/*
 * Copyright 1999-2018 Alibaba Group Holding Ltd.
 *
 * 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 com.alibaba.nacos.common.codec;

/**
 * From apache common codec, and remove some useless method. Provides Base64 encoding and decoding as defined by <a
 * href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>.
 *
 * <p>This class implements section <cite>6.8. Base64 Content-Transfer-Encoding</cite> from RFC 2045
 *
 * <cite>Multipurpose
 * Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</cite> by Freed and Borenstein. </p> <p>
 * The class can be parameterized in the following manner with various constructors: <ul> <li>URL-safe mode: Default
 * off.</li> <li>Line length: Default 76. Line length that aren't multiples of 4 will still essentially end up being
 * multiples of 4 in the encoded data. <li>Line separator: Default is CRLF ("\r\n")</li> </ul> </p> <p> Since this class
 * operates directly on byte streams, and not character streams, it is hard-coded to only encode/decode character
 * encodings which are compatible with the lower 127 ASCII chart (ISO-8859-1, Windows-1252, UTF-8, etc). </p> <p> This
 * class is not thread-safe. Each thread should use its own instance. </p>
 *
 * @author Apache Software Foundation
 * @version $Revision: 1080712 $
 * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>
 * @since 1.0
 */
public class Base64 {
    
    /**
     * BASE32 characters are 6 bits in length. They are formed by taking a block of 3 octets to form a 24-bit string,
     * which is converted into 4 BASE64 characters.
     */
    private static final int BITS_PER_ENCODED_BYTE = 6;
    
    private static final int BYTES_PER_UNENCODED_BLOCK = 3;
    
    private static final int BYTES_PER_ENCODED_BLOCK = 4;
    
    /**
     * Chunk separator per RFC 2045 section 2.1.
     *
     * <p>N.B. The next major release may break compatibility and make this field private. </p>
     *
     * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 2.1</a>
     */
    static final byte[] CHUNK_SEPARATOR = {'\r', '\n'};
    
    /**
     * This array is a lookup table that translates 6-bit positive integer index values into their "Base64 Alphabet"
     * equivalents as specified in Table 1 of RFC 2045.
     *
     * <p>Thanks to "commons" project in ws.apache.org for this code.
     *
     * <p>http://svn.apache.org/repos/asf/webservices/commons/trunk/modules/util/
     */
    private static final byte[] STANDARD_ENCODE_TABLE = {'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', '+', '/'};
    
    /**
     * This is a copy of the STANDARD_ENCODE_TABLE above, but with + and / changed to - and _ to make the encoded Base64
     * results more URL-SAFE. This table is only used when the Base64's mode is set to URL-SAFE.
     */
    private static final byte[] URL_SAFE_ENCODE_TABLE = {'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', '-', '_'};
    
    /**
     * This array is a lookup table that translates Unicode characters drawn from the "Base64 Alphabet" (as specified in
     * Table 1 of RFC 2045) into their 6-bit positive integer equivalents. Characters that are not in the Base64
     * alphabet but fall within the bounds of the array are translated to -1.
     *
     * <p>Note: '+' and '-' both decode to 62. '/' and '_' both decode to 63. This means decoder seamlessly handles
     * both URL_SAFE and STANDARD base64. (The encoder, on the other hand, needs to know ahead of time what to emit).
     *
     * <p>Thanks to "commons" project in ws.apache.org for this code.
     *
     * <p>http://svn.apache.org/repos/asf/webservices/commons/trunk/modules/util/
     */
    private static final byte[] DECODE_TABLE = {-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1,
            62, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8,
            9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, 63, -1, 26, 27, 28, 29,
            30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51};
    
    /**
     * Base64 uses 6-bit fields. Mask used to extract 6 bits, used when encoding
     */
    private static final int MASK_6BITS = 0x3f;
    
    // The static final fields above are used for the original static byte[] methods on Base64.
    // The private member fields below are used with the new streaming approach, which requires
    // some state be preserved between calls of encode() and decode().
    
