/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.codec.binary;

import org.apache.commons.codec.CodecPolicy;

/**
 * Provides Base32 encoding and decoding as defined by <a href="http://www.ietf.org/rfc/rfc4648.txt">RFC 4648</a>.
 *
 * <p>
 * The class can be parameterized in the following manner with various constructors:
 * </p>
 * <ul>
 * <li>Whether to use the "base32hex" variant instead of the default "base32"</li>
 * <li>Line length: Default 76. Line length that aren't multiples of 8 will still essentially end up being multiples of
 * 8 in the encoded data.
 * <li>Line separator: Default is CRLF ("\r\n")</li>
 * </ul>
 * <p>
 * This class operates directly on byte streams, and not character streams.
 * </p>
 * <p>
 * This class is thread-safe.
 * </p>
 *
 * @see <a href="http://www.ietf.org/rfc/rfc4648.txt">RFC 4648</a>
 *
 * @since 1.5
 */
public class Base32 extends BaseNCodec {

    /**
     * BASE32 characters are 5 bits in length.
     * They are formed by taking a block of five octets to form a 40-bit string,
     * which is converted into eight BASE32 characters.
     */
    private static final int BITS_PER_ENCODED_BYTE = 5;
    private static final int BYTES_PER_ENCODED_BLOCK = 8;
    private static final int BYTES_PER_UNENCODED_BLOCK = 5;

    /**
     * This array is a lookup table that translates Unicode characters drawn from the "Base32 Alphabet" (as specified
     * in Table 3 of RFC 4648) into their 5-bit positive integer equivalents. Characters that are not in the Base32
     * alphabet but fall within the bounds of the array are translated to -1.
     */
    private static final byte[] DECODE_TABLE = {
         //  0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 00-0f
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-1f
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 20-2f
            -1, -1, 26, 27, 28, 29, 30, 31, -1, -1, -1, -1, -1, -1, -1, -1, // 30-3f 2-7
            -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, // 40-4f A-O
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,                     // 50-5a P-Z
                                                        -1, -1, -1, -1, -1, // 5b-5f
            -1,  0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, // 60-6f a-o
            15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25,                     // 70-7a p-z
    };

    /**
     * This array is a lookup table that translates 5-bit positive integer index values into their "Base32 Alphabet"
     * equivalents as specified in Table 3 of RFC 4648.
     */
    private static final byte[] 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',
            '2', '3', '4', '5', '6', '7',
    };

    /**
     * This array is a lookup table that translates Unicode characters drawn from the "Base32 Hex Alphabet" (as
     * specified in Table 4 of RFC 4648) into their 5-bit positive integer equivalents. Characters that are not in the
     * Base32 Hex alphabet but fall within the bounds of the array are translated to -1.
     */
    private static final byte[] HEX_DECODE_TABLE = {
         //  0   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 00-0f
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 10-1f
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, // 20-2f
             0,  1,  2,  3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1, // 30-3f 0-9
            -1, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, // 40-4f A-O
            25, 26, 27, 28, 29, 30, 31,                                     // 50-56 P-V
                                        -1, -1, -1, -1, -1, -1, -1, -1, -1, // 57-5f
            -1, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, // 60-6f a-o
            25, 26, 27, 28, 29, 30, 31                                      // 70-76 p-v
    };

    /**
     * This array is a lookup table that translates 5-bit positive integer index values into their
     * "Base32 Hex Alphabet" equivalents as specified in Table 4 of RFC 4648.
     */
    private static final byte[] HEX_ENCODE_TABLE = {
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
            'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M',
            'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V',
    };

    /** Mask used to extract 5 bits, used when encoding Base32 bytes */
    private static final int MASK_5BITS = 0x1f;
    /** Mask used to extract 4 bits, used when decoding final trailing character. */
    private static final long MASK_4BITS = 0x0fL;
    /** Mask used to extract 3 bits, used when decoding final trailing character. */
    private static final long MASK_3BITS = 0x07L;
    /** Mask used to extract 2 bits, used when decoding final trailing character. */
    private static final long MASK_2BITS = 0x03L;
    /** Mask used to extract 1 bits, used when decoding final trailing character. */
    private static final long MASK_1BITS = 0x01L;

    // The static final fields above are used for the original static byte[] methods on Base32.
    // The private member fields below are used with the new streaming approach, which requires
    // some state be preserved between calls of encode() and decode().

