/*
 * Hunt - A refined core library for D programming language.
 *
 * Copyright (C) 2018-2019 HuntLabs
 *
 * Website: https://www.huntlabs.net/
 *
 * Licensed under the Apache-2.0 License.
 *
 */

module hunt.io.BufferUtils;

import hunt.Exceptions;
import hunt.io.ByteBuffer;
import hunt.io.HeapByteBuffer;

import hunt.util.ConverterUtils;
import hunt.util.StringBuilder;

import std.conv;
import std.range;


/**
 * Buffer utility methods.
 * <p>
 * The standard JVM {@link ByteBuffer} can exist in two modes: In fill mode the
 * valid data is between 0 and pos; In flush mode the valid data is between the
 * pos and the limit. The various ByteBuffer methods assume a mode and some of
 * them will switch or enforce a mode: Allocate and clear set fill mode; flip
 * and compact switch modes; read and write assume fill and flush modes. This
 * duality can result in confusing code such as:
 * </p>
 * <p>
 * <pre>
 * buffer.clear();
 * channel.write(buffer);
 * </pre>
 * <p>
 * Which looks as if it should write no data, but in fact writes the buffer
 * worth of garbage.
 * </p>
 * <p>
 * The BufferUtils class provides a set of utilities that operate on the
 * convention that ByteBuffers will always be left, passed in an API or returned
 * from a method in the flush mode - ie with valid data between the pos and
 * limit. This convention is adopted so as to avoid confusion as to what state a
 * buffer is in and to avoid excessive copying of data that can result with the
 * usage of compress.
 * </p>
 * <p>
 * Thus this class provides alternate implementations of {@link #allocate(int)},
 * {@link #allocateDirect(int)} and {@link #clear(ByteBuffer)} that leave the
 * buffer in flush mode. Thus the following tests will pass:
 * </p>
 * <p>
 * <pre>
 * ByteBuffer buffer = BufferUtils.allocate(1024);
 * assert (buffer.remaining() == 0);
 * BufferUtils.clear(buffer);
 * assert (buffer.remaining() == 0);
 * </pre>
 * <p>
 * If the BufferUtils methods {@link #fill(ByteBuffer, byte[], int, int)},
 * {@link #append(ByteBuffer, byte[], int, int)} or
 * {@link #put(ByteBuffer, ByteBuffer)} are used, then the caller does not need
 * to explicitly switch the buffer to fill mode. If the caller wishes to use
 * other ByteBuffer bases libraries to fill a buffer, then they can use explicit
 * calls of #flipToFill(ByteBuffer) and #flipToFlush(ByteBuffer, int) to change
 * modes. Note because this convention attempts to avoid the copies of compact,
 * the position is not set to zero on each fill cycle and so its value must be
 * remembered:
 * </p>
 * <p>
 * <pre>
 * int pos = BufferUtils.flipToFill(buffer);
 * try {
 * 	buffer.put(data);
 * } finally {
 * 	flipToFlush(buffer, pos);
 * }
 * </pre>
 * <p>
 * The flipToFill method will effectively clear the buffer if it is empty and
 * will compact the buffer if there is no space.
 * </p>
 */
class BufferUtils {

    __gshared ByteBuffer EMPTY_BUFFER;
    __gshared ByteBuffer[] EMPTY_BYTE_BUFFER_ARRAY;

    enum int TEMP_BUFFER_SIZE = 4096;
    enum byte SPACE = 0x20;
    enum byte MINUS = '-';
    enum byte[] DIGIT = [
            '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'
        ];

    shared static this() {
        EMPTY_BUFFER = new HeapByteBuffer(new byte[0], 0, 0); 
        EMPTY_BYTE_BUFFER_ARRAY = new ByteBuffer[0];
    }
    /* ------------------------------------------------------------ */

    /**
     * Allocate ByteBuffer in flush mode.
     * The position and limit will both be zero, indicating that the buffer is
     * empty and must be flipped before any data is put to it.
     *
     * @param capacity capacity of the allocated ByteBuffer
     * @return Buffer
     */
    static ByteBuffer allocate(size_t capacity) {
        ByteBuffer buf = new HeapByteBuffer(cast(int)capacity, cast(int)capacity);
        // FIXME: Needing refactor or cleanup -@zxp at 3/20/2019, 5:49:08 PM
        // 
        // buf.limit(0);
        return buf;
    }

    /* ------------------------------------------------------------ */

    /**
     * Allocate ByteBuffer in flush mode.
     * The position and limit will both be zero, indicating that the buffer is
     * empty and in flush mode.
     *
     * @param capacity capacity of the allocated ByteBuffer
     * @return Buffer
     */
    static ByteBuffer allocateDirect(int capacity) {
        // FIXME: Needing refactor or cleanup -@zxp at 8/17/2019, 1:03:57 PM        
        // 
        ByteBuffer buf = new HeapByteBuffer(capacity, capacity); // DirectByteBuffer(capacity); 
        // buf.limit(0);
        return buf;
    }


