MainEngine.java

import java.util.*;

public class MainEngine {
    
    public static void main(String[] args) {
        System.out.println(" Starting Routing Simulator...\n");
        
        // STEP 1: Load routers from config file
        // List<Router> routers = Initializer.loadRouters("config.txt");
        // Change this filename if you want to java MainEnginetest different configs!

        String configFile = "config3.txt"; // Try: config.txt, config2.txt, config3.txt
        List<Router> routers = Initializer.loadRouters(configFile);
        
        if (routers.isEmpty()) {
            System.out.println(" No routers loaded. Check your config.txt file!");
            return;
        }
        
        // STEP 2: Run Builder and Listener (simulate routing protocol)
        System.out.println(" Routers exchanging routing information...\n");
        
        // Run multiple rounds to let routing tables converge
        for (int round = 1; round <= 5; round++) {
            System.out.println("--- Round " + round + " ---");
            
            // Each router builds and sends packets
            for (Router sender : routers) {
                String packet = sender.builder();
                
                // All other routers listen to this packet
                for (Router receiver : routers) {
                    if (!receiver.getName().equals(sender.getName())) {
                        receiver.listener(packet, routers);
                    }
                }
            }
        }
        
        System.out.println("\n Routing tables converged!\n");
        
        // Display all routing tables
        for (Router router : routers) {
            router.displayTable();
        }
        
        // STEP 3: Test change_cost
        System.out.println("\n Testing CHANGE_COST...\n");
        
        // Find R1 and change cost to its second neighbor
        Router r1 = findRouter(routers, "R1");
        if (r1 != null) {
            // Get R1's neighbors
            List<String> neighborNames = new ArrayList<>(r1.getNeighbors().keySet());
            if (neighborNames.size() >= 2) {
                String secondNeighbor = neighborNames.get(1);
                System.out.println("Changing cost between R1 and " + secondNeighbor + " to 400\n");
                r1.changeCost(secondNeighbor, 400);
                
                // Re-run routing protocol after change
                for (int round = 1; round <= 5; round++) {
                    for (Router sender : routers) {
                        String packet = sender.builder();
                        for (Router receiver : routers) {
                            if (!receiver.getName().equals(sender.getName())) {
                                receiver.listener(packet, routers);
                            }
                        }
                    }
                }
                
                System.out.println("\n Updated Routing Tables:\n");
                for (Router router : routers) {
                    router.displayTable();
                }
            }
        }
        
        System.out.println(" Simulation complete!");
    }
    
    // Helper method to find a router by name
    private static Router findRouter(List<Router> routers, String name) {
        for (Router r : routers) {
            if (r.getName().equals(name)) {
                return r;
            }
        }
        return null;
    }
}