Move vehicle route advancement to intersection arrival

Dev

.github/workflows/maven.yml

@@ -0,0 +1,61 @@
+name: Java CI with Maven
+
+on:
+  push:
+    branches: [ "main" ]
+    tags:
+      - 'v*.*.*'
+  pull_request:
+    branches: [ "main" ]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up JDK 17
+      uses: actions/setup-java@v4
+      with:
+        java-version: '17'
+        distribution: 'temurin'
+        cache: maven
+
+    - name: Build with Maven
+      run: mvn -B package
+      working-directory: main
+
+    - name: Upload built JAR
+      uses: actions/upload-artifact@v4
+      with:
+        name: package
+        path: main/target/*.jar
+
+    - name: Generate dependency graph
+      run: mvn -B -f main/pom.xml com.github.ferstl:depgraph-maven-plugin:4.0.1:graph
+
+    - name: Upload dependency graph artifact
+      uses: actions/upload-artifact@v4
+      with:
+        name: dependency-graph
+        path: main/target/**
+
+  publish-release:
+    runs-on: ubuntu-latest
+    needs: [build]
+    if: startsWith(github.ref, 'refs/tags/')
+    permissions:
+      contents: write
+
+    steps:
+    - name: Download built JAR
+      uses: actions/download-artifact@v4
+      with:
+        name: package
+        path: main/target/
+
+    - name: Create GitHub Release
+      uses: softprops/action-gh-release@v2
+      with:
+        files: main/target/*.jar

STEP2_SUMMARY.md

@@ -0,0 +1,134 @@
+# 🏁 Single-Process Prototype — Implementation Summary
+
+**Status:** ✅ Complete
+**Date:** October 22, 2025
+**Branch:** `8-single-process-prototype`
+
+---
+
+## Overview
+
+The single-process prototype implements a **discrete event simulation (DES)** of a 3×3 urban grid with five intersections, realistic vehicle behavior, and fully synchronized traffic lights. Everything runs under one process, laying the groundwork for the distributed architecture in Phase 3.
+
+---
+
+## Core Architecture
+
+### **SimulationEngine**
+
+Drives the DES loop with a priority queue of timestamped events — vehicles, lights, crossings, and periodic stats updates. Handles five intersections (Cr1–Cr5) and six event types.
+
+**Main loop:**
+
+```
+while (events && time < duration):
+    event = nextEvent()
+    time = event.timestamp
+    handle(event)
+```
+
+### **VehicleGenerator**
+
+Spawns vehicles via:
+
+* **Poisson arrivals** (λ = 0.5 veh/s) or fixed intervals
+* **Probabilistic routes** from E1–E3
+* **Type distribution**: 20% BIKE, 60% LIGHT, 20% HEAVY
+
+### **StatisticsCollector**
+
+Tracks system-wide and per-type metrics: throughput, avg. wait, queue sizes, light cycles — updated every 10 s and at simulation end.
+
+---
+
+## Model Highlights
+
+* **Vehicle** – type, route, timings, lifecycle.
+* **Intersection** – routing tables, traffic lights, queues.
+* **TrafficLight** – red/green cycles with FIFO queues.
+* **Event** – timestamped, comparable; 6 types for all DES actions.
+
+---
+
+## Configuration (`simulation.properties`)
+
+```properties
+simulation.duration=60.0
+simulation.arrival.model=POISSON
+simulation.arrival.rate=0.5
+
+vehicle.bike.crossingTime=1.5
+vehicle.light.crossingTime=2.0
+vehicle.heavy.crossingTime=4.0
+
+statistics.update.interval=10.0
+```
+
+**Speed logic:**
+`t_bike = 0.5×t_car`, `t_heavy = 2×t_car`.
+
+---
+
+## Topology
+
+```
+E1→Cr1→Cr4→Cr5→S
+E2→Cr2→Cr5→S
+E3→Cr3→S
+Bi-dir: Cr1↔Cr2, Cr2↔Cr3
+```
+
+---
+
+## Results
+
+**Unit Tests:** 7/7 ✅
+**60-Second Simulation:**
+
+* Generated: 22 vehicles
+* Completed: 5 (22.7%)
+* Avg system time: 15.47 s
+* Throughput: 0.08 veh/s
+* All lights & intersections operational
+
+**Performance:**
+~0.03 s real-time run (≈2000× speed-up), < 50 MB RAM.
+
+---
+
+## Code Structure
+
+```
+sd/
+├── engine/SimulationEngine.java
+├── model/{Vehicle,Intersection,TrafficLight,Event}.java
+├── util/{VehicleGenerator,StatisticsCollector}.java
+└── config/SimulationConfig.java
+```
+
+---
+
+## Key Flow
+
+1. Initialize intersections, lights, first events.
+2. Process events chronologically.
+3. Vehicles follow routes → queue → cross → exit.
+4. Lights toggle, queues drain, stats update.
+5. Print summary and performance metrics.
+
+---
+
+## Next Steps — Phase 3
+
+* Split intersections into independent **processes**.
+* Add **socket-based communication**.
+* Run **traffic lights as threads**.
+* Enable **distributed synchronization** and fault handling.
+
+---
+
+## TL;DR
+
+Solid single-process DES ✅
+Everything’s working — traffic lights, routing, vehicles, stats.
+Ready to go distributed next.

TODO.md

@@ -1,3 +1,26 @@
+## ✅ SINGLE-PROCESS PROTOTYPE - COMPLETED
+
+### Phase 2 Status: DONE ✅
+
+All components for the single-process prototype have been successfully implemented and tested:
+
+- ✅ **SimulationEngine** - Priority queue-based discrete event simulation
+- ✅ **VehicleGenerator** - Poisson and Fixed arrival models
+- ✅ **StatisticsCollector** - Comprehensive metrics tracking
+- ✅ **Entry point** - Main simulation runner
+- ✅ **60s test simulation** - Successfully validated event processing and routing
+
+### Test Results:
+- All 7 unit tests passing
+- 60-second simulation completed successfully
+- Generated 22 vehicles with 5 completing their routes
+- Traffic light state changes working correctly
+- Vehicle routing through intersections validated
+
+---
+
+## NEXT: Distributed Architecture Implementation
+
 ### Compreender os Conceitos Fundamentais
 
 Primeiro, as tecnologias e paradigmas chave necessários para este projeto devem ser totalmente compreendidos.
@@ -16,7 +39,7 @@ Primeiro, as tecnologias e paradigmas chave necessários para este projeto devem
         
     - Uma **lista de eventos** central, frequentemente uma fila de prioridades, será necessária para armazenar eventos futuros, ordenados pelo seu timestamp. O ciclo principal da simulação retira o próximo evento da lista, processa-o e adiciona quaisquer novos eventos que resultem dele.
         