    /**
     * Convenience variable to help us determine when our buffer is going to run out of room and needs resizing.
     * {@code decodeSize = {@link #BYTES_PER_ENCODED_BLOCK} - 1 + lineSeparator.length;}
     */
    private final int decodeSize;

    /**
     * Decode table to use.
     */
    private final byte[] decodeTable;

    /**
     * Convenience variable to help us determine when our buffer is going to run out of room and needs resizing.
     * {@code encodeSize = {@link #BYTES_PER_ENCODED_BLOCK} + lineSeparator.length;}
     */
    private final int encodeSize;

    /**
     * Encode table to use.
     */
    private final byte[] encodeTable;

    /**
     * Line separator for encoding. Not used when decoding. Only used if lineLength &gt; 0.
     */
    private final byte[] lineSeparator;

    /**
     * Creates a Base32 codec used for decoding and encoding.
     * <p>
     * When encoding the line length is 0 (no chunking).
     * </p>
     */
    public Base32() {
        this(false);
    }

    /**
     * Creates a Base32 codec used for decoding and encoding.
     * <p>
     * When encoding the line length is 0 (no chunking).
     * </p>
     * @param useHex if {@code true} then use Base32 Hex alphabet
     */
    public Base32(final boolean useHex) {
        this(0, null, useHex, PAD_DEFAULT);
    }

    /**
     * Creates a Base32 codec used for decoding and encoding.
     * <p>
     * When encoding the line length is 0 (no chunking).
     * </p>
     * @param useHex if {@code true} then use Base32 Hex alphabet
     * @param padding byte used as padding byte.
     */
    public Base32(final boolean useHex, final byte padding) {
        this(0, null, useHex, padding);
    }

    /**
     * Creates a Base32 codec used for decoding and encoding.
     * <p>
     * When encoding the line length is 0 (no chunking).
     * </p>
     * @param pad byte used as padding byte.
     */
    public Base32(final byte pad) {
        this(false, pad);
    }

    /**
     * Creates a Base32 codec used for decoding and encoding.
     * <p>
     * When encoding the line length is given in the constructor, the line separator is CRLF.
     * </p>
     *
     * @param lineLength
     *            Each line of encoded data will be at most of the given length (rounded down to the nearest multiple of
     *            8). If lineLength &lt;= 0, then the output will not be divided into lines (chunks). Ignored when
     *            decoding.
     */
    public Base32(final int lineLength) {
        this(lineLength, CHUNK_SEPARATOR);
    }

    /**
     * Creates a Base32 codec used for decoding and encoding.
     * <p>
     * When encoding the line length and line separator are given in the constructor.
     * </p>
     * <p>
     * Line lengths that aren't multiples of 8 will still essentially end up being multiples of 8 in the encoded data.
     * </p>
     *
     * @param lineLength
     *            Each line of encoded data will be at most of the given length (rounded down to the nearest multiple of
     *            8). If lineLength &lt;= 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.
     * @throws IllegalArgumentException
     *             Thrown when the {@code lineSeparator} contains Base32 characters.
     */
    public Base32(final int lineLength, final byte[] lineSeparator) {
        this(lineLength, lineSeparator, false, PAD_DEFAULT);
    }

    /**
     * Creates a Base32 / Base32 Hex codec used for decoding and encoding.
     * <p>
     * When encoding the line length and line separator are given in the constructor.
     * </p>
     * <p>
     * Line lengths that aren't multiples of 8 will still essentially end up being multiples of 8 in the encoded data.
     * </p>
     *
     * @param lineLength
     *            Each line of encoded data will be at most of the given length (rounded down to the nearest multiple of
     *            8). If lineLength &lt;= 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 useHex
     *            if {@code true}, then use Base32 Hex alphabet, otherwise use Base32 alphabet
     * @throws IllegalArgumentException
     *             Thrown when the {@code lineSeparator} contains Base32 characters. Or the
     *             lineLength &gt; 0 and lineSeparator is null.
     */
    public Base32(final int lineLength, final byte[] lineSeparator, final boolean useHex) {
        this(lineLength, lineSeparator, useHex, PAD_DEFAULT);
    }

    /**
     * Creates a Base32 / Base32 Hex codec used for decoding and encoding.
     * <p>
     * When encoding the line length and line separator are given in the constructor.
     * </p>
     * <p>
     * Line lengths that aren't multiples of 8 will still essentially end up being multiples of 8 in the encoded data.
     * </p>
     *
     * @param lineLength
     *            Each line of encoded data will be at most of the given length (rounded down to the nearest multiple of
     *            8). If lineLength &lt;= 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 useHex
     *            if {@code true}, then use Base32 Hex alphabet, otherwise use Base32 alphabet
     * @param padding byte used as padding byte.
     * @throws IllegalArgumentException
     *             Thrown when the {@code lineSeparator} contains Base32 characters. Or the
     *             lineLength &gt; 0 and lineSeparator is null.
     */
    public Base32(final int lineLength, final byte[] lineSeparator, final boolean useHex, final byte padding) {
        this(lineLength, lineSeparator, useHex, padding, DECODING_POLICY_DEFAULT);
    }

