Replica4 changes

3 files changed, 597 insertions, 127 deletions

diff --git a/src/main/java/derms/Replica4.java b/src/main/java/derms/Replica4.java
deleted file mode 100644
index ed7e90b..0000000
--- a/src/main/java/derms/Replica4.java
+++ /dev/null
@@ -1,108 +0,0 @@
-//package derms;
-//
-////import derms.Replica3pkg.ResponderClient;
-//import java.io.*;
-//import java.util.*;
-//
-//import derms.Replica4pkg.RemoteServer;
-//
-//public class Replica4 implements Replica {
-//
-//    private ReplicaManager replicaManager;
-//    private RemoteServer remoteServer;
-//    private boolean alive = true;
-//
-//    public Replica4(ReplicaManager replicaManager){
-//        this.replicaManager = replicaManager;
-//    }
-//
-//    @Override
-//    public boolean isAlive() {
-//        return alive;
-//    }
-//
-//    @Override
-//    public void startProcess() {
-//        this.remoteServer = new RemoteServer();
-//        System.out.println("[Replica 4] Process started.");
-//    }
-//
-//    @Override
-//    public void processRequest(Request request) {
-//        ResponderClient responderClient;
-//        CoordinatorClient coordinatorClient;
-//        String responseMessage;
-//        switch (request.getFunction()) {
-//            case "addResource":
-//                responderClient = new ResponderClient(request.getClientID());
-//                responseMessage = responderClient.addResource(request.getResourceID(), request.getResourceType(), request.getDuration());
-//                break;
-//            case "removeResource":
-//                responderClient = new ResponderClient(request.getClientID());
-//                responseMessage = responderClient.removeResource(request.getResourceID(), request.getDuration());
-//                break;
-//            case "listResourceAvailability":
-//                responderClient = new ResponderClient(request.getClientID());
-//                responseMessage = responderClient.listResourceAvailability(request.getResourceType());
-//                break;
-//            case "requestResource":
-//                coordinatorClient = new CoordinatorClient(request.getClientID());
-//                responseMessage = coordinatorClient.requestResource(request.getResourceID(), request.getDuration());
-//                break;
-//            case "findResource":
-//                coordinatorClient = new CoordinatorClient(request.getClientID());
-//                responseMessage = coordinatorClient.findResource(request.getResourceType());
-//                break;
-//            case "returnResource":
-//                coordinatorClient = new CoordinatorClient(request.getClientID());
-//                responseMessage = coordinatorClient.returnResource(request.getResourceID());
-//                break;
-//            case "swapResource":
-//                coordinatorClient = new CoordinatorClient(request.getClientID());
-//                responseMessage = coordinatorClient.swapResource(
-//                        request.getClientID(),
-//                        request.getOldResourceID(),
-//                        request.getOldResourceType(),
-//                        request.getResourceID(),
-//                        request.getResourceType()
-//                );
-//                break;
-//            default:
-//                responseMessage = "Unrecognized function: " + request.getFunction();
-//                log("Unrecognized function in request: " + request.getFunction());
-//                break;
-//        }
-//
-//        Response response = new Response(request.getSequenceNumber(), responseMessage);
-//        log("Replica " + 4 + " processed request: " + request + ", response: " + response);
-//        replicaManager.sendResponseToFE(response);
-//    }
-//
-//    @Override
-//    public void restart() {
-//        shutDown();
-//        startProcess();
-//    }
-//
-//    public void shutDown(){
-//        this.remoteServer.stopServers();
-//    }
-//
-//    @Override
-//    public int getId() {
-//        return 4;
-//    }
-//
-//    public synchronized void log(String message) {
-//        String logMessage = new Date() + " - " + message;
-//        System.out.println(logMessage);
-//
-//        try (FileWriter fw = new FileWriter("Replica4_log.txt", true);
-//             BufferedWriter bw = new BufferedWriter(fw);
-//             PrintWriter out = new PrintWriter(bw)) {
-//            out.println(logMessage);
-//        } catch (IOException e) {
