {
         return selectBlockWithMostVotes(blocks);
     }
 
+    /**
+     * Determines what block is our pre-voted block for the current round
+     * if we receive a vote message from the network with a
+     * block that's greater than or equal to the current pre-voted block
+     * and greater than the best final candidate from the last round, we choose that.
+     * otherwise, we simply choose the head of our chain.
+     *
+     * @return the best pre-voted block
+     */
+    public Vote getBestPreVoteCandidate() {
+        Vote currentVote = getGrandpaGhost();
+        VoteMessage voteMessage = roundState.getVoteMessage();
+        SignedMessage signedMessage = voteMessage.getMessage();
+
+        if (signedMessage != null && signedMessage.getBlockNumber().compareTo(currentVote.getBlockNumber()) > 0) {
+            return new Vote(signedMessage.getBlockHash(), signedMessage.getBlockNumber());
+        }
+
+        return currentVote;
+    }
+
     /**
      * Selects the block with the most votes from the provided map of blocks.
      * If multiple blocks have the same number of votes, it returns the one with the highest block number.

src/main/java/com/limechain/grandpa/state/RoundState.java

@@ -3,6 +3,7 @@
 import com.limechain.chain.lightsyncstate.Authority;
 import com.limechain.network.protocol.grandpa.messages.catchup.res.SignedVote;
 import com.limechain.network.protocol.grandpa.messages.commit.Vote;
+import com.limechain.network.protocol.grandpa.messages.vote.VoteMessage;
 import io.libp2p.core.crypto.PubKey;
 import lombok.Getter;
 import lombok.Setter;
@@ -34,6 +35,8 @@ public class RoundState {
     private Map<PubKey, Vote> prevotes = new ConcurrentHashMap<>();
     private Map<PubKey, SignedVote> pvEquivocations = new ConcurrentHashMap<>();
     private Map<PubKey, SignedVote> pcEquivocations = new ConcurrentHashMap<>();
+    //TODO: Figure out if we need to store vote messages in round state
+    private VoteMessage voteMessage;
 
     /**
      * The threshold is determined as the total weight of authorities
@@ -57,4 +60,8 @@ public BigInteger derivePrimary() {
         var votersCount = BigInteger.valueOf(voters.size());
         return roundNumber.remainder(votersCount);
     }
+
+    public void updateVoteMessage(VoteMessage voteMessage) {
+        this.voteMessage = voteMessage;
+    }
 }

src/main/java/com/limechain/network/protocol/grandpa/GrandpaEngine.java

@@ -1,6 +1,7 @@
 package com.limechain.network.protocol.grandpa;
 
 import com.limechain.exception.scale.ScaleEncodingException;
+import com.limechain.grandpa.state.RoundState;
 import com.limechain.network.ConnectionManager;
 import com.limechain.network.protocol.blockannounce.messages.BlockAnnounceHandshakeBuilder;
 import com.limechain.network.protocol.grandpa.messages.GrandpaMessageType;
@@ -41,11 +42,13 @@ public class GrandpaEngine {
     protected ConnectionManager connectionManager;
     protected WarpSyncState warpSyncState;
     protected BlockAnnounceHandshakeBuilder handshakeBuilder;
+    protected RoundState roundState;
 
     public GrandpaEngine() {
         connectionManager = ConnectionManager.getInstance();
         warpSyncState = AppBean.getBean(WarpSyncState.class);
         handshakeBuilder = new BlockAnnounceHandshakeBuilder();
+        roundState = AppBean.getBean(RoundState.class);
     }
 
     /**
@@ -140,6 +143,8 @@ private void handleNeighbourMessage(byte[] message, PeerId peerId) {
     private void handleVoteMessage(byte[] message, PeerId peerId) {
         ScaleCodecReader reader = new ScaleCodecReader(message);
         VoteMessage voteMessage = reader.read(VoteMessageScaleReader.getInstance());
+        //Maybe we need to add possible roundNumber check
+        roundState.updateVoteMessage(voteMessage);
         //todo: handle vote message (authoring node responsibility?)
         log.log(Level.INFO, "Received vote message from Peer " + peerId + "\n" + voteMessage);
     }

src/test/java/com/limechain/grandpa/GrandpaServiceTest.java

@@ -4,7 +4,9 @@
 import com.limechain.grandpa.state.RoundState;
 import com.limechain.network.protocol.grandpa.messages.catchup.res.SignedVote;
 import com.limechain.network.protocol.grandpa.messages.commit.Vote;
+import com.limechain.network.protocol.grandpa.messages.vote.SignedMessage;
 import com.limechain.network.protocol.grandpa.messages.vote.Subround;
+import com.limechain.network.protocol.grandpa.messages.vote.VoteMessage;
 import com.limechain.network.protocol.warp.dto.BlockHeader;
 import com.limechain.network.protocol.warp.dto.ConsensusEngine;
 import com.limechain.network.protocol.warp.dto.DigestType;
@@ -49,6 +51,7 @@ void setUp() {
         roundState = mock(RoundState.class);
         blockState = mock(BlockState.class);
         grandpaService = new GrandpaService(roundState, blockState);
+
     }
 
     @Test
@@ -157,6 +160,96 @@ void testGetBestFinalCandidateWhereRoundNumberIsZero() {
         assertEquals(blockHeader.getBlockNumber(), result.getBlockNumber());
     }
 