-- **Processo de Poisson:** Para o modelo "mais realista" de chegadas de veículos, é especificado um processo de Poisson. A principal conclusão é que o tempo _entre_ chegadas consecutivas de veículos segue uma **distribuição exponencial**. Em Java, este intervalo pode ser gerado usando `Math.log(1 - Math.random()) / -lambda`, onde `lambda` (λi​) é a taxa de chegada especificada.
+- **Processo de Poisson:** Para o modelo 'mais realista' de chegadas de veículos, é especificado um processo de Poisson. A principal conclusão é que o tempo _entre_ chegadas consecutivas de veículos segue uma **distribuição exponencial**. Em Java, este intervalo pode ser gerado usando `Math.log(1 - Math.random()) / -lambda`, onde `lambda` (λi​) é a taxa de chegada especificada.
     
 
 ---

main/pom.xml

@@ -42,6 +42,26 @@
                     <mainClass>sd.Entry</mainClass>
                 </configuration>
             </plugin>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-shade-plugin</artifactId>
+                <version>3.5.2</version>
+                <executions>
+                    <execution>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>shade</goal>
+                        </goals>
+                        <configuration>
+                            <transformers>
+                                <transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
+                                    <mainClass>sd.Entry</mainClass>
+                                </transformer>
+                            </transformers>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
         </plugins>
     </build>
 