    /**
     * Wraps a byte array into a buffer.
     *
     * <p> The new buffer will be backed by the given byte array;
     * that is, modifications to the buffer will cause the array to be modified
     * and vice versa.  The new buffer's capacity will be
     * <tt>array.length</tt>, its position will be <tt>offset</tt>, its limit
     * will be <tt>offset + length</tt>, and its mark will be undefined.  Its
     * {@link #array backing array} will be the given array, and
     * its {@link #arrayOffset array offset} will be zero.  </p>
     *
     * @param  array
     *         The array that will back the new buffer
     *
     * @param  offset
     *         The offset of the subarray to be used; must be non-negative and
     *         no larger than <tt>array.length</tt>.  The new buffer's position
     *         will be set to this value.
     *
     * @param  length
     *         The length of the subarray to be used;
     *         must be non-negative and no larger than
     *         <tt>array.length - offset</tt>.
     *         The new buffer's limit will be set to <tt>offset + length</tt>.
     *
     * @return  The new byte buffer
     *
     * @throws  IndexOutOfBoundsException
     *          If the preconditions on the <tt>offset</tt> and <tt>length</tt>
     *          parameters do not hold
     */
    static ByteBuffer wrap(byte[] array, int offset, int length)
    {
        try {
            return new HeapByteBuffer(array, offset, length);
        } catch (IllegalArgumentException x) {
            throw new IndexOutOfBoundsException("");
        }
    }

    /**
     * Wraps a byte array into a buffer.
     *
     * <p> The new buffer will be backed by the given byte array;
     * that is, modifications to the buffer will cause the array to be modified
     * and vice versa.  The new buffer's capacity and limit will be
     * <tt>array.length</tt>, its position will be zero, and its mark will be
     * undefined.  Its {@link #array backing array} will be the
     * given array, and its {@link #arrayOffset array offset>} will
     * be zero.  </p>
     *
     * @param  array
     *         The array that will back this buffer
     *
     * @return  The new byte buffer
     */
    static ByteBuffer wrap(byte[] array) {
        return wrap(array, 0, cast(int)array.length);
    }


    /* ------------------------------------------------------------ */

    /**
     * Clear the buffer to be empty in flush mode.
     * The position and limit are set to 0;
     *
     * @param buffer The buffer to clear.
     */
    static void clear(ByteBuffer buffer) {
        if (buffer !is null) {
            buffer.position(0);
            buffer.limit(0);
        }
    }

    /* ------------------------------------------------------------ */

    /**
     * Clear the buffer to be empty in fill mode.
     * The position is set to 0 and the limit is set to the capacity.
     *
     * @param buffer The buffer to clear.
     */
    static void clearToFill(ByteBuffer buffer) {
        if (buffer !is null) {
            buffer.position(0);
            buffer.limit(buffer.capacity());
        }
    }

    /* ------------------------------------------------------------ */

    /**
     * Flip the buffer to fill mode.
     * The position is set to the first unused position in the buffer
     * (the old limit) and the limit is set to the capacity.
     * If the buffer is empty, then this call is effectively {@link #clearToFill(ByteBuffer)}.
     * If there is no unused space to fill, a {@link ByteBuffer#compact()} is done to attempt
     * to create space.
     * <p>
     * This method is used as a replacement to {@link ByteBuffer#compact()}.
     *
     * @param buffer The buffer to flip
     * @return The position of the valid data before the flipped position. This value should be
     * passed to a subsequent call to {@link #flipToFlush(ByteBuffer, int)}
     */
    static int flipToFill(ByteBuffer buffer) {
        int position = buffer.position();
        int limit = buffer.limit();
        if (position == limit) {
            buffer.position(0);
            buffer.limit(buffer.capacity());
            return 0;
        }

        int capacity = buffer.capacity();
        if (limit == capacity) {
            buffer.compact();
            return 0;
        }

        buffer.position(limit);
        buffer.limit(capacity);
        return position;
    }

    /* ------------------------------------------------------------ */

    /**
     * Flip the buffer to Flush mode.
     * The limit is set to the first unused byte(the old position) and
     * the position is set to the passed position.
     * <p>
     * This method is used as a replacement of {@link Buffer#flip()}.
     *
     * @param buffer   the buffer to be flipped
     * @param position The position of valid data to flip to. This should
     *                 be the return value of the previous call to {@link #flipToFill(ByteBuffer)}
     */
    static void flipToFlush(ByteBuffer buffer, int position) {
        buffer.limit(buffer.position());
        buffer.position(position);
    }

