Add traffic light coordination and tests

Sorry to add this on this branch ahah

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/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");
+    }
+}