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

@@ -0,0 +1,501 @@
+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.model.Intersection;
+import sd.model.MessageType;
+import sd.model.TrafficLight;
+import sd.model.TrafficLightState;
+import sd.model.Vehicle;
+import sd.protocol.MessageProtocol;
+import sd.protocol.SocketConnection;
+
+/**
+ * Main class for an Intersection Process in the distributed traffic simulation.
+ * * Each IntersectionProcess runs as an independent Java application (JVM instance)
+ * representing one of the five intersections (Cr1-Cr5) in the network.
+ */
+public class IntersectionProcess {
+
+    private final String intersectionId;
+    
+    private final SimulationConfig config;
+    
+    private final Intersection intersection;
+    
+    private ServerSocket serverSocket;
+    
+    private final Map<String, SocketConnection> outgoingConnections;
+    
+    private final ExecutorService connectionHandlerPool;
+    
+    private final ExecutorService trafficLightPool;
+    
+    private volatile boolean running;   //Quando uma thread escreve um valor volatile, todas as outras
+                                        //threads veem a mudança imediatamente.
+    
+    /**
+     * Constructs a new IntersectionProcess.
+     *
+     * @param intersectionId The ID of this intersection (e.g., "Cr1").
+     * @param configFilePath Path to the simulation.properties file.
+     * @throws IOException If configuration cannot be loaded.
+     */
+    public IntersectionProcess(String intersectionId, String configFilePath) throws IOException {
+        this.intersectionId = intersectionId;
+        this.config = new SimulationConfig(configFilePath);
+        this.intersection = new Intersection(intersectionId);
+        this.outgoingConnections = new HashMap<>();
+        this.connectionHandlerPool = Executors.newCachedThreadPool();
+        this.trafficLightPool = Executors.newFixedThreadPool(4); // Max 4 directions
+        this.running = false;
+        
+        System.out.println("=".repeat(60));
+        System.out.println("INTERSECTION PROCESS: " + intersectionId);
+        System.out.println("=".repeat(60));
+    }
+    
+    public void initialize() {
+        System.out.println("\n[" + intersectionId + "] Initializing intersection...");
+        
+        createTrafficLights();
+        
+        configureRouting();
+        
+        startTrafficLights();
+        
+        System.out.println("[" + intersectionId + "] Initialization complete.");
+    }
+
+    /**
+     * Creates traffic lights for this intersection based on its physical connections.
+     * Each intersection has different number and directions of traffic lights
+     * according to the network topology.
+     */
+    private void createTrafficLights() {
+        System.out.println("\n[" + intersectionId + "] Creating traffic lights...");
+        
+        String[] directions = new String[0];
+        switch (intersectionId) {
+            case "Cr1":
+                directions = new String[]{"East", "South"};
+                break;
+            case "Cr2":
+                directions = new String[]{"West", "East", "South"};
+                break;
+            case "Cr3":
+                directions = new String[]{"West", "South"};
+                break;
+            case "Cr4":
+                directions = new String[]{"East"};
+                break;
+            case "Cr5":
+                directions = new String[]{"East"};
+                break;
+        }
+        
+        for (String direction : directions) {
+            double greenTime = config.getTrafficLightGreenTime(intersectionId, direction);
+            double redTime = config.getTrafficLightRedTime(intersectionId, direction);
+            
+            TrafficLight light = new TrafficLight(
+                intersectionId + "-" + direction,
+                direction,
+                greenTime,
+                redTime
+            );
+            
+            intersection.addTrafficLight(light);
+            System.out.println("  Created traffic light: " + direction + 
+                             " (Green: " + greenTime + "s, Red: " + redTime + "s)");
+        }
+    }
+    
+    private void configureRouting() {
+        System.out.println("\n[" + intersectionId + "] Configuring routing...");
+        
+        switch (intersectionId) {
+            case "Cr1":
+                intersection.configureRoute("Cr2", "East");
+                intersection.configureRoute("Cr4", "South"); 
+                break;
+                
+            case "Cr2":
+                intersection.configureRoute("Cr1", "West");
+                intersection.configureRoute("Cr3", "East");
+                intersection.configureRoute("Cr5", "South");
+                break;
+                
+            case "Cr3":
+                intersection.configureRoute("Cr2", "West");
+                intersection.configureRoute("S", "South");
+                break;
+                
+            case "Cr4":
+                intersection.configureRoute("Cr5", "East");
+                break;
+                
+            case "Cr5":
+                intersection.configureRoute("S", "East");
+                break;
+                
+            default:
+                System.err.println("  Error: unknown intersection ID: " + intersectionId);
+        }
+        
+        System.out.println("  Routing configured.");
+    }
+    
+    /**
+     * Starts all traffic light threads.
+     */
+    private void startTrafficLights() {
+        System.out.println("\n[" + intersectionId + "] Starting traffic light threads...");
+        
+        for (TrafficLight light : intersection.getTrafficLights()) {
+            trafficLightPool.submit(() -> runTrafficLightCycle(light));
+            System.out.println("  Started thread for: " + light.getDirection());
+        }
+    }
+    
+    /**
+     * The main loop for a traffic light thread.
+     * Continuously cycles between GREEN and RED states.
+     *
+     * @param light The traffic light to control.
+     */
+    private void runTrafficLightCycle(TrafficLight light) {
+        System.out.println("[" + light.getId() + "] Traffic light thread started.");
+        
+        while (running) {
+            try {
+                // Green state
+                light.changeState(TrafficLightState.GREEN);
+                System.out.println("[" + light.getId() + "] State: GREEN");
+                
+                // Process vehicles while green
+                processGreenLight(light);
+                
+                // Wait for green duration
+                Thread.sleep((long) (light.getGreenTime() * 1000));
+                
+                // RED state
+                light.changeState(TrafficLightState.RED);
+                System.out.println("[" + light.getId() + "] State: RED");
+                
+                // Wait for red duration
+                Thread.sleep((long) (light.getRedTime() * 1000));
+                
+            } catch (InterruptedException e) {
+                System.out.println("[" + light.getId() + "] Traffic light thread interrupted.");
+                break;
+            }
+        }
+        
+        System.out.println("[" + light.getId() + "] Traffic light thread stopped.");
+    }
+    
+    /**
+     * Processes vehicles when a traffic light is GREEN.
+     * Dequeues vehicles and sends them to their next destination.
+     *
+     * @param light The traffic light that is currently green.
+     */
+    private void processGreenLight(TrafficLight light) {
+        while (light.getState() == TrafficLightState.GREEN && light.getQueueSize() > 0) {
+            Vehicle vehicle = light.removeVehicle();
+            
+            if (vehicle != null) {
+                // Get crossing time based on vehicle type
+                double crossingTime = getCrossingTimeForVehicle(vehicle);
+                
+                // Simulate crossing time
+                try {
+                    Thread.sleep((long) (crossingTime * 1000));
+                } catch (InterruptedException e) {
+                    Thread.currentThread().interrupt();
+                    break;
+                }
+                
+                // Update vehicle statistics
+                vehicle.addCrossingTime(crossingTime);
+                
+                // Update intersection statistics
+                intersection.incrementVehiclesSent();
+                
+                // Send vehicle to next destination
+                sendVehicleToNextDestination(vehicle);
+            }
+        }
+    }
+    
+    /**
+     * Gets the crossing time for a vehicle based on its type.
+     *
+     * @param vehicle The vehicle.
+     * @return The crossing time in seconds.
+     */
+    private double getCrossingTimeForVehicle(Vehicle vehicle) {
+        switch (vehicle.getType()) {
+            case BIKE:
+                return config.getBikeVehicleCrossingTime();
+            case LIGHT:
+                return config.getLightVehicleCrossingTime();
+            case HEAVY:
+                return config.getHeavyVehicleCrossingTime();
+            default:
+                return config.getLightVehicleCrossingTime();
+        }
+    }
+    
+    /**
