Implementation of the Coordinator Process

main/src/main/java/sd/coordinator/CoordinatorProcess.java

@@ -0,0 +1,204 @@
+package sd.coordinator;
+
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+
+import sd.config.SimulationConfig;
+import sd.model.Message;
+import sd.model.MessageType;
+import sd.model.Vehicle;
+import sd.serialization.SerializationException;
+import sd.util.VehicleGenerator;
+
+/**
+ * Coordinator process responsible for:
+ * 1. Vehicle generation (using VehicleGenerator)
+ * 2. Distributing vehicles to intersection processes via sockets
+ * 3. Managing simulation timing and shutdown
+ * 
+ * This is the main entry point for the distributed simulation architecture.
+ */
+public class CoordinatorProcess {
+    
+    private final SimulationConfig config;
+    private final VehicleGenerator vehicleGenerator;
+    private final Map<String, SocketClient> intersectionClients;
+    private double currentTime;
+    private int vehicleCounter;
+    private boolean running;
+    private double nextGenerationTime;
+    
+    public static void main(String[] args) {
+        System.out.println("=".repeat(60));
+        System.out.println("COORDINATOR PROCESS - DISTRIBUTED TRAFFIC SIMULATION");
+        System.out.println("=".repeat(60));
+        
+        try {
+            // 1. Load configuration
+            String configFile = args.length > 0 ? args[0] : "src/main/resources/simulation.properties";
+            System.out.println("Loading configuration from: " + configFile);
+            
+            SimulationConfig config = new SimulationConfig(configFile);
+            CoordinatorProcess coordinator = new CoordinatorProcess(config);
+            
+            // 2. Connect to intersection processes
+            System.out.println("\n" + "=".repeat(60));
+            coordinator.initialize();
+            
+            // 3. Run the sim
+            System.out.println("\n" + "=".repeat(60));
+            coordinator.run();
+            
+        } catch (IOException e) {
+            System.err.println("Failed to load configuration: " + e.getMessage());
+            System.exit(1);
+        } catch (Exception e) {
+            System.err.println("Coordinator error: " + e.getMessage());
+            System.exit(1);
+        }
+    }
+    
+    public CoordinatorProcess(SimulationConfig config) {
+        this.config = config;
+        this.vehicleGenerator = new VehicleGenerator(config);
+        this.intersectionClients = new HashMap<>();
+        this.currentTime = 0.0;
+        this.vehicleCounter = 0;
+        this.running = false;
+        this.nextGenerationTime = 0.0;
+        
+        System.out.println("Coordinator initialized with configuration:");
+        System.out.println("  - Simulation duration: " + config.getSimulationDuration() + "s");
+        System.out.println("  - Arrival model: " + config.getArrivalModel());
+        System.out.println("  - Arrival rate: " + config.getArrivalRate() + " vehicles/s");
+    }
+    
+    public void initialize() {
+        System.out.println("Connecting to intersection processes...");
+        
+        String[] intersectionIds = {"Cr1", "Cr2", "Cr3", "Cr4", "Cr5"};
+        
+        for (String intersectionId : intersectionIds) {
+            try {
+                String host = config.getIntersectionHost(intersectionId);
+                int port = config.getIntersectionPort(intersectionId);
+                
+                SocketClient client = new SocketClient(intersectionId, host, port);
+                client.connect();
+                intersectionClients.put(intersectionId, client);
+                
+            } catch (IOException e) {
+                System.err.println("Failed to connect to " + intersectionId + ": " + e.getMessage());
+            }
+        }
+        
+        System.out.println("Successfully connected to " + intersectionClients.size() + " intersection(s)");
+        
+        if (intersectionClients.isEmpty()) {
+            System.err.println("WARNING: No intersections connected. Simulation cannot proceed.");