    /**
     * Creates a Base32 / Base32 Hex codec used for decoding and encoding.
     * <p>
     * When encoding the line length and line separator are given in the constructor.
     * </p>
     * <p>
     * Line lengths that aren't multiples of 8 will still essentially end up being multiples of 8 in the encoded data.
     * </p>
     *
     * @param lineLength
     *            Each line of encoded data will be at most of the given length (rounded down to the nearest multiple of
     *            8). If lineLength &lt;= 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 useHex
     *            if {@code true}, then use Base32 Hex alphabet, otherwise use Base32 alphabet
     * @param padding byte used as padding byte.
     * @param decodingPolicy The decoding policy.
     * @throws IllegalArgumentException
     *             Thrown when the {@code lineSeparator} contains Base32 characters. Or the
     *             lineLength &gt; 0 and lineSeparator is null.
     * @since 1.15
     */
    public Base32(final int lineLength, final byte[] lineSeparator, final boolean useHex,
                  final byte padding, final CodecPolicy decodingPolicy) {
        super(BYTES_PER_UNENCODED_BLOCK, BYTES_PER_ENCODED_BLOCK, lineLength,
                lineSeparator == null ? 0 : lineSeparator.length, padding, decodingPolicy);
        if (useHex) {
            this.encodeTable = HEX_ENCODE_TABLE;
            this.decodeTable = HEX_DECODE_TABLE;
        } else {
            this.encodeTable = ENCODE_TABLE;
            this.decodeTable = DECODE_TABLE;
        }
        if (lineLength > 0) {
            if (lineSeparator == null) {
                throw new IllegalArgumentException("lineLength " + lineLength + " > 0, but lineSeparator is null");
            }
            // Must be done after initializing the tables
            if (containsAlphabetOrPad(lineSeparator)) {
                final String sep = StringUtils.newStringUtf8(lineSeparator);
                throw new IllegalArgumentException("lineSeparator must not contain Base32 characters: [" + sep + "]");
            }
            this.encodeSize = BYTES_PER_ENCODED_BLOCK + lineSeparator.length;
            this.lineSeparator = lineSeparator.clone();
        } else {
            this.encodeSize = BYTES_PER_ENCODED_BLOCK;
            this.lineSeparator = null;
        }
        this.decodeSize = this.encodeSize - 1;

        if (isInAlphabet(padding) || Character.isWhitespace(padding)) {
            throw new IllegalArgumentException("pad must not be in alphabet or whitespace");
        }
    }

    /**
     * <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-Base32 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>
     * Output is written to {@link org.apache.commons.codec.binary.BaseNCodec.Context#buffer Context#buffer} as 8-bit
     * octets, using {@link org.apache.commons.codec.binary.BaseNCodec.Context#pos Context#pos} as the buffer position
     * </p>
     *
     * @param input byte[] array of ASCII data to Base32 decode.
     * @param inPos Position to start reading data from.
     * @param inAvail Amount of bytes available from input for decoding.
     * @param context the context to be used
     */
    @Override
    void decode(final byte[] input, int inPos, final int inAvail, final Context context) {
        // package protected for access from I/O streams

        if (context.eof) {
            return;
        }
        if (inAvail < 0) {
            context.eof = true;
        }
        for (int i = 0; i < inAvail; i++) {
            final byte b = input[inPos++];
            if (b == pad) {
                // We're done.
                context.eof = true;
                break;
            }
            final byte[] buffer = ensureBufferSize(decodeSize, context);
            if (b >= 0 && b < this.decodeTable.length) {
                final int result = this.decodeTable[b];
                if (result >= 0) {
                    context.modulus = (context.modulus+1) % BYTES_PER_ENCODED_BLOCK;
                    // collect decoded bytes
                    context.lbitWorkArea = (context.lbitWorkArea << BITS_PER_ENCODED_BYTE) + result;
                    if (context.modulus == 0) { // we can output the 5 bytes
                        buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 32) & MASK_8BITS);
                        buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 24) & MASK_8BITS);
                        buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 16) & MASK_8BITS);
                        buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 8) & MASK_8BITS);
                        buffer[context.pos++] = (byte) (context.lbitWorkArea & MASK_8BITS);
                    }
                }
            }
        }