+     * Sends a vehicle to its next destination via socket connection.
+     *
+     * @param vehicle The vehicle that has crossed this intersection.
+     */
+    private void sendVehicleToNextDestination(Vehicle vehicle) {
+        String nextDestination = vehicle.getCurrentDestination();
+        
+        try {
+            // Get or create connection to next destination
+            SocketConnection connection = getOrCreateConnection(nextDestination);
+            
+            // Create and send message
+            MessageProtocol message = new VehicleTransferMessage(
+                intersectionId,
+                nextDestination,
+                vehicle
+            );
+            
+            connection.sendMessage(message);
+            
+            System.out.println("[" + intersectionId + "] Sent vehicle " + vehicle.getId() + 
+                             " to " + nextDestination);
+            
+            // Note: vehicle route is advanced when it arrives at the next intersection
+            
+        } catch (IOException | InterruptedException e) {
+            System.err.println("[" + intersectionId + "] Failed to send vehicle " + 
+                             vehicle.getId() + " to " + nextDestination + ": " + e.getMessage());
+        }
+    }
+    
+    /**
+     * Gets an existing connection to a destination or creates a new one.
+     *
+     * @param destinationId The ID of the destination node.
+     * @return The SocketConnection to that destination.
+     * @throws IOException If connection cannot be established.
+     * @throws InterruptedException If connection attempt is interrupted.
+     */
+    private synchronized SocketConnection getOrCreateConnection(String destinationId) 
+            throws IOException, InterruptedException {
+        
+        if (!outgoingConnections.containsKey(destinationId)) {
+            String host = getHostForDestination(destinationId);
+            int port = getPortForDestination(destinationId);
+            
+            System.out.println("[" + intersectionId + "] Creating connection to " + 
+                             destinationId + " at " + host + ":" + port);
+            
+            SocketConnection connection = new SocketConnection(host, port);
+            outgoingConnections.put(destinationId, connection);
+        }
+        
+        return outgoingConnections.get(destinationId);
+    }
+    
+    /**
+     * Gets the host address for a destination node from configuration.
+     *
+     * @param destinationId The destination node ID.
+     * @return The host address.
+     */
+    private String getHostForDestination(String destinationId) {
+        if (destinationId.equals("S")) {
+            return config.getExitHost();
+        } else {
+            return config.getIntersectionHost(destinationId);
+        }
+    }
+    
+    /**
+     * Gets the port number for a destination node from configuration.
+     *
+     * @param destinationId The destination node ID.
+     * @return The port number.
+     */
+    private int getPortForDestination(String destinationId) {
+        if (destinationId.equals("S")) {
+            return config.getExitPort();
+        } else {
+            return config.getIntersectionPort(destinationId);
+        }
+    }
+    
+    /**
+     * Starts the server socket and begins accepting incoming connections.
+     * This is the main listening loop of the process.
+     *
+     * @throws IOException If the server socket cannot be created.
+     */
+    public void start() throws IOException {
+        int port = config.getIntersectionPort(intersectionId);
+        serverSocket = new ServerSocket(port);
+        running = true;
+        
+        System.out.println("\n[" + intersectionId + "] Server started on port " + port);
+        System.out.println("[" + intersectionId + "] Waiting for incoming connections...\n");
+        
+        // Main accept loop
+        while (running) {
+            try {
+                Socket clientSocket = serverSocket.accept();
+                
+                // Handle each connection in a separate thread
+                connectionHandlerPool.submit(() -> handleIncomingConnection(clientSocket));
+                
+            } catch (IOException e) {
+                if (running) {
+                    System.err.println("[" + intersectionId + "] Error accepting connection: " + 
+                                     e.getMessage());
+                }
+            }
+        }
+    }
+    
+    /**
+     * Handles an incoming connection from another process.
+     * Continuously listens for vehicle transfer messages.
+     *
+     * @param clientSocket The accepted socket connection.
+     */
+    private void handleIncomingConnection(Socket clientSocket) {
+        try (SocketConnection connection = new SocketConnection(clientSocket)) {
+            
+            System.out.println("[" + intersectionId + "] New connection accepted from " +
+                             clientSocket.getInetAddress().getHostAddress());
+            
+            // Continuously receive messages while connection is active
+            while (running && connection.isConnected()) {
+                try {
+                    MessageProtocol message = connection.receiveMessage();
+                    
+                    if (message.getType() == MessageType.VEHICLE_TRANSFER) {
+                        Vehicle vehicle = (Vehicle) message.getPayload();
+                        
+                        System.out.println("[" + intersectionId + "] Received vehicle: " + 
+                                         vehicle.getId() + " from " + message.getSourceNode());
+                        
+                        // Add vehicle to appropriate queue
+                        intersection.receiveVehicle(vehicle);
+                    }
+                    
+                } catch (ClassNotFoundException e) {
+                    System.err.println("[" + intersectionId + "] Unknown message type received: " + 
+                                     e.getMessage());
+                }
+            }
+            
+        } catch (IOException e) {
+            if (running) {
+                System.err.println("[" + intersectionId + "] Connection error: " + e.getMessage());
+            }
+        }
+    }
+    
+    /**
+     * Stops the intersection process gracefully.
+     * Shuts down all threads and closes all connections.
+     */
+    public void shutdown() {
+        System.out.println("\n[" + intersectionId + "] Shutting down...");
+        running = false;
+        
+        // Close server socket
+        try {
+            if (serverSocket != null && !serverSocket.isClosed()) {
+                serverSocket.close();
+            }
+        } catch (IOException e) {
+            System.err.println("[" + intersectionId + "] Error closing server socket: " + 
+                             e.getMessage());
+        }
+        
+        // Shutdown thread pools
+        trafficLightPool.shutdown();
+        connectionHandlerPool.shutdown();
+        
+        try {
+            if (!trafficLightPool.awaitTermination(5, TimeUnit.SECONDS)) {
+                trafficLightPool.shutdownNow();
+            }
+            if (!connectionHandlerPool.awaitTermination(5, TimeUnit.SECONDS)) {
+                connectionHandlerPool.shutdownNow();
+            }
+        } catch (InterruptedException e) {
+            trafficLightPool.shutdownNow();
+            connectionHandlerPool.shutdownNow();
+        }
+        
+        // Close all outgoing connections
+        for (Map.Entry<String, SocketConnection> entry : outgoingConnections.entrySet()) {
+            try {
+                entry.getValue().close();
+            } catch (IOException e) {
+                System.err.println("[" + intersectionId + "] Error closing connection to " + 
+                                 entry.getKey() + ": " + e.getMessage());
+            }
+        }
+        
+        System.out.println("[" + intersectionId + "] Shutdown complete.");
+        System.out.println("=".repeat(60));
+    }
+    
+    // --- Inner class for Vehicle Transfer Messages ---
+    
+    /**
+     * Implementation of MessageProtocol for vehicle transfers between processes.
+     */
+    private static class VehicleTransferMessage implements MessageProtocol {
+        private static final long serialVersionUID = 1L;
+        
+        private final String sourceNode;
+        private final String destinationNode;
+        private final Vehicle payload;
+        
+        public VehicleTransferMessage(String sourceNode, String destinationNode, Vehicle vehicle) {
+            this.sourceNode = sourceNode;
+            this.destinationNode = destinationNode;
+            this.payload = vehicle;
+        }
+        
+        @Override
+        public MessageType getType() {
+            return MessageType.VEHICLE_TRANSFER;
+        }
+        
+        @Override
+        public Object getPayload() {
+            return payload;
+        }
+        
+        @Override
+        public String getSourceNode() {
+            return sourceNode;
+        }
+        
+        @Override
+        public String getDestinationNode() {
+            return destinationNode;
+        }
+    }
+}

main/src/main/java/sd/config/SimulationConfig.java

@@ -31,7 +31,7 @@ public class SimulationConfig {
          * (por exemplo quando executado a partir do classpath/jar),
          * faz fallback para carregar a partir do classpath usando o ClassLoader.
         */
-        IOException lastException = null;
+        IOException lastException = null; //FIXME: melhorar esta parte para reportar erros de forma mais clara
 
         try {
             try (InputStream input = new FileInputStream(filePath)) {

main/src/main/java/sd/engine/SimulationEngine.java

@@ -264,32 +264,19 @@ public class SimulationEngine {
      */
     private void processEvent(Event event) {
         switch (event.getType()) {
-            case VEHICLE_GENERATION:
+            case VEHICLE_GENERATION -> handleVehicleGeneration();
-                handleVehicleGeneration();
-                break;
                 
-            case VEHICLE_ARRIVAL:
+            case VEHICLE_ARRIVAL -> handleVehicleArrival(event);
-                handleVehicleArrival(event);
-                break;
                 
-            case TRAFFIC_LIGHT_CHANGE:
+            case TRAFFIC_LIGHT_CHANGE -> handleTrafficLightChange(event);
-                handleTrafficLightChange(event);
-                break;
                 
-            case CROSSING_START:
+            case CROSSING_START -> handleCrossingStart(event);
-                handleCrossingStart(event);
-                break;
                 
-            case CROSSING_END:
+            case CROSSING_END -> handleCrossingEnd(event);
-                handleCrossingEnd(event);
-                break;
                 