+        }
+    }
+    
+    public void run() {
+        double duration = config.getSimulationDuration();
+        running = true;
+        
+        System.out.println("Starting vehicle generation simulation...");
+        System.out.println("Duration: " + duration + " seconds");
+        System.out.println();
+        
+        nextGenerationTime = vehicleGenerator.getNextArrivalTime(currentTime);
+        final double TIME_STEP = 0.1;
+        
+        while (running && currentTime < duration) {
+            if (currentTime >= nextGenerationTime) {
+                generateAndSendVehicle();
+                nextGenerationTime = vehicleGenerator.getNextArrivalTime(currentTime);
+            }            
+            currentTime += TIME_STEP;
+        }
+        
+        System.out.println();
+        System.out.println("Simulation complete at t=" + String.format("%.2f", currentTime) + "s");
+        System.out.println("Total vehicles generated: " + vehicleCounter);
+        
+        shutdown();
+    }
+    
+    private void generateAndSendVehicle() {
+        Vehicle vehicle = vehicleGenerator.generateVehicle("V" + (++vehicleCounter), currentTime);
+        
+        System.out.printf("[t=%.2f] Vehicle %s generated (type=%s, route=%s)%n",
+            currentTime, vehicle.getId(), vehicle.getType(), vehicle.getRoute());
+        
+        if (vehicle.getRoute().isEmpty()) {
+            System.err.println("ERROR: Vehicle " + vehicle.getId() + " has empty route!");
+            return;
+        }
+        
+        String entryIntersection = vehicle.getRoute().get(0);
+        sendVehicleToIntersection(vehicle, entryIntersection);
+    }
+    
+    private void sendVehicleToIntersection(Vehicle vehicle, String intersectionId) {
+        SocketClient client = intersectionClients.get(intersectionId);
+        
+        if (client == null || !client.isConnected()) {
+            System.err.println("ERROR: No connection to " + intersectionId + " for vehicle " + vehicle.getId());
+            return;
+        }
+        
+        try {
+            Message message = new Message(
+                MessageType.VEHICLE_SPAWN,
+                "COORDINATOR",
+                intersectionId,
+                vehicle
+            );
+            
+            client.send(message);
+            System.out.printf("->Sent to %s%n", intersectionId);
+            
+        } catch (SerializationException | IOException e) {
+            System.err.println("ERROR: Failed to send vehicle " + vehicle.getId() + " to " + intersectionId);
+            System.err.println("Reason: " + e.getMessage());
+        }
+    }
+    
+    public void shutdown() {
+        System.out.println();
+        System.out.println("=".repeat(60));
+        System.out.println("Shutting down coordinator...");
+        
+        for (Map.Entry<String, SocketClient> entry : intersectionClients.entrySet()) {
+            String intersectionId = entry.getKey();
+            SocketClient client = entry.getValue();
+            
+            try {
+                if (client.isConnected()) {
+                    Message personalizedShutdown = new Message(
+                        MessageType.SHUTDOWN,
+                        "COORDINATOR",
+                        intersectionId,
+                        "Simulation complete"
+                    );
+                    client.send(personalizedShutdown);
+                    System.out.println("Sent shutdown message to " + intersectionId);
+                }
+            } catch (SerializationException | IOException e) {
+                System.err.println("Error sending shutdown to " + intersectionId + ": " + e.getMessage());
+            } finally {
+                client.close();
+            }
+        }
+        
+        System.out.println("Coordinator shutdown complete");
+        System.out.println("=".repeat(60));
+    }
+    
+    public void stop() {
+        System.out.println("\nStop signal received...");
+        running = false;
+    }
+}

