create the LeaderHttpRegistry class

src/main/java/com/distributed/search/cluster/LeaderHttpRegistry.java

+package com.distributed.search.cluster;
+
+import org.apache.zookeeper.*;
+import org.apache.zookeeper.data.Stat;
+import java.util.List;
+
+/**
+ * This class acts as a shared registry in Zookeeper where the elected Leader
+ * publishes its HTTP server address so the Frontend can discover it.
+ */
+public class LeaderHttpRegistry implements Watcher {
+    private static final String LEADER_HTTP_ZNODE = "/leader_http_registry";
+    private final ZooKeeper zooKeeper;
+    private String leaderAddress = null;
+
+    public LeaderHttpRegistry(ZooKeeper zooKeeper) {
+        this.zooKeeper = zooKeeper;
+        createRegistryZnode();
+    }
+
+    /**
+     * Ensures that the parent Znode for the registry exists.
+     */
+    private void createRegistryZnode() {
+        try {
+            if (zooKeeper.exists(LEADER_HTTP_ZNODE, false) == null) {
+                zooKeeper.create(LEADER_HTTP_ZNODE, new byte[]{}, ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
+            }
+        } catch (KeeperException | InterruptedException e) {
+            e.printStackTrace();
+        }
+    }
+
+    /**
+     * Leader uses this method to register its HTTP address (IP:Port).
+     * We use an EPHEMERAL node so that if the leader crashes, the registry is cleared.
+     */
+    public void registerLeader(String address) throws KeeperException, InterruptedException {
+        String leaderPath = LEADER_HTTP_ZNODE + "/address";
+
+        // If an old address exists, delete it first
+        if (zooKeeper.exists(leaderPath, false) != null) {
+            zooKeeper.delete(leaderPath, -1);
+        }
+
+        zooKeeper.create(leaderPath, address.getBytes(),
+                ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.EPHEMERAL);
+
+        System.out.println("Leader HTTP address registered: " + address);
+    }
+
+    /**
+     * Frontend uses this method to get the current leader's HTTP address.
+     * It also sets a watcher to stay updated if the leader changes.
+     */
+    public synchronized String getLeaderAddress() {
+        try {
+            updateLeaderAddress();
+        } catch (KeeperException | InterruptedException e) {
+            e.printStackTrace();
+        }
+        return leaderAddress;
+    }
+
+    private synchronized void updateLeaderAddress() throws KeeperException, InterruptedException {
+        String leaderPath = LEADER_HTTP_ZNODE + "/address";
+        Stat stat = zooKeeper.exists(leaderPath, this);
+
+        if (stat != null) {
+            byte[] data = zooKeeper.getData(leaderPath, this, stat);
+            this.leaderAddress = new String(data);
+        } else {
+            this.leaderAddress = null;
+        }
+    }
+
+    /**
+     * Watcher to handle events if the leader node is created, deleted, or data changes.
+     */
+    @Override
+    public void process(WatchedEvent event) {
+        try {
+            updateLeaderAddress();
+            System.out.println("Leader registry updated. Current leader: " + leaderAddress);
+        } catch (KeeperException | InterruptedException e) {
+            e.printStackTrace();
+        }
+    }
+}
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