feat: add grandpa state with derivePrimary method

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

@@ -0,0 +1,46 @@
+package com.limechain.grandpa.state;
+
+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 lombok.Getter;
+import org.bouncycastle.math.ec.rfc8032.Ed25519;
+import org.springframework.stereotype.Component;
+
+import java.math.BigInteger;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+// TODO: GrandpaState is not fully implemented
+/**
+ * Represents the state information for the current round and authorities that are needed
+ * for block finalization with GRANDPA.
+ * Note: Intended for use only when the host is configured as an Authoring Node.
+ */
+@Getter
+@Component
+public class GrandpaState {
+
+    private static final long THRESHOLD_NUMERATOR = 2L;
+    private static final long THRESHOLD_DENOMINATOR = 3L;
+
+    private List<Authority> voters;
+    private BigInteger setId;
+    private BigInteger roundNumber;
+
+    //TODO: This may not be the best place for those maps
+    private Map<Ed25519, Vote> precommits = new ConcurrentHashMap<>();
+    private Map<Ed25519, Vote> prevotes = new ConcurrentHashMap<>();
+    private Map<Ed25519, SignedVote> pvEquivocations = new ConcurrentHashMap<>();
+    private Map<Ed25519, SignedVote> pcEquivocations = new ConcurrentHashMap<>();
+
+    public long getThreshold() {
+        return (THRESHOLD_NUMERATOR * voters.size()) / THRESHOLD_DENOMINATOR;
+    }
+
+    public BigInteger derivePrimary() {
+        var votersCount = BigInteger.valueOf(voters.size());
+        return roundNumber.remainder(votersCount);
+    }
+}