        // Two forms of EOF as far as Base32 decoder is concerned: actual
        // EOF (-1) and first time '=' character is encountered in stream.
        // This approach makes the '=' padding characters completely optional.
        if (context.eof && context.modulus > 0) { // if modulus == 0, nothing to do
            final byte[] buffer = ensureBufferSize(decodeSize, context);

            // We ignore partial bytes, i.e. only multiples of 8 count.
            // Any combination not part of a valid encoding is either partially decoded
            // or will raise an exception. Possible trailing characters are 2, 4, 5, 7.
            // It is not possible to encode with 1, 3, 6 trailing characters.
            // For backwards compatibility 3 & 6 chars are decoded anyway rather than discarded.
            // See the encode(byte[]) method EOF section.
            switch (context.modulus) {
//              case 0 : // impossible, as excluded above
                case 1 : // 5 bits - either ignore entirely, or raise an exception
                    validateTrailingCharacters();
                case 2 : // 10 bits, drop 2 and output one byte
                    validateCharacter(MASK_2BITS, context);
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 2) & MASK_8BITS);
                    break;
                case 3 : // 15 bits, drop 7 and output 1 byte, or raise an exception
                    validateTrailingCharacters();
                    // Not possible from a valid encoding but decode anyway
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 7) & MASK_8BITS);
                    break;
                case 4 : // 20 bits = 2*8 + 4
                    validateCharacter(MASK_4BITS, context);
                    context.lbitWorkArea = context.lbitWorkArea >> 4; // drop 4 bits
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 8) & MASK_8BITS);
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea) & MASK_8BITS);
                    break;
                case 5 : // 25 bits = 3*8 + 1
                    validateCharacter(MASK_1BITS, context);
                    context.lbitWorkArea = context.lbitWorkArea >> 1;
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 16) & MASK_8BITS);
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 8) & MASK_8BITS);
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea) & MASK_8BITS);
                    break;
                case 6 : // 30 bits = 3*8 + 6, or raise an exception
                    validateTrailingCharacters();
                    // Not possible from a valid encoding but decode anyway
                    context.lbitWorkArea = context.lbitWorkArea >> 6;
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 16) & MASK_8BITS);
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 8) & MASK_8BITS);
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea) & MASK_8BITS);
                    break;
                case 7 : // 35 bits = 4*8 +3
                    validateCharacter(MASK_3BITS, context);
                    context.lbitWorkArea = context.lbitWorkArea >> 3;
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 24) & MASK_8BITS);
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 16) & MASK_8BITS);
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea >> 8) & MASK_8BITS);
                    buffer[context.pos++] = (byte) ((context.lbitWorkArea) & MASK_8BITS);
                    break;
                default:
                    // modulus can be 0-7, and we excluded 0,1 already
                    throw new IllegalStateException("Impossible modulus " + context.modulus);
            }
        }
    }

    /**
     * <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 5).
     * </p>
     *
     * @param input
     *            byte[] array of binary data to Base32 encode.
     * @param inPos
     *            Position to start reading data from.
     * @param inAvail
     *            Amount of bytes available from input for encoding.
     * @param context the context to be used
     */
    @Override
    void encode(final byte[] input, int inPos, final int inAvail, final Context context) {
        // package protected for access from I/O streams

