import java.util.Scanner;

/* GCD_Tester.java
** Java application for testing a recursive method that computes the
** GCD (greatest common divisor) of two integers recursively.
**
** Authors: R. McCloskey and < lab team members >
** Known defects: ...
*/

public class GCD_Tester {

   private static Scanner keyboard;
   private static int depth;

   /* Returns the greatest common divisor of the two int values given.
   ** Uses recursion and narrates its execution!
   ** pre: k >= 0 && m >= 0 && k+m > 0
   */
   public static int gcdViaRec(int k, int m) {
      depth++;
      printMessage(String.format("Received k:%d and m:%d\n", k, m));

      int result;


      // MISSING CODE GOES HERE


      printMessage(String.format("Returning %d having received k:%d and m:%d\n", 
                                 result, k, m));
      depth--;

      return result;
   }


   /* Returns the greatest common divisor of the two int values given.
   ** Uses a loop.
   ** pre: k >= 0 && m >= 0 && k+m > 0
   */
   public static int gcdViaLoop(int k, int m) {
      // ensure that k >= m by swapping their values if k < m
      if (k < m) { int temp = k; k = m; m = temp; }

      while (m != 0) {
         int newM = k % m;    // replace k by m and m by k % m
         k = m;
         m = newM;
      }
      return k;
   }


  // main () method for testing
  // --------------------------

   public static void main(String[] args) {

      final String kPrompt = "Enter a value for k: ";
      final String mPrompt = "Enter a value for m: ";

      keyboard = new Scanner(System.in);
      int k, m = 0;
      do {
         k = getInt(kPrompt);
         if (k >= 0) { 
            depth = -1;
            m = getInt(mPrompt);
            int result = gcdViaRec(k, m);
            int correctResult = gcdViaLoop(k,m);
            System.out.println("\nYour method produced  " + result);
            System.out.println("The correct result is " + correctResult);
            System.out.println();
         }
      }
      while (k >= 0);
      System.out.println("Goodbye.");
   }

   /* Prints the specified string, indented according to the value of 'depth'.
   */
   private static void printMessage(String s) {
      printSpaces(3*depth);
      System.out.print(s);
   }

   /* Prints the specified # of spaces.
   */
   private static void printSpaces(int r) {
      for (int i = 0; i !=r; i++) { System.out.print(' '); }
   }

   /* Displays the given prompt and returns the String entered at the keyboard
   ** in response.
   */
   private static int getInt(String prompt) {
      int result = -1;
      boolean tryAgain = true;
      while (tryAgain) {
         System.out.print(prompt);
         try {
            String response = keyboard.nextLine().trim();
            result = Integer.parseInt(response);
            tryAgain = false;
         }
         catch (NumberFormatException e) {
            System.out.println("** Invalid response; try again\n");
         }
      }
      return result;
   }

}