Add traffic light coordination and tests

Sorry to add this on this branch ahah

main/src/main/java/sd/ExitNodeProcess.java

@@ -0,0 +1,382 @@
+package sd;
+
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+
+import sd.config.SimulationConfig;
+import sd.coordinator.SocketClient;
+import sd.model.Message;
+import sd.model.MessageType;
+import sd.model.Vehicle;
+import sd.model.VehicleType;
+import sd.protocol.MessageProtocol;
+import sd.protocol.SocketConnection;
+import sd.serialization.SerializationException;
+
+/**
+ * Processo responsável pelo nó de saída do sistema de simulação de tráfego distribuído.
+ * 
+ * Este processo representa o ponto final ("S") onde os veículos completam as suas rotas.
+ * As suas principais responsabilidades são:
+ * - Receber veículos que terminam a sua rota vindos das interseções
+ * - Calcular e agregar estatísticas finais dos veículos
+ * - Enviar estatísticas periódicas para o dashboard
+ * - Gerar relatórios finais ao terminar a simulação
+ */
+public class ExitNodeProcess {
+
+    private final SimulationConfig config;
+    private ServerSocket serverSocket;
+    private final ExecutorService connectionHandlerPool;
+    
+    /** Flag para controlar a execução do processo (volatile para visibilidade entre threads) */
+    private volatile boolean running;
+    
+    /** Counter de veículos que completaram a rota */
+    private int totalVehiclesReceived;
+    
+    /** Soma dos tempos no sistema de todos os veículos */
+    private double totalSystemTime;
+    
+    /** Soma dos tempos de espera de todos os veículos */
+    private double totalWaitingTime;
+    
+    /** Soma dos tempos de travessia de todos os veículos */
+    private double totalCrossingTime;
+    
+    /** Contagem de veículos por tipo */
+    private final Map<VehicleType, Integer> vehicleTypeCount;
+    
+    /** Tempo total de espera acumulado por tipo de veículo */
+    private final Map<VehicleType, Double> vehicleTypeWaitTime;
+    
+    /** Socket para comunicação com o dashboard */
+    private SocketClient dashboardClient;
+    
+    /**
+     * Método para iniciar o processo
+     * 
+     * @param args Argumentos da linha de comandos. Se fornecido, args[0] deve ser
+     *             o caminho para um ficheiro de configuração personalizado.
+     */
+    public static void main(String[] args) {
+        System.out.println("=".repeat(60));
+        System.out.println("EXIT NODE PROCESS");
+        System.out.println("=".repeat(60));
+        
+        try {
+            String configFile = args.length > 0 ? args[0] : "src/main/resources/simulation.properties";
+            System.out.println("Loading configuration from: " + configFile);
+            
+            SimulationConfig config = new SimulationConfig(configFile);
+            ExitNodeProcess exitNode = new ExitNodeProcess(config);
+            
+            System.out.println("\n" + "=".repeat(60));
+            exitNode.initialize();
+            
+            System.out.println("\n" + "=".repeat(60));
+            exitNode.start();
+            
+        } catch (IOException e) {
+            System.err.println("Failed to start exit node: " + e.getMessage());
+            System.exit(1);
+        } catch (Exception e) {
+            System.err.println("Exit node error: " + e.getMessage());
+            System.exit(1);
+        }
+    }
+    
+    /**
+     * Constrói um novo processo de nó de saída.
+     * 
+     * Inicializa todas as estruturas de dados necessárias para recolher estatísticas
+     * e configura o pool de threads para processar as ligações concorrentes.
+     * 
+     * @param config Configuração da simulação contendo portas e endereços dos serviços
+     */
+    public ExitNodeProcess(SimulationConfig config) {
+        this.config = config;
+        this.connectionHandlerPool = Executors.newCachedThreadPool();
+        this.running = false;
+        
+        this.totalVehiclesReceived = 0;
+        this.totalSystemTime = 0.0;
+        this.totalWaitingTime = 0.0;
+        this.totalCrossingTime = 0.0;
+        this.vehicleTypeCount = new HashMap<>();
+        this.vehicleTypeWaitTime = new HashMap<>();
+        
+        // Inicializa os counters para cada tipo de veículo
+        for (VehicleType type : VehicleType.values()) {
+            vehicleTypeCount.put(type, 0);
+            vehicleTypeWaitTime.put(type, 0.0);
+        }
+        
+        System.out.println("Exit node initialized");
+        System.out.println("  - Exit port: " + config.getExitPort());
+        System.out.println("  - Dashboard: " + config.getDashboardHost() + ":" + config.getDashboardPort());
+    }
+    
+    /**
+     * Inicializa o processo de ligação ao dashboard.
+     * 
+     * Tenta conectar-se ao dashboard. Se a ligação falhar, o processo
+     * continua a funcionar normalmente, mas sem enviar estatísticas.
+     * 
+     */
+    public void initialize() {
+        System.out.println("Connecting to dashboard...");