        if (context.eof) {
            return;
        }
        // inAvail < 0 is how we're informed of EOF in the underlying data we're
        // encoding.
        if (inAvail < 0) {
            context.eof = true;
            if (0 == context.modulus && lineLength == 0) {
                return; // no leftovers to process and not using chunking
            }
            final byte[] buffer = ensureBufferSize(encodeSize, context);
            final int savedPos = context.pos;
            switch (context.modulus) { // % 5
                case 0 :
                    break;
                case 1 : // Only 1 octet; take top 5 bits then remainder
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 3) & MASK_5BITS]; // 8-1*5 = 3
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea << 2) & MASK_5BITS]; // 5-3=2
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    break;
                case 2 : // 2 octets = 16 bits to use
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 11) & MASK_5BITS]; // 16-1*5 = 11
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >>  6) & MASK_5BITS]; // 16-2*5 = 6
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >>  1) & MASK_5BITS]; // 16-3*5 = 1
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea <<  4) & MASK_5BITS]; // 5-1 = 4
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    break;
                case 3 : // 3 octets = 24 bits to use
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 19) & MASK_5BITS]; // 24-1*5 = 19
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 14) & MASK_5BITS]; // 24-2*5 = 14
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >>  9) & MASK_5BITS]; // 24-3*5 = 9
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >>  4) & MASK_5BITS]; // 24-4*5 = 4
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea <<  1) & MASK_5BITS]; // 5-4 = 1
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    buffer[context.pos++] = pad;
                    break;
                case 4 : // 4 octets = 32 bits to use
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 27) & MASK_5BITS]; // 32-1*5 = 27
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 22) & MASK_5BITS]; // 32-2*5 = 22
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 17) & MASK_5BITS]; // 32-3*5 = 17
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 12) & MASK_5BITS]; // 32-4*5 = 12
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >>  7) & MASK_5BITS]; // 32-5*5 =  7
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >>  2) & MASK_5BITS]; // 32-6*5 =  2
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea <<  3) & MASK_5BITS]; // 5-2 = 3
                    buffer[context.pos++] = pad;
                    break;
                default:
                    throw new IllegalStateException("Impossible modulus " + context.modulus);
            }
            context.currentLinePos += context.pos - savedPos; // keep track of current line position
            // if currentPos == 0 we are at the start of a line, so don't add CRLF
            if (lineLength > 0 && context.currentLinePos > 0){ // add chunk separator if required
                System.arraycopy(lineSeparator, 0, buffer, context.pos, lineSeparator.length);
                context.pos += lineSeparator.length;
            }
        } else {
            for (int i = 0; i < inAvail; i++) {
                final byte[] buffer = ensureBufferSize(encodeSize, context);
                context.modulus = (context.modulus+1) % BYTES_PER_UNENCODED_BLOCK;
                int b = input[inPos++];
                if (b < 0) {
                    b += 256;
                }
                context.lbitWorkArea = (context.lbitWorkArea << 8) + b; // BITS_PER_BYTE
                if (0 == context.modulus) { // we have enough bytes to create our output
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 35) & MASK_5BITS];
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 30) & MASK_5BITS];
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 25) & MASK_5BITS];
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 20) & MASK_5BITS];
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 15) & MASK_5BITS];
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 10) & MASK_5BITS];
                    buffer[context.pos++] = encodeTable[(int)(context.lbitWorkArea >> 5) & MASK_5BITS];
                    buffer[context.pos++] = encodeTable[(int)context.lbitWorkArea & MASK_5BITS];
                    context.currentLinePos += BYTES_PER_ENCODED_BLOCK;
                    if (lineLength > 0 && lineLength <= context.currentLinePos) {
                        System.arraycopy(lineSeparator, 0, buffer, context.pos, lineSeparator.length);
                        context.pos += lineSeparator.length;
                        context.currentLinePos = 0;
                    }
                }
            }
        }
    }

    /**
     * Returns whether or not the {@code octet} is in the Base32 alphabet.
     *
     * @param octet
     *            The value to test
     * @return {@code true} if the value is defined in the Base32 alphabet {@code false} otherwise.
     */
    @Override
    public boolean isInAlphabet(final byte octet) {
        return octet >= 0 && octet < decodeTable.length && decodeTable[octet] != -1;
    }

    /**
     * Validates whether decoding the final trailing character is possible in the context
     * of the set of possible base 32 values.
     * <p>
     * The character is valid if the lower bits within the provided mask are zero. This
     * is used to test the final trailing base-32 digit is zero in the bits that will be discarded.
     * </p>
     *
     * @param emptyBitsMask The mask of the lower bits that should be empty
     * @param context the context to be used
     *
     * @throws IllegalArgumentException if the bits being checked contain any non-zero value
     */
    private void validateCharacter(final long emptyBitsMask, final Context context) {
        // Use the long bit work area
        if (isStrictDecoding() && (context.lbitWorkArea & emptyBitsMask) != 0) {
            throw new IllegalArgumentException(
                "Strict decoding: Last encoded character (before the paddings if any) is a valid " +
                "base 32 alphabet but not a possible encoding. " +
                "Expected the discarded bits from the character to be zero.");
        }
    }

    /**
     * Validates whether decoding allows final trailing characters that cannot be
     * created during encoding.
     *
     * @throws IllegalArgumentException if strict decoding is enabled
     */
    private void validateTrailingCharacters() {
        if (isStrictDecoding()) {
            throw new IllegalArgumentException(
                "Strict decoding: Last encoded character(s) (before the paddings if any) are valid " +
                "base 32 alphabet but not a possible encoding. " +
                "Decoding requires either 2, 4, 5, or 7 trailing 5-bit characters to create bytes.");
        }
    }
}
