/* TowersOfHanoi.java       Authors: Koffman & Wolz
 * Class that solves the towers of Hanoi problem.
 * Uses KeyIn and JOptionPane.
 */
import psJava.KeyIn;
import javax.swing.JOptionPane;

public class TowersOfHanoi {

  // Data fields
  private int numDisks;
  private char sourcePeg;
  private char destinationPeg;
  private char sparePeg;

  // Methods
  // precondition : fromPeg, toPeg, auxPeg, and
  //   n are defined.
  // postcondition: Displays a list of instructions to
  //   move n disks from fromPeg to toPeg
  //   using auxPeg as an intermediary.
  private void tower(char fromPeg, char toPeg,
                    char auxPeg, int n) {
    if (n == 1)
       System.out.println("Move disk 1 from peg " +
                          fromPeg + " to peg " + toPeg);
    else { // recursive step
       tower (fromPeg, auxPeg, toPeg, n-1);
       System.out.println("Move disk " + n +
              " from peg " + fromPeg + " to peg " + toPeg);
       tower(auxPeg, toPeg, fromPeg, n-1);
    }
  }

  // precondition: arguments are defined.
  // postcondition: recursive method is started.
  public void tower() {
    tower(sourcePeg, destinationPeg, sparePeg, numDisks);
  }

  // postcondition: Reads the number of disks and sourcePeg
  //   and destinationPeg. Sets sparePeg to the unused peg.
  public void readTowerData() {
     numDisks = KeyIn.readInt("How many disks", 1, 8);

     // Get source and destination pegs.
     sourcePeg = KeyIn.readChar("Enter the source peg (A,B,C)");
     destinationPeg =
          KeyIn.readChar("Enter the destination peg (A,B,C)");
     while (sourcePeg == destinationPeg) {
        JOptionPane.showMessageDialog(null,
              "source and destination can't be the same!",
              "Error", JOptionPane.ERROR_MESSAGE);
        destinationPeg =
              KeyIn.readChar("Enter destination (A,B,C)");
     }

     // Set sparePeg to the unused peg.
     String pegsUsed = "" + sourcePeg + destinationPeg;
     // Find peg that is not used.
     for (char nextCh = 'A'; nextCh <= 'C'; nextCh++) {
        if (pegsUsed.indexOf(nextCh) < 0) {
          sparePeg = nextCh;
          return;
        }
     }
  }

} // class TowersOfHanoi