/**
 * Provides static methods for encoding and decoding strings of base 64
 * characters, such as those used for HTTP basic authorization.
 *
 * No warranty -- you may use this code in your own projects so long as you
 * preserve this message and the author tag below.
 *
 * @author <A HREF="mailto:wes@cacas.org">Wes Biggs</A>
 */
public class Base64 {
  private static final String alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

  private static final int b64val(char c) {
    int b = alphabet.indexOf(c);
    return (b == -1) ? 0 : b;
  }

  private static final char b64char(int i) {
    return ((i >= 0) && (i < 64)) ? alphabet.charAt(i) : '=';
  }

  /**
   * Creates a base 64 encoding of the input text.
   *
   * @param f_text the String to be encoded.
   */
  public static final String encode(String f_text) {
    StringBuffer output = new StringBuffer();
    // read 3 chars, make 4
    int l = f_text.length();
    int a,b,c,d;
    for (int i = 0; i < l;) {
      b = c = d = 0;
      a = (int) f_text.charAt(i++);
      output.append(b64char(a >> 2));
      if (i < l) { 
	b = (int) f_text.charAt(i++);
	output.append(b64char((b >> 4) | ((a << 4) & 63)));
	
	if (i < l) {
	  c = (int) f_text.charAt(i++);
	  output.append(b64char((c >> 6) | ((b << 2) & 63)));
	  output.append(b64char(c & 63));
	} else { 
	  output.append(b64char((b << 2) & 63)); 
	  output.append('=');
	}
      } else {
	output.append(b64char((a << 4) & 63));
	output.append("==");
      }
    }
    return output.toString();
  }

  /**
   * Decodes a base 64 encoding of a string.
   *
   * @param f_text the String to be decoded.
   */
  public static final String decode(String f_text) {
    StringBuffer output = new StringBuffer();
    for (int i = 0; (i + 3) < f_text.length();) {
      int a = b64val(f_text.charAt(i++));
      int b = b64val(f_text.charAt(i++));
      int c = b64val(f_text.charAt(i++));
      int d = b64val(f_text.charAt(i++));

      a = ((a << 2) & 255) | (b >> 4);
      b = ((b << 4) & 255) | (c >> 2);
      c = ((c << 6) & 255) | d;
      
      output.append((char) a);
      if (b != 0) output.append((char) b);
      if (c != 0) output.append((char) c);
    }
    return output.toString();
  }
}