    /* ------------------------------------------------------------ */

    /**
     * Convert a ByteBuffer to a byte array.
     *
     * @param buffer The buffer to convert in flush mode. The buffer is not altered.
     * @return An array of bytes duplicated from the buffer.
     */
    static byte[] toArray(ByteBuffer buffer, bool canDuplicate = true) {
        if (buffer.hasArray()) {
            byte[] array = buffer.array();
            int from = buffer.arrayOffset() + buffer.position();
            if (canDuplicate)
                return array[from .. from + buffer.remaining()].dup;
            else
                return array[from .. from + buffer.remaining()];
        } else {
            byte[] to = new byte[buffer.remaining()];
            buffer.slice().get(to);
            return to;
        }
    }

    /* ------------------------------------------------------------ */

    /**
     * Check for an empty or null buffer.
     *
     * @param buf the buffer to check
     * @return true if the buffer is null or empty.
     */
    static bool isEmpty(ByteBuffer buf) {
        return buf is null || buf.remaining() == 0;
    }

    /* ------------------------------------------------------------ */

    /**
     * Check for a non null and non empty buffer.
     *
     * @param buf the buffer to check
     * @return true if the buffer is not null and not empty.
     */
    static bool hasContent(ByteBuffer buf) {
        return buf !is null && buf.remaining() > 0;
    }

    /* ------------------------------------------------------------ */

    /**
     * Check for a non null and full buffer.
     *
     * @param buf the buffer to check
     * @return true if the buffer is not null and the limit equals the capacity.
     */
    static bool isFull(ByteBuffer buf) {
        return buf !is null && buf.limit() == buf.capacity();
    }

    /* ------------------------------------------------------------ */

    /**
     * Get remaining from null checked buffer
     *
     * @param buffer The buffer to get the remaining from, in flush mode.
     * @return 0 if the buffer is null, else the bytes remaining in the buffer.
     */
    static int length(ByteBuffer buffer) {
        return buffer is null ? 0 : buffer.remaining();
    }

    /* ------------------------------------------------------------ */

    /**
     * Get the space from the limit to the capacity
     *
     * @param buffer the buffer to get the space from
     * @return space
     */
    static int space(ByteBuffer buffer) {
        if (buffer is null)
            return 0;
        return buffer.capacity() - buffer.limit();
    }

    /* ------------------------------------------------------------ */

    /**
     * Compact the buffer
     *
     * @param buffer the buffer to compact
     * @return true if the compact made a full buffer have space
     */
    static bool compact(ByteBuffer buffer) {
        if (buffer.position() == 0)
            return false;
        bool full = buffer.limit() == buffer.capacity();
        buffer.compact().flip();
        return full && buffer.limit() < buffer.capacity();
    }

    /* ------------------------------------------------------------ */

    /**
     * Put data from one buffer into another, avoiding over/under flows
     *
     * @param from Buffer to take bytes from in flush mode
     * @param to   Buffer to put bytes to in fill mode.
     * @return number of bytes moved
     */
    static int put(ByteBuffer from, ByteBuffer to) {
        int put;
        int remaining = from.remaining();
        if (remaining > 0) {
            if (remaining <= to.remaining()) {
                to.put(from);
                put = remaining;
                from.position(from.limit());
            } else if (from.hasArray()) {
                put = to.remaining();
                to.put(from.array(), from.arrayOffset() + from.position(), put);
                from.position(from.position() + put);
            } else {
                put = to.remaining();
                ByteBuffer slice = from.slice();
                slice.limit(put);
                to.put(slice);
                from.position(from.position() + put);
            }
        } else
            put = 0;

        return put;
    }

    /* ------------------------------------------------------------ */

    /**
     * Put data from one buffer into another, avoiding over/under flows
     *
     * @param from Buffer to take bytes from in flush mode
     * @param to   Buffer to put bytes to in flush mode. The buffer is flipToFill before the put and flipToFlush after.
     * @return number of bytes moved
     * @deprecated use {@link #append(ByteBuffer, ByteBuffer)}
     */
    static int flipPutFlip(ByteBuffer from, ByteBuffer to) {
        return append(to, from);
    }

    /* ------------------------------------------------------------ */

    /**
     * Append bytes to a buffer.
     *
     * @param to  Buffer is flush mode
     * @param b   bytes to append
     * @param off offset into byte
     * @param len length to append
     * @throws BufferOverflowException if unable to append buffer due to space limits
     */
    static void append(ByteBuffer to, byte[] b, int off, int len) {
        int pos = flipToFill(to);
        try {
            to.put(b, off, len);
        } finally {
            flipToFlush(to, pos);
        }
    }

    /* ------------------------------------------------------------ */

    /**
     * Appends a byte to a buffer
     *
     * @param to Buffer is flush mode
     * @param b  byte to append
     */
    static void append(ByteBuffer to, byte b) {
        int pos = flipToFill(to);
        try {
            to.put(b);
        } finally {
            flipToFlush(to, pos);
        }
    }

    /* ------------------------------------------------------------ */

    /**
     * Appends a buffer to a buffer
     *
     * @param to Buffer is flush mode
     * @param b  buffer to append
     * @return The position of the valid data before the flipped position.
     */
    static int append(ByteBuffer to, ByteBuffer b) {
        int pos = flipToFill(to);
        try {
            return put(b, to);
        } finally {
            flipToFlush(to, pos);
        }
    }

