// This example is from _Java Examples in a Nutshell_. (http://www.oreilly.com)
// Copyright (c) 1997 by David Flanagan
// This example is provided WITHOUT ANY WARRANTY either expressed or implied.
// You may study, use, modify, and distribute it for non-commercial purposes.
// For any commercial use, see http://www.davidflanagan.com/javaexamples

import java.io.*;  // We're doing input, so import I/O classes

/**
 * This program reads lines of text from the user, encodes them using the 
 * trivial "Rot13" substitution cipher, and then prints out the encoded lines.
 **/
public class Rot13Input {
  public static void main(String[] args) throws IOException {
    // Get set up to read lines of text from the user
    BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    for(;;) {                                    // Loop forever
      System.out.print("> ");                    // Print a prompt
      String line = in.readLine();               // Read a line
      if ((line == null) || line.equals("quit")) // If EOF or "quit" then...
        break;                                   // ... break out of the loop
      StringBuffer buf = new StringBuffer(line); // Convert to a StringBuffer
      for(int i = 0; i < buf.length(); i++)      // For each character...
        buf.setCharAt(i, rot13(buf.charAt(i)));  //   read, encode, put it back
      System.out.println(buf);                   // Print encoded line
    }
  }

  /**
   * This method performs the Rot13 substitution cipher.  It "rotates"
   * each letter 13 places through the alphabet.  Since the Latin alphabet
   * has 26 letters, this method both encodes and decodes.
   **/
  public static char rot13(char c) {
    if ((c >= 'A') && (c <= 'Z')) {  // For uppercase letters
      c += 13;                       // Rotate forward 13
      if (c > 'Z') c -= 26;         // And subtract 26 if necessary
    }
    if ((c >= 'a') && (c <= 'z')) {  // Do the same for lowercase letters
      c += 13;
      if (c > 'z') c -= 26;
    }
    return c;                        // Return the modified letter
  }
}