-//            e.printStackTrace();
-//        }
-//    }
-//}
\ No newline at end of file
diff --git a/src/main/java/derms/Replica4pkg/RemoteServer.java b/src/main/java/derms/Replica4pkg/RemoteServer.java
index a572dbe..6bc7411 100644
--- a/src/main/java/derms/Replica4pkg/RemoteServer.java
+++ b/src/main/java/derms/Replica4pkg/RemoteServer.java
@@ -5,25 +5,25 @@ import javax.xml.ws.Endpoint;
 import java.util.*;
 
 public class RemoteServer {
-    private List<Endpoint> endpoints = new ArrayList<>();
-
-    public RemoteServer() {
-        try {
-            Map<String, Integer> UDPPorts = new HashMap<>();
-            UDPPorts.put("MTL", 4000);
-            UDPPorts.put("QUE", 5000);
-            UDPPorts.put("SHE", 6000);
-
-            String[] serverNames = {"MTL", "QUE", "SHE"};
-            int i = 0;
-            for (String serverName : serverNames) {
-                int UDPPort = UDPPorts.get(serverName);
-                Server server = new Server();
-                server.initServer(serverName, UDPPort, UDPPorts);
-                int port = 8080 + i;
-                String url = "http://localhost:" + port + "/DERMS/" + serverName;
-                Endpoint endpoint = Endpoint.publish(url, server);
-                endpoints.add(endpoint);  // Keep track of the Endpoint
+    private static List<Endpoint> endpoints = new ArrayList<>();
+    
+        public static void main(String[] args) {
+            try {
+                Map<String, Integer> UDPPorts = new HashMap<>();
+                UDPPorts.put("MTL", 4000);
+                UDPPorts.put("QUE", 5000);
+                UDPPorts.put("SHE", 6000);
+    
+                String[] serverNames = {"MTL", "QUE", "SHE"};
+                int i = 0;
+                for (String serverName : serverNames) {
+                    int UDPPort = UDPPorts.get(serverName);
+                    Server server = new Server();
+                    server.initServer(serverName, UDPPort, UDPPorts);
+                    int port = 8080 + i;
+                    String url = "http://localhost:" + port + "/DERMS/" + serverName;
+                    Endpoint endpoint = Endpoint.publish(url, server);
+                    endpoints.add(endpoint);  // Keep track of the Endpoint
                 i++;
                 System.out.println(serverName + " Server ready and waiting ...");
             }
diff --git a/src/main/java/derms/Replica4pkg/Replica4.java b/src/main/java/derms/Replica4pkg/Replica4.java
new file mode 100644
index 0000000..91bc303
--- /dev/null
+++ b/src/main/java/derms/Replica4pkg/Replica4.java
@@ -0,0 +1,578 @@
+package derms.Replica4pkg;
+
+import java.io.*;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.util.*;
+
+import javax.jws.WebMethod;
+
+import derms.Replica;
+import derms.ReplicaManager;
+import derms.Request;
+import derms.Response;
+import derms.util.TestLogger;
+import derms.util.ThreadPool;
+
+
+
+public class Replica4 implements Replica {
+
+    private ReplicaManager replicaManager;
+    private boolean alive = true;
+    private boolean byzFailure;
+
+    private String serverName;
+    private int udpPort;
+    private Map<String, Map<String, Resource>> resourceMap; //resourceName -> (resourceID -> Resource)
+    private Map<String, Set<String>> coordinatorResources; //coordinatorID -> Set<resourceID>
+    private Map<String, Map<String, Integer>> coordinatorResourceDurations; //coordinatorID -> (resourceID -> allocatedDuration)
+    private Map<String, Integer> serverUdpPorts; //serverName -> UDP port
+
+    public Replica4(ReplicaManager replicaManager){
+        this.replicaManager = replicaManager;
+        this.resourceMap = new HashMap<>();
+        this.coordinatorResources = new HashMap<>();
+        this.coordinatorResourceDurations = new HashMap<>();
+        startUDPListener();
+    }
+
+    @Override
+    public boolean isAlive() {
+        return alive;
+    }
+
+    @Override
+    public void startProcess(int byzantine, int crash) {
+        // [TEST] Detect crash
+        if (crash == 1) {
+            alive = false;
+        } else {
+            alive = true;
+        }
+
+        // [TEST] Detect byzantine failure
+        if (byzantine == 1) {
+            byzFailure = true;
+        } else {
+            byzFailure = false;
+        }
+
+        System.out.println("[Replica 4] Process started.");
+    }
+
+    @Override
+	public void processRequest(Request request) {
+		log(request.toString());
+