main/src/main/java/sd/coordinator/SocketClient.java

@@ -0,0 +1,124 @@
+package sd.coordinator;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.Socket;
+
+import sd.model.Message;
+import sd.serialization.MessageSerializer;
+import sd.serialization.SerializationException;
+import sd.serialization.SerializerFactory;
+
+/**
+ * Socket client for communication with a single intersection process.
+ * 
+ * Handles a persistent TCP connection to one intersection,
+ * providing a simple way to send serialized messages.
+ */
+public class SocketClient {
+    
+    private final String intersectionId;
+    private final String host;
+    private final int port;
+    private Socket socket;
+    private OutputStream outputStream;
+    private MessageSerializer serializer;
+    
+    /**
+     * Creates a new SocketClient for a given intersection.
+     *
+     * @param intersectionId Intersection ID (ex. "Cr1")
+     * @param host Host address (ex. "localhost")
+     * @param port Port number
+     */
+    public SocketClient(String intersectionId, String host, int port) {
+        this.intersectionId = intersectionId;
+        this.host = host;
+        this.port = port;
+        this.serializer = SerializerFactory.createDefault();
+    }
+    
+    /**
+     * Connects to the intersection process via TCP.
+     * 
+     * @throws IOException if the connection cannot be established
+     */
+
+    public void connect() throws IOException {
+        try {
+            socket = new Socket(host, port);
+            outputStream = socket.getOutputStream();
+            System.out.println("Connected to " + intersectionId + " at " + host + ":" + port);
+        } catch (IOException e) {
+            System.err.println("Failed to connect to " + intersectionId + " at " + host + ":" + port);
+            throw e;
+        }
+    }
+    
+    /**
+     * Sends a message to the connected intersection.
+     * The message is serialized and written over the socket.
+     *
+     * @param message The message to send
+     * @throws SerializationException if serialization fails
+     * @throws IOException if the socket write fails
+     */
+    public void send(Message message) throws SerializationException, IOException {
+        if (socket == null || socket.isClosed()) {
+            throw new IOException("Socket is not connected to " + intersectionId);
+        }
+        
+        try {
+            byte[] data = serializer.serialize(message);
+            
+            // Prefix with message length (so receiver knows how much to read)
+            int length = data.length;
+            outputStream.write((length >> 24) & 0xFF);
+            outputStream.write((length >> 16) & 0xFF);
+            outputStream.write((length >> 8) & 0xFF);
+            outputStream.write(length & 0xFF);
+            
+            outputStream.write(data);
+            outputStream.flush();
+            
+        } catch (SerializationException | IOException e) {
+            System.err.println("Error sending message to " + intersectionId + ": " + e.getMessage());
+            throw e;
+        }
+    }
+    
+    /**
+     * Closes the socket connection safely.
+     * Calling it multiple times won’t cause issues.
+     */
+    public void close() {
+        try {
+            if (outputStream != null) {
+                outputStream.close();
+            }
+            if (socket != null && !socket.isClosed()) {
+                socket.close();
+                System.out.println("Closed connection to " + intersectionId);
+            }
+        } catch (IOException e) {
+            System.err.println("Error closing connection to " + intersectionId + ": " + e.getMessage());
+        }
+    }
+    
+    /**
+     * @return true if connected and socket is open, false otherwise
+     */
+    public boolean isConnected() {
+        return socket != null && socket.isConnected() && !socket.isClosed();
+    }
+    
+    public String getIntersectionId() {
+        return intersectionId;
+    }
+    
+    @Override
+    public String toString() {
+        return String.format("SocketClient[intersection=%s, host=%s, port=%d, connected=%s]",
+            intersectionId, host, port, isConnected());
+    }
+}

main/src/main/java/sd/protocol/SocketConnection.java

@@ -1,15 +1,22 @@
 package sd.protocol; 
 
 import java.io.Closeable;
+import java.io.DataInputStream;
+import java.io.DataOutputStream;
 import java.io.IOException;
-import java.io.ObjectInputStream;
+import java.io.InputStream;
-import java.io.ObjectOutputStream;
+import java.io.OutputStream;
 import java.net.ConnectException;
 import java.net.Socket;
 import java.net.SocketTimeoutException;
 import java.net.UnknownHostException;
 import java.util.concurrent.TimeUnit;
 
+import sd.serialization.MessageSerializer;
+import sd.serialization.SerializationException;
+import sd.serialization.SerializerFactory;
+
+
 /**
  * Wrapper class that simplifies communication via Sockets.
  * Includes connection retry logic for robustness.
@@ -17,8 +24,9 @@ import java.util.concurrent.TimeUnit;
 public class SocketConnection implements Closeable {
 
     private final Socket socket;
-    private final ObjectOutputStream outputStream;
+    private final OutputStream outputStream;
-    private final ObjectInputStream inputStream;
+    private final InputStream inputStream;
+    private final MessageSerializer serializer;
 
     // --- Configuration for Retry Logic ---
     /** Maximum number of connection attempts. */
@@ -88,16 +96,11 @@ public class SocketConnection implements Closeable {
 