    /**
     * Encode table to use: either STANDARD or URL_SAFE. Note: the DECODE_TABLE above remains static because it is able
     * to decode both STANDARD and URL_SAFE streams, but the encodeTable must be a member variable so we can switch
     * between the two modes.
     */
    private final byte[] encodeTable;
    
    /**
     * Only one decode table currently; keep for consistency with Base32 code.
     */
    private final byte[] decodeTable = DECODE_TABLE;
    
    /**
     * Line separator for encoding. Not used when decoding. Only used if lineLength > 0.
     */
    private final byte[] lineSeparator;
    
    /**
     * Convenience variable to help us determine when our buffer is going to run out of room and needs resizing.
     * <code>decodeSize = 3 + lineSeparator.length;</code>
     */
    private final int decodeSize;
    
    /**
     * Convenience variable to help us determine when our buffer is going to run out of room and needs resizing.
     * <code>encodeSize = 4 + lineSeparator.length;</code>
     */
    private final int encodeSize;
    
    /**
     * Place holder for the bytes we're dealing with for our based logic. Bitwise operations store and extract the
     * encoding or decoding from this variable.
     */
    private int bitWorkArea;
    
    /**
     * Creates a Base64 codec used for decoding (all modes) and encoding in URL-unsafe mode. <p> When encoding the line
     * length is 0 (no chunking), and the encoding table is STANDARD_ENCODE_TABLE. </p>
     *
     * <p>When decoding all variants are supported. </p>
     */
    public Base64() {
        this(0, CHUNK_SEPARATOR, false);
    }
    
    /**
     * Creates a Base64 codec used for decoding (all modes) and encoding in URL-unsafe mode. <p> When encoding the line
     * length and line separator are given in the constructor, and the encoding table is STANDARD_ENCODE_TABLE. </p> <p>
     * Line lengths that aren't multiples of 4 will still essentially end up being multiples of 4 in the encoded data.
     * </p> <p> When decoding all variants are supported. </p>
     *
     * @param lineLength    Each line of encoded data will be at most of the given length (rounded down to nearest
     *                      multiple of 4). If lineLength <= 0, then the output will not be divided into lines (chunks).
     *                      Ignored when decoding.
     * @param lineSeparator Each line of encoded data will end with this sequence of bytes.
     * @param urlSafe       Instead of emitting '+' and '/' we emit '-' and '_' respectively. urlSafe is only applied to
     *                      encode operations. Decoding seamlessly handles both modes.
     * @throws IllegalArgumentException The provided lineSeparator included some base64 characters. That's not going to
     *                                  work!
     * @since 1.4
     */
    private Base64(int lineLength, byte[] lineSeparator, boolean urlSafe) {
        chunkSeparatorLength = lineSeparator.length;
        unencodedBlockSize = BYTES_PER_UNENCODED_BLOCK;
        encodedBlockSize = BYTES_PER_ENCODED_BLOCK;
        this.lineLength =
                (lineLength > 0 && chunkSeparatorLength > 0) ? (lineLength / encodedBlockSize) * encodedBlockSize : 0;
        if (lineLength > 0) {
            this.encodeSize = BYTES_PER_ENCODED_BLOCK + lineSeparator.length;
            this.lineSeparator = new byte[lineSeparator.length];
            System.arraycopy(lineSeparator, 0, this.lineSeparator, 0, lineSeparator.length);
        } else {
            this.encodeSize = BYTES_PER_ENCODED_BLOCK;
            this.lineSeparator = null;
        }
        this.decodeSize = this.encodeSize - 1;
        this.encodeTable = urlSafe ? URL_SAFE_ENCODE_TABLE : STANDARD_ENCODE_TABLE;
    }
    
    /**
     * Encodes a byte[] containing binary data, into a byte[] containing characters in the alphabet.
     *
     * @param pArray a byte array containing binary data
     * @return A byte array containing only the basen alphabetic character data
     */
    private byte[] encode(byte[] pArray) {
        reset();
        encode(pArray, 0, pArray.length);
        encode(pArray, 0, -1);
        byte[] buf = new byte[pos - readPos];
        readResults(buf, 0, buf.length);
        return buf;
    }
    