+		// [TEST] Simulate byzantine failure (return incorrect value)
+        if (byzFailure == true) {
+            Response response = new Response(request, replicaManager.getReplicaId(), "BYZANTINE FAILURE", false);
+            replicaManager.sendResponseToFE(response);
+            return;
+        }
+
+		String status = "";
+		try {
+			switch (request.getFunction()) {
+				case "addResource":
+					status = addResource(request.getResourceID(), request.getResourceType(), request.getDuration());
+					break;
+				case "removeResource":
+					status = removeResource(request.getResourceID(), request.getDuration());
+					break;
+				case "listResourceAvailability":
+					status = listResourceAvailability(request.getResourceType());
+					break;
+				case "requestResource":
+					status = requestResource(request.getClientID(), request.getResourceID(), request.getDuration());
+					break;
+				case "findResource":
+					status = findResource(request.getClientID(), request.getResourceType());
+					break;
+				case "returnResource":
+					status = returnResource(request.getClientID(), request.getResourceID());
+					break;
+				case "swapResource":
+					status = swapResource(request.getClientID(), request.getOldResourceID(), request.getOldResourceType(), request.getResourceID(), request.getResourceType());
+					break;
+				default:
+					status = "Failure: unknown function '" + request.getFunction() + "'";
+			}
+		} catch (Exception e) {
+			log(e.getMessage());
+			status = "Failure: " + request.getFunction() + ": " + e.getMessage();
+		}
+
+		Response response = new Response(request, replicaManager.getReplicaId(), status, false); // TODO: isSuccess flag
+		log("Processed request " + request + "; response: " + response);
+		replicaManager.sendResponseToFE(response);
+	}
+
+    @Override
+	public void restart() {
+		shutdown();
+
+		// [TEST] Restart process without byzantine failure or crash
+		TestLogger.log("REPLICA 2: {RESTARTED}");
+		startProcess(0, 0);
+	}
+
+    public void shutdown() {
+		log("Shutting down...");
+		alive = false;
+		log("Finished shutting down.");
+	}
+
+    @Override
+    public int getId() {
+        return 4;
+    }
+
+    public synchronized void log(String message) {
+        String logMessage = new Date() + " - " + message;
+        System.out.println(logMessage);
+
+        try (FileWriter fw = new FileWriter("Replica4_log.txt", true);
+             BufferedWriter bw = new BufferedWriter(fw);
+             PrintWriter out = new PrintWriter(bw)) {
+            out.println(logMessage);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    @WebMethod(exclude = true)
+    public void initReplica4(String serverName, int udpPort, Map<String, Integer> serverUdpPorts) {
+        this.serverName = serverName;
+        this.udpPort = udpPort;
+        this.serverUdpPorts = serverUdpPorts;
+    }
+
+    //Start UDP Listener
+    private void startUDPListener() {
+        new Thread(() -> {
+            try (DatagramSocket socket = new DatagramSocket(udpPort)) {
+                byte[] buffer = new byte[4096];
+                System.out.println(serverName + " UDP Server started on port " + udpPort);
+
+                while (true) {
+                    DatagramPacket request = new DatagramPacket(buffer, buffer.length);
+                    socket.receive(request);
+                    new Thread(() -> handleUDPRequest(request)).start();
+                }
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+        }).start();
+    }
+
+    //Handle UDP Request
+    private void handleUDPRequest(DatagramPacket requestPacket) {
+        try {
+            String requestData = new String(requestPacket.getData(), 0, requestPacket.getLength());
+            String[] parts = requestData.split(":");
+            String methodName = parts[0];
+            String[] params = Arrays.copyOfRange(parts, 1, parts.length);
+
+            String responseData = "";
+
+            switch (methodName) {
+                case "listResourceAvailability":
+                    responseData = handleListResourceAvailability(params[0]);
+                    break;
+                case "requestResource":
+                    responseData = handleLocalResourceRequest(params[0], params[1], Integer.parseInt(params[2]));
+                    break;
+                case "findResource":
+                    responseData = handleFindResource(params[0], params[1]);
+                    break;
+                case "returnResource":