         // If connection was successful, assign to final variable and create streams
         this.socket = tempSocket;
-        try {
+          
-            // IMPORTANT: The order is crucial. OutputStream first.
+        this.outputStream = socket.getOutputStream();
-            this.outputStream = new ObjectOutputStream(socket.getOutputStream());
+        this.inputStream = socket.getInputStream();
-            this.inputStream = new ObjectInputStream(socket.getInputStream());
+        this.serializer = SerializerFactory.createDefault();
-        } catch (IOException e) {
+
-             // If stream creation fails even after successful socket connection, clean up.
-             System.err.println("[SocketConnection] Failed to create streams after connection: " + e.getMessage());
-             try { socket.close(); } catch (IOException closeEx) { /* ignore */ }
-             throw e; // Re-throw the stream creation exception
-        }
     }
 
 
@@ -111,12 +114,10 @@ public class SocketConnection implements Closeable {
      */
     public SocketConnection(Socket acceptedSocket) throws IOException {
         this.socket = acceptedSocket;
-
+        this.outputStream = socket.getOutputStream();
-        // IMPORTANT: The order is crucial. OutputStream first.
+        this.inputStream = socket.getInputStream();
-        this.outputStream = new ObjectOutputStream(socket.getOutputStream());
+        this.serializer = SerializerFactory.createDefault();
-        this.inputStream = new ObjectInputStream(socket.getInputStream());
+        
-        System.out.printf("[SocketConnection] Connection accepted from %s:%d.%n",
-            acceptedSocket.getInetAddress().getHostAddress(), acceptedSocket.getPort());
     }
 
     /**
@@ -126,52 +127,66 @@ public class SocketConnection implements Closeable {
      * @throws IOException If writing to the stream fails or socket is not connected.
      */
     public void sendMessage(MessageProtocol message) throws IOException {
-        if (!isConnected()) {
+   if (socket == null || !socket.isConnected()) {
-            throw new IOException("Socket is not connected.");
+            throw new IOException("Socket is not connected");
         }
-        synchronized (outputStream) {
+
-            outputStream.writeObject(message);
+        try {
-            outputStream.flush(); // Ensures the message is sent immediately.
+            // Serializa para bytes JSON
+            byte[] data = serializer.serialize(message);
+            
+            // Write 4-byte length prefix
+            DataOutputStream dataOut = new DataOutputStream(outputStream);
+            dataOut.writeInt(data.length);
+            dataOut.write(data);
+            dataOut.flush();
+            
+        } catch (SerializationException e) {
+            throw new IOException("Failed to serialize message", e);
         }
     }
 
     /**
      * Tries to read (deserialize) a MessageProtocol object from the socket.
-     * This call is "blocked" until an object is received.
      *
      * @return The "envelope" (MessageProtocol) that was received.
      * @throws IOException If the connection is lost, the stream is corrupted, or socket is not connected.
      * @throws ClassNotFoundException If the received object is unknown.
      */
     public MessageProtocol receiveMessage() throws IOException, ClassNotFoundException {
-       if (!isConnected()) {
+       if (socket == null || !socket.isConnected()) {
-            throw new IOException("Socket is not connected.");
+            throw new IOException("Socket is not connected");
         }
-        synchronized (inputStream) {
+
-            return (MessageProtocol) inputStream.readObject();
+        try {
+            // Lê um prefixo de 4 bytes - indicador de tamanho
+            DataInputStream dataIn = new DataInputStream(inputStream);
+            int length = dataIn.readInt();
+            
+            if (length <= 0 || length > 10_000_000) { // Sanity check (10MB max)
+                throw new IOException("Invalid message length: " + length);
+            }
+            
+            // Ler dados da mensagem
+            byte[] data = new byte[length];
+            dataIn.readFully(data);
+            
+            // Deserialize do JSON
+            return serializer.deserialize(data, MessageProtocol.class);
+            
+        } catch (SerializationException e) {
+            throw new IOException("Failed to deserialize message", e);
         }
     }
 
     /**
      * Closes the socket and all streams (Input and Output).
-     * It is called automatically if you use 'try-with-resources'.
      */
     @Override
     public void close() throws IOException {
-         System.out.printf("[SocketConnection] Closing connection to %s:%d.%n",
+        if (inputStream != null) inputStream.close();
-            socket != null ? socket.getInetAddress().getHostAddress() : "N/A",
+        if (outputStream != null) outputStream.close();
-            socket != null ? socket.getPort() : -1);
+        if (socket != null) socket.close();
-        try {
-            if (inputStream != null) inputStream.close();
-        } catch (IOException e) { /* ignore */ }
-
-        try {
-            if (outputStream != null) outputStream.close();
-        } catch (IOException e) { /* ignore */ }
-
-        if (socket != null && !socket.isClosed()) {
-            socket.close();
-        }
     }
 
