//
   //  NOTE: The following source code is heavily derived from the
   //  iHarder.net public domain Base64 library.  See the original at
   //  http://iharder.sourceforge.net/current/java/base64/
   //
   
   package org.eclipse.jgit.util;
   
   import java.io.UnsupportedEncodingException;
  import java.nio.charset.StandardCharsets;
  import java.text.MessageFormat;
  import java.util.Arrays;
  
  import org.eclipse.jgit.internal.JGitText;
  
  /**
   * Encodes and decodes to and from Base64 notation.
   * <p>
   * I am placing this code in the Public Domain. Do with it as you will. This
   * software comes with no guarantees or warranties but with plenty of
   * well-wishing instead! Please visit <a
   * href="http://iharder.net/base64">http://iharder.net/base64</a> periodically
   * to check for updates or to contribute improvements.
   * </p>
   *
   * @author Robert Harder
   * @author rob@iharder.net
   * @version 2.1, stripped to minimum feature set used by JGit.
   */
  public class Base64 {
  	/** The equals sign (=) as a byte. */
  	private final static byte EQUALS_SIGN = (byte) '=';
  
  	/** Indicates equals sign in encoding. */
  	private final static byte EQUALS_SIGN_DEC = -1;
  
  	/** Indicates white space in encoding. */
  	private final static byte WHITE_SPACE_DEC = -2;
  
  	/** Indicates an invalid byte during decoding. */
  	private final static byte INVALID_DEC = -3;
  
  	/** Preferred encoding. */
  	private final static String UTF_8 = "UTF-8"; //$NON-NLS-1$
  
  	/** The 64 valid Base64 values. */
  	private final static byte[] ENC;
  
  	/**
  	 * Translates a Base64 value to either its 6-bit reconstruction value or a
  	 * negative number indicating some other meaning. The table is only 7 bits
  	 * wide, as the 8th bit is discarded during decoding.
  	 */
  	private final static byte[] DEC;
  
  	static {
  		try {
  			ENC = ("ABCDEFGHIJKLMNOPQRSTUVWXYZ" // //$NON-NLS-1$
  					+ "abcdefghijklmnopqrstuvwxyz" // //$NON-NLS-1$
  					+ "0123456789" // //$NON-NLS-1$
  					+ "+/" // //$NON-NLS-1$
  			).getBytes(UTF_8);
  		} catch (UnsupportedEncodingException uee) {
  			throw new RuntimeException(uee.getMessage(), uee);
  		}
  
  		DEC = new byte[128];
  		Arrays.fill(DEC, INVALID_DEC);
  
  		for (int i = 0; i < 64; i++)
  			DEC[ENC[i]] = (byte) i;
  		DEC[EQUALS_SIGN] = EQUALS_SIGN_DEC;
  
  		DEC['\t'] = WHITE_SPACE_DEC;
  		DEC['\n'] = WHITE_SPACE_DEC;
  		DEC['\r'] = WHITE_SPACE_DEC;
  		DEC[' '] = WHITE_SPACE_DEC;
  	}
  
  	/** Defeats instantiation. */
  	private Base64() {
  		// Suppress empty block warning.
  	}
  
  	/**
  	 * Encodes up to three bytes of the array <var>source</var> and writes the
  	 * resulting four Base64 bytes to <var>destination</var>. The source and
  	 * destination arrays can be manipulated anywhere along their length by
  	 * specifying <var>srcOffset</var> and <var>destOffset</var>. This method
  	 * does not check to make sure your arrays are large enough to accommodate
  	 * <var>srcOffset</var> + 3 for the <var>source</var> array or
  	 * <var>destOffset</var> + 4 for the <var>destination</var> array. The
  	 * actual number of significant bytes in your array is given by
  	 * <var>numSigBytes</var>.
  	 *
  	 * @param source
  	 *            the array to convert
  	 * @param srcOffset
  	 *            the index where conversion begins
 	 * @param numSigBytes
 	 *            the number of significant bytes in your array
 	 * @param destination
 	 *            the array to hold the conversion
 	 * @param destOffset
 	 *            the index where output will be put
 	 */
 	private static void encode3to4(byte[] source, int srcOffset,
 			int numSigBytes, byte[] destination, int destOffset) {
 		// We have to shift left 24 in order to flush out the 1's that appear
 		// when Java treats a value as negative that is cast from a byte.
 