+                    responseData = handleReturnResource(params[0], params[1]);
+                    break;
+                case "swapRequestResource":
+                    responseData = handleSwapRequestResource(params[0], params[1], Integer.parseInt(params[2]));
+                    break;    
+                case "swapReturnResource":
+                    responseData = handleSwapReturnResource(params[0], params[1]);
+                    break;
+                case "checkCoordinatorResource":
+                    responseData = checkCoordinatorHasResource(params[0], params[1]);
+                    break;
+                case "getCoordinatorResourceDuration":
+                    int duration = getCoordinatorResourceDuration(params[0], params[1]);
+                    responseData = String.valueOf(duration);
+                    break;
+                default:
+                    responseData = "Invalid method";
+            }
+
+            //Send response
+            byte[] responseBytes = responseData.getBytes();
+            DatagramPacket responsePacket = new DatagramPacket(responseBytes, responseBytes.length, requestPacket.getAddress(), requestPacket.getPort());
+            DatagramSocket socket = new DatagramSocket();
+            socket.send(responsePacket);
+            socket.close();
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
+    //Operation Handlers
+    private synchronized String handleListResourceAvailability(String resourceName) {
+        StringBuilder result = new StringBuilder();
+        resourceName = resourceName.toUpperCase();
+        Map<String, Resource> resources = resourceMap.get(resourceName);
+
+        if (resources != null) {
+            for (Resource resource : resources.values()) {
+            	if (resource.getDuration() > 0) {
+                    result.append(resource.getResourceName()).append(" - ").append(serverName).append(" ").append(resource.getDuration()).append("\n");
+            	}
+            }
+        }
+        return result.toString();
+    }
+
+    private synchronized String handleLocalResourceRequest(String coordinatorID, String resourceID, int duration) {
+        for (Map<String, Resource> resources : resourceMap.values()) {
+            Resource resource = resources.get(resourceID);
+            if (resource != null) {
+                if (resource.getDuration() >= duration) {
+                    resource.subDuration(duration);
+                    coordinatorResources.computeIfAbsent(coordinatorID, k -> new HashSet<>()).add(resourceID);
+                    coordinatorResourceDurations.computeIfAbsent(coordinatorID, k -> new HashMap<>()).put(resourceID, duration);
+
+                    log("Resource " + resourceID + " allocated to " + coordinatorID + " for duration " + duration);
+                    return "Resource " + resourceID + " allocated successfully.";
+                } else {
+                    return "Insufficient duration for resource " + resourceID;
+                }
+            }
+        }
+        return "Resource " + resourceID + " not found.";
+    }
+
+    private synchronized String handleFindResource(String coordinatorID, String resourceName) {
+        StringBuilder result = new StringBuilder();
+        resourceName = resourceName.toUpperCase();
+        Set<String> resources = coordinatorResources.get(coordinatorID);
+        if (resources != null) {
+            Map<String, Integer> resourceDurations = coordinatorResourceDurations.get(coordinatorID);
+            if (resourceDurations != null) {
+                for (String resourceID : resources) {
+                    Resource resource = getResourceByID(resourceID);
+                    if (resource != null && resource.getResourceName().equals(resourceName)) {
+                        Integer allocatedDuration = resourceDurations.get(resourceID);
+                        if (allocatedDuration != null) {
+                            result.append(resource.getResourceName()).append(" - ").append(resourceID).append(" ").append(allocatedDuration).append("\n");
+                        }
+                    }
+                }
+            }
+        }
+        return result.toString();
+    }
+
+    private synchronized String handleReturnResource(String coordinatorID, String resourceID) {
+        Set<String> resources = coordinatorResources.get(coordinatorID);
+        if (resources != null && resources.contains(resourceID)) {
+            resources.remove(resourceID);