     /**

main/src/test/java/sd/coordinator/CoordinatorIntegrationTest.java

@@ -0,0 +1,302 @@
+package sd.coordinator;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ConcurrentLinkedQueue;
+
+import org.junit.jupiter.api.AfterEach;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.Timeout;
+
+import sd.model.Message;
+import sd.model.MessageType;
+import sd.model.Vehicle;
+import sd.serialization.MessageSerializer;
+import sd.serialization.SerializerFactory;
+
+/**
+ * Integration tests for the Coordinator-side networking.
+ *
+ * What we’re checking here:
+ *  1. A SocketClient can actually connect to something listening
+ *  2. Messages go over the wire and can be deserialized
+ *  3. Vehicle payloads survive the trip
+ *  4. Shutdown messages can be broadcast to multiple intersections
+ *
+ * We do this by spinning up a tiny mock intersection server in-process.
+ */
+class CoordinatorIntegrationTest {
+    
+    private List<MockIntersectionServer> mockServers;
+    private static final int BASE_PORT = 9001; // keep clear of real ports
+    
+    @BeforeEach
+    void setUp() {
+        mockServers = new ArrayList<>();
+    }
+    
+    @AfterEach
+    void tearDown() {
+        // Stop all mock servers
+        for (MockIntersectionServer server : mockServers) {
+            server.stop();
+        }
+        mockServers.clear();
+    }
+    
+    /**
+     * Can the client open a TCP connection to our fake intersection?
+     */
+    @Test
+    @Timeout(5)
+    void testSocketClientConnection() throws IOException, InterruptedException {
+        MockIntersectionServer server = new MockIntersectionServer("Cr1", BASE_PORT);
+        server.start();
+        mockServers.add(server);
+        
+        // tiny pause to let the server bind
+        Thread.sleep(100);
+        
+        SocketClient client = new SocketClient("Cr1", "localhost", BASE_PORT);
+        client.connect();
+        
+        assertTrue(client.isConnected(), "Client should be connected to mock intersection");
+        
+        client.close();
+    }
+    
+    /**
+     * End-to-end: send a message, make sure the server actually receives it.
+     */
+    @Test
+    @Timeout(5)
+    void testMessageTransmission() throws Exception {
+        MockIntersectionServer server = new MockIntersectionServer("Cr1", BASE_PORT);
+        server.start();
+        mockServers.add(server);
+        
+        Thread.sleep(100);
+        
+        SocketClient client = new SocketClient("Cr1", "localhost", BASE_PORT);
+        client.connect();
+        
+        Message testMessage = new Message(
+            MessageType.VEHICLE_SPAWN,
+            "COORDINATOR",
+            "Cr1",
+            "Test payload"
+        );
+        
+        client.send(testMessage);
+        
+        // give the server a moment to read and deserialize
+        Thread.sleep(200);
+        
+        assertFalse(
+            server.getReceivedMessages().isEmpty(),
+            "Mock server should have received at least one message"
+        );
+        
+        Message receivedMsg = server.getReceivedMessages().poll();
+        assertNotNull(receivedMsg, "Server should have actually received a message");
+        assertEquals(MessageType.VEHICLE_SPAWN, receivedMsg.getType(), "Message type should match what we sent");
+        assertEquals("COORDINATOR", receivedMsg.getSenderId(), "Sender ID should be preserved");
+        assertEquals("Cr1", receivedMsg.getDestinationId(), "Destination ID should be preserved");
+        
+        client.close();
+    }
+    
+    /**
+     * Make sure vehicle payloads survive the trip and arrive non-null.
+     */
+    @Test
+    @Timeout(5)
+    void testVehicleSpawnMessage() throws Exception {
+        MockIntersectionServer server = new MockIntersectionServer("Cr1", BASE_PORT);
+        server.start();
+        mockServers.add(server);
+        
+        Thread.sleep(100);
+        
+        SocketClient client = new SocketClient("Cr1", "localhost", BASE_PORT);
+        client.connect();
+        
+        // fake a vehicle like the coordinator would send
+        List<String> route = List.of("Cr1", "Cr4", "Cr5", "S");
+        Vehicle vehicle = new Vehicle("V1", sd.model.VehicleType.LIGHT, 0.0, route);
+        
+        Message spawnMessage = new Message(
+            MessageType.VEHICLE_SPAWN,
+            "COORDINATOR",
+            "Cr1",
+            vehicle
+        );
+        
+        client.send(spawnMessage);
+        
+        Thread.sleep(200);
+        
+        Message receivedMsg = server.getReceivedMessages().poll();
+        assertNotNull(receivedMsg, "Mock server should receive the spawn message");
+        assertEquals(MessageType.VEHICLE_SPAWN, receivedMsg.getType(), "Message should be of type VEHICLE_SPAWN");
+        assertNotNull(receivedMsg.getPayload(), "Payload should not be null (vehicle must arrive)");
+        
+        client.close();
+    }
+    
+    /**
+     * Broadcast shutdown to multiple mock intersections and see if all of them get it.
+     */
+    @Test
+    @Timeout(5)
+    void testShutdownMessageBroadcast() throws Exception {
+        // Start a couple of fake intersections
+        for (int i = 1; i <= 3; i++) {
+            MockIntersectionServer server = new MockIntersectionServer("Cr" + i, BASE_PORT + i - 1);
