/*Purpose: Memory Management Unit Simulation*/
/*Authors: Martin Payne                     */
/*         Jeremy Libner                    */
/*         Tyler Makovicka                  */
/*         Kushal Tiwari                    */
/*         Trebor Asher                     */
/*         Kimberly Batton                  */

import java.util.Random;
import java.util.Scanner;

public class MemoryManagementUnit {
   public static void main(String [] args) {
         //The following arrays simulating RAM, Virtual Memory space of a single program, and the disk.
         int[] RAM = new int [8];
         //the 1st dimintion of VM array gives where the page is located on the disk
         //the 2nd dimintion of VM array gives page location in RAM or is 8 if not in RAM
         int[][] VM = new int [16][2];
         int[] disk = new int [64];
         int randomNumber;
         //location of program on disk
         int nextOpenSlot = 0;
         int pageRequest;
         boolean enterAgain = true;
         
         Scanner in = new Scanner(System.in);
         Random rng = new Random();
         int programStartSlot = rng.nextInt(48);
         
         //fills every slot on disk with a random number
         for (int i=0; i<64; i++) {
            randomNumber = rng.nextInt(1000);
            disk[i] = randomNumber;
         }
         
         //stores program addresses into virtual memory
         for (int i=0; i<16; i++) {
            VM[i][0] = programStartSlot + i;
            VM[i][1] = 8;
         }
         
         //while loop runs while user simulates program requesting pages of memory
         while (enterAgain == true) {
            System.out.println("Enter the page segment of the program that you need to access 1-16.");
            pageRequest = in.nextInt() - 1;
            
            //handles case of page not being in RAM and moves it to RAM then displays it
            if (VM[pageRequest][1] == 8) {
               System.out.println("Page is not in RAM, moving page to RAM slot " + nextOpenSlot + " from disk.");
               RAM[nextOpenSlot] = disk[VM[pageRequest][0]];
               VM[pageRequest][1] = nextOpenSlot;
               if (nextOpenSlot != 7) {
                  nextOpenSlot++;
               }else {
                  nextOpenSlot = 0;
               }
               System.out.println("Page moved to RAM the value stored in it is: " + RAM[VM[pageRequest][1]]);
            //handles case of page being in RAM and displays the value 
            }else {
               System.out.println("Page in RAM, the value stored in the page is: " + RAM[VM[pageRequest][1]]);
            }
            //displays values in RAM and virtual memory every time a page request is made
            System.out.println("Current values in RAM: [" + RAM[0] + "] [" + RAM[1] + "] [" + RAM[2] + "] [" + RAM[3] + "] [" + RAM[4] + "] [" + RAM[5] + "] [" + RAM[6] + "] [" + RAM[7] + "]");
            System.out.println("Current values in Virtual Memory:");
            for (int i=0; i<16; i++) {
               if (VM[i][1] == 8) {
                  System.out.println("Disk Location [" + VM[i][0] + "] not in RAM");
               }else {
                  System.out.println("Disk Location [" + VM[i][0] + "] in RAM slot [" + VM[i][1] + "]");
               }
            }
            System.out.println("To request another page enter 1, enter 0 to exit.");
            if (in.nextInt() != 1) {
               enterAgain = false;
            }
         }
   }
}