+            if (resources.isEmpty()) {
+                coordinatorResources.remove(coordinatorID);
+            }
+            Resource resource = getResourceByID(resourceID);
+            if (resource != null) {
+                Map<String, Integer> resourceDurations = coordinatorResourceDurations.get(coordinatorID);
+                if (resourceDurations != null) {
+                    Integer allocatedDuration = resourceDurations.remove(resourceID);
+                    if (allocatedDuration != null) {
+                        resource.addDuration(allocatedDuration);
+                    }
+                    if (resourceDurations.isEmpty()) {
+                        coordinatorResourceDurations.remove(coordinatorID);
+                    }
+                }
+                log("Coordinator " + coordinatorID + " returned resource " + resourceID);
+                return "Resource " + resourceID + " returned successfully.";
+            } else {
+                return "Resource " + resourceID + " not found.";
+            }
+        } else {
+            return "You do not occupy resource " + resourceID + ".";
+        }
+    }
+
+    //Helper Methods
+    private Resource getResourceByID(String resourceID) {
+        for (Map<String, Resource> resources : resourceMap.values()) {
+            if (resources.containsKey(resourceID)) {
+                return resources.get(resourceID);
+            }
+        }
+        return null;
+    }
+    
+    private synchronized String handleSwapRequestResource(String coordinatorID, String resourceID, int duration) {
+        //Attempt to allocate the resource to the coordinator
+        for (Map<String, Resource> resources : resourceMap.values()) {
+            Resource resource = resources.get(resourceID);
+            if (resource != null) {
+                if (resource.getDuration() >= duration) {
+                    resource.subDuration(duration);
+                    coordinatorResources.computeIfAbsent(coordinatorID, k -> new HashSet<>()).add(resourceID);
+                    coordinatorResourceDurations.computeIfAbsent(coordinatorID, k -> new HashMap<>()).put(resourceID, duration);
+                    log("Resource " + resourceID + " temporarily allocated to " + coordinatorID + " for swapping, duration " + duration);
+                    return "Success";
+                } else {
+                    return "Insufficient duration for resource " + resourceID;
+                }
+            }
+        }
+        return "Resource " + resourceID + " not found.";
+    }
+    
+    private synchronized String handleSwapReturnResource(String coordinatorID, String resourceID) {
+        Set<String> resources = coordinatorResources.get(coordinatorID);
+        if (resources != null && resources.contains(resourceID)) {
+            resources.remove(resourceID);
+            if (resources.isEmpty()) {
+                coordinatorResources.remove(coordinatorID);
+            }
+            Resource resource = getResourceByID(resourceID);
+            if (resource != null) {
+                Map<String, Integer> resourceDurations = coordinatorResourceDurations.get(coordinatorID);
+                if (resourceDurations != null) {
+                    Integer allocatedDuration = resourceDurations.remove(resourceID);
+                    if (allocatedDuration != null) {
+                        resource.addDuration(allocatedDuration);
+                    }
+                    if (resourceDurations.isEmpty()) {
+                        coordinatorResourceDurations.remove(coordinatorID);
+                    }
+                }
+                log("Coordinator " + coordinatorID + " resource " + resourceID + " allocation undone during swap");
+                return "Success";
+            } else {
+                return "Resource " + resourceID + " not found.";
+            }
+        } else {
+            return "Coordinator did not acquire resource " + resourceID;
+        }
+    }
+
+    private String sendUDPRequest(String serverName, String methodName, String... params) {
+        String response = "";
+        try {
+            InetAddress host = InetAddress.getByName("localhost");
+            int port = serverUdpPorts.get(serverName);
+            String requestData = methodName + ":" + String.join(":", params);
+
+            byte[] requestBytes = requestData.getBytes();
+            DatagramPacket requestPacket = new DatagramPacket(requestBytes, requestBytes.length, host, port);