+    @Test
+    void testGetBestPreVoteCandidate_WithSignedMessage() {
+        Vote currentVote = new Vote(new Hash256(ONES_ARRAY), BigInteger.valueOf(3));
+        VoteMessage voteMessage = mock(VoteMessage.class);
+        SignedMessage signedMessage = mock(SignedMessage.class);
+
+        when(roundState.getVoteMessage()).thenReturn(voteMessage);
+        BlockHeader blockHeader = createBlockHeader();
+        blockHeader.setBlockNumber(BigInteger.valueOf(1));
+
+        when(roundState.getThreshold()).thenReturn(BigInteger.valueOf(1));
+        when(roundState.getRoundNumber()).thenReturn(BigInteger.valueOf(1));
+
+        when(roundState.getPrecommits()).thenReturn(Map.of());
+        when(roundState.getPrevotes()).thenReturn(Map.of(
+                Ed25519Utils.generateKeyPair().publicKey(), currentVote
+        ));
+
+        when(blockState.getHighestFinalizedHeader()).thenReturn(blockHeader);
+        when(blockState.isDescendantOf(currentVote.getBlockHash(), currentVote.getBlockHash())).thenReturn(true);
+        when(voteMessage.getMessage()).thenReturn(signedMessage);
+        when(signedMessage.getBlockNumber()).thenReturn(BigInteger.valueOf(4));
+        when(signedMessage.getBlockHash()).thenReturn(new Hash256(TWOS_ARRAY));
+
+        Vote result = grandpaService.getBestPreVoteCandidate();
+
+
+        assertNotNull(result);
+        assertEquals(new Hash256(TWOS_ARRAY), result.getBlockHash());
+        assertEquals(BigInteger.valueOf(4), result.getBlockNumber());
+    }
+
+    @Test
+    void testGetBestPreVoteCandidate_WithoutSignedMessage() {
+        Vote currentVote = new Vote(new Hash256(ONES_ARRAY), BigInteger.valueOf(3));
+        VoteMessage voteMessage = mock(VoteMessage.class);
+
+        when(roundState.getVoteMessage()).thenReturn(voteMessage);
+        BlockHeader blockHeader = createBlockHeader();
+        blockHeader.setBlockNumber(BigInteger.valueOf(1));
+
+        when(roundState.getThreshold()).thenReturn(BigInteger.valueOf(1));
+        when(roundState.getRoundNumber()).thenReturn(BigInteger.valueOf(1));
+
+        when(roundState.getPrecommits()).thenReturn(Map.of());
+        when(roundState.getPrevotes()).thenReturn(Map.of(
+                Ed25519Utils.generateKeyPair().publicKey(), currentVote
+        ));
+
+        when(blockState.getHighestFinalizedHeader()).thenReturn(blockHeader);
+        when(blockState.isDescendantOf(currentVote.getBlockHash(), currentVote.getBlockHash())).thenReturn(true);
+
+        Vote result = grandpaService.getBestPreVoteCandidate();
+
+        assertNotNull(result);
+        assertEquals(currentVote.getBlockHash(), result.getBlockHash());
+        assertEquals(currentVote.getBlockNumber(), result.getBlockNumber());
+    }
+
+    @Test
+    void testGetBestPreVoteCandidate_WithSignedMessageAndBlockNumberLessThanCurrentVote() {
+        Vote currentVote = new Vote(new Hash256(ONES_ARRAY), BigInteger.valueOf(4));
+        VoteMessage voteMessage = mock(VoteMessage.class);
+        SignedMessage signedMessage = mock(SignedMessage.class);
+
+        when(roundState.getVoteMessage()).thenReturn(voteMessage);
+        BlockHeader blockHeader = createBlockHeader();
+        blockHeader.setBlockNumber(BigInteger.valueOf(1));
+
+        when(roundState.getThreshold()).thenReturn(BigInteger.valueOf(1));
+        when(roundState.getRoundNumber()).thenReturn(BigInteger.valueOf(1));
+
+        when(roundState.getPrecommits()).thenReturn(Map.of());
+        when(roundState.getPrevotes()).thenReturn(Map.of(
+                Ed25519Utils.generateKeyPair().publicKey(), currentVote
+        ));
+
+        when(blockState.getHighestFinalizedHeader()).thenReturn(blockHeader);
+        when(blockState.isDescendantOf(currentVote.getBlockHash(), currentVote.getBlockHash())).thenReturn(true);
+        when(voteMessage.getMessage()).thenReturn(signedMessage);
+        when(signedMessage.getBlockNumber()).thenReturn(BigInteger.valueOf(3));
+        when(signedMessage.getBlockHash()).thenReturn(new Hash256(TWOS_ARRAY));
+
+        Vote result = grandpaService.getBestPreVoteCandidate();
+
+        assertNotNull(result);
+        assertEquals(currentVote.getBlockHash(), result.getBlockHash());
+        assertEquals(currentVote.getBlockNumber(), result.getBlockNumber());
+    }
+
     @Test
     void testGetGrandpaGHOSTWhereNoBlocksPassThreshold() {
         when(roundState.getThreshold()).thenReturn(BigInteger.valueOf(10));

src/test/java/com/limechain/network/protocol/grandpa/GrandpaEngineTest.java

@@ -1,5 +1,6 @@
 package com.limechain.network.protocol.grandpa;
 
+import com.limechain.grandpa.state.RoundState;
 import com.limechain.network.ConnectionManager;
 import com.limechain.network.dto.PeerInfo;
 import com.limechain.network.protocol.blockannounce.NodeRole;
@@ -48,6 +49,8 @@ class GrandpaEngineTest {
     @Mock
     private WarpSyncState warpSyncState;
     @Mock
+    private RoundState roundState;
+    @Mock
     private BlockAnnounceHandshakeBuilder blockAnnounceHandshakeBuilder;
 
     private final NeighbourMessage neighbourMessage =