 		int inBuff = 0;
 		switch (numSigBytes) {
 		case 3:
 			inBuff |= (source[srcOffset + 2] << 24) >>> 24;
 			//$FALL-THROUGH$
 
 		case 2:
 			inBuff |= (source[srcOffset + 1] << 24) >>> 16;
 			//$FALL-THROUGH$
 
 		case 1:
 			inBuff |= (source[srcOffset] << 24) >>> 8;
 		}
 
 		switch (numSigBytes) {
 		case 3:
 			destination[destOffset] = ENC[(inBuff >>> 18)];
 			destination[destOffset + 1] = ENC[(inBuff >>> 12) & 0x3f];
 			destination[destOffset + 2] = ENC[(inBuff >>> 6) & 0x3f];
 			destination[destOffset + 3] = ENC[(inBuff) & 0x3f];
 			break;
 
 		case 2:
 			destination[destOffset] = ENC[(inBuff >>> 18)];
 			destination[destOffset + 1] = ENC[(inBuff >>> 12) & 0x3f];
 			destination[destOffset + 2] = ENC[(inBuff >>> 6) & 0x3f];
 			destination[destOffset + 3] = EQUALS_SIGN;
 			break;
 
 		case 1:
 			destination[destOffset] = ENC[(inBuff >>> 18)];
 			destination[destOffset + 1] = ENC[(inBuff >>> 12) & 0x3f];
 			destination[destOffset + 2] = EQUALS_SIGN;
 			destination[destOffset + 3] = EQUALS_SIGN;
 			break;
 		}
 	}
 
 	/**
 	 * Encodes a byte array into Base64 notation.
 	 *
 	 * @param source
 	 *            The data to convert
 	 * @return encoded base64 representation of source.
 	 */
 	public static String encodeBytes(byte[] source) {
 		return encodeBytes(source, 0, source.length);
 	}
 
 	/**
 	 * Encodes a byte array into Base64 notation.
 	 *
 	 * @param source
 	 *            The data to convert
 	 * @param off
 	 *            Offset in array where conversion should begin
 	 * @param len
 	 *            Length of data to convert
 	 * @return encoded base64 representation of source.
 	 */
 	public static String encodeBytes(byte[] source, int off, int len) {
 		final int len43 = len * 4 / 3;
 
 		byte[] outBuff = new byte[len43 + ((len % 3) > 0 ? 4 : 0)];
 		int d = 0;
 		int e = 0;
 		int len2 = len - 2;
 
 		for (; d < len2; d += 3, e += 4)
 			encode3to4(source, d + off, 3, outBuff, e);
 
 		if (d < len) {
 			encode3to4(source, d + off, len - d, outBuff, e);
 			e += 4;
 		}
 
 		return new String(outBuff, 0, e, StandardCharsets.UTF_8);
 	}
 
 	/**
 	 * Decodes four bytes from array <var>source</var> and writes the resulting
 	 * bytes (up to three of them) to <var>destination</var>. The source and
 	 * destination arrays can be manipulated anywhere along their length by
 	 * specifying <var>srcOffset</var> and <var>destOffset</var>. This method
 	 * does not check to make sure your arrays are large enough to accommodate
 	 * <var>srcOffset</var> + 4 for the <var>source</var> array or
 	 * <var>destOffset</var> + 3 for the <var>destination</var> array. This
 	 * method returns the actual number of bytes that were converted from the
 	 * Base64 encoding.
 	 *
 	 * @param source
 	 *            the array to convert
 	 * @param srcOffset
 	 *            the index where conversion begins
 	 * @param destination
 	 *            the array to hold the conversion
 	 * @param destOffset
 	 *            the index where output will be put
 	 * @return the number of decoded bytes converted
 	 */
 	private static int decode4to3(byte[] source, int srcOffset,
 			byte[] destination, int destOffset) {
 		// Example: Dk==
 		if (source[srcOffset + 2] == EQUALS_SIGN) {
 			int outBuff = ((DEC[source[srcOffset]] & 0xFF) << 18)
 					| ((DEC[source[srcOffset + 1]] & 0xFF) << 12);
 			destination[destOffset] = (byte) (outBuff >>> 16);
 			return 1;
 		}
 