+
+            DatagramSocket socket = new DatagramSocket();
+            socket.send(requestPacket);
+
+            byte[] buffer = new byte[4096];
+            DatagramPacket responsePacket = new DatagramPacket(buffer, buffer.length);
+            socket.receive(responsePacket);
+
+            response = new String(responsePacket.getData(), 0, responsePacket.getLength());
+            socket.close();
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+        return response;
+    }
+
+    //Implement ResponderInterface Methods
+    public synchronized String addResource(String resourceID, String resourceName, int duration) {
+        resourceName = resourceName.toUpperCase();
+        Map<String, Resource> resources = resourceMap.computeIfAbsent(resourceName, k -> new HashMap<>());
+        Resource resource = resources.get(resourceID);
+
+        if (resource != null) {
+            if (duration > resource.getDuration()) {
+                resource.setDuration(duration);
+                log("Updated duration of resource " + resourceID);
+                return "Resource " + resourceID + " duration updated.";
+            } else {
+                log("Resource " + resourceID + " already exists with greater or equal duration.");
+                return "Resource " + resourceID + " already exists with greater or equal duration.";
+            }
+        } else {
+            resource = new Resource(resourceName, duration);
+            resources.put(resourceID, resource);
+            log("Added new resource " + resourceID);
+            return "Resource " + resourceID + " added successfully.";
+        }
+    }
+
+    public synchronized String removeResource(String resourceID, int duration) {
+        for (Map<String, Resource> resources : resourceMap.values()) {
+            Resource resource = resources.get(resourceID);
+            if (resource != null) {
+                if (duration >= resource.getDuration()) {
+                    resources.remove(resourceID);
+                    log("Resource " + resourceID + " completely removed.");
+                    return "Resource " + resourceID + " completely removed.";
+                } else {
+                    resource.subDuration(duration);
+                    log("Decreased duration of resource " + resourceID);
+                    return "Resource " + resourceID + " duration decreased by " + duration + ".";
+                }
+            }
+        }
+        log("Resource " + resourceID + " not found.");
+        return "Resource " + resourceID + " not found.";
+    }
+
+    public String listResourceAvailability(String resourceName) {
+        resourceName = resourceName.toUpperCase();
+        StringBuilder result = new StringBuilder();
+
+        synchronized (this) {
+            Map<String, Resource> resources = resourceMap.get(resourceName);
+            if (resources != null) {
+                for (Resource resource : resources.values()) {
+                	if (resource.getDuration() > 0) {
+	                    result.append(resource.getResourceName()).append(" - ").append(serverName).append(" ").append(resource.getDuration()).append("\n");
+	                }
+                }
+            }
+        }
+
+        for (String otherServer : serverUdpPorts.keySet()) {
+            if (!otherServer.equals(serverName)) {
+                String response = sendUDPRequest(otherServer, "listResourceAvailability", resourceName);
+                result.append(response);
+            }
+        }
+
+        return result.toString();
+    }
+
+    public String requestResource(String coordinatorID, String resourceID, int duration) {
+        String resourceServer = resourceID.substring(0, 3).toUpperCase();
+        String response;
+
+        if (resourceServer.equals(serverName)) {
+            response = handleLocalResourceRequest(coordinatorID, resourceID, duration);
+        } else {
+            response = sendUDPRequest(resourceServer, "requestResource", coordinatorID, resourceID, String.valueOf(duration));
+        }
+
+        log("Coordinator " + coordinatorID + " requested resource " + resourceID + ": " + response);
+        return response;
+    }
+
+    public String findResource(String coordinatorID, String resourceName) {
+        resourceName = resourceName.toUpperCase();
+        StringBuilder result = new StringBuilder();
+
+        for (String otherServer : serverUdpPorts.keySet()) {
+            String response;