+        
+        try {
+            String host = config.getDashboardHost();
+            int port = config.getDashboardPort();
+            
+            dashboardClient = new SocketClient("Dashboard", host, port);
+            dashboardClient.connect();
+            
+            System.out.println("Successfully connected to dashboard");
+        } catch (IOException e) {
+            System.err.println("WARNING: Failed to connect to dashboard: " + e.getMessage());
+            System.err.println("Exit node will continue without dashboard connection");
+        }
+    }
+    
+    /**
+     * Inicia o socket e começa a aceitar ligações.
+     * 
+     * Este é o loop principal do processo que:
+     * 1. Cria um socket na porta definida
+     * 2. Aguarda pelas ligações das interseções
+     * 3. Delega cada ligação a uma thread da pool para processamento assíncrono
+     * 
+     * @throws IOException Se o socket não puder ser criado ou houver erro na aceitação
+     */
+    public void start() throws IOException {
+        int port = config.getExitPort();
+        serverSocket = new ServerSocket(port);
+        running = true;
+        
+        System.out.println("Exit node started on port " + port);
+        System.out.println("Waiting for vehicles...\n");
+        
+        while (running) {
+            try {
+                Socket clientSocket = serverSocket.accept();
+                connectionHandlerPool.submit(() -> handleIncomingConnection(clientSocket));
+            } catch (IOException e) {
+                if (running) {
+                    System.err.println("Error accepting connection: " + e.getMessage());
+                }
+            }
+        }
+    }
+    
+    /**
+     * Processa uma ligação recebida de uma interseção.
+     * 
+     * Mantém a ligação aberta e processa continuamente mensagens do tipo
+     * VEHICLE_TRANSFER. Cada mensagem representa um veículo que chegou ao nó de saída.
+     * 
+     * @param clientSocket Socket da ligação estabelecida com a interseção
+     */
+    private void handleIncomingConnection(Socket clientSocket) {
+        try (SocketConnection connection = new SocketConnection(clientSocket)) {
+            
+            System.out.println("New connection accepted from " +
+                             clientSocket.getInetAddress().getHostAddress());
+            
+            while (running && connection.isConnected()) {
+                try {
+                    MessageProtocol message = connection.receiveMessage();
+                    
+                    if (message.getType() == MessageType.VEHICLE_TRANSFER) {
+                        Vehicle vehicle = (Vehicle) message.getPayload();
+                        processExitingVehicle(vehicle);
+                    }
+                    
+                } catch (ClassNotFoundException e) {
+                    System.err.println("Unknown message type received: " + e.getMessage());
+                }
+            }
+            
+        } catch (IOException e) {
+            if (running) {
+                System.err.println("Connection error: " + e.getMessage());
+            }
+        }
+    }
+    
+    /**
+     * Processa um veículo que chegou ao nó de saída.
+     * 
+     * Método sincronizado para garantir thread-safety ao atualizar as estatísticas.
+     * Calcula as métricas finais do veículo e atualiza:
+     * - Counters globais;
+     * - Estatísticas por tipo de veículo;
+     * - Faz update ao dashboard a cada 10 veículos.
+     * 
+     * @param vehicle Veículo que completou a sua rota
+     */
+    private synchronized void processExitingVehicle(Vehicle vehicle) {
+        totalVehiclesReceived++;
+        
+        double systemTime = vehicle.getTotalTravelTime(getCurrentTime());
+        double waitTime = vehicle.getTotalWaitingTime();
+        double crossingTime = vehicle.getTotalCrossingTime();
+        
+        totalSystemTime += systemTime;
+        totalWaitingTime += waitTime;
+        totalCrossingTime += crossingTime;
+        
+        VehicleType type = vehicle.getType();
+        vehicleTypeCount.put(type, vehicleTypeCount.get(type) + 1);
+        vehicleTypeWaitTime.put(type, vehicleTypeWaitTime.get(type) + waitTime);
+        
+        System.out.printf("[Exit] Vehicle %s completed (type=%s, system_time=%.2fs, wait=%.2fs)%n",
+            vehicle.getId(), vehicle.getType(), systemTime, waitTime);
+        
+        if (totalVehiclesReceived % 10 == 0) {
+            sendStatsToDashboard();
+        }
+    }
+    
+    /**
+     * Obtém o tempo atual da simulação em segundos.
+     * 
+     * @return Tempo atual em segundos desde "epoch"
+     * 
+     * "Epoch" é um ponto de referência temporal Unix (1 de janeiro de 1970).
+     * Este método retorna os segundos decorridos desde esse momento.
+     */
+    private double getCurrentTime() {
+        return System.currentTimeMillis() / 1000.0;
+    }
+    
+    /**
+     * Envia as estatísticas para o dashboard.
