app.py

import csv
import sys
import os

router_matrix = []
matrix_set = 0
nodes = []
distances = {}
unvisited = {}
previous = {}
visited = {}
interface = {}
path = []
start = 0
end = 0

# Function to print the choices when program starts.

def print_choices():

    os.system("figlet Link State Routing Simulator")
    print("\n######################################################\n")
    print("(1) Input Network Topology File")
    print("(2) Build a Connection Table")
    print("(3) Shortest Path to Destination Router")
    print("(4) Exit")
    print("\n######################################################\n")
    pass


def check_choices(command):
    
    if not command.isdigit():
        print("Please enter a number as command from given choices..")
        return -1
    else:
        command = int(command)
        
        if command > 4 or command < 1 :
            print("Please enter a valid command from given choices..")
            return -1
        else:
            return command


# Function to process the given input file.


def process_file(fname):
    
    global matrix_set
    global router_matrix
    matrix_set = 0
    router_matrix = []

    with open(fname) as f:
        router_matrix=[list(map(int,x.split())) for x in f]      # Data from input file is stored in a two dimensional list(array).
    matrix_set = 1

    print("\nReview original topology matrix:\n")
    for line in router_matrix :
        for item in line :
            print(item, end=' ')
        print()
    print()

    set_distances(router_matrix)        # Distances are stored in a dictionary - key,value pair - with source router as key and distances in form of a dictionary as value.


# Function to store the distances in dictionary format.


def set_distances(router_matrix):

    global distances
    global nodes
    
    distances = {}
    nodes = []

    num_nodes = len(router_matrix)

    for i in range(num_nodes):
        tempdict = {}
        for j in range(num_nodes):
            if i!=j and router_matrix[i][j]!=-1:
                tempdict[j+1] = router_matrix[i][j]
        distances[i+1] = tempdict
        nodes.append(i+1)
    
    # print("Distances:- \n",distances)
    # print("Nodes:- \n",nodes)

def dijkstra(start):

    global distances
    global nodes
    global unvisited
    global previous
    global visited
    global interface

    # set the values to none for initialization.
    
    unvisited = {node: None for node in nodes}
    previous = {node: None for node in nodes}
    interface = {node: None for node in nodes}
    visited = {node: None for node in nodes}

    current = int(start)
    currentDist = 0
    unvisited[current] = currentDist

    while True:
        for next, distance in list(distances[current].items()):

            if next not in unvisited: continue
            
            newDist = currentDist + distance

            if not unvisited[next] or unvisited[next] > newDist:
                unvisited[next] = newDist
                previous[next] = current

                if not interface[current]:
                    interface[next] = next
                else:
                    interface[next] = interface[current]
                    
        visited[current] = currentDist
        del unvisited[current]
        
        done = 1
        for x in unvisited:
            if unvisited[x]:
                done = 0
                break
        if not unvisited or done:
            break

        elements = [node for node in list(unvisited.items()) if node[1]]

        current, currentDist = sorted(elements, key = lambda x: x[1])[0]


# Function to generate the shortest path using the parent table generated by function dijkstra.

def shortest_path(start, end):
    
    global path

    path = []
    dest = int(end)
    src = int(start)
    path.append(dest)

    while dest != src:
        path.append(previous[dest])
        dest = previous[dest]

    path.reverse()


if __name__ == "__main__":
    
    print_choices()

    command = 0

    # Run till user wants to exit.

    while command !=4 :

        command = check_choices(input("Choice: "))
    
        # Accept the topology file.
    
        if command == 1:
        
            if matrix_set == 1:
                answer = input("\nThe network topology is already uploaded. Do you want to overwrite? (Y/N) :")

            if matrix_set == 0 or answer == 'Y' or answer == 'y':
        
                filename = input("\nInput original network topology matrix data file[ NxN distance matrix. (value : -1 for no link, 0 for self loop) : ")

                if os.path.isfile(filename):
                    process_file(filename)
                    start = 0
                    end = 0
                else:
                    print("\nThe file does not exist. Please try again..")

        # Accept the source router and display the connection table.

        elif command == 2:
        
            if matrix_set == 1 :
            
                start = input("\nSelect a source router : ")

                if start.isdigit() and int(start) > 0 and int(start) <= len(router_matrix):
                    dijkstra(start)
                    print("\nDestination Next Hop")
                    for key in interface:
                        print(key,"\t\t", interface[key])
                else:
                    start = 0
                    print("\nPlease enter a valid source router.")

            else:
                print("\nNo network topology matrix exist. Please upload the data file first.. ")

        # Accept the destination router and display the shortest path and cost.

        elif command == 3:
    
            if matrix_set == 1 :

                end = input("\nSelect a destination router : ")
            
                if end.isdigit() and int(end) > 0 and int(end) <= len(router_matrix):
                    if int(start) == 0:
                        print("\nNo source router selected yet. Please select a source router using choice : 2.")
                    elif int(start) == int(end):
                        print("\nSource and Destination routers are same. Please select a different destination router.")
                    elif not previous[int(end)] :
                        print("\nThere does not exist any route from Source : %s to Destination : %s. \nPlease select a different destination router. "  %(start, end))
                    else:
                        shortest_path(start,end)
                        print("\nThe shortest path from router %s to router %s : " %(start, end), end=' ')
                        for item in path:
                            print(str(item) + '  ', end=' ')
                        print('')
                        cost = 0
                        if visited[int(end)]:
                            cost = visited[int(end)]
                        print("\nThe total cost is : ",  cost)
        
                else:
                    print("\nPlease enter a valid destination router.")

                pass

            else :
                print("\nNo network topology matrix exist. Please upload the data file first.. ")

    #Exit if command is 4.

    print("\nBye!\n")