/*
 * 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
 *
 *      https://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 java.util.Arrays;

import org.apache.commons.codec.CodecPolicy;

/**
 * Provides Base32 encoding and decoding as defined by <a href="https://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>
 * <p>
 * To configure a new instance, use a {@link Builder}. For example:
 * </p>
 * <pre>
 * Base32 base32 = Base32.builder()
 *   .setDecodingPolicy(DecodingPolicy.LENIENT) // default is lenient
 *   .setLineLength(0)                          // default is none
 *   .setLineSeparator('\r', '\n')              // default is CR LF
 *   .setPadding('=')                           // default is '='
 *   .setEncodeTable(customEncodeTable)         // default is RFC 4648 Section 6, Table 3: The Base 32 Alphabet
 *   .get()
 * </pre>
 *
 * @see Base32InputStream
 * @see Base32OutputStream
 * @see <a href="https://www.ietf.org/rfc/rfc4648.txt">RFC 4648</a>
 * @since 1.5
 */
public class Base32 extends BaseNCodec {

    /**
     * Builds {@link Base32} instances.
     *
     * <p>
     * To configure a new instance, use a {@link Builder}. For example:
     * </p>
     *
     * <pre>
     * Base32 base32 = Base32.builder()
     *   .setDecodingPolicy(DecodingPolicy.LENIENT) // default is lenient
     *   .setLineLength(0)                          // default is none
     *   .setLineSeparator('\r', '\n')              // default is CR LF
     *   .setPadding('=')                           // default is '='
     *   .setEncodeTable(customEncodeTable)         // default is RFC 4648 Section 6, Table 3: The Base 32 Alphabet
     *   .get()
     * </pre>
     *
     * @since 1.17.0
     */
    public static class Builder extends AbstractBuilder<Base32, Builder> {

        /**
         * Constructs a new instance using <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32
         * Alphabet</a>.
         */
        public Builder() {
            super(ENCODE_TABLE);
            setDecodeTableRaw(DECODE_TABLE);
            setEncodeTableRaw(ENCODE_TABLE);
            setEncodedBlockSize(BYTES_PER_ENCODED_BLOCK);
            setUnencodedBlockSize(BYTES_PER_UNENCODED_BLOCK);
        }

        @Override
        public Base32 get() {
            return new Base32(this);
        }

        @Override
        public Builder setEncodeTable(final byte... encodeTable) {
            super.setDecodeTableRaw(Arrays.equals(encodeTable, HEX_ENCODE_TABLE) ? HEX_DECODE_TABLE : DECODE_TABLE);
            return super.setEncodeTable(encodeTable);
        }

        /**
         * Sets the decode table to use Base32 hexadecimal if {@code true}, otherwise use the Base32 alphabet.
         * <p>
         * This overrides a value previously set with {@link #setEncodeTable(byte...)}.
         * </p>
         *
         * @param useHex use Base32 hexadecimal if {@code true}, otherwise use the Base32 alphabet.
         * @return {@code this} instance.
         * @since 1.18.0
         */
        public Builder setHexDecodeTable(final boolean useHex) {
            return setEncodeTable(decodeTable(useHex));
        }

        /**
         * Sets the encode table to use Base32 hexadecimal if {@code true}, otherwise use the Base32 alphabet.
         * <p>
         * This overrides a value previously set with {@link #setEncodeTable(byte...)}.
         * </p>
         *
         * @param useHex
         *               <ul>
         *               <li>If true, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-7">RFC 4648 Section 7, Table 4: Base 32 Encoding
         *               with Extended Hex Alphabet</a></li>
         *               <li>If false, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32
         *               Alphabet</a></li>
         *               </ul>
         * @return {@code this} instance.
         * @since 1.18.0
         */
        public Builder setHexEncodeTable(final boolean useHex) {
            return setEncodeTable(encodeTable(useHex));
        }
    }

    /**
     * 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.
     */
    // @formatter:off
    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
    };
    // @formatter:on

    /**
     * This array is a lookup table that translates 5-bit positive integer index values into their "Base32 Alphabet" equivalents as specified in
     * <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32 Alphabet</a>.
     *
     * @see <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32 Alphabet</a>
     */
    // @formatter:off
    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',
    };
    // @formatter:on

    /**
     * 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.
     */
    // @formatter:off
    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
    };
    // @formatter:on

    /**
     * This array is a lookup table that translates 5-bit positive integer index values into their "Base 32 Encoding with Extended Hex Alphabet" equivalents as
     * specified in <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-7">RFC 4648 Section 7, Table 4: Base 32 Encoding with Extended Hex
     * Alphabet</a>.
     *
     * @see <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-7">RFC 4648 Section 7, Table 4: Base 32 Encoding with Extended Hex Alphabet</a>
     */
    // @formatter:off
    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',
    };
    // @formatter:on

    /** Mask used to extract 5 bits, used when encoding Base32 bytes */
    private static final int MASK_5_BITS = 0x1f;

    /** Mask used to extract 4 bits, used when decoding final trailing character. */
    private static final long MASK_4_BITS = 0x0fL;

    /** Mask used to extract 3 bits, used when decoding final trailing character. */
    private static final long MASK_3_BITS = 0x07L;

    /** Mask used to extract 2 bits, used when decoding final trailing character. */
    private static final long MASK_2_BITS = 0x03L;

    /** Mask used to extract 1 bits, used when decoding final trailing character. */
    private static final long MASK_1_BITS = 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().

