//
//  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 static java.nio.charset.StandardCharsets.UTF_8;

import java.text.MessageFormat;
import java.util.Arrays;

import org.eclipse.jgit.internal.JGitText;

Encodes and decodes to and from Base64 notation.

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
http://iharder.net/base64
periodically to check for updates or to contribute improvements.

Author:
Robert Harder, rob@iharder.net/**
 * 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
 */
public class Base64 {
	
The equals sign (=) as a byte. /** The equals sign (=) as a byte. */
	private final static byte EQUALS_SIGN = (byte) '=';

	
Indicates equals sign in encoding. /** Indicates equals sign in encoding. */
	private final static byte EQUALS_SIGN_DEC = -1;

	
Indicates white space in encoding. /** Indicates white space in encoding. */
	private final static byte WHITE_SPACE_DEC = -2;

	
Indicates an invalid byte during decoding. /** Indicates an invalid byte during decoding. */
	private final static byte INVALID_DEC = -3;

	
The 64 valid Base64 values. /** 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.
/**
	 * 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 {
		ENC = ("ABCDEFGHIJKLMNOPQRSTUVWXYZ" // //$NON-NLS-1$
				+ "abcdefghijklmnopqrstuvwxyz" // //$NON-NLS-1$
				+ "0123456789" // //$NON-NLS-1$
				+ "+/" // //$NON-NLS-1$
		).getBytes(UTF_8);

		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. /** Defeats instantiation. */
	private Base64() {
		// Suppress empty block warning.
	}

	
Encodes up to three bytes of the array source and writes the
resulting four Base64 bytes to destination. The source and
destination arrays can be manipulated anywhere along their length by
specifying srcOffset and destOffset. This method
does not check to make sure your arrays are large enough to accommodate
srcOffset + 3 for the source array or
destOffset + 4 for the destination array. The
actual number of significant bytes in your array is given by
numSigBytes.
Params:
source – 
           the array to convert
srcOffset – 
           the index where conversion begins
numSigBytes – 
           the number of significant bytes in your array
destination – 
           the array to hold the conversion
destOffset – 
           the index where output will be put/**
	 * 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.
Params:
source – 
           The data to convert
Returns:
encoded base64 representation of source./**
	 * 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.
Params:
source – 
           The data to convert
off – 
           Offset in array where conversion should begin
len – 
           Length of data to convert
Returns:
encoded base64 representation of source./**
	 * 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, UTF_8);
	}

	
Decodes four bytes from array source and writes the resulting
bytes (up to three of them) to destination. The source and
destination arrays can be manipulated anywhere along their length by
specifying srcOffset and destOffset. This method
does not check to make sure your arrays are large enough to accommodate
srcOffset + 4 for the source array or
destOffset + 3 for the destination array. This
method returns the actual number of bytes that were converted from the
Base64 encoding.
Params:
source – 
           the array to convert
srcOffset – 
           the index where conversion begins
destination – 
           the array to hold the conversion
destOffset – 
           the index where output will be put
Returns:
the number of decoded bytes converted/**
	 * 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.
Params:
source – 
           The Base64 encoded data
off – 
           The offset of where to begin decoding
len – 
           The length of characters to decode
Throws:
IllegalArgumentException – 
            the input is not a valid Base64 sequence.
Returns:
decoded data/**
	 * 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 java.lang.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.
Params:
s – 
           the string to decode
Returns:
the decoded data/**
	 * 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(UTF_8);
		return decode(bytes, 0, bytes.length);
	}
}