feat: Implement Finalize stage in Play-Grandpa-Round.

src/main/java/com/limechain/grandpa/round/FinalizeStage.java

@@ -1,13 +1,51 @@
 package com.limechain.grandpa.round;
 
+import com.limechain.exception.grandpa.GrandpaGenericException;
+import com.limechain.network.protocol.warp.dto.BlockHeader;
+import lombok.extern.java.Log;
+
+@Log
 public class FinalizeStage implements StageState {
 
     @Override
     public void start(GrandpaRound round) {
+
+        log.fine(String.format("Round %d entered the Finalize stage.", round.getRoundNumber()));
+
+        if (isRoundReadyToBeFinalized(round)) {
+            end(round);
+            return;
+        }
+
+        Runnable onFinalizeHandler = () -> {
+            if (isRoundReadyToBeFinalized(round)) {
+                end(round);
+            }
+        };
+        round.setOnFinalizeHandler(onFinalizeHandler);
     }
 
     @Override
     public void end(GrandpaRound round) {
+        log.info(String.format("Round %d met finalization conditions and will be finalized.", round.getRoundNumber()));
+        round.setOnFinalizeHandler(null);
+        round.attemptToFinalizeAt();
+        log.fine(String.format("Round %d exits Finalize stage.", round.getRoundNumber()));
+
+        round.end();
     }
-}
 
+    private boolean isRoundReadyToBeFinalized(GrandpaRound round) {
+        BlockHeader finalized;
+        try {
+            finalized = round.getFinalizedBlock();
+        } catch (GrandpaGenericException e) {
+            return false;
+        }
+
+        BlockHeader prevBestFinalCandidate = round.getPrevBestFinalCandidate();
+
+        return prevBestFinalCandidate != null
+                && finalized.getBlockNumber().compareTo(prevBestFinalCandidate.getBlockNumber()) >= 0;
+    }
+}

src/main/java/com/limechain/grandpa/round/GrandpaRound.java

@@ -182,7 +182,7 @@ public BlockHeader getBestFinalCandidate() {
         return Optional.ofNullable(finalizeEstimate).orElse(lastFinalizedBlock);
     }
 
-    private void attemptToFinalizeAt() {
+    public void attemptToFinalizeAt() {
 
         BlockState blockState = stateManager.getBlockState();
         BigInteger lastFinalizedBlockNumber = blockState.getHighestFinalizedNumber();