+            if (otherServer.equals(serverName)) {
+                response = handleFindResource(coordinatorID, resourceName);
+            } else {
+                response = sendUDPRequest(otherServer, "findResource", coordinatorID, resourceName);
+            }
+            result.append(response);
+        }
+
+        return result.toString();
+    }
+
+    public String returnResource(String coordinatorID, String resourceID) {
+        String resourceServer = resourceID.substring(0, 3).toUpperCase();
+        String response;
+
+        if (resourceServer.equals(serverName)) {
+            response = handleReturnResource(coordinatorID, resourceID);
+        } else {
+            response = sendUDPRequest(resourceServer, "returnResource", coordinatorID, resourceID);
+        }
+
+        log("Coordinator " + coordinatorID + " returned resource " + resourceID + ": " + response);
+        return response;
+    }
+    
+    private synchronized int getCoordinatorResourceDuration(String coordinatorID, String resourceID) {
+        Map<String, Integer> resourceDurations = coordinatorResourceDurations.get(coordinatorID);
+        if (resourceDurations != null && resourceDurations.containsKey(resourceID)) {
+            return resourceDurations.get(resourceID);
+        }
+        return 0;
+    }
+    
+    private synchronized String checkCoordinatorHasResource(String coordinatorID, String resourceID) {
+        Set<String> resources = coordinatorResources.get(coordinatorID);
+        if (resources != null && resources.contains(resourceID)) {
+            return "true";
+        }
+        return "false";
+    }
+    
+    public String swapResource(String coordinatorID, String oldResourceID, String oldResourceType, String newResourceID, String newResourceType) {
+        String oldResourceServer = oldResourceID.substring(0, 3).toUpperCase();
+        String newResourceServer = newResourceID.substring(0, 3).toUpperCase();
+
+        //Check if the coordinator has the old resource
+        String checkOldResourceResponse;
+        if (oldResourceServer.equals(serverName)) {
+            checkOldResourceResponse = checkCoordinatorHasResource(coordinatorID, oldResourceID);
+        } else {
+            checkOldResourceResponse = sendUDPRequest(oldResourceServer, "checkCoordinatorResource", coordinatorID, oldResourceID);
+        }
+
+        if (!checkOldResourceResponse.equals("true")) {
+            return "Coordinator has not acquired the old resource.";
+        }
+
+        //Get the duration allocated to the old resource
+        int duration;
+        if (oldResourceServer.equals(serverName)) {
+            duration = getCoordinatorResourceDuration(coordinatorID, oldResourceID);
+        } else {
+            String durationStr = sendUDPRequest(oldResourceServer, "getCoordinatorResourceDuration", coordinatorID, oldResourceID);
+            duration = Integer.parseInt(durationStr);
+        }
+
+        //Attempt to acquire the new resource
+        String requestResponse;
+        if (newResourceServer.equals(serverName)) {
+            requestResponse = handleLocalResourceRequest(coordinatorID, newResourceID, duration);
+        } else {
+            requestResponse = sendUDPRequest(newResourceServer, "requestResource", coordinatorID, newResourceID, String.valueOf(duration));
+        }
+
+        if (!requestResponse.contains("allocated successfully")) {
+            return "Failed to acquire new resource: " + requestResponse;
+        }
+
+        //Return the old resource
+        String returnResponse;
+        if (oldResourceServer.equals(serverName)) {
+            returnResponse = handleReturnResource(coordinatorID, oldResourceID);
+        } else {
+            returnResponse = sendUDPRequest(oldResourceServer, "returnResource", coordinatorID, oldResourceID);
+        }
+
+        if (!returnResponse.contains("returned successfully")) {
+            //Undo the allocation of the new resource
+            if (newResourceServer.equals(serverName)) {
+                handleReturnResource(coordinatorID, newResourceID);
+            } else {
+                sendUDPRequest(newResourceServer, "returnResource", coordinatorID, newResourceID);
+            }
+            return "Failed to return old resource: " + returnResponse;
+        }
+
+        log("Coordinator " + coordinatorID + " swapped resource " + oldResourceID + " with " + newResourceID);
+
+        return "Resource swap successful.";
+    }
+}
+