    /* ------------------------------------------------------------ */

    /**
     * Like append, but does not throw {@link BufferOverflowException}
     *
     * @param to  Buffer is flush mode
     * @param b   bytes to fill
     * @param off offset into byte
     * @param len length to fill
     * @return The position of the valid data before the flipped position.
     */
    static int fill(ByteBuffer to, byte[] b, int off, int len) {
        int pos = flipToFill(to);
        try {
            int remaining = to.remaining();
            int take = remaining < len ? remaining : len;
            to.put(b, off, take);
            return take;
        } finally {
            flipToFlush(to, pos);
        }
    }

    // /* ------------------------------------------------------------ */
    // static void readFrom(File file, ByteBuffer buffer) throws IOException {
    //     try (RandomAccessFile raf = new RandomAccessFile(file, "r")) {
    //         FileChannel channel = raf.getChannel();
    //         long needed = raf.length();

    //         while (needed > 0 && buffer.hasRemaining())
    //             needed = needed - channel.read(buffer);
    //     }
    // }

    // /* ------------------------------------------------------------ */
    // static void readFrom(InputStream is, int needed, ByteBuffer buffer) throws IOException {
    //     ByteBuffer tmp = allocate(8192);

    //     while (needed > 0 && buffer.hasRemaining()) {
    //         int l = is.read(tmp.array(), 0, 8192);
    //         if (l < 0)
    //             break;
    //         tmp.position(0);
    //         tmp.limit(l);
    //         buffer.put(tmp);
    //     }
    // }

    /* ------------------------------------------------------------ */
    static void writeTo(ByteBuffer buffer, ref Appender!(byte[]) ot) {
        if (buffer.hasArray()) {
            // out.write(buffer.array(), buffer.arrayOffset() + buffer.position(), buffer.remaining());
            auto array = buffer.array();
            int from = buffer.arrayOffset() + buffer.position();
            int to = from + buffer.remaining();
            ot.put(array[from .. to]);

            // update buffer position, in way similar to non-array version of writeTo
            buffer.position = buffer.position() + buffer.remaining();
        } else {
            implementationMissing();
            // byte[] bytes = new byte[TEMP_BUFFER_SIZE];
            // while (buffer.hasRemaining()) {
            //     int byteCountToWrite = std.algorithm.min(buffer.remaining(), TEMP_BUFFER_SIZE);
            //     buffer.get(bytes, 0, byteCountToWrite);
            //     out.write(bytes, 0, byteCountToWrite);
            // }
        }
    }

    /* ------------------------------------------------------------ */

    /**
     * Convert the buffer to an ISO-8859-1 string
     *
     * @param buffer The buffer to convert in flush mode. The buffer is unchanged
     * @return The buffer as a string.
     */
    static string toString(ByteBuffer buffer) {
        if (buffer is null || buffer.remaining() == 0)
            return null;

        byte[] array = buffer.hasArray() ? buffer.array() : null;
        if (array is null) {
            return cast(string) buffer.array[0 .. buffer.remaining()];
        } else {
            int start = buffer.arrayOffset() + buffer.position();
            int end = start + buffer.remaining();
            return cast(string) array[start .. end];
        }
    }

    // /* ------------------------------------------------------------ */

    // /**
    //  * Convert the buffer to an UTF-8 string
    //  *
    //  * @param buffer The buffer to convert in flush mode. The buffer is unchanged
    //  * @return The buffer as a string.
    //  */
    // static string toUTF8String(ByteBuffer buffer) {
    //     return toString(buffer, StandardCharsets.UTF_8);
    // }

    // /* ------------------------------------------------------------ */

    // /**
    //  * Convert the buffer to an ISO-8859-1 string
    //  *
    //  * @param buffer  The buffer to convert in flush mode. The buffer is unchanged
    //  * @param charset The {@link Charset} to use to convert the bytes
    //  * @return The buffer as a string.
    //  */
    // static string toString(ByteBuffer buffer, Charset charset) {
    //     if (buffer is null)
    //         return null;
    //     byte[] array = buffer.hasArray() ? buffer.array() : null;
    //     if (array is null) {
    //         byte[] to = new byte[buffer.remaining()];
    //         buffer.slice().get(to);
    //         return new string(to, 0, to.length, charset);
    //     }
    //     return new string(array, buffer.arrayOffset() + buffer.position(), buffer.remaining(), charset);
    // }