    /**
     * <p> Encodes all of the provided data, starting at inPos, for inAvail bytes. Must be called at least twice: once
     * with the data to encode, and once with inAvail set to "-1" to alert encoder that EOF has been reached, so flush
     * last remaining bytes (if not multiple of 3). </p> <p> Thanks to "commons" project in ws.apache.org for the
     * bitwise operations, and general approach. http://svn.apache.org/repos/asf/webservices/commons/trunk/modules/util/
     * </p>
     *
     * @param in      byte[] array of binary data to base64 encode.
     * @param inPos   Position to start reading data from.
     * @param inAvail Amount of bytes available from input for encoding.
     */
    void encode(byte[] in, int inPos, int inAvail) {
        if (eof) {
            return;
        }
        if (inAvail < 0) {
            eof = true;
            if (0 == modulus && lineLength == 0) {
                return;
            }
            ensureBufferSize(encodeSize);
            int savedPos = pos;
            switch (modulus) {
                case 1:
                    buffer[pos++] = encodeTable[(bitWorkArea >> 2) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(bitWorkArea << 4) & MASK_6BITS];
                    
                    if (encodeTable == STANDARD_ENCODE_TABLE) {
                        buffer[pos++] = PAD;
                        buffer[pos++] = PAD;
                    }
                    break;
                
                case 2:
                    buffer[pos++] = encodeTable[(bitWorkArea >> 10) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(bitWorkArea >> 4) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(bitWorkArea << 2) & MASK_6BITS];
                    
                    if (encodeTable == STANDARD_ENCODE_TABLE) {
                        buffer[pos++] = PAD;
                    }
                    break;
                default:
                    break;
            }
            currentLinePos += pos - savedPos;
            /*
             if currentPos == 0 we are at the start of a line, so don't add CRLF
             */
            if (lineLength > 0 && currentLinePos > 0) {
                System.arraycopy(lineSeparator, 0, buffer, pos, lineSeparator.length);
                pos += lineSeparator.length;
            }
        } else {
            for (int i = 0; i < inAvail; i++) {
                ensureBufferSize(encodeSize);
                modulus = (modulus + 1) % BYTES_PER_UNENCODED_BLOCK;
                int b = in[inPos++];
                if (b < 0) {
                    b += 256;
                }
                bitWorkArea = (bitWorkArea << 8) + b;
                if (0 == modulus) {
                    buffer[pos++] = encodeTable[(bitWorkArea >> 18) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(bitWorkArea >> 12) & MASK_6BITS];
                    buffer[pos++] = encodeTable[(bitWorkArea >> 6) & MASK_6BITS];
                    buffer[pos++] = encodeTable[bitWorkArea & MASK_6BITS];
                    currentLinePos += BYTES_PER_ENCODED_BLOCK;
                    if (lineLength > 0 && lineLength <= currentLinePos) {
                        System.arraycopy(lineSeparator, 0, buffer, pos, lineSeparator.length);
                        pos += lineSeparator.length;
                        currentLinePos = 0;
                    }
                }
            }
        }
    }
    
    /**
     * Decodes a byte[] containing characters in the Base-N alphabet.
     *
     * @param pArray A byte array containing Base-N character data
     * @return a byte array containing binary data
     */
    private byte[] decode(byte[] pArray) {
        reset();
        if (pArray == null || pArray.length == 0) {
            return pArray;
        }
        decode(pArray, 0, pArray.length);
        decode(pArray, 0, -1);
        byte[] result = new byte[pos];
        readResults(result, 0, result.length);
        return result;
    }
    
    /**
     * <p> Decodes all of the provided data, starting at inPos, for inAvail bytes. Should be called at least twice:
     * once with the data to decode, and once with inAvail set to "-1" to alert decoder that EOF has been reached. The
     * "-1" call is not necessary when decoding, but it doesn't hurt, either. </p> <p> Ignores all non-base64
     * characters. This is how chunked (e.g. 76 character) data is handled, since CR and LF are silently ignored, but
     * has implications for other bytes, too. This method subscribes to the garbage-in, garbage-out philosophy: it will
     * not check the provided data for validity. </p> <p> Thanks to "commons" project in ws.apache.org for the bitwise
     * operations, and general approach. http://svn.apache.org/repos/asf/webservices/commons/trunk/modules/util/ </p>
     *
     * @param in      byte[] array of ascii data to base64 decode.
     * @param inPos   Position to start reading data from.
     * @param inAvail Amount of bytes available from input for encoding.
     */
    void decode(byte[] in, int inPos, int inAvail) {
        if (eof) {
            return;
        }
        if (inAvail < 0) {
            eof = true;
        }
        for (int i = 0; i < inAvail; i++) {
            ensureBufferSize(decodeSize);
            byte b = in[inPos++];
            if (b == PAD) {
                // We're done.
                eof = true;
                break;
            } else {
                if (b >= 0 && b < DECODE_TABLE.length) {
                    int result = DECODE_TABLE[b];
                    if (result >= 0) {
                        modulus = (modulus + 1) % BYTES_PER_ENCODED_BLOCK;
                        bitWorkArea = (bitWorkArea << BITS_PER_ENCODED_BYTE) + result;
                        if (modulus == 0) {
                            buffer[pos++] = (byte) ((bitWorkArea >> 16) & MASK_8BITS);
                            buffer[pos++] = (byte) ((bitWorkArea >> 8) & MASK_8BITS);
                            buffer[pos++] = (byte) (bitWorkArea & MASK_8BITS);
                        }
                    }
                }
            }
        }
        
