
package ca.uwaterloo.crysp.otr;

/**
* A Base64 Encoder/Decoder.
*
* <p>
* This class is used to encode and decode data in Base64 format as described in RFC 1521.
*
* <p>
* This is "Open Source" software and released under the <a href="http://www.gnu.org/licenses/lgpl.html">GNU/LGPL</a> license.<br>
* It is provided "as is" without warranty of any kind.<br>
* Copyright 2003: Christian d'Heureuse, Inventec Informatik AG, Switzerland.<br>
* Home page: <a href="http://www.source-code.biz">www.source-code.biz</a><br>
*/

public class Base64Coder {

// Mapping table from 6-bit nibbles to Base64 characters.
private static char[]    map1 = new char[64];
   static {
      int i=0;
      for (char c='A'; c<='Z'; c++) map1[i++] = c;
      for (char c='a'; c<='z'; c++) map1[i++] = c;
      for (char c='0'; c<='9'; c++) map1[i++] = c;
      map1[i++] = '+'; map1[i++] = '/'; }

// Mapping table from Base64 characters to 6-bit nibbles.
private static byte[]    map2 = new byte[128];
   static {
      for (int i=0; i<map2.length; i++) map2[i] = -1;
      for (int i=0; i<64; i++) map2[map1[i]] = (byte)i; }

/**
* Encodes a string into Base64 format.
* No blanks or line breaks are inserted.
* @param s  a String to be encoded.
* @return   A String with the Base64 encoded data.
*/
public static String encodeString (String s) {
   return new String(encode(s.getBytes())); }

/**
* Encodes a byte array into Base64 format.
* No blanks or line breaks are inserted.
* @param in  an array containing the data bytes to be encoded.
* @return    A character array with the Base64 encoded data.
*/
public static char[] encode (byte[] in) {
   return encode(in,in.length); }

/**
* Encodes a byte array into Base64 format.
* No blanks or line breaks are inserted.
* @param in   an array containing the data bytes to be encoded.
* @param iLen number of bytes to process in <code>in</code>.
* @return     A character array with the Base64 encoded data.
*/
public static char[] encode (byte[] in, int iLen) {
   int oDataLen = (iLen*4+2)/3+5;       // output length without padding
   int oLen = ((iLen+2)/3)*4;         // output length including padding
   char[] out = new char[5+oLen+1];
   int ip = 0;
   int op = 0;
   out[0]='?';
   out[1]='O';
   out[2]='T';
   out[3]='R';
   out[4]=':';
   op+=5;
   while (ip < iLen) {
      int i0 = in[ip++] & 0xff;
      int i1 = ip < iLen ? in[ip++] & 0xff : 0;
      int i2 = ip < iLen ? in[ip++] & 0xff : 0;
      int o0 = i0 >>> 2;
      int o1 = ((i0 &   3) << 4) | (i1 >>> 4);
      int o2 = ((i1 & 0xf) << 2) | (i2 >>> 6);
      int o3 = i2 & 0x3F;
      out[op++] = map1[o0];
      out[op++] = map1[o1];
      out[op] = op < oDataLen ? map1[o2] : '='; op++;
      out[op] = op < oDataLen ? map1[o3] : '='; op++; }
   out[op]='.';
   return out; }

/**
* Decodes a string from Base64 format.
* @param s  a Base64 String to be decoded.
* @return   A String containing the decoded data.
* @throws   IllegalArgumentException if the input is not valid Base64 encoded data.
*/
public static String decodeString (String s) {
   return new String(decode(s)); }

/**
* Decodes a byte array from Base64 format.
* @param s  a Base64 String to be decoded.
* @return   An array containing the decoded data bytes.
* @throws   IllegalArgumentException if the input is not valid Base64 encoded data.
*/
public static byte[] decode (String s) {
   return decode(s.toCharArray()); }

/**
* Decodes a byte array from Base64 format.
* No blanks or line breaks are allowed within the Base64 encoded data.
* @param in  a character array containing the Base64 encoded data.
* @return    An array containing the decoded data bytes.
* @throws    IllegalArgumentException if the input is not valid Base64 encoded data.
*/
public static byte[] decode (char[] in) {
   int iLen = in.length-6;
   if (iLen%4 != 0) throw new IllegalArgumentException ("Length of Base64 encoded input string is not a multiple of 4.");
   if(in[0]!='?'||in[1]!='O'||in[2]!='T'||in[3]!='R'||in[4]!=':'||in[in.length-1]!='.'){
	   throw new IllegalArgumentException ("Input is not a valid OTR Base64 message");
   }
   char[] newin = new char[iLen];
   System.arraycopy(in, 5, newin, 0, iLen);
   while (iLen > 0 && newin[iLen-1] == '=') iLen--;
   int oLen = (iLen*3) / 4;
   byte[] out = new byte[oLen];
   int ip = 0;
   int op = 0;
   while (ip < iLen) {
      int i0 = newin[ip++];
      int i1 = newin[ip++];
      int i2 = ip < iLen ? newin[ip++] : 'A';
      int i3 = ip < iLen ? newin[ip++] : 'A';
      if (i0 > 127 || i1 > 127 || i2 > 127 || i3 > 127)
         throw new IllegalArgumentException ("Illegal character in Base64 encoded data."+ip);
      int b0 = map2[i0];
      int b1 = map2[i1];
      int b2 = map2[i2];
      int b3 = map2[i3];
      if (b0 < 0 || b1 < 0 || b2 < 0 || b3 < 0)
         throw new IllegalArgumentException ("Illegal character in Base64 encoded data."+ip);
      int o0 = ( b0       <<2) | (b1>>>4);
      int o1 = ((b1 & 0xf)<<4) | (b2>>>2);
      int o2 = ((b2 &   3)<<6) |  b3;
      out[op++] = (byte)o0;
      if (op<oLen) out[op++] = (byte)o1;
      if (op<oLen) out[op++] = (byte)o2; }
   return out; }
// Dummy constructor.
private Base64Coder() {}

} // end class Base64Coder