    // /* ------------------------------------------------------------ */

    /**
     * Convert a partial buffer to a string.
     *
     * @param buffer   the buffer to convert
     * @param position The position in the buffer to start the string from
     * @param length   The length of the buffer
     * @param charset  The {@link Charset} to use to convert the bytes
     * @return The buffer as a string.
     */
    static string toString(ByteBuffer buffer, int position, int length) {
        if (buffer is null)
            return null;
        byte[] array = buffer.hasArray() ? buffer.array() : null;
        if (array is null) {
            ByteBuffer ro = buffer.asReadOnlyBuffer();
            ro.position(position);
            ro.limit(position + length);
            byte[] to = new byte[length];
            ro.get(to);
            return cast(string) to;
        }
        int startIndex = buffer.arrayOffset() + position;
        int endIndex = startIndex + length;
        return cast(string) array[startIndex .. endIndex];
    }

    // /* ------------------------------------------------------------ */

    /**
     * Convert buffer to an integer. Parses up to the first non-numeric character. If no number is found an IllegalArgumentException is thrown
     *
     * @param buffer A buffer containing an integer in flush mode. The position is not changed.
     * @return an int
     */
    static int toInt(ByteBuffer buffer) {
        return toInt(buffer, buffer.position(), buffer.remaining());
    }

    /* ------------------------------------------------------------ */

    /**
     * Convert buffer to an integer. Parses up to the first non-numeric character. If no number is found an
     * IllegalArgumentException is thrown
     *
     * @param buffer   A buffer containing an integer in flush mode. The position is not changed.
     * @param position the position in the buffer to start reading from
     * @param length   the length of the buffer to use for conversion
     * @return an int of the buffer bytes
     */
    static int toInt(ByteBuffer buffer, int position, int length) {
        int val = 0;
        bool started = false;
        bool minus = false;

        int limit = position + length;

        if (length <= 0)
            throw new NumberFormatException(toString(buffer, position, length));

        for (int i = position; i < limit; i++) {
            byte b = buffer.get(i);
            if (b <= SPACE) {
                if (started)
                    break;
            } else if (b >= '0' && b <= '9') {
                val = val * 10 + (b - '0');
                started = true;
            } else if (b == MINUS && !started) {
                minus = true;
            } else
                break;
        }

        if (started)
            return minus ? (-val) : val;
        throw new NumberFormatException(toString(buffer));
    }

    /* ------------------------------------------------------------ */

    /**
     * Convert buffer to an integer. Parses up to the first non-numeric character. If no number is found an IllegalArgumentException is thrown
     *
     * @param buffer A buffer containing an integer in flush mode. The position is updated.
     * @return an int
     */
    static int takeInt(ByteBuffer buffer) {
        int val = 0;
        bool started = false;
        bool minus = false;
        int i;
        for (i = buffer.position(); i < buffer.limit(); i++) {
            byte b = buffer.get(i);
            if (b <= SPACE) {
                if (started)
                    break;
            } else if (b >= '0' && b <= '9') {
                val = val * 10 + (b - '0');
                started = true;
            } else if (b == MINUS && !started) {
                minus = true;
            } else
                break;
        }

        if (started) {
            buffer.position(i);
            return minus ? (-val) : val;
        }
        throw new NumberFormatException(toString(buffer));
    }

    /**
     * Convert buffer to an long. Parses up to the first non-numeric character. If no number is found an IllegalArgumentException is thrown
     *
     * @param buffer A buffer containing an integer in flush mode. The position is not changed.
     * @return an int
     */
    static long toLong(ByteBuffer buffer) {
        long val = 0;
        bool started = false;
        bool minus = false;

        for (int i = buffer.position(); i < buffer.limit(); i++) {
            byte b = buffer.get(i);
            if (b <= SPACE) {
                if (started)
                    break;
            } else if (b >= '0' && b <= '9') {
                val = val * 10L + (b - '0');
                started = true;
            } else if (b == MINUS && !started) {
                minus = true;
            } else
                break;
        }

        if (started)
            return minus ? (-val) : val;
        throw new NumberFormatException(toString(buffer));
    }

    static void putHexInt(ByteBuffer buffer, int n) {
        if (n < 0) {
            buffer.put(cast(byte) '-');

            if (n == int.min) {
                buffer.put(cast(byte)(0x7f & '8'));
                buffer.put(cast(byte)(0x7f & '0'));
                buffer.put(cast(byte)(0x7f & '0'));
                buffer.put(cast(byte)(0x7f & '0'));
                buffer.put(cast(byte)(0x7f & '0'));
                buffer.put(cast(byte)(0x7f & '0'));
                buffer.put(cast(byte)(0x7f & '0'));
                buffer.put(cast(byte)(0x7f & '0'));

                return;
            }
            n = -n;
        }

        if (n < 0x10) {
            buffer.put(DIGIT[n]);
        } else {
            bool started = false;
            // This assumes constant time int arithmatic
            foreach (int hexDivisor; hexDivisors) {
                if (n < hexDivisor) {
                    if (started)
                        buffer.put(cast(byte) '0');
                    continue;
                }

                started = true;
                int d = n / hexDivisor;
                buffer.put(DIGIT[d]);
                n = n - d * hexDivisor;
            }
        }
    }

