package com.efounder.chat.utils;

import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;

public class Base64Decoder extends FilterInputStream {

private static final char[] chars = {
 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd',
 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x',
 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7',
 '8', '9', '+', '/'
};

// A mapping between char values and six-bit integers
private static final int[] ints = new int[128];
static {
 for (int i = 0; i < 64; i++) {
   ints[chars[i]] = i;
 }
}

private int charCount;
private int carryOver;

/***
* Constructs a new Base64 decoder that reads input from the given
* InputStream.
*
* @param in the input stream
*/
public Base64Decoder(InputStream in) {
 super(in);
}

/***
* Returns the next decoded character from the stream, or -1 if
* end of stream was reached.
*
* @return  the decoded character, or -1 if the end of the
*      input stream is reached
* @exception IOException if an I/O error occurs
*/
public int read() throws IOException {
 // Read the next non-whitespace character
 int x;
 do {
   x = in.read();
   if (x == -1) {
     return -1;
   }
 } while (Character.isWhitespace((char)x));
 charCount++;

 // The '=' sign is just padding
 if (x == '=') {
   return -1;  // effective end of stream
 }

 // Convert from raw form to 6-bit form
 x = ints[x];

 // Calculate which character we're decoding now
 int mode = (charCount - 1) % 4;

 // First char save all six bits, go for another
 if (mode == 0) {
   carryOver = x & 63;
   return read();
 }
 // Second char use previous six bits and first two new bits,
 // save last four bits
 else if (mode == 1) {
   int decoded = ((carryOver << 2) + (x >> 4)) & 255;
   carryOver = x & 15;
   return decoded;
 }
 // Third char use previous four bits and first four new bits,
 // save last two bits
 else if (mode == 2) {
   int decoded = ((carryOver << 4) + (x >> 2)) & 255;
   carryOver = x & 3;
   return decoded;
 }
 // Fourth char use previous two bits and all six new bits
 else if (mode == 3) {
   int decoded = ((carryOver << 6) + x) & 255;
   return decoded;
 }
 return -1;  // can't actually reach this line
}

/***
* Reads decoded data into an array of bytes and returns the actual 
* number of bytes read, or -1 if end of stream was reached.
*
* @param buf the buffer into which the data is read
* @param off the start offset of the data
* @param len the maximum number of bytes to read
* @return  the actual number of bytes read, or -1 if the end of the
*      input stream is reached
* @exception IOException if an I/O error occurs
*/
public int read(byte[] buf, int off, int len) throws IOException {
 if (buf.length < (len + off - 1)) {
   throw new IOException("The input buffer is too small: " + len + 
    " bytes requested starting at offset " + off + " while the buffer " +
    " is only " + buf.length + " bytes long.");
 }

 // This could of course be optimized
 int i;
 for (i = 0; i < len; i++) {
   int x = read();
   if (x == -1 && i == 0) {  // an immediate -1 returns -1
     return -1;
   }
   else if (x == -1) {       // a later -1 returns the chars read so far
     break;
   }
   buf[off + i] = (byte) x;
 }
 return i;
}

/***
* Returns the decoded form of the given encoded string, as a String.
* Note that not all binary data can be represented as a String, so this
* method should only be used for encoded String data.  Use decodeToBytes()
* otherwise.
*
* @param encoded the string to decode
* @return the decoded form of the encoded string
*/
public static String decode(String encoded) {
 return new String(decodeToBytes(encoded));
}

/***
* Returns the decoded form of the given encoded string, as bytes.
*
* @param encoded the string to decode
* @return the decoded form of the encoded string
*/
public static byte[] decodeToBytes(String encoded) {
 byte[] bytes = null;
 try {
   bytes = encoded.getBytes("UTF-8");
 }
 catch (UnsupportedEncodingException ignored) { }

 Base64Decoder in = new Base64Decoder(
                    new ByteArrayInputStream(bytes));
 
 ByteArrayOutputStream out = 
   new ByteArrayOutputStream((int) (bytes.length * 0.67));

 try {
   byte[] buf = new byte[4 * 1024];  // 4K buffer
   int bytesRead;
   while ((bytesRead = in.read(buf)) != -1) {
     out.write(buf, 0, bytesRead);
   }
   out.close();

   return out.toByteArray();
 }
 catch (IOException ignored) { return null; }
}

public static void main(String[] args) throws Exception {
 if (args.length != 1) {
   System.err.println("Usage: java Base64Decoder fileToDecode");
   return;
 }

 Base64Decoder decoder = null;
 try {
   decoder = new Base64Decoder(
             new BufferedInputStream(
             new FileInputStream(args[0])));
   byte[] buf = new byte[4 * 1024];  // 4K buffer
   int bytesRead;
   while ((bytesRead = decoder.read(buf)) != -1) {
     System.out.write(buf, 0, bytesRead);
   }
 }
 finally {
   if (decoder != null) decoder.close();
 }
}
}