 		// Example: DkL=
 		else if (source[srcOffset + 3] == EQUALS_SIGN) {
 			int outBuff = ((DEC[source[srcOffset]] & 0xFF) << 18)
 					| ((DEC[source[srcOffset + 1]] & 0xFF) << 12)
 					| ((DEC[source[srcOffset + 2]] & 0xFF) << 6);
 			destination[destOffset] = (byte) (outBuff >>> 16);
 			destination[destOffset + 1] = (byte) (outBuff >>> 8);
 			return 2;
 		}
 
 		// Example: DkLE
 		else {
 			int outBuff = ((DEC[source[srcOffset]] & 0xFF) << 18)
 					| ((DEC[source[srcOffset + 1]] & 0xFF) << 12)
 					| ((DEC[source[srcOffset + 2]] & 0xFF) << 6)
 					| ((DEC[source[srcOffset + 3]] & 0xFF));
 
 			destination[destOffset] = (byte) (outBuff >> 16);
 			destination[destOffset + 1] = (byte) (outBuff >> 8);
 			destination[destOffset + 2] = (byte) (outBuff);
 
 			return 3;
 		}
 	}
 
 	/**
 	 * Low-level decoding ASCII characters from a byte array.
 	 *
 	 * @param source
 	 *            The Base64 encoded data
 	 * @param off
 	 *            The offset of where to begin decoding
 	 * @param len
 	 *            The length of characters to decode
 	 * @return decoded data
 	 * @throws IllegalArgumentException
 	 *             the input is not a valid Base64 sequence.
 	 */
 	public static byte[] decode(byte[] source, int off, int len) {
 		byte[] outBuff = new byte[len * 3 / 4]; // Upper limit on size of output
 		int outBuffPosn = 0;
 
 		byte[] b4 = new byte[4];
 		int b4Posn = 0;
 
 		for (int i = off; i < off + len; i++) {
 			byte sbiCrop = (byte) (source[i] & 0x7f);
 			byte sbiDecode = DEC[sbiCrop];
 
 			if (EQUALS_SIGN_DEC <= sbiDecode) {
 				b4[b4Posn++] = sbiCrop;
 				if (b4Posn > 3) {
 					outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn);
 					b4Posn = 0;
 
 					// If that was the equals sign, break out of 'for' loop
 					if (sbiCrop == EQUALS_SIGN)
 						break;
 				}
 
 			} else if (sbiDecode != WHITE_SPACE_DEC)
 				throw new IllegalArgumentException(MessageFormat.format(
 						JGitText.get().badBase64InputCharacterAt,
 						Integer.valueOf(i), Integer.valueOf(source[i] & 0xff)));
 		}
 
 		if (outBuff.length == outBuffPosn)
 			return outBuff;
 
 		byte[] out = new byte[outBuffPosn];
 		System.arraycopy(outBuff, 0, out, 0, outBuffPosn);
 		return out;
 	}
 
 	/**
 	 * Decodes data from Base64 notation.
 	 *
 	 * @param s
 	 *            the string to decode
 	 * @return the decoded data
 	 */
 	public static byte[] decode(String s) {
 		byte[] bytes = s.getBytes(StandardCharsets.UTF_8);
 		return decode(bytes, 0, bytes.length);
 	}
 }