-            case STATISTICS_UPDATE:
+            case STATISTICS_UPDATE -> handleStatisticsUpdate();
-                handleStatisticsUpdate();
-                break;
                 
-            default:
+            default -> System.err.println("Unknown event type: " + event.getType());
-                System.err.println("Unknown event type: " + event.getType());
         }
     }
     
@@ -386,7 +373,7 @@ public class SimulationEngine {
      * @param vehicle The vehicle to process.
      * @param intersection The intersection where the vehicle is.
      */
-    private void tryProcessVehicle(Vehicle vehicle, Intersection intersection) {
+    private void tryProcessVehicle(Vehicle vehicle, Intersection intersection) { //FIXME
         // Find the direction (and light) this vehicle is queued at
         // This logic is a bit flawed: it just finds the *first* non-empty queue
         // A better approach would be to get the light from the vehicle's route
@@ -591,16 +578,12 @@ public class SimulationEngine {
      * @return The crossing time in seconds.
      */
     private double getCrossingTime(VehicleType type) {
-        switch (type) {
+        return switch (type) {
-            case BIKE:
+            case BIKE -> config.getBikeVehicleCrossingTime();
-                return config.getBikeVehicleCrossingTime();
+            case LIGHT -> config.getLightVehicleCrossingTime();
-            case LIGHT:
+            case HEAVY -> config.getHeavyVehicleCrossingTime();
-                return config.getLightVehicleCrossingTime();
+            default -> 2.0;
-            case HEAVY:
+        }; // Default fallback
-                return config.getHeavyVehicleCrossingTime();
-            default:
-                return 2.0; // Default fallback
-        }
     }
     
     /**

main/src/main/java/sd/model/Intersection.java

@@ -104,16 +104,28 @@ public class Intersection {
      * Accepts an incoming vehicle and places it in the correct queue.
      * * This method:
      * 1. Increments the {@link #totalVehiclesReceived} counter.
-     * 2. Gets the vehicle's *next* destination (from {@link Vehicle#getCurrentDestination()}).
+     * 2. Advances the vehicle's route (since it just arrived here)
-     * 3. Uses the {@link #routing} map to find the correct *direction* for that destination.
+     * 3. Gets the vehicle's *next* destination (from {@link Vehicle#getCurrentDestination()}).
-     * 4. Adds the vehicle to the queue of the {@link TrafficLight} for that direction.
+     * 4. Uses the {@link #routing} map to find the correct *direction* for that destination.
+     * 5. Adds the vehicle to the queue of the {@link TrafficLight} for that direction.
      *
      * @param vehicle The {@link Vehicle} arriving at the intersection.
      */
     public void receiveVehicle(Vehicle vehicle) {
         totalVehiclesReceived++;
 
+        // Advance route since vehicle just arrived at this intersection
+        vehicle.advanceRoute();
+        
         String nextDestination = vehicle.getCurrentDestination();
+        
+        // Check if vehicle reached final destination
+        if (nextDestination == null) {
+            System.out.printf("[%s] Vehicle %s reached final destination%n", 
+                this.id, vehicle.getId());
+            return;
+        }
+        
         String direction = routing.get(nextDestination);
 
         if (direction != null && trafficLights.containsKey(direction)) {

main/src/main/java/sd/protocol/MessageProtocol.java

@@ -0,0 +1,41 @@
+package sd.protocol;
+
+import java.io.Serializable;
+import sd.model.MessageType; // Assuming MessageType is in sd.model or sd.protocol
+
+/**
+ * Interface defining the contract for all messages exchanged in the simulator.
+ * Ensures that any message can be identified and routed.
+ * * This interface extends Serializable to allow objects that implement it
+ * to be sent over Sockets (ObjectOutputStream).
+ *
+ */
+public interface MessageProtocol extends Serializable {
+
+    /**
+     * Returns the type of the message, indicating its purpose.
+     * @return The MessageType (e.g., VEHICLE_TRANSFER, STATS_UPDATE).
+     */
+    MessageType getType();
+
+    /**
+     * Returns the data object (payload) that this message carries.
+     * The type of object will depend on the MessageType.
+     * * - If getType() == VEHICLE_TRANSFER, the payload will be a {@link sd.model.Vehicle} object.
+     * - If getType() == STATS_UPDATE, the payload will be a statistics object.
+     * * @return The data object (payload), which must also be Serializable.
+     */
+    Object getPayload();
+
+    /**
+     * Returns the ID of the node (Process) that sent this message.
+     * @return String (e.g., "Cr1", "Cr5", "S").
+     */
+    String getSourceNode();
+
+    /**
+     * Returns the ID of the destination node (Process) for this message.
+     * @return String (e.g., "Cr2", "DashboardServer").
+     */
+    String getDestinationNode();
+}

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

@@ -0,0 +1,183 @@
+package sd.protocol; 
+
+import java.io.Closeable;
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+import java.net.ConnectException;
+import java.net.Socket;
+import java.net.SocketTimeoutException;
+import java.net.UnknownHostException;
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Wrapper class that simplifies communication via Sockets.
+ * Includes connection retry logic for robustness.
+ */
+public class SocketConnection implements Closeable {
+
+    private final Socket socket;
+    private final ObjectOutputStream outputStream;
+    private final ObjectInputStream inputStream;
+
+    // --- Configuration for Retry Logic ---
+    /** Maximum number of connection attempts. */
+    private static final int MAX_RETRIES = 5; 
+    /** Delay between retry attempts in milliseconds. */
+    private static final long RETRY_DELAY_MS = 1000; 
+
+    /**
+     * Constructor for the "Client" (who initiates the connection).
+     * Tries to connect to a process that is already listening (Server).
+     * Includes retry logic in case of initial connection failure.
+     *
+     * @param host The host address (e.g., "localhost" from your simulation.properties)
+     * @param port The port (e.g., 8001 from your simulation.properties)
+     * @throws IOException If connection fails after all retries.
+     * @throws UnknownHostException If the host is not found (this error usually doesn't need retry).
+     * @throws InterruptedException If the thread is interrupted while waiting between retries.
+     */
+    public SocketConnection(String host, int port) throws IOException, UnknownHostException, InterruptedException {
+        Socket tempSocket = null;
+        IOException lastException = null;
+
+        System.out.printf("[SocketConnection] Attempting to connect to %s:%d...%n", host, port);
+
+        // --- Retry Loop ---
+        for (int attempt = 1; attempt <= MAX_RETRIES; attempt++) {
+            try {
+                // Try to establish the connection
+                tempSocket = new Socket(host, port);
+
+                // If successful, break out of the retry loop
+                System.out.printf("[SocketConnection] Connected successfully on attempt %d.%n", attempt);
+                lastException = null; // Clear last error on success
+                break;
+
+            } catch (ConnectException | SocketTimeoutException e) {
+                // These are common errors indicating the server might not be ready.
+                lastException = e;
+                System.out.printf("[SocketConnection] Attempt %d/%d failed: %s. Retrying in %d ms...%n",
+                        attempt, MAX_RETRIES, e.getMessage(), RETRY_DELAY_MS);
+
+                if (attempt < MAX_RETRIES) {
+                    // Wait before the next attempt
+                    TimeUnit.MILLISECONDS.sleep(RETRY_DELAY_MS);
+                }
+            } catch (IOException e) {
+                // Other IOExceptions might be more permanent, but we retry anyway.
+                 lastException = e;
+                 System.out.printf("[SocketConnection] Attempt %d/%d failed with IOException: %s. Retrying in %d ms...%n",
+                        attempt, MAX_RETRIES, e.getMessage(), RETRY_DELAY_MS);
+                 if (attempt < MAX_RETRIES) {
+                     TimeUnit.MILLISECONDS.sleep(RETRY_DELAY_MS);
+                 }
+            }
+        } // --- End of Retry Loop ---
+
+        // If after all retries tempSocket is still null, it means connection failed permanently.
+        if (tempSocket == null) {
+            System.err.printf("[SocketConnection] Failed to connect to %s:%d after %d attempts.%n", host, port, MAX_RETRIES);
+            if (lastException != null) {
+                 throw lastException; // Throw the last exception encountered
+            } else {
+                 // Should not happen if loop ran, but as a fallback
+                 throw new IOException("Failed to connect after " + MAX_RETRIES + " attempts, reason unknown.");
+            }
+        }
+
+        // If connection was successful, assign to final variable and create streams
+        this.socket = tempSocket;
+        try {
+            // IMPORTANT: The order is crucial. OutputStream first.
+            this.outputStream = new ObjectOutputStream(socket.getOutputStream());
+            this.inputStream = new ObjectInputStream(socket.getInputStream());
+        } 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
+        }
+    }
+
+
+    /**
+     * Constructor for the "Server" (who accepts the connection).
+     * Receives a Socket that has already been accepted by a ServerSocket.
+     * No retry logic needed here as the connection is already established.
+     *
+     * @param acceptedSocket The Socket returned by serverSocket.accept().
+     * @throws IOException If stream creation fails.
+     */
+    public SocketConnection(Socket acceptedSocket) throws IOException {
+        this.socket = acceptedSocket;
+
+        // IMPORTANT: The order is crucial. OutputStream first.
+        this.outputStream = new ObjectOutputStream(socket.getOutputStream());
+        this.inputStream = new ObjectInputStream(socket.getInputStream());
+        System.out.printf("[SocketConnection] Connection accepted from %s:%d.%n",
+            acceptedSocket.getInetAddress().getHostAddress(), acceptedSocket.getPort());
+    }
+
+    /**
+     * Sends (serializes) a MessageProtocol object over the socket.
+     *
+     * @param message The "envelope" (which contains the Vehicle) to be sent.
+     * @throws IOException If writing to the stream fails or socket is not connected.
+     */
+    public void sendMessage(MessageProtocol message) throws IOException {
+        if (!isConnected()) {
+            throw new IOException("Socket is not connected.");
+        }
+        synchronized (outputStream) {
+            outputStream.writeObject(message);
+            outputStream.flush(); // Ensures the message is sent immediately.
+        }
+    }
+
+    /**
+     * 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()) {
+            throw new IOException("Socket is not connected.");
+        }
+        synchronized (inputStream) {
+            return (MessageProtocol) inputStream.readObject();
+        }
+    }
+
+    /**
+     * 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",
+            socket != null ? socket.getInetAddress().getHostAddress() : "N/A",
+            socket != null ? socket.getPort() : -1);
+        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();
+        }
+    }
+
+    /**
+     * @return true if the socket is still connected and not closed.
+     */
+    public boolean isConnected() {
+        return socket != null && socket.isConnected() && !socket.isClosed();
+    }
+}

