/*
 * Copyright 2004-2007 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *	  http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.springframework.webflow.util;

/**
 * Encodes and decodes to and from Base64 notation.
 * <p>
 * Based on Base64 encoder and decoder version 2.2.1 written by Robert Harder (<a
 * href="http://iharder.net/base64">http://iharder.net/base64</a>). Modified by Erwin Vervaet to use the '.' character
 * as padding character when using URL safe encoding, like in the Bouncy Castle URLBase64 encoder (<a
 * href="http://www.bouncycastle.org/java.html">http://www.bouncycastle.org/java.html</a>).
 * 
 * @author Robert Harder
 * @author Erwin Vervaet
 */
public class Base64 {

	/*
	 * static data used by the encoding and decoding algorithm
	 */

	/*
	 * The equals sign (=) as a byte.
	 */
	private static final byte EQUALS_SIGN = (byte) '=';
	/* The dot (.) as a byte. */
	private static final byte DOT = (byte) '.';

	private static final byte WHITE_SPACE_ENC = -5; // Indicates white space in encoding
	private static final byte PADDING_CHAR_ENC = -1; // Indicates padding char in encoding

	/* ******** S T A N D A R D B A S E 6 4 A L P H A B E T ******** */

	/** The 64 valid Base64 values. */
	/* Host platform may be something funny like EBCDIC, so we hardcode these values. */
	private static final byte[] STANDARD_ALPHABET = { (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E',
			(byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N',
			(byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W',
			(byte) 'X', (byte) 'Y', (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f',
			(byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o',
			(byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x',
			(byte) 'y', (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6',
			(byte) '7', (byte) '8', (byte) '9', (byte) '+', (byte) '/' };

	/**
	 * Translates a Base64 value to either its 6-bit reconstruction value or a negative number indicating some other
	 * meaning.
	 */
	private static final byte[] STANDARD_DECODABET = { -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 0 - 8
			-5, -5, // Whitespace: Tab and Linefeed
			-9, -9, // Decimal 11 - 12
			-5, // Whitespace: Carriage Return
			-9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 - 26
			-9, -9, -9, -9, -9, // Decimal 27 - 31
			-5, // Whitespace: Space
			-9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
			62, // Plus sign at decimal 43
			-9, -9, -9, // Decimal 44 - 46
			63, // Slash at decimal 47
			52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
			-9, -9, -9, // Decimal 58 - 60
			-1, // Equals sign at decimal 61
			-9, -9, -9, // Decimal 62 - 64
			0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through 'N'
			14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O' through 'Z'
			-9, -9, -9, -9, -9, -9, // Decimal 91 - 96
			26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a' through 'm'
			39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n' through 'z'
			-9, -9, -9, -9 // Decimal 123 - 126
	};

	/* ******** U R L S A F E B A S E 6 4 A L P H A B E T ******** */

	/**
	 * Used in the URL- and Filename-safe dialect described in Section 4 of RFC3548: <a
	 * href="http://www.faqs.org/rfcs/rfc3548.html">http://www.faqs.org/rfcs/rfc3548.html</a>. Notice that the last two
	 * bytes become "hyphen" and "underscore" instead of "plus" and "slash."
	 */
	private static final byte[] URL_SAFE_ALPHABET = { (byte) 'A', (byte) 'B', (byte) 'C', (byte) 'D', (byte) 'E',
			(byte) 'F', (byte) 'G', (byte) 'H', (byte) 'I', (byte) 'J', (byte) 'K', (byte) 'L', (byte) 'M', (byte) 'N',
			(byte) 'O', (byte) 'P', (byte) 'Q', (byte) 'R', (byte) 'S', (byte) 'T', (byte) 'U', (byte) 'V', (byte) 'W',
			(byte) 'X', (byte) 'Y', (byte) 'Z', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f',
			(byte) 'g', (byte) 'h', (byte) 'i', (byte) 'j', (byte) 'k', (byte) 'l', (byte) 'm', (byte) 'n', (byte) 'o',
			(byte) 'p', (byte) 'q', (byte) 'r', (byte) 's', (byte) 't', (byte) 'u', (byte) 'v', (byte) 'w', (byte) 'x',
			(byte) 'y', (byte) 'z', (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6',
			(byte) '7', (byte) '8', (byte) '9', (byte) '-', (byte) '_' };

	/**
	 * Used in decoding URL- and Filename-safe dialects of Base64.
	 */
	private static final byte[] URL_SAFE_DECODABET = { -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 0 - 8
			-5, -5, // Whitespace: Tab and Linefeed
			-9, -9, // Decimal 11 - 12
			-5, // Whitespace: Carriage Return
			-9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 14 - 26
			-9, -9, -9, -9, -9, // Decimal 27 - 31
			-5, // Whitespace: Space
			-9, -9, -9, -9, -9, -9, -9, -9, -9, -9, // Decimal 33 - 42
			-9, // Plus sign at decimal 43
			-9, // Decimal 44
			62, // Minus sign at decimal 45
			-1, // Dot at decimal 46
			-9, // Slash at decimal 47
			52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // Numbers zero through nine
			-9, -9, -9, // Decimal 58 - 60
			-9, // Equals sign at decimal 61
			-9, -9, -9, // Decimal 62 - 64
			0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, // Letters 'A' through 'N'
			14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, // Letters 'O' through 'Z'
			-9, -9, -9, -9, // Decimal 91 - 94
			63, // Underscore at decimal 95
			-9, // Decimal 96
			26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, // Letters 'a' through 'm'
			39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, // Letters 'n' through 'z'
			-9, -9, -9, -9 // Decimal 123 - 126
	};