+     * 
+     * Prepara e envia uma mensagem STATS_UPDATE com:
+     * - O total de veículos processados;
+     * - A média dos tempos (sistema, espera, travessia);
+     * - As contagens e médias por cada tipo de veículo.
+     * 
+     */
+    private void sendStatsToDashboard() {
+        if (dashboardClient == null || !dashboardClient.isConnected()) {
+            return;
+        }
+        
+        try {
+            Map<String, Object> stats = new HashMap<>();
+            stats.put("totalVehicles", totalVehiclesReceived);
+            stats.put("avgSystemTime", totalVehiclesReceived > 0 ? totalSystemTime / totalVehiclesReceived : 0.0);
+            stats.put("avgWaitingTime", totalVehiclesReceived > 0 ? totalWaitingTime / totalVehiclesReceived : 0.0);
+            stats.put("avgCrossingTime", totalVehiclesReceived > 0 ? totalCrossingTime / totalVehiclesReceived : 0.0);
+            
+            Map<String, Integer> typeCounts = new HashMap<>();
+            Map<String, Double> typeAvgWait = new HashMap<>();
+            for (VehicleType type : VehicleType.values()) {
+                int count = vehicleTypeCount.get(type);
+                typeCounts.put(type.name(), count);
+                if (count > 0) {
+                    typeAvgWait.put(type.name(), vehicleTypeWaitTime.get(type) / count);
+                }
+            }
+            stats.put("vehicleTypeCounts", typeCounts);
+            stats.put("vehicleTypeAvgWait", typeAvgWait);
+            
+            Message message = new Message(MessageType.STATS_UPDATE, "ExitNode", "Dashboard", stats);
+            dashboardClient.send(message);
+            
+            System.out.printf("[Exit] Sent stats to dashboard (total=%d, avg_wait=%.2fs)%n",
+                totalVehiclesReceived, totalWaitingTime / totalVehiclesReceived);
+                
+        } catch (SerializationException | IOException e) {
+            System.err.println("Failed to send stats to dashboard: " + e.getMessage());
+        }
+    }
+    
+    /**
+     * Termina o processo
+     * 
+     * Executa a seguinte sequência:
+     *  Imprime as estatísticas finais no terminal;
+     *  Envia a última atualização de estatísticas ao dashboard;
+     *  Fecha o socket;
+     *  Aguarda pela finalização das threads;
+     *  Fecha a ligação com o dashboard;
+     */
+    public void shutdown() {
+        System.out.println("\n[Exit] Shutting down...");
+        running = false;
+        
+        printFinalStatistics();
+        
+        sendStatsToDashboard();
+        
+        try {
+            if (serverSocket != null && !serverSocket.isClosed()) {
+                serverSocket.close();
+            }
+        } catch (IOException e) {
+            System.err.println("Error closing server socket: " + e.getMessage());
+        }
+        
+        connectionHandlerPool.shutdown();
+        try {
+            if (!connectionHandlerPool.awaitTermination(5, TimeUnit.SECONDS)) {
+                connectionHandlerPool.shutdownNow();
+            }
+        } catch (InterruptedException e) {
+            connectionHandlerPool.shutdownNow();
+        }
+        
+        if (dashboardClient != null) {
+            dashboardClient.close();
+        }
+        
+        System.out.println("[Exit] Shutdown complete.");
+        System.out.println("=".repeat(60));
+    }
+    
+    /**
+     * Imprime as estatísticas finais detalhadas no terminal
+     * 
+     * Gera um relatório com:
+     * Total de veículos que completaram a rota;
+     * Médias de tempo no sistema, espera e travessia;
+     * Distribuição e médias pelo tipo de veículo (BIKE, LIGHT, HEAVY);
+     * 
+     * Este método é chamado durante o shutdown para fornecer um resumo
+     * da simulação antes de terminar o processo.
+     */
+    private void printFinalStatistics() {
+        System.out.println("\n=== EXIT NODE STATISTICS ===");
+        System.out.printf("Total Vehicles Completed: %d%n", totalVehiclesReceived);
+        
+        if (totalVehiclesReceived > 0) {
+            System.out.printf("%nAVERAGE METRICS:%n");
+            System.out.printf("  System Time: %.2f seconds%n", totalSystemTime / totalVehiclesReceived);
+            System.out.printf("  Waiting Time: %.2f seconds%n", totalWaitingTime / totalVehiclesReceived);
+            System.out.printf("  Crossing Time: %.2f seconds%n", totalCrossingTime / totalVehiclesReceived);
+        }
+        
+        System.out.println("\nVEHICLE TYPE DISTRIBUTION:");
+        for (VehicleType type : VehicleType.values()) {
+            int count = vehicleTypeCount.get(type);
+            if (count > 0) {
+                double percentage = (count * 100.0) / totalVehiclesReceived;
+                double avgWait = vehicleTypeWaitTime.get(type) / count;
+                System.out.printf("  %s: %d (%.1f%%), Avg Wait: %.2fs%n",
+                    type, count, percentage, avgWait);
+            }
+        }
+    }
+    
+}