    /* ------------------------------------------------------------ */
    static void putDecInt(ByteBuffer buffer, int n) {
        if (n < 0) {
            buffer.put(cast(byte) '-');

            if (n == int.min) {
                buffer.put(cast(byte) '2');
                n = 147483648;
            } else
                n = -n;
        }

        if (n < 10) {
            buffer.put(DIGIT[n]);
        } else {
            bool started = false;
            // This assumes constant time int arithmatic
            foreach (int decDivisor; decDivisors) {
                if (n < decDivisor) {
                    if (started)
                        buffer.put(cast(byte) '0');
                    continue;
                }

                started = true;
                int d = n / decDivisor;
                buffer.put(DIGIT[d]);
                n = n - d * decDivisor;
            }
        }
    }

    static void putDecLong(ByteBuffer buffer, long n) {
        if (n < 0) {
            buffer.put(cast(byte) '-');

            if (n == long.min) {
                buffer.put(cast(byte) '9');
                n = 223372036854775808L;
            } else
                n = -n;
        }

        if (n < 10) {
            buffer.put(DIGIT[cast(int) n]);
        } else {
            bool started = false;
            // This assumes constant time int arithmatic
            foreach (long aDecDivisorsL; decDivisorsL) {
                if (n < aDecDivisorsL) {
                    if (started)
                        buffer.put(cast(byte) '0');
                    continue;
                }

                started = true;
                long d = n / aDecDivisorsL;
                buffer.put(DIGIT[cast(int) d]);
                n = n - d * aDecDivisorsL;
            }
        }
    }

    static ByteBuffer toBuffer(int value) {
        ByteBuffer buf = allocate(32);
        putDecInt(buf, value);
        return buf;
    }

    static ByteBuffer toBuffer(long value) {
        ByteBuffer buf = allocate(32);
        putDecLong(buf, value);
        return buf;
    }

    static ByteBuffer toBuffer(string s) {
        return toBuffer(cast(byte[]) s.dup);
    }

    // static ByteBuffer toBuffer(string s, Charset charset) {
    //     if (s is null)
    //         return EMPTY_BUFFER;
    //     return toBuffer(s.getBytes(charset));
    // }

    /**
     * Create a new ByteBuffer using provided byte array.
     *
     * @param array the byte array to back buffer with.
     * @return ByteBuffer with provided byte array, in flush mode
     */
    static ByteBuffer toBuffer(byte[] array) {
        if (array is null)
            return EMPTY_BUFFER;
        return toBuffer(array, 0, cast(int) array.length);
    }

    /**
     * Create a new ByteBuffer using the provided byte array.
     *
     * @param array  the byte array to use.
     * @param offset the offset within the byte array to use from
     * @param length the length in bytes of the array to use
     * @return ByteBuffer with provided byte array, in flush mode
     */
    static ByteBuffer toBuffer(byte[] array, int offset, int length) {
        if (array is null)
            return EMPTY_BUFFER;
        try {
            return new HeapByteBuffer(array, offset, length);
        } catch (IllegalArgumentException x) {
            throw new IndexOutOfBoundsException("");
        }
    }

    static ByteBuffer toDirectBuffer(string s) {
        if (s.empty)
            return EMPTY_BUFFER;
        byte[] bytes = cast(byte[]) s.dup;
        // TODO: Tasks pending completion -@zxp at 8/25/2018, 3:11:29 PM
        // ByteBuffer.allocateDirect(bytes.length); 
        ByteBuffer buf = new HeapByteBuffer(cast(int) bytes.length, cast(int) bytes.length);
        buf.put(bytes);
        buf.flip();
        return buf;
        // return toDirectBuffer(s, "StandardCharsets.ISO_8859_1");
    }

    // static ByteBuffer toDirectBuffer(string s, Charset charset) {
    //     if (s is null)
    //         return EMPTY_BUFFER;
    //     byte[] bytes = s.getBytes(charset);
    //     ByteBuffer buf = ByteBuffer.allocateDirect(bytes.length);
    //     buf.put(bytes);
    //     buf.flip();
    //     return buf;
    // }

    // static ByteBuffer toMappedBuffer(File file) throws IOException {
    //     try (FileChannel channel = FileChannel.open(file.toPath(), StandardOpenOption.READ)) {
    //         return channel.map(MapMode.READ_ONLY, 0, file.length());
    //     }
    // }

    // static bool isMappedBuffer(ByteBuffer buffer) {
    //     if (!(buffer instanceof MappedByteBuffer))
    //         return false;
    //     MappedByteBuffer mapped = (MappedByteBuffer) buffer;

    //     try {
    //         // Check if it really is a mapped buffer
    //         mapped.isLoaded();
    //         return true;
    //     } catch (UnsupportedOperationException e) {
    //         return false;
    //     }
    // }