	// instance members

	/**
	 * Encode using Base64-like encoding that is URL- and Filename-safe as described in Section 4 of RFC3548: <a
	 * href="http://www.faqs.org/rfcs/rfc3548.html">http://www.faqs.org/rfcs/rfc3548.html</a>.
	 */
	private boolean urlSafe;

	private byte[] ALPHABET;
	private byte[] DECODABET;
	private byte PADDING_CHAR;

	/**
	 * Create a new Base64 encoder and decoder using the standard Base64 alphabet. Note that the resulting encoded
	 * strings are not <i>URL-safe</i>: they will can contain characters that are subject to URL encoding.
	 */
	public Base64() {
		this(false);
	}

	/**
	 * Create a new Base64 encoder and decoder.
	 * <p>
	 * Allows Base64-like encoding that is URL- and Filename-safe as described in Section 4 of RFC3548: <a
	 * href="http://www.faqs.org/rfcs/rfc3548.html">http://www.faqs.org/rfcs/rfc3548.html</a>. When URL-safe encoding
	 * is used, the standard "=" Base64 padding character is replaced with the '.' character.
	 * <p>
	 * It is important to note that data encoded this way is <em>not</em> officially valid Base64, or at the very
	 * least should not be called Base64 without also specifying that is was encoded using the URL- and Filename-safe
	 * dialect
	 * 
	 * @param urlSafe if true, URL safe encoding and decoding will be used
	 */
	public Base64(boolean urlSafe) {
		this.urlSafe = urlSafe;
		if (urlSafe) {
			ALPHABET = URL_SAFE_ALPHABET;
			DECODABET = URL_SAFE_DECODABET;
			PADDING_CHAR = DOT;
		} else {
			ALPHABET = STANDARD_ALPHABET;
			DECODABET = STANDARD_DECODABET;
			PADDING_CHAR = EQUALS_SIGN;
		}
	}

	/**
	 * Returns whether or not this coder is using Base64-like encoding that is URL- and Filename-safe as described in
	 * Section 4 of RFC3548: <a href="http://www.faqs.org/rfcs/rfc3548.html">http://www.faqs.org/rfcs/rfc3548.html</a>.
	 * When URL-safe encoding is used, the standard "=" Base64 padding character is replaced with the '.' character.
	 * <p>
	 * It is important to note that data encoded this way is <em>not</em> officially valid Base64, or at the very
	 * least should not be called Base64 without also specifying that is was encoded using the URL- and Filename-safe
	 * dialect.
	 * @return true or false
	 */
	public boolean isUrlSafe() {
		return urlSafe;
	}

	/* ******** E N C O D I N G M E T H O D S ******** */

	/**
	 * 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 accomodate <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>.
	 * </p>
	 * <p>
	 * This is the lowest level of the encoding methods with all possible parameters.
	 * </p>
	 * @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
	 * @return the <var>destination</var> array
	 */
	private byte[] encode3to4(byte[] source, int srcOffset, int numSigBytes, byte[] destination, int destOffset) {
		// 1 2 3
		// 01234567890123456789012345678901 Bit position
		// --------000000001111111122222222 Array position from threeBytes
		// --------| || || || | Six bit groups to index ALPHABET
		// >>18 >>12 >> 6 >> 0 Right shift necessary
		// 0x3f 0x3f 0x3f Additional AND

		// Create buffer with zero-padding if there are only one or two
		// significant bytes passed in the array.
		// 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 to an int.
		int inBuff = (numSigBytes > 0 ? ((source[srcOffset] << 24) >>> 8) : 0)
				| (numSigBytes > 1 ? ((source[srcOffset + 1] << 24) >>> 16) : 0)
				| (numSigBytes > 2 ? ((source[srcOffset + 2] << 24) >>> 24) : 0);

		switch (numSigBytes) {
		case 3:
			destination[destOffset] = ALPHABET[(inBuff >>> 18)];
			destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f];
			destination[destOffset + 2] = ALPHABET[(inBuff >>> 6) & 0x3f];
			destination[destOffset + 3] = ALPHABET[(inBuff) & 0x3f];
			return destination;

		case 2:
			destination[destOffset] = ALPHABET[(inBuff >>> 18)];
			destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f];
			destination[destOffset + 2] = ALPHABET[(inBuff >>> 6) & 0x3f];
			destination[destOffset + 3] = PADDING_CHAR;
			return destination;

		case 1:
			destination[destOffset] = ALPHABET[(inBuff >>> 18)];
			destination[destOffset + 1] = ALPHABET[(inBuff >>> 12) & 0x3f];
			destination[destOffset + 2] = PADDING_CHAR;
			destination[destOffset + 3] = PADDING_CHAR;
			return destination;

		default:
			return destination;
		}
	}

	/**
	 * 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 the encoded data
	 */
	public final byte[] encode(byte[] source, int off, int len) {
		int len43 = len * 4 / 3;
		byte[] outBuff = new byte[(len43) // main 4:3
				+ ((len % 3) > 0 ? 4 : 0)]; // account for padding
		int d = 0;
		int e = 0;
		int len2 = len - 2;
		int lineLength = 0;
		for (; d < len2; d += 3, e += 4) {
			encode3to4(source, d + off, 3, outBuff, e);

			lineLength += 4;
		} // end for: each piece of array

		if (d < len) {
			encode3to4(source, d + off, len - d, outBuff, e);
			e += 4;
		} // end if: some padding needed

		byte[] out = new byte[e];
		System.arraycopy(outBuff, 0, out, 0, e);
		return out;
	}

	/**
	 * Encodes a byte array into Base64 notation.
	 * @param source the data to encode
	 * @return the encoded data
	 */
	public final byte[] encode(byte[] source) {
		return encode(source, 0, source.length);
	}

	/**
	 * Encodes a byte array into Base64 notation. The resulting string will be created using the platform default
	 * encoding.
	 * @param source the source data to encode
	 * @return the encoded data
	 */
	public final String encodeToString(byte[] source) {
		return new String(encode(source));
	}

	/* ******** D E C O D I N G M E T H O D S ******** */

	/**
	 * 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 accomodate <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.
	 * <p>
	 * This is the lowest level of the decoding methods with all possible parameters.
	 * </p>
	 * @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 final int decode4to3(byte[] source, int srcOffset, byte[] destination, int destOffset) {
		// Example: Dk== or Dk..
		if (source[srcOffset + 2] == PADDING_CHAR) {
			int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
					| ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12);

			destination[destOffset] = (byte) (outBuff >>> 16);
			return 1;
		}

		// Example: DkL= or DkL.
		else if (source[srcOffset + 3] == PADDING_CHAR) {
			int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
					| ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12)
					| ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6);

			destination[destOffset] = (byte) (outBuff >>> 16);
			destination[destOffset + 1] = (byte) (outBuff >>> 8);
			return 2;
		}

		// Example: DkLE
		else {
			int outBuff = ((DECODABET[source[srcOffset]] & 0xFF) << 18)
					| ((DECODABET[source[srcOffset + 1]] & 0xFF) << 12)
					| ((DECODABET[source[srcOffset + 2]] & 0xFF) << 6) | ((DECODABET[source[srcOffset + 3]] & 0xFF));

			destination[destOffset] = (byte) (outBuff >> 16);
			destination[destOffset + 1] = (byte) (outBuff >> 8);
			destination[destOffset + 2] = (byte) (outBuff);

			return 3;
		}
	}

	/**
	 * Very low-level access to decoding ASCII characters in the form of 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
	 */
	public final byte[] decode(byte[] source, int off, int len) {
		int len34 = len * 3 / 4;
		byte[] outBuff = new byte[len34]; // upper limit on size of output
		int outBuffPosn = 0;

		byte[] b4 = new byte[4];
		int b4Posn = 0;
		int i = 0;
		byte sbiCrop = 0;
		byte sbiDecode = 0;
		for (i = off; i < off + len; i++) {
			sbiCrop = (byte) (source[i] & 0x7f); // only the low seven bits
			sbiDecode = DECODABET[sbiCrop];

			if (sbiDecode >= WHITE_SPACE_ENC) { // white space, equals sign or better
				if (sbiDecode >= PADDING_CHAR_ENC) {
					b4[b4Posn++] = sbiCrop;
					if (b4Posn > 3) {
						outBuffPosn += decode4to3(b4, 0, outBuff, outBuffPosn);
						b4Posn = 0;

						// if that was the padding char, break out of 'for' loop
						if (sbiCrop == PADDING_CHAR) {
							break;
						}
					} // end if: quartet built
				} // end if: equals sign or better
			} // end if: white space, equals sign or better
			else {
				// discard
			}
		} // each input character

		byte[] out = new byte[outBuffPosn];
		System.arraycopy(outBuff, 0, out, 0, outBuffPosn);
		return out;
	}

	/**
	 * Decodes data from Base64 notation.
	 * @param source the source data
	 * @return the decoded data
	 */
	public final byte[] decode(byte[] source) {
		return decode(source, 0, source.length);
	}

	/**
	 * Decodes data from Base64 notation. Uses the platform default character set to obtain bytes from given string.
	 * @param s the string to decode
	 * @return the decoded data
	 */
	public final byte[] decodeFromString(String s) {
		return decode(s.getBytes());
	}
}