+            server.start();
+            mockServers.add(server);
+        }
+        
+        Thread.sleep(200);
+        
+        // Connect to all of them
+        List<SocketClient> clients = new ArrayList<>();
+        for (int i = 1; i <= 3; i++) {
+            SocketClient client = new SocketClient("Cr" + i, "localhost", BASE_PORT + i - 1);
+            client.connect();
+            clients.add(client);
+        }
+        
+        Message shutdownMessage = new Message(
+            MessageType.SHUTDOWN,
+            "COORDINATOR",
+            "ALL",
+            "Simulation complete"
+        );
+        
+        for (SocketClient client : clients) {
+            client.send(shutdownMessage);
+        }
+        
+        Thread.sleep(200);
+        
+        for (MockIntersectionServer server : mockServers) {
+            assertFalse(
+                server.getReceivedMessages().isEmpty(),
+                "Server " + server.getIntersectionId() + " should have received the shutdown message"
+            );
+            
+            Message msg = server.getReceivedMessages().poll();
+            assertEquals(MessageType.SHUTDOWN, msg.getType(), "Server should receive a SHUTDOWN message");
+        }
+        
+        for (SocketClient client : clients) {
+            client.close();
+        }
+    }
+    
+    /**
+     * Tiny TCP server that pretends to be an intersection.
+     * It:
+     *  - listens on a port
+     *  - accepts connections
+     *  - reads length-prefixed messages
+     *  - deserializes them and stores them for the test to inspect
+     */
+    private static class MockIntersectionServer {
+        private final String intersectionId;
+        private final int port;
+        private ServerSocket serverSocket;
+        private Thread serverThread;
+        private volatile boolean running;
+        private final ConcurrentLinkedQueue<Message> receivedMessages;
+        private final MessageSerializer serializer;
+        
+        public MockIntersectionServer(String intersectionId, int port) {
+            this.intersectionId = intersectionId;
+            this.port = port;
+            this.receivedMessages = new ConcurrentLinkedQueue<>();
+            this.serializer = SerializerFactory.createDefault();
+            this.running = false;
+        }
+        
+        public void start() throws IOException {
+            serverSocket = new ServerSocket(port);
+            running = true;
+            
+            System.out.printf("Mock %s listening on port %d%n", intersectionId, port);
+            
+            serverThread = new Thread(() -> {
+                try {
+                    while (running) {
+                        Socket clientSocket = serverSocket.accept();
+                        handleClient(clientSocket);
+                    }
+                } catch (IOException e) {
+                    if (running) {
+                        System.err.println("Mock " + intersectionId + " server error: " + e.getMessage());
+                    }
+                }
+            }, "mock-" + intersectionId + "-listener");
+            
+            serverThread.start();
+        }
+        
+        private void handleClient(Socket clientSocket) {
+            new Thread(() -> {
+                try (DataInputStream input = new DataInputStream(clientSocket.getInputStream())) {
+                    while (running) {
+                        // Read length prefix (4 bytes, big-endian)
+                        int length = input.readInt();
+                        byte[] data = new byte[length];
+                        input.readFully(data);
+                        
+                        Message message = serializer.deserialize(data, Message.class);
+                        receivedMessages.offer(message);
+                        
+                        System.out.println("Mock " + intersectionId + " received: " + message.getType());
+                    }
+                } catch (IOException e) {
+                    if (running) {
+                        System.err.println("Mock " + intersectionId + " client handler error: " + e.getMessage());
+                    }
+                } catch (Exception e) {
+                    System.err.println("Mock " + intersectionId + " deserialization error: " + e.getMessage());
+                }
+            }, "mock-" + intersectionId + "-client").start();
+        }
+        
+        public void stop() {
+            running = false;
+            try {
+                if (serverSocket != null && !serverSocket.isClosed()) {
+                    serverSocket.close();
+                }
+                if (serverThread != null) {
+                    serverThread.interrupt();
+                    serverThread.join(1000);
+                }
+                System.out.printf("Mock %s stopped%n", intersectionId);
+            } catch (IOException | InterruptedException e) {
+                System.err.println("Error stopping mock server " + intersectionId + ": " + e.getMessage());
+            }
+        }
+        
+        public ConcurrentLinkedQueue<Message> getReceivedMessages() {
+            return receivedMessages;
+        }
+        
+        public String getIntersectionId() {
+            return intersectionId;
+        }
+    }
+}