        // Two forms of EOF as far as base64 decoder is concerned: actual
        // EOF (-1) and first time '=' character is encountered in stream.
        // This approach makes the '=' padding characters completely optional.
        if (eof && modulus != 0) {
            ensureBufferSize(decodeSize);
            
            // We have some spare bits remaining
            // Output all whole multiples of 8 bits and ignore the rest
            switch (modulus) {
                //   case 1: // 6 bits - ignore entirely
                //       break;
                case 2:
                    bitWorkArea = bitWorkArea >> 4;
                    buffer[pos++] = (byte) ((bitWorkArea) & MASK_8BITS);
                    break;
                case 3:
                    bitWorkArea = bitWorkArea >> 2;
                    buffer[pos++] = (byte) ((bitWorkArea >> 8) & MASK_8BITS);
                    buffer[pos++] = (byte) ((bitWorkArea) & MASK_8BITS);
                    break;
                default:
                    break;
            }
        }
    }
    
    /**
     * Encodes binary data using the base64 algorithm but does not chunk the output.
     *
     * @param binaryData binary data to encode
     * @return byte[] containing Base64 characters in their UTF-8 representation.
     */
    public static byte[] encodeBase64(byte[] binaryData) {
        return encodeBase64(binaryData, false, false, Integer.MAX_VALUE);
    }
    
    /**
     * Encodes binary data using the base64 algorithm, optionally chunking the output into 76 character blocks.
     *
     * @param binaryData    Array containing binary data to encode.
     * @param isChunked     if <code>true</code> this encoder will chunk the base64 output into 76 character blocks
     * @param urlSafe       if <code>true</code> this encoder will emit - and _ instead of the usual + and /
     *                      characters.
     * @param maxResultSize The maximum result size to accept.
     * @return Base64-encoded data.
     * @throws IllegalArgumentException Thrown when the input array needs an output array bigger than maxResultSize
     * @since 1.4
     */
    public static byte[] encodeBase64(byte[] binaryData, boolean isChunked, boolean urlSafe, int maxResultSize) {
        if (binaryData == null || binaryData.length == 0) {
            return binaryData;
        }
        
        // Create this so can use the super-class method
        // Also ensures that the same roundings are performed by the ctor and the code
        Base64 b64 = isChunked ? new Base64(MIME_CHUNK_SIZE, CHUNK_SEPARATOR, urlSafe)
                : new Base64(0, CHUNK_SEPARATOR, urlSafe);
        long len = b64.getEncodedLength(binaryData);
        if (len > maxResultSize) {
            throw new IllegalArgumentException("Input array too big, the output array would be bigger (" + len
                    + ") than the specified maximum size of " + maxResultSize);
        }
        
        return b64.encode(binaryData);
    }
    
    /**
     * Decodes Base64 data into octets.
     *
     * @param base64Data Byte array containing Base64 data
     * @return Array containing decoded data.
     */
    public static byte[] decodeBase64(byte[] base64Data) {
        return new Base64().decode(base64Data);
    }
    
    /**
     * MIME chunk size per RFC 2045 section 6.8.
     *
     * <p> The {@value} character limit does not count the trailing CRLF, but counts all other characters, including
     * any equal signs. </p>
     *
     * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 6.8</a>
     */
    private static final int MIME_CHUNK_SIZE = 76;
    
    private static final int DEFAULT_BUFFER_RESIZE_FACTOR = 2;
    