main/src/main/java/sd/IntersectionProcess.java

@@ -8,6 +8,8 @@ import java.util.Map;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.TimeUnit;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
 
 import sd.config.SimulationConfig;
 import sd.model.Intersection;
@@ -42,6 +44,19 @@ public class IntersectionProcess {
     private volatile boolean running;   //Quando uma thread escreve um valor volatile, todas as outras
                                         //threads veem a mudança imediatamente.
     
+    // Traffic Light Coordination
+    /**
+     * Lock to ensure mutual exclusion between traffic lights.
+     * Only one traffic light can be green at any given time within this intersection.
+     */
+    private final Lock trafficCoordinationLock;
+    
+    /**
+     * Tracks which direction currently has the green light.
+     * null means no direction is currently green (all are red).
+     */
+    private volatile String currentGreenDirection;
+    
     /**
      * Constructs a new IntersectionProcess.
      *
@@ -57,6 +72,8 @@ public class IntersectionProcess {
         this.connectionHandlerPool = Executors.newCachedThreadPool();
         this.trafficLightPool = Executors.newFixedThreadPool(4); // Max 4 directions
         this.running = false;
+        this.trafficCoordinationLock = new ReentrantLock();
+        this.currentGreenDirection = null;
         
         System.out.println("=".repeat(60));
         System.out.println("INTERSECTION PROCESS: " + intersectionId);
@@ -70,8 +87,6 @@ public class IntersectionProcess {
         
         configureRouting();
         
-        startTrafficLights();
-        
         System.out.println("[" + intersectionId + "] Initialization complete.");
     }
 
@@ -168,7 +183,9 @@ public class IntersectionProcess {
     
     /**
      * The main loop for a traffic light thread.
-     * Continuously cycles between GREEN and RED states.
+     * Continuously cycles between green and red states.
+     * 
+     * only one traffic light can be green at any given time in this intersection.
      *
      * @param light The traffic light to control.
      */
@@ -177,9 +194,28 @@ public class IntersectionProcess {
         
         while (running) {
             try {
-                // Green state
+                // Acquire coordination lock to become green
-                light.changeState(TrafficLightState.GREEN);
+                trafficCoordinationLock.lock();
-                System.out.println("[" + light.getId() + "] State: GREEN");
+                try {
+                    // Wait until no other direction is green
+                    while (currentGreenDirection != null && running) {
+                        trafficCoordinationLock.unlock();
+                        Thread.sleep(100); // Brief wait before retrying
+                        trafficCoordinationLock.lock();
+                    }
+                    
+                    if (!running) {
+                        break; // Exit if shutting down
+                    }
+                    
+                    // Mark this direction as the current green light
+                    currentGreenDirection = light.getDirection();
+                    light.changeState(TrafficLightState.GREEN);
+                    System.out.println("[" + light.getId() + "] State: GREEN");
+                    
+                } finally {
+                    trafficCoordinationLock.unlock();
+                }
                 
                 // Process vehicles while green
                 processGreenLight(light);
@@ -187,9 +223,15 @@ public class IntersectionProcess {
                 // Wait for green duration
                 Thread.sleep((long) (light.getGreenTime() * 1000));
                 
-                // RED state
+                // Release coordination lock (turn red)
-                light.changeState(TrafficLightState.RED);
+                trafficCoordinationLock.lock();
-                System.out.println("[" + light.getId() + "] State: RED");
+                try {
+                    light.changeState(TrafficLightState.RED);
+                    currentGreenDirection = null; // Release exclusive access
+                    System.out.println("[" + light.getId() + "] State: RED (RELEASED ACCESS)");
+                } finally {
+                    trafficCoordinationLock.unlock();
+                }
                 
                 // Wait for red duration
                 Thread.sleep((long) (light.getRedTime() * 1000));
@@ -353,6 +395,10 @@ public class IntersectionProcess {
         running = true;
         
         System.out.println("\n[" + intersectionId + "] Server started on port " + port);
+        
+        // Start traffic light threads when running is true
+        startTrafficLights();
+        
         System.out.println("[" + intersectionId + "] Waiting for incoming connections...\n");
         
         // Main accept loop
@@ -460,6 +506,16 @@ public class IntersectionProcess {
         System.out.println("=".repeat(60));
     }
     
+    /**
+     * Gets the Intersection object managed by this process.
+     * Useful for testing and monitoring.
+     * 
+     * @return The Intersection object.
+     */
+    public Intersection getIntersection() {
+        return intersection;
+    }
+    
     // --- Inner class for Vehicle Transfer Messages ---
     
     /**

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/model/Intersection.java

@@ -114,8 +114,8 @@ public class Intersection {
     public void receiveVehicle(Vehicle vehicle) {
         totalVehiclesReceived++;
 
-        // Advance route since vehicle just arrived at this intersection
+        // Note: Route advancement is handled by SimulationEngine.handleVehicleArrival()
-        vehicle.advanceRoute();
+        // before calling this method, so we don't advance here.
         
         String nextDestination = vehicle.getCurrentDestination();
         

main/src/test/java/sd/ExitNodeProcessTest.java

@@ -0,0 +1,327 @@
+package sd;
+
+import java.io.IOException;
+import java.net.Socket;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.jupiter.api.AfterEach;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+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 org.junit.jupiter.api.io.TempDir;
+
+import sd.config.SimulationConfig;
+
+/**
+ * Testes unitários para a classe ExitNodeProcess.
+ * 
+ * Esta classe de testes verifica:
+ * - Construção e inicialização do processo
+ * - Criação e aceitação de conexões do servidor socket
+ * - Gestão do ciclo de vida (start/shutdown)
+ * - Processamento concorrente de múltiplas conexões
+ * - Impressão de estatísticas finais
+ * 
+ * Os testes utilizam configurações temporárias e portas dedicadas (19001)
+ * para evitar conflitos com outros testes ou processos em execução.
+ */
+public class ExitNodeProcessTest {
+
+    @TempDir
+    Path tempDir;
+
+    private Path configFile;
+    private ExitNodeProcess exitNodeProcess;
+    private Thread exitNodeThread;
+
+    /**
+     * Configura o ambiente de teste antes de cada teste.
+     * Cria um ficheiro de configuração temporário com as definições necessárias.
+     */
+    @BeforeEach
+    public void setUp() throws IOException {
+        configFile = tempDir.resolve("test-simulation.properties");
+        
+        String configContent = """
+                # Test Exit Node Configuration
+                
+                # Exit Configuration
+                exit.host=localhost
+                exit.port=19001
+                
+                # Dashboard Configuration (will not be running in tests)
+                dashboard.host=localhost
+                dashboard.port=19000
+                
+                # Vehicle Crossing Times
+                vehicle.bike.crossingTime=2.0
+                vehicle.light.crossingTime=3.0
+                vehicle.heavy.crossingTime=5.0
+                
+                # Simulation Duration
+                simulation.duration=60.0
+                """;
+        
+        Files.writeString(configFile, configContent);
+    }
+
+    /**
+     * Limpa os recursos após cada teste.
+     * Garante que o processo e threads são terminados corretamente.
+     */
+    @AfterEach
+    public void tearDown() {
+        if (exitNodeProcess != null) {
+            exitNodeProcess.shutdown();
+        }
+        if (exitNodeThread != null && exitNodeThread.isAlive()) {
+            exitNodeThread.interrupt();
+            try {
+                exitNodeThread.join(1000);
+            } catch (InterruptedException e) {
+                Thread.currentThread().interrupt();
+            }
+        }
+    }
+
+    /**
+     * Testa a construção bem-sucedida do ExitNodeProcess com configuração válida.
+     */
+    @Test
+    public void testConstructor_Success() throws IOException {
+        SimulationConfig config = new SimulationConfig(configFile.toString());
+        exitNodeProcess = new ExitNodeProcess(config);
+        assertNotNull(exitNodeProcess);
+    }
+
+    /**
+     * Testa que uma exceção é lançada quando a configuração é inválida.
+     */
+    @Test
+    public void testConstructor_InvalidConfig() {
+        Exception exception = assertThrows(IOException.class, () -> {
+            new SimulationConfig("non-existent-config.properties");
+        });
+        assertNotNull(exception);
+    }
+
+    /**
+     * Testa a inicialização sem dashboard disponível.
+     * Verifica que o processo continua a funcionar mesmo sem conexão ao dashboard.
+     */
+    @Test
+    public void testInitialize_WithoutDashboard() throws IOException {
+        SimulationConfig config = new SimulationConfig(configFile.toString());
+        exitNodeProcess = new ExitNodeProcess(config);
+        assertDoesNotThrow(() -> exitNodeProcess.initialize());
+    }
+
+    /**
+     * Testa que o servidor socket é criado corretamente na porta configurada.
+     * Verifica que é possível estabelecer uma conexão ao socket do servidor.
+     */
+    @Test
+    @Timeout(value = 3, unit = TimeUnit.SECONDS)
+    public void testStart_ServerSocketCreated() throws IOException {
+        SimulationConfig config = new SimulationConfig(configFile.toString());
+        exitNodeProcess = new ExitNodeProcess(config);
+        exitNodeProcess.initialize();
+        
+        CountDownLatch latch = new CountDownLatch(1);
+        
+        exitNodeThread = new Thread(() -> {
+            try {
+                latch.countDown();
+                exitNodeProcess.start();
+            } catch (IOException e) {
+                // expected when shutdown
+            }
+        });
+        
+        exitNodeThread.start();
+        
+        try {
+            assertTrue(latch.await(2, TimeUnit.SECONDS), "Exit node should start within timeout");
+            Thread.sleep(100);
+            
+            assertDoesNotThrow(() -> {
+                try (Socket testSocket = new Socket("localhost", 19001)) {
+                    assertTrue(testSocket.isConnected());
+                }
+            });
+        } catch (InterruptedException e) {
+            Thread.currentThread().interrupt();
+        }
+    }
+
+    /**
+     * Testa que o servidor aceita conexões de clientes.
+     */
+    @Test
+    @Timeout(value = 3, unit = TimeUnit.SECONDS)
+    public void testStart_AcceptsConnection() throws IOException, InterruptedException {
+        SimulationConfig config = new SimulationConfig(configFile.toString());
+        exitNodeProcess = new ExitNodeProcess(config);
+        exitNodeProcess.initialize();
+        
+        CountDownLatch latch = new CountDownLatch(1);
+        
+        exitNodeThread = new Thread(() -> {
+            try {
+                latch.countDown();
+                exitNodeProcess.start();
+            } catch (IOException e) {
+                // expected
+            }
+        });
+        
+        exitNodeThread.start();
+        
+        assertTrue(latch.await(2, TimeUnit.SECONDS));
+        Thread.sleep(200);
+        
+        assertDoesNotThrow(() -> {
+            try (Socket socket = new Socket("localhost", 19001)) {
+                assertTrue(socket.isConnected());
+            }
+        });
+    }
+
+    /**
+     * Testa múltiplas inicializações e encerramentos do processo.
+     * Verifica que o processo pode ser iniciado e parado múltiplas vezes,
+     * permitindo reutilização da porta.
+     */
+    @Test
+    @Timeout(value = 3, unit = TimeUnit.SECONDS)
+    public void testMultipleStartStop() throws IOException, InterruptedException {
+        SimulationConfig config = new SimulationConfig(configFile.toString());
+        exitNodeProcess = new ExitNodeProcess(config);
+        exitNodeProcess.initialize();
+        
+        CountDownLatch latch = new CountDownLatch(1);
+        
+        exitNodeThread = new Thread(() -> {
+            try {
+                latch.countDown();
+                exitNodeProcess.start();
+            } catch (IOException e) {
+                // expected
+            }
+        });
+        
+        exitNodeThread.start();
+        assertTrue(latch.await(2, TimeUnit.SECONDS));
+        Thread.sleep(100);
+        
+        exitNodeProcess.shutdown();
+        Thread.sleep(100);
+        
+        assertDoesNotThrow(() -> {
+            SimulationConfig config2 = new SimulationConfig(configFile.toString());
+            ExitNodeProcess exitNode2 = new ExitNodeProcess(config2);
+            exitNode2.initialize();
+            exitNode2.shutdown();
+        });
+    }
+
+    /**
+     * Testa que o shutdown fecha corretamente o servidor socket.
+     * Após o shutdown, novas conexões ao socket devem falhar.
+     */
+    @Test
+    @Timeout(value = 3, unit = TimeUnit.SECONDS)
+    public void testShutdown_ClosesServerSocket() throws IOException, InterruptedException {
+        SimulationConfig config = new SimulationConfig(configFile.toString());
+        exitNodeProcess = new ExitNodeProcess(config);
+        exitNodeProcess.initialize();
+        
+        CountDownLatch startLatch = new CountDownLatch(1);
+        
+        exitNodeThread = new Thread(() -> {
+            try {
+                startLatch.countDown();
+                exitNodeProcess.start();
+            } catch (IOException e) {
+                // expected
+            }
+        });
+        
+        exitNodeThread.start();
+        assertTrue(startLatch.await(2, TimeUnit.SECONDS));
+        Thread.sleep(200);
+        
+        exitNodeProcess.shutdown();
+        Thread.sleep(200);
+        
+        assertThrows(IOException.class, () -> {
+            Socket socket = new Socket("localhost", 19001);
+            socket.close();
+        });
+    }
+
+    /**
+     * Testa que as estatísticas finais são impressas corretamente durante o shutdown.
+     * Verifica que o método não lança exceções mesmo sem dados processados.
+     */
+    @Test
+    public void testPrintFinalStatistics() throws IOException {
+        SimulationConfig config = new SimulationConfig(configFile.toString());
+        exitNodeProcess = new ExitNodeProcess(config);
+        exitNodeProcess.initialize();
+        
+        assertDoesNotThrow(() -> exitNodeProcess.shutdown());
+    }
+
+    /**
+     * Testa o processamento de múltiplas conexões concorrentes.
+     * Verifica que o servidor consegue lidar com vários clientes simultaneamente
+     * usando o pool de threads.
+     */
+    @Test
+    @Timeout(value = 3, unit = TimeUnit.SECONDS)
+    public void testMultipleConcurrentConnections() throws IOException, InterruptedException {
+        SimulationConfig config = new SimulationConfig(configFile.toString());
+        exitNodeProcess = new ExitNodeProcess(config);
+        exitNodeProcess.initialize();
+        
+        CountDownLatch latch = new CountDownLatch(1);
+        
+        exitNodeThread = new Thread(() -> {
+            try {
+                latch.countDown();
+                exitNodeProcess.start();
+            } catch (IOException e) {
+                // expected
+            }
+        });
+        
+        exitNodeThread.start();
+        assertTrue(latch.await(2, TimeUnit.SECONDS));
+        Thread.sleep(200);
+        
+        Thread[] clients = new Thread[3];
+        for (int i = 0; i < 3; i++) {
+            clients[i] = new Thread(() -> {
+                try (Socket socket = new Socket("localhost", 19001)) {
+                    assertTrue(socket.isConnected());
+                    Thread.sleep(100);
+                } catch (IOException | InterruptedException e) {
+                    // ignore
+                }
+            });
+            clients[i].start();
+        }
+        
+        for (Thread client : clients) {
+            client.join(1000);
+        }
+    }
+}

main/src/test/java/sd/TrafficLightCoordinationTest.java

@@ -0,0 +1,206 @@
+package sd;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+
+import sd.model.TrafficLight;
+import sd.model.TrafficLightState;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Test class to verify traffic light coordination within an intersection.
+ * Ensures that only ONE traffic light can be GREEN at any given time.
+ */
+public class TrafficLightCoordinationTest {
+
+    private IntersectionProcess intersectionProcess;
+
+    @BeforeEach
+    public void setUp() throws IOException {
+        // Create an intersection with multiple traffic lights
+        intersectionProcess = new IntersectionProcess("Cr2", "src/main/resources/simulation.properties");
+        intersectionProcess.initialize();
+    }
+
+    @AfterEach
+    public void tearDown() throws InterruptedException {
+        if (intersectionProcess != null) {
+            intersectionProcess.shutdown();
+        }
+    }
+
+    /**
+     * Test that verifies mutual exclusion between traffic lights.
+     * Monitors all traffic lights for 10 seconds and ensures that
+     * at most ONE light is GREEN at any point in time.
+     */
+    @Test
+    public void testOnlyOneGreenLightAtATime() throws InterruptedException {
+        System.out.println("\n=== Testing Traffic Light Mutual Exclusion ===");
+        
+        // Start the intersection
+        Thread intersectionThread = new Thread(() -> {
+            try {
+                intersectionProcess.start();
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+        });
+        intersectionThread.start();
+
+        // Monitor traffic lights for violations
+        AtomicInteger maxGreenSimultaneously = new AtomicInteger(0);
+        AtomicInteger violationCount = new AtomicInteger(0);
+        List<String> violations = new ArrayList<>();
+        
+        // Monitor for 10 seconds
+        long endTime = System.currentTimeMillis() + 10000;
+        
+        while (System.currentTimeMillis() < endTime) {
+            int greenCount = 0;
+            StringBuilder currentState = new StringBuilder("States: ");
+            
+            for (TrafficLight light : intersectionProcess.getIntersection().getTrafficLights()) {
+                TrafficLightState state = light.getState();
+                currentState.append(light.getDirection()).append("=").append(state).append(" ");
+                
+                if (state == TrafficLightState.GREEN) {
+                    greenCount++;
+                }
+            }
+            
+            // Update maximum simultaneous green lights
+            if (greenCount > maxGreenSimultaneously.get()) {
+                maxGreenSimultaneously.set(greenCount);
+            }
+            
+            // Check for violations (more than one green)
+            if (greenCount > 1) {
+                violationCount.incrementAndGet();
+                String violation = String.format("[VIOLATION] %d lights GREEN simultaneously: %s", 
+                    greenCount, currentState.toString());
+                violations.add(violation);
+                System.err.println(violation);
+            }
+            
+            Thread.sleep(50); // Check every 50ms
+        }
+        
+        System.out.println("\n=== Test Results ===");
+        System.out.println("Maximum simultaneous GREEN lights: " + maxGreenSimultaneously.get());
+        System.out.println("Total violations detected: " + violationCount.get());
+        
+        if (!violations.isEmpty()) {
+            System.err.println("\nViolation details:");
+            violations.forEach(System.err::println);
+        }
+        
+        // Assert that we never had more than one green light
+        assertEquals(0, violationCount.get(), 
+            "Traffic light coordination violated! Multiple lights were GREEN simultaneously.");
+        assertTrue(maxGreenSimultaneously.get() <= 1, 
+            "At most ONE light should be GREEN at any time. Found: " + maxGreenSimultaneously.get());
+        
+        System.out.println("\n✅ Traffic light coordination working correctly!");
+    }
+
+    /**
+     * Test that verifies all traffic lights get a chance to be GREEN.
+     * Ensures fairness in the coordination mechanism.
+     */
+    @Test
+    public void testAllLightsGetGreenTime() throws InterruptedException {
+        System.out.println("\n=== Testing Traffic Light Fairness ===");
+        
+        // Start the intersection
+        Thread intersectionThread = new Thread(() -> {
+            try {
+                intersectionProcess.start();
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+        });
+        intersectionThread.start();
+
+        // Track which lights have been green
+        List<TrafficLight> lights = intersectionProcess.getIntersection().getTrafficLights();
+        boolean[] hasBeenGreen = new boolean[lights.size()];
+        
+        // Monitor for 15 seconds (enough time for all lights to cycle)
+        long endTime = System.currentTimeMillis() + 15000;
+        
+        while (System.currentTimeMillis() < endTime) {
+            for (int i = 0; i < lights.size(); i++) {
+                if (lights.get(i).getState() == TrafficLightState.GREEN) {
+                    hasBeenGreen[i] = true;
+                    System.out.println("✓ " + lights.get(i).getDirection() + " has been GREEN");
+                }
+            }
+            Thread.sleep(100);
+        }
+        
+        // Check if all lights got green time
+        int greenCount = 0;
+        System.out.println("\n=== Fairness Results ===");
+        for (int i = 0; i < lights.size(); i++) {
+            String status = hasBeenGreen[i] ? "✓ YES" : "✗ NO";
+            System.out.println(lights.get(i).getDirection() + " got GREEN time: " + status);
+            if (hasBeenGreen[i]) greenCount++;
+        }
+        
+        assertTrue(greenCount > 0, "At least one light should have been GREEN during the test");
+        System.out.println("\n" + greenCount + "/" + lights.size() + " lights were GREEN during test period");
+    }
+
+    /**
+     * Test that verifies the state transitions are consistent.
+     */
+    @Test
+    public void testStateTransitionsAreConsistent() throws InterruptedException {
+        System.out.println("\n=== Testing State Transition Consistency ===");
+        
+        Thread intersectionThread = new Thread(() -> {
+            try {
+                intersectionProcess.start();
+            } catch (IOException e) {
+                e.printStackTrace();
+            }
+        });
+        intersectionThread.start();
+
+        List<TrafficLight> lights = intersectionProcess.getIntersection().getTrafficLights();
+        TrafficLightState[] previousStates = new TrafficLightState[lights.size()];
+        
+        // Initialize previous states
+        for (int i = 0; i < lights.size(); i++) {
+            previousStates[i] = lights.get(i).getState();
+        }
+        
+        int transitionCount = 0;
+        long endTime = System.currentTimeMillis() + 8000;
+        
+        while (System.currentTimeMillis() < endTime) {
+            for (int i = 0; i < lights.size(); i++) {
+                TrafficLightState currentState = lights.get(i).getState();
+                
+                if (currentState != previousStates[i]) {
+                    transitionCount++;
+                    System.out.println(lights.get(i).getDirection() + " transitioned: " + 
+                        previousStates[i] + " → " + currentState);
+                    previousStates[i] = currentState;
+                }
+            }
+            Thread.sleep(100);
+        }
+        
+        System.out.println("\nTotal state transitions observed: " + transitionCount);
+        assertTrue(transitionCount > 0, "There should be state transitions during the test period");
+    }
+}

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"
+        );
+    }
+}