main/src/test/java/sd/coordinator/CoordinatorProcessTest.java

@@ -0,0 +1,194 @@
+package sd.coordinator;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.jupiter.api.AfterEach;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import sd.config.SimulationConfig;
+import sd.model.Vehicle;
+import sd.util.VehicleGenerator;
+
+/**
+ * Tests for the Coordinator/vehicle-generation layer.
+ *
+ * What we’re checking here:
+ *  1. Coordinator can be created with a valid config
+ *  2. Vehicle arrival times are monotonic and sane
+ *  3. Vehicle IDs are created in the format we expect (V1, V2, ...)
+ *  4. Generated vehicles have proper routes (start at CrX, end at S)
+ *  5. Config actually has intersection info
+ *  6. Duration in config is not something crazy
+ */
+class CoordinatorProcessTest {
+    
+    private SimulationConfig config;
+    private static final String TEST_CONFIG = "src/main/resources/simulation.properties";
+    
+    @BeforeEach
+    void setUp() throws IOException {
+        config = new SimulationConfig(TEST_CONFIG);
+    }
+    
+    @AfterEach
+    void tearDown() {
+        config = null;
+    }
+    
+    /**
+     * Basic smoke test: can we build a coordinator with this config?
+     */
+    @Test
+    void testCoordinatorInitialization() {
+        CoordinatorProcess coordinator = new CoordinatorProcess(config);
+        assertNotNull(coordinator, "Coordinator should be created with a valid config");
+    }
+    
+    /**
+     * Make sure the VehicleGenerator is giving us increasing arrival times,
+     * i.e. time doesn’t go backwards and intervals look reasonable.
+     */
+    @Test
+    void testVehicleGenerationTiming() {
+        VehicleGenerator generator = new VehicleGenerator(config);
+        
+        double currentTime = 0.0;
+        List<Double> arrivalTimes = new ArrayList<>();
+        
+        // generate a small batch to inspect
+        for (int i = 0; i < 10; i++) {
+            double nextArrival = generator.getNextArrivalTime(currentTime);
+            arrivalTimes.add(nextArrival);
+            currentTime = nextArrival;
+        }
+        
+        // times should strictly increase
+        for (int i = 1; i < arrivalTimes.size(); i++) {
+            assertTrue(
+                arrivalTimes.get(i) > arrivalTimes.get(i - 1),
+                "Arrival times must increase — got " + arrivalTimes.get(i - 1) + " then " + arrivalTimes.get(i)
+            );
+        }
+        
+        // and they shouldn't be nonsense
+        for (double time : arrivalTimes) {
+            assertTrue(time >= 0, "Arrival time should not be negative (got " + time + ")");
+            assertTrue(time < 1000, "Arrival time looks suspiciously large: " + time);
+        }
+    }
+    
+    /**
+     * We generate V1..V5 manually and make sure the IDs are exactly those.
+     */
+    @Test
+    void testVehicleIdGeneration() {
+        VehicleGenerator generator = new VehicleGenerator(config);
+        
+        List<Vehicle> vehicles = new ArrayList<>();
+        for (int i = 1; i <= 5; i++) {
+            Vehicle v = generator.generateVehicle("V" + i, 0.0);
+            vehicles.add(v);
+            assertEquals("V" + i, v.getId(), "Vehicle ID should be 'V" + i + "' but got " + v.getId());
+        }
+        
+        // just to be safe, no duplicates in that small set
+        long distinctCount = vehicles.stream().map(Vehicle::getId).distinct().count();
+        assertEquals(5, distinctCount, "Vehicle IDs in this batch should all be unique");