    /**
     * Defines the default buffer size - currently {@value} - must be large enough for at least one encoded
     * block+separator.
     */
    private static final int DEFAULT_BUFFER_SIZE = 8192;
    
    /**
     * Mask used to extract 8 bits, used in decoding bytes.
     */
    private static final int MASK_8BITS = 0xff;
    
    /**
     * Byte used to pad output.
     */
    private static final byte PAD_DEFAULT = '=';
    
    private static final byte PAD = PAD_DEFAULT;
    
    /**
     * Number of bytes in each full block of unencoded data, e.g. 4 for Base64 and 5 for Base32
     */
    private final int unencodedBlockSize;
    
    /**
     * Number of bytes in each full block of encoded data, e.g. 3 for Base64 and 8 for Base32
     */
    private final int encodedBlockSize;
    
    /**
     * Chunksize for encoding. Not used when decoding. A value of zero or less implies no chunking of the encoded data.
     * Rounded down to nearest multiple of encodedBlockSize.
     */
    private final int lineLength;
    
    /**
     * Size of chunk separator. Not used unless {@link #lineLength} > 0.
     */
    private final int chunkSeparatorLength;
    
    /**
     * Buffer for streaming.
     */
    private byte[] buffer;
    
    /**
     * Position where next character should be written in the buffer.
     */
    private int pos;
    
    /**
     * Position where next character should be read from the buffer.
     */
    private int readPos;
    
    /**
     * Boolean flag to indicate the EOF has been reached. Once EOF has been reached, this object becomes useless, and
     * must be thrown away.
     */
    private boolean eof;
    
    /**
     * Variable tracks how many characters have been written to the current line. Only used when encoding. We use it to
     * make sure each encoded line never goes beyond lineLength (if lineLength > 0).
     */
    private int currentLinePos;
    
    /**
     * Writes to the buffer only occur after every 3/5 reads when encoding, and every 4/8 reads when decoding. This
     * variable helps track that.
     */
    private int modulus;
    
    /**
     * Ensure that the buffer has room for <code>size</code> bytes.
     *
     * @param size minimum spare space required
     */
    private void ensureBufferSize(int size) {
        if ((buffer == null) || (buffer.length < pos + size)) {
            if (buffer == null) {
                buffer = new byte[DEFAULT_BUFFER_SIZE];
                pos = 0;
                readPos = 0;
            } else {
                byte[] b = new byte[buffer.length * DEFAULT_BUFFER_RESIZE_FACTOR];
                System.arraycopy(buffer, 0, b, 0, buffer.length);
                buffer = b;
            }
        }
    }
    
    /**
     * Extracts buffered data into the provided byte[] array, starting at position bPos, up to a maximum of bAvail
     * bytes. Returns how many bytes were actually extracted.
     *
     * @param b      byte[] array to extract the buffered data into.
     * @param bPos   position in byte[] array to start extraction at.
     * @param bAvail amount of bytes we're allowed to extract. We may extract fewer (if fewer are available).
     * @return The number of bytes successfully extracted into the provided byte[] array.
     */
    private int readResults(byte[] b, int bPos, int bAvail) {
        if (buffer != null) {
            int len = Math.min(pos - readPos, bAvail);
            System.arraycopy(buffer, readPos, b, bPos, len);
            readPos += len;
            if (readPos >= pos) {
                buffer = null;
            }
            return len;
        }
        return eof ? -1 : 0;
    }
    
    /**
     * Resets this object to its initial newly constructed state.
     */
    private void reset() {
        buffer = null;
        pos = 0;
        readPos = 0;
        currentLinePos = 0;
        modulus = 0;
        eof = false;
    }
    
    /**
     * Calculates the amount of space needed to encode the supplied array.
     *
     * @param pArray byte[] array which will later be encoded
     * @return amount of space needed to encoded the supplied array. Returns a long since a max-len array will require >
     * Integer.MAX_VALUE
     */
    private long getEncodedLength(byte[] pArray) {
        // Calculate non-chunked size - rounded up to allow for padding
        // cast to long is needed to avoid possibility of overflow
        long len = ((pArray.length + unencodedBlockSize - 1) / unencodedBlockSize) * (long) encodedBlockSize;
        if (lineLength > 0) {
            /*
             Round up to nearest multiple
             */
            len += ((len + lineLength - 1) / lineLength) * chunkSeparatorLength;
        }
        return len;
    }
}