    /**
     * Creates a new Builder.
     *
     * <p>
     * To configure a new instance, use a {@link Builder}. For example:
     * </p>
     *
     * <pre>
     * Base32 base32 = Base32.builder()
     *   .setDecodingPolicy(DecodingPolicy.LENIENT) // default is lenient
     *   .setLineLength(0)                          // default is none
     *   .setLineSeparator('\r', '\n')              // default is CR LF
     *   .setPadding('=')                           // default is '='
     *   .setEncodeTable(customEncodeTable)         // default is RFC 4648 Section 6, Table 3: The Base 32 Alphabet
     *   .get()
     * </pre>
     *
     * @return a new Builder.
     * @since 1.17.0
     */
    public static Builder builder() {
        return new Builder();
    }

    private static byte[] decodeTable(final boolean useHex) {
        return useHex ? HEX_DECODE_TABLE : DECODE_TABLE;
    }

    /**
     * Gets the encoding table that matches {@code useHex}.
     *
     * @param useHex
     *               <ul>
     *               <li>If true, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-7">RFC 4648 Section 7, Table 4: Base 32 Encoding with
     *               Extended Hex Alphabet</a></li>
     *               <li>If false, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32
     *               Alphabet</a></li>
     *               </ul>
     * @return the encoding table that matches {@code useHex}.
     */
    private static byte[] encodeTable(final boolean useHex) {
        return useHex ? HEX_ENCODE_TABLE : ENCODE_TABLE;
    }

    /**
     * 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;

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

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

    /**
     * Constructs a Base32 codec used for decoding and encoding.
     * <p>
     * When encoding the line length is 0 (no chunking).
     * </p>
     *
     * @param useHex
     *               <ul>
     *               <li>If true, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-7">RFC 4648 Section 7, Table 4: Base 32 Encoding with
     *               Extended Hex Alphabet</a></li>
     *               <li>If false, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32
     *               Alphabet</a></li>
     *               </ul>
     * @deprecated Use {@link #builder()} and {@link Builder}.
     */
    @Deprecated
    public Base32(final boolean useHex) {
        this(0, null, useHex, PAD_DEFAULT);
    }

    /**
     * Constructs a Base32 codec used for decoding and encoding.
     * <p>
     * When encoding the line length is 0 (no chunking).
     * </p>
     *
     * @param useHex
     *               <ul>
     *               <li>If true, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-7">RFC 4648 Section 7, Table 4: Base 32 Encoding with
     *               Extended Hex Alphabet</a></li>
     *               <li>If false, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32
     *               Alphabet</a></li>
     *               </ul>
     * @param padding byte used as padding byte.
     * @deprecated Use {@link #builder()} and {@link Builder}.
     */
    @Deprecated
    public Base32(final boolean useHex, final byte padding) {
        this(0, null, useHex, padding);
    }

    private Base32(final Builder builder) {
        super(builder);
        if (builder.getLineLength() > 0) {
            final byte[] lineSeparator = builder.getLineSeparator();
            // 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;
        } else {
            this.encodeSize = BYTES_PER_ENCODED_BLOCK;
            this.lineSeparator = null;
        }
        if (isInAlphabet(builder.getPadding()) || Character.isWhitespace(builder.getPadding())) {
            throw new IllegalArgumentException("pad must not be in alphabet or whitespace");
        }
    }

    /**
     * Constructs 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.
     * @deprecated Use {@link #builder()} and {@link Builder}.
     */
    @Deprecated
    public Base32(final byte pad) {
        this(false, pad);
    }

    /**
     * Constructs 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.
     * @deprecated Use {@link #builder()} and {@link Builder}.
     */
    @Deprecated
    public Base32(final int lineLength) {
        this(lineLength, CHUNK_SEPARATOR);
    }

    /**
     * Constructs 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.
     * @deprecated Use {@link #builder()} and {@link Builder}.
     */
    @Deprecated
    public Base32(final int lineLength, final byte[] lineSeparator) {
        this(lineLength, lineSeparator, false, PAD_DEFAULT);
    }