main/src/test/java/IntersectionProcessTest.java

@@ -0,0 +1,473 @@
+import java.io.IOException;
+import java.io.ObjectOutputStream;
+import java.net.Socket;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+
+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.IntersectionProcess;
+import sd.model.MessageType;
+import sd.model.Vehicle;
+import sd.model.VehicleType;
+
+/**
+ * Tests for IntersectionProcess - covers initialization, traffic lights, 
+ * vehicle transfer and network stuff
+ */
+public class IntersectionProcessTest {
+
+    @TempDir
+    Path tempDir;
+
+    private Path configFile;
+    private IntersectionProcess intersectionProcess;
+
+    // setup test config before each test
+    @BeforeEach
+    public void setUp() throws IOException {
+        // create temp config file
+        configFile = tempDir.resolve("test-simulation.properties");
+        
+        String configContent = """
+                # Test Simulation Configuration
+                
+                # Intersection Network Configuration
+                intersection.Cr1.host=localhost
+                intersection.Cr1.port=18001
+                intersection.Cr2.host=localhost
+                intersection.Cr2.port=18002
+                intersection.Cr3.host=localhost
+                intersection.Cr3.port=18003
+                intersection.Cr4.host=localhost
+                intersection.Cr4.port=18004
+                intersection.Cr5.host=localhost
+                intersection.Cr5.port=18005
+                
+                # Exit Configuration
+                exit.host=localhost
+                exit.port=18099
+                
+                # Dashboard Configuration
+                dashboard.host=localhost
+                dashboard.port=18100
+                
+                # Traffic Light Timing (seconds)
+                trafficLight.Cr1.East.greenTime=5.0
+                trafficLight.Cr1.East.redTime=5.0
+                trafficLight.Cr1.South.greenTime=5.0
+                trafficLight.Cr1.South.redTime=5.0
+                trafficLight.Cr1.West.greenTime=5.0
+                trafficLight.Cr1.West.redTime=5.0
+                
+                trafficLight.Cr2.West.greenTime=4.0
+                trafficLight.Cr2.West.redTime=6.0
+                trafficLight.Cr2.East.greenTime=4.0
+                trafficLight.Cr2.East.redTime=6.0
+                trafficLight.Cr2.South.greenTime=4.0
+                trafficLight.Cr2.South.redTime=6.0
+                
+                trafficLight.Cr3.West.greenTime=3.0
+                trafficLight.Cr3.West.redTime=7.0
+                trafficLight.Cr3.East.greenTime=3.0
+                trafficLight.Cr3.East.redTime=7.0
+                
+                trafficLight.Cr4.East.greenTime=6.0
+                trafficLight.Cr4.East.redTime=4.0
+                
+                trafficLight.Cr5.East.greenTime=5.0
+                trafficLight.Cr5.East.redTime=5.0
+                
+                # Vehicle Crossing Times (seconds)
+                vehicle.bike.crossingTime=2.0
+                vehicle.light.crossingTime=3.0
+                vehicle.heavy.crossingTime=5.0
+                """;
+        
+        Files.writeString(configFile, configContent);
+    }
+
+    // cleanup after tests
+    @AfterEach
+    public void tearDown() {
+        if (intersectionProcess != null) {
+            intersectionProcess.shutdown();
+        }
+    }
+
+    // ==================== Initialization Tests ====================
+
+    @Test
+    public void testConstructor_Success() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr1", configFile.toString());
+        assertNotNull(intersectionProcess);
+    }
+
+    @Test
+    public void testConstructor_InvalidConfig() {
+        Exception exception = assertThrows(IOException.class, () -> {
+            new IntersectionProcess("Cr1", "non-existent-config.properties");
+        });
+        assertNotNull(exception);
+    }
+
+    @Test
+    public void testInitialize_Cr1() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr1", configFile.toString());
+        assertDoesNotThrow(() -> intersectionProcess.initialize());
+    }
+
+    @Test
+    public void testInitialize_Cr2() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr2", configFile.toString());
+        assertDoesNotThrow(() -> intersectionProcess.initialize());
+    }
+
+    @Test
+    public void testInitialize_Cr3() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr3", configFile.toString());
+        assertDoesNotThrow(() -> intersectionProcess.initialize());
+    }
+
+    @Test
+    public void testInitialize_Cr4() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr4", configFile.toString());
+        assertDoesNotThrow(() -> intersectionProcess.initialize());
+    }
+
+    @Test
+    public void testInitialize_Cr5() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr5", configFile.toString());
+        assertDoesNotThrow(() -> intersectionProcess.initialize());
+    }
+
+    // traffic light creation tests
+
+    @Test
+    public void testTrafficLightCreation_Cr1_HasCorrectDirections() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr1", configFile.toString());
+        intersectionProcess.initialize();
+        
+        // cant access private fields but initialization succeds
+        assertNotNull(intersectionProcess);
+    }
+
+    @Test
+    public void testTrafficLightCreation_Cr3_HasCorrectDirections() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr3", configFile.toString());
+        intersectionProcess.initialize();
+        
+        // Cr3 has west and south only
+        assertNotNull(intersectionProcess);
+    }
+
+    @Test
+    public void testTrafficLightCreation_Cr4_HasSingleDirection() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr4", configFile.toString());
+        intersectionProcess.initialize();
+        
+        // Cr4 only has east direction
+        assertNotNull(intersectionProcess);
+    }
+
+    // server startup tests
+
+    @Test
+    @Timeout(5)
+    public void testServerStart_BindsToCorrectPort() throws IOException, InterruptedException {
+        intersectionProcess = new IntersectionProcess("Cr1", configFile.toString());
+        intersectionProcess.initialize();
+        
+        // start server in seperate thread
+        Thread serverThread = new Thread(() -> {
+            try {
+                intersectionProcess.start();
+            } catch (IOException e) {
+                // expected on shutdown
+            }
+        });
+        serverThread.start();
+        
+        Thread.sleep(500); // wait for server to start
+        
+        // try connecting to check if its running
+        try (Socket clientSocket = new Socket("localhost", 18001)) {
+            assertTrue(clientSocket.isConnected());
+        }
+        
+        intersectionProcess.shutdown();
+        serverThread.join(2000);
+    }
+
+    @Test
+    @Timeout(5)
+    public void testServerStart_MultipleIntersections() throws IOException, InterruptedException {
+        // test 2 intersections on diferent ports
+        IntersectionProcess cr1 = new IntersectionProcess("Cr1", configFile.toString());
+        IntersectionProcess cr2 = new IntersectionProcess("Cr2", configFile.toString());
+        
+        cr1.initialize();
+        cr2.initialize();
+        
+        Thread thread1 = new Thread(() -> {
+            try { cr1.start(); } catch (IOException e) { }
+        });
+        
+        Thread thread2 = new Thread(() -> {
+            try { cr2.start(); } catch (IOException e) { }
+        });
+        
+        thread1.start();
+        thread2.start();
+        
+        Thread.sleep(500);
+        
+        // check both are running
+        try (Socket socket1 = new Socket("localhost", 18001);
+             Socket socket2 = new Socket("localhost", 18002)) {
+            assertTrue(socket1.isConnected());
+            assertTrue(socket2.isConnected());
+        }
+        
+        cr1.shutdown();
+        cr2.shutdown();
+        thread1.join(2000);
+        thread2.join(2000);
+    }
+
+    // vehicle transfer tests
+
+    @Test
+    @Timeout(10)
+    public void testVehicleTransfer_ReceiveVehicle() throws IOException, InterruptedException {
+        // setup reciever intersection
+        intersectionProcess = new IntersectionProcess("Cr2", configFile.toString());
+        intersectionProcess.initialize();
+        
+        Thread serverThread = new Thread(() -> {
+            try {
+                intersectionProcess.start();
+            } catch (IOException e) { }
+        });
+        serverThread.start();
+        
+        Thread.sleep(500);
+        
+        // create test vehicle
+        java.util.List<String> route = Arrays.asList("Cr2", "Cr3", "S");
+        Vehicle vehicle = new Vehicle("V001", VehicleType.LIGHT, 0.0, route);
+        
+        // send vehicle from Cr1 to Cr2
+        try (Socket socket = new Socket("localhost", 18002)) {
+            ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
+            
+            TestVehicleMessage message = new TestVehicleMessage("Cr1", "Cr2", vehicle);
+            out.writeObject(message);
+            out.flush();
+            
+            Thread.sleep(1000); // wait for procesing
+        }
+        
+        intersectionProcess.shutdown();
+        serverThread.join(2000);
+    }
+
+    // routing config tests
+
+    @Test
+    public void testRoutingConfiguration_Cr1() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr1", configFile.toString());
+        intersectionProcess.initialize();
+        
+        // indirect test - if init works routing should be ok
+        assertNotNull(intersectionProcess);
+    }
+
+    @Test
+    public void testRoutingConfiguration_Cr5() throws IOException {
+        intersectionProcess = new IntersectionProcess("Cr5", configFile.toString());
+        intersectionProcess.initialize();
+        
+        // Cr5 routes to exit
+        assertNotNull(intersectionProcess);
+    }
+
+    // shutdown tests
+
+    @Test
+    @Timeout(5)
+    public void testShutdown_GracefulTermination() throws IOException, InterruptedException {
+        intersectionProcess = new IntersectionProcess("Cr1", configFile.toString());
+        intersectionProcess.initialize();
+        
+        Thread serverThread = new Thread(() -> {
+            try {
+                intersectionProcess.start();
+            } catch (IOException e) { }
+        });
+        serverThread.start();
+        
+        Thread.sleep(500);
+        
+        // shutdown should be fast
+        assertDoesNotThrow(() -> intersectionProcess.shutdown());
+        
+        serverThread.join(2000);
+    }
+
+    @Test
+    @Timeout(5)
+    public void testShutdown_ClosesServerSocket() throws IOException, InterruptedException {
+        intersectionProcess = new IntersectionProcess("Cr1", configFile.toString());
+        intersectionProcess.initialize();
+        
+        Thread serverThread = new Thread(() -> {
+            try {
+                intersectionProcess.start();
+            } catch (IOException e) { }
+        });
+        serverThread.start();
+        
+        Thread.sleep(500);
+        
+        // verify server running
+        try (Socket socket = new Socket("localhost", 18001)) {
+            assertTrue(socket.isConnected());
+        }
+        
+        intersectionProcess.shutdown();
+        serverThread.join(2000);
+        
+        // after shutdown conection should fail
+        Thread.sleep(500);
+        Exception exception = assertThrows(IOException.class, () -> {
+            Socket socket = new Socket("localhost", 18001);
+            socket.close();
+        });
+        assertNotNull(exception);
+    }
+
+    @Test
+    @Timeout(5)
+    public void testShutdown_StopsTrafficLightThreads() throws IOException, InterruptedException {
+        intersectionProcess = new IntersectionProcess("Cr1", configFile.toString());
+        intersectionProcess.initialize();
+        
+        Thread serverThread = new Thread(() -> {
+            try {
+                intersectionProcess.start();
+            } catch (IOException e) { }
+        });
+        serverThread.start();
+        
+        Thread.sleep(500);
+        
+        int threadCountBefore = Thread.activeCount();
+        
+        intersectionProcess.shutdown();
+        serverThread.join(2000);
+        
+        Thread.sleep(500); // wait for threads to die
+        
+        // thread count should decrese (traffic light threads stop)
+        int threadCountAfter = Thread.activeCount();
+        assertTrue(threadCountAfter <= threadCountBefore);
+    }
+
+    // integration tests
+
+    @Test
+    @Timeout(15)
+    public void testIntegration_TwoIntersectionsVehicleTransfer() throws IOException, InterruptedException {
+        // setup 2 intersections
+        IntersectionProcess cr1 = new IntersectionProcess("Cr1", configFile.toString());
+        IntersectionProcess cr2 = new IntersectionProcess("Cr2", configFile.toString());
+        
+        cr1.initialize();
+        cr2.initialize();
+        
+        // start both
+        Thread thread1 = new Thread(() -> {
+            try { cr1.start(); } catch (IOException e) { }
+        });
+        
+        Thread thread2 = new Thread(() -> {
+            try { cr2.start(); } catch (IOException e) { }
+        });
+        
+        thread1.start();
+        thread2.start();
+        
+        Thread.sleep(1000); // wait for servers
+        
+        // send vehicle to Cr1 that goes to Cr2
+        java.util.List<String> route = Arrays.asList("Cr1", "Cr2", "S");
+        Vehicle vehicle = new Vehicle("V001", VehicleType.LIGHT, 0.0, route);
+        
+        try (Socket socket = new Socket("localhost", 18001)) {
+            ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
+            
+            TestVehicleMessage message = new TestVehicleMessage("Entry", "Cr1", vehicle);
+            out.writeObject(message);
+            out.flush();
+            
+            Thread.sleep(2000); // time for processing
+        }
+        
+        cr1.shutdown();
+        cr2.shutdown();
+        thread1.join(2000);
+        thread2.join(2000);
+    }
+
+    @Test
+    public void testMain_MissingArguments() {
+        // main needs intersection ID as argument
+        // cant test System.exit easily in modern java
+        assertTrue(true, "Main method expects intersection ID as first argument");
+    }
+
+    // helper class for testing vehicle messages
+    private static class TestVehicleMessage implements sd.protocol.MessageProtocol {
+        private static final long serialVersionUID = 1L;
+        
+        private final String sourceNode;
+        private final String destinationNode;
+        private final Vehicle payload;
+        
+        public TestVehicleMessage(String sourceNode, String destinationNode, Vehicle vehicle) {
+            this.sourceNode = sourceNode;
+            this.destinationNode = destinationNode;
+            this.payload = vehicle;
+        }
+        
+        @Override
+        public MessageType getType() {
+            return MessageType.VEHICLE_TRANSFER;
+        }
+        
+        @Override
+        public Object getPayload() {
+            return payload;
+        }
+        
+        @Override
+        public String getSourceNode() {
+            return sourceNode;
+        }
+        
+        @Override
+        public String getDestinationNode() {
+            return destinationNode;
+        }
+    }
+}

main/src/test/java/SimulationTest.java

@@ -43,7 +43,7 @@ class SimulationTest {
         assertEquals("TEST1", vehicle.getId());
         assertNotNull(vehicle.getType());
         assertNotNull(vehicle.getRoute());
-        assertTrue(vehicle.getRoute().size() > 0);
+        assertTrue(!vehicle.getRoute().isEmpty());
     }
     
     @Test