+    }
+    
+    /**
+     * A generated vehicle should:
+     *  - have a non-empty route
+     *  - start in a known intersection (Cr1..Cr5)
+     *  - end in S (exit)
+     */
+    @Test
+    void testVehicleRouteValidity() {
+        VehicleGenerator generator = new VehicleGenerator(config);
+        
+        for (int i = 0; i < 20; i++) {
+            Vehicle vehicle = generator.generateVehicle("V" + i, 0.0);
+            
+            assertNotNull(vehicle.getRoute(), "Vehicle route should not be null");
+            assertFalse(vehicle.getRoute().isEmpty(), "Vehicle route should not be empty");
+            
+            String firstHop = vehicle.getRoute().get(0);
+            assertTrue(
+                firstHop.matches("Cr[1-5]"),
+                "First hop should be a valid intersection (Cr1..Cr5), got: " + firstHop
+            );
+            
+            String lastHop = vehicle.getRoute().get(vehicle.getRoute().size() - 1);
+            assertEquals("S", lastHop, "Last hop should be exit 'S' but got: " + lastHop);
+        }
+    }
+    
+    /**
+     * Whatever is in simulation.properties should give us a sane duration.
+     */
+    @Test
+    void testSimulationDuration() {
+        double duration = config.getSimulationDuration();
+        assertTrue(duration > 0, "Simulation duration must be positive");
+        assertTrue(duration >= 1.0, "Simulation should run at least 1 second (got " + duration + ")");
+        assertTrue(duration <= 86400.0, "Simulation should not run more than a day (got " + duration + ")");
+    }
+    
+    /**
+     * Check that the 5 intersections defined in the architecture
+     * actually exist in the config and have valid network data.
+     */
+    @Test
+    void testIntersectionConfiguration() {
+        String[] intersectionIds = {"Cr1", "Cr2", "Cr3", "Cr4", "Cr5"};
+        
+        for (String id : intersectionIds) {
+            String host = config.getIntersectionHost(id);
+            int port = config.getIntersectionPort(id);
+            
+            assertNotNull(host, "Host should not be null for " + id);
+            assertFalse(host.isEmpty(), "Host should not be empty for " + id);
+            assertTrue(port > 0, "Port should be > 0 for " + id + " (got " + port + ")");
+            assertTrue(port < 65536, "Port should be a valid TCP port for " + id + " (got " + port + ")");
+        }
+    }
+    
+    /**
+     * Quick sanity check: over a bunch of generated vehicles,
+     * we should eventually see the different vehicle types appear.
+     *
+     * Note: this is probabilistic, so we're not being super strict.
+     */
+    @Test
+    void testVehicleTypeDistribution() {
+        VehicleGenerator generator = new VehicleGenerator(config);
+        
+        boolean hasBike = false;
+        boolean hasLight = false;
+        boolean hasHeavy = false;
+        
+        // 50 is enough for a "we're probably fine" test
+        for (int i = 0; i < 50; i++) {
+            Vehicle vehicle = generator.generateVehicle("V" + i, 0.0);
+            
+            switch (vehicle.getType()) {
+                case BIKE -> hasBike = true;
+                case LIGHT -> hasLight = true;
+                case HEAVY -> hasHeavy = true;
+            }
+        }
+        
+        // at least one of them should have shown up — if not, RNG is cursed
+        assertTrue(
+            hasBike || hasLight || hasHeavy,
+            "Expected to see at least one vehicle type after 50 generations"
+        );
+    }
+}