    /**
     * Constructs 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
     *               <ul>
     *               <li>If true, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-7">RFC 4648 Section 7, Table 4: Base 32 Encoding with
     *               Extended Hex Alphabet</a></li>
     *               <li>If false, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32
     *               Alphabet</a></li>
     *               </ul>
     * @throws IllegalArgumentException Thrown when the {@code lineSeparator} contains Base32 characters. Or the lineLength &gt; 0 and lineSeparator is null.
     * @deprecated Use {@link #builder()} and {@link Builder}.
     */
    @Deprecated
    public Base32(final int lineLength, final byte[] lineSeparator, final boolean useHex) {
        this(lineLength, lineSeparator, useHex, PAD_DEFAULT);
    }

    /**
     * Constructs 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
     *               <ul>
     *               <li>If true, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-7">RFC 4648 Section 7, Table 4: Base 32 Encoding with
     *               Extended Hex Alphabet</a></li>
     *               <li>If false, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32
     *               Alphabet</a></li>
     *               </ul>
     * @param padding       padding byte.
     * @throws IllegalArgumentException Thrown when the {@code lineSeparator} contains Base32 characters. Or the lineLength &gt; 0 and lineSeparator is null.
     * @deprecated Use {@link #builder()} and {@link Builder}.
     */
    @Deprecated
    public Base32(final int lineLength, final byte[] lineSeparator, final boolean useHex, final byte padding) {
        this(lineLength, lineSeparator, useHex, padding, DECODING_POLICY_DEFAULT);
    }

    /**
     * Constructs 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
     *               <ul>
     *               <li>If true, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-7">RFC 4648 Section 7, Table 4: Base 32 Encoding with
     *               Extended Hex Alphabet</a></li>
     *               <li>If false, then use <a href="https://datatracker.ietf.org/doc/html/rfc4648#section-6">RFC 4648 Section 6, Table 3: The Base 32
     *               Alphabet</a></li>
     *               </ul>
     * @param padding        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
     * @deprecated Use {@link #builder()} and {@link Builder}.
     */
    @Deprecated
    public Base32(final int lineLength, final byte[] lineSeparator, final boolean useHex, final byte padding, final CodecPolicy decodingPolicy) {
        // @formatter:off
        this(builder()
                .setLineLength(lineLength)
                .setLineSeparator(lineSeparator != null ? lineSeparator : EMPTY_BYTE_ARRAY)
                .setDecodeTable(decodeTable(useHex))
                .setEncodeTableRaw(encodeTable(useHex))
                .setPadding(padding)
                .setDecodingPolicy(decodingPolicy));
        // @formatter:on
    }

    /**
     * <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 (for example 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;
        }
        final int decodeSize = this.encodeSize - 1;
        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();
                // falls-through
            case 2: // 10 bits, drop 2 and output one byte
                validateCharacter(MASK_2_BITS, 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_4_BITS, 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_1_BITS, 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_3_BITS, 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_5_BITS]; // 8-1*5 = 3
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea << 2) & MASK_5_BITS]; // 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_5_BITS]; // 16-1*5 = 11
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 6) & MASK_5_BITS]; // 16-2*5 = 6
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 1) & MASK_5_BITS]; // 16-3*5 = 1
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea << 4) & MASK_5_BITS]; // 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_5_BITS]; // 24-1*5 = 19
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 14) & MASK_5_BITS]; // 24-2*5 = 14
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 9) & MASK_5_BITS]; // 24-3*5 = 9
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 4) & MASK_5_BITS]; // 24-4*5 = 4
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea << 1) & MASK_5_BITS]; // 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_5_BITS]; // 32-1*5 = 27
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 22) & MASK_5_BITS]; // 32-2*5 = 22
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 17) & MASK_5_BITS]; // 32-3*5 = 17
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 12) & MASK_5_BITS]; // 32-4*5 = 12
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 7) & MASK_5_BITS]; // 32-5*5 = 7
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 2) & MASK_5_BITS]; // 32-6*5 = 2
                buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea << 3) & MASK_5_BITS]; // 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_5_BITS];
                    buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 30) & MASK_5_BITS];
                    buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 25) & MASK_5_BITS];
                    buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 20) & MASK_5_BITS];
                    buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 15) & MASK_5_BITS];
                    buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 10) & MASK_5_BITS];
                    buffer[context.pos++] = encodeTable[(int) (context.lbitWorkArea >> 5) & MASK_5_BITS];
                    buffer[context.pos++] = encodeTable[(int) context.lbitWorkArea & MASK_5_BITS];
                    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;
                    }
                }
            }
        }
    }

    /**
     * Gets the line separator (for testing only).
     *
     * @return the line separator.
     */
    byte[] getLineSeparator() {
        return lineSeparator;
    }

    /**
     * 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 isInAlphabet(octet, decodeTable);
    }

    /**
     * Validates whether decoding the final trailing character is possible in the context of the set of possible Base32 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 " +
                    "Base32 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 " +
                    "Base32 alphabet but not a possible encoding. Decoding requires either 2, 4, 5, or 7 trailing 5-bit characters to create bytes.");
        }
    }
}