    /* ------------------------------------------------------------ */

    /**
     * Convert Buffer to string ID independent of content
     */
    private static void idString(ByteBuffer buffer, StringBuilder ot) {
        // ot.append(typeof(buffer).stringof);
        ot.append(typeid(buffer).name);
        ot.append("@");
        if (buffer.hasArray() && buffer.arrayOffset() == 4) {
            ot.append('T');
            byte[] array = buffer.array();
            ConverterUtils.toHex(array[0], ot);
            ConverterUtils.toHex(array[1], ot);
            ConverterUtils.toHex(array[2], ot);
            ConverterUtils.toHex(array[3], ot);
        } else {
            size_t hashCode = hashOf(buffer);
            ot.append(to!string(hashCode, 16));
            // ot.append(Integer.toHexString(System.identityHashCode(buffer)));
        }
    }

    /* ------------------------------------------------------------ */

    /**
     * Convert Buffer to string ID independent of content
     *
     * @param buffer the buffet to generate a string ID from
     * @return A string showing the buffer ID
     */
    static string toIDString(ByteBuffer buffer) {
        StringBuilder buf = new StringBuilder();
        idString(buffer, buf);
        return buf.toString();
    }

    /* ------------------------------------------------------------ */

    static string toSummaryString(ByteBuffer buffer) {
        if (buffer is null)
            return "null";
        StringBuilder buf = new StringBuilder();
        buf.append("[p=");
        buf.append(buffer.position());
        buf.append(",l=");
        buf.append(buffer.limit());
        buf.append(",c=");
        buf.append(buffer.capacity());
        buf.append(",r=");
        buf.append(buffer.remaining());
        buf.append("]");
        return buf.toString();
    }

    static string toDetailString(ByteBuffer[] buffer) {
        StringBuilder builder = new StringBuilder();
        builder.append('[');
        for (int i = 0; i < buffer.length; i++) {
            if (i > 0)
                builder.append(',');
            builder.append(toDetailString(buffer[i]));
        }
        builder.append(']');
        return builder.toString();
    }

    /**
     * Convert Buffer to a detail debug string of pointers and content
     *
     * @param buffer the buffer to generate a detail string from
     * @return A string showing the pointers and content of the buffer
     */
    static string toDetailString(ByteBuffer buffer) {
        if (buffer is null)
            return "null";

        StringBuilder buf = new StringBuilder();
        idString(buffer, buf);
        buf.append("[p=");
        buf.append(buffer.position());
        buf.append(",l=");
        buf.append(buffer.limit());
        buf.append(",c=");
        buf.append(buffer.capacity());
        buf.append(",r=");
        buf.append(buffer.remaining());
        buf.append("]={");

        appendDebugString(buf, buffer);

        buf.append("}");

        return buf.toString();
    }

    private static void appendDebugString(StringBuilder buf, ByteBuffer buffer) {
        try {
            for (int i = 0; i < buffer.position(); i++) {
                appendContentChar(buf, buffer.get(i));
                if (i == 16 && buffer.position() > 32) {
                    buf.append("...");
                    i = buffer.position() - 16;
                }
            }
            buf.append("<<<");
            for (int i = buffer.position(); i < buffer.limit(); i++) {
                appendContentChar(buf, buffer.get(i));
                if (i == buffer.position() + 16 && buffer.limit() > buffer.position() + 32) {
                    buf.append("...");
                    i = buffer.limit() - 16;
                }
            }
            buf.append(">>>");

            // int limit = buffer.limit();
            // buffer.limit(buffer.capacity());
            // for (int i = limit; i < buffer.capacity(); i++) {
            //     appendContentChar(buf, buffer.get(i));
            //     if (i == limit + 16 && buffer.capacity() > limit + 32) {
            //         buf.append("...");
            //         i = buffer.capacity() - 16;
            //     }
            // }
            // buffer.limit(limit);
        } catch (Exception x) {
            buf.append("!!concurrent mod!!");
        }
    }

    private static void appendContentChar(StringBuilder buf, byte b) {
        if (b == '\\')
            buf.append("\\\\");
        else if (b >= ' ')
            buf.append(cast(char) b);
        else if (b == '\r')
            buf.append("\\r");
        else if (b == '\n')
            buf.append("\\n");
        else if (b == '\t')
            buf.append("\\t");
        else
            buf.append("\\x").append(ConverterUtils.toHexString(b));
    }

    /* ------------------------------------------------------------ */

    /**
     * Convert buffer to a Hex Summary string.
     *
     * @param buffer the buffer to generate a hex byte summary from
     * @return A string showing a summary of the content in hex
     */
    static string toHexSummary(ByteBuffer buffer) {
        if (buffer is null)
            return "null";
        StringBuilder buf = new StringBuilder();

        buf.append("b[").append(buffer.remaining()).append("]=");
        for (int i = buffer.position(); i < buffer.limit(); i++) {
            ConverterUtils.toHex(buffer.get(i), buf);
            if (i == buffer.position() + 24 && buffer.limit() > buffer.position() + 32) {
                buf.append("...");
                i = buffer.limit() - 8;
            }
        }
        return buf.toString();
    }

    /* ------------------------------------------------------------ */

    /**
     * Convert buffer to a Hex string.
     *
     * @param buffer the buffer to generate a hex byte summary from
     * @return A hex string
     */
    static string toHexString(ByteBuffer buffer) {
        if (buffer is null)
            return "null";
        return ConverterUtils.toHexString(toArray(buffer));
    }

    private enum int[] decDivisors = [
            1000000000, 100000000, 10000000, 1000000, 100000, 10000, 1000, 100, 10, 1
        ];

    private enum int[] hexDivisors = [
            0x10000000, 0x1000000, 0x100000, 0x10000, 0x1000, 0x100, 0x10, 0x1
        ];

    private enum long[] decDivisorsL = [
            1000000000000000000L, 100000000000000000L, 10000000000000000L,
            1000000000000000L, 100000000000000L, 10000000000000L, 1000000000000L,
            100000000000L, 10000000000L, 1000000000L, 100000000L, 10000000L,
            1000000L, 100000L, 10000L, 1000L, 100L, 10L, 1L
        ];

    static void putCRLF(ByteBuffer buffer) {
        buffer.put(cast(byte) 13);
        buffer.put(cast(byte) 10);
    }

    static bool isPrefix(ByteBuffer prefix, ByteBuffer buffer) {
        if (prefix.remaining() > buffer.remaining())
            return false;
        int bi = buffer.position();
        for (int i = prefix.position(); i < prefix.limit(); i++)
            if (prefix.get(i) != buffer.get(bi++))
                return false;
        return true;
    }

    static ByteBuffer ensureCapacity(ByteBuffer buffer, size_t capacity) {
        if (buffer is null)
            return allocate(capacity);

        if (buffer.capacity() >= capacity)
            return buffer;

        if (buffer.hasArray()) {
            byte[] b = buffer.array();
            size_t offset = buffer.arrayOffset();
            size_t remaining = b.length - offset;
            byte[] copy = new byte[capacity];
            assert(remaining <= capacity);
            // if(remaining  > capacity)
            //     copy[0.. capacity] = b[offset .. offset+capacity];
            // else
            copy[0 .. remaining] = b[offset .. $];
            return toBuffer(copy, buffer.position(), buffer.remaining());
        }

        throw new UnsupportedOperationException();
    }

    /**
     * The capacity modulo 1024 is 0
     *
     * @param capacity the buffer size
     * @return the buffer size that modulo 1024 is 0
     */
    static int normalizeBufferSize(int capacity) {
        int q = capacity >>> 10;
        int r = capacity & 1023;
        if (r != 0) {
            q++;
        }
        return q << 10;
    }

    // static string toString(List!(ByteBuffer) list) {
    //     Appender!(byte[]) ot;
    //     try {
    //         foreach (ByteBuffer buffer; list) {
    //             // auto array = buffer.array();
    //             // int from = buffer.arrayOffset() + buffer.position();
    //             // int to = from + buffer.remaining();
    //             // ot.put(array[from .. to]);
    //             // buffer.position = buffer.position() + buffer.remaining();
    //             writeTo(buffer, ot);
    //         }
    //         return cast(string) ot.data;
    //     } catch (IOException e) {
    //         return null;
    //     }
    // }

    // static List!(ByteBuffer) split(ByteBuffer buffer, int maxSize) {
    //     if (buffer.remaining() <= maxSize) {
    //         return Collections.singletonList(buffer.duplicate());
    //     } else {
    //         ByteBuffer tmpBuffer = buffer.duplicate();
    //         int num = (buffer.remaining() + maxSize - 1) / maxSize;
    //         List!(ByteBuffer) list = new ArrayList<>(num);
    //         for (int i = 1; i <= num; i++) {
    //             ByteBuffer b = ByteBuffer.allocate(maxSize);
    //             byte[] data = new byte[std.algorithm.min(maxSize, tmpBuffer.remaining())];
    //             tmpBuffer.get(data);
    //             b.put(data).flip();
    //             list.add(b);
    //         }
    //         return list;
    //     }

    // }

    static long remaining(ByteBuffer[] byteBuffers) {
        long count = 0;
        foreach (ByteBuffer byteBuffer; byteBuffers) {
            count += byteBuffer.remaining();
        }
        return count;
    }

    // static long remaining(Collection!ByteBuffer collection) {
    //     long count = 0;
    //     foreach (ByteBuffer byteBuffer; collection) {
    //         count += byteBuffer.remaining();
    //     }
    //     return count;
    // }

    // static byte[] toArray(List!(ByteBuffer) list) {
    //     Appender!(byte[]) ot;
    //     try {
    //         foreach (ByteBuffer buffer; list) {
    //             // BufferUtils.writeTo(buf, out);
    //             // auto array = buffer.array();
    //             // int from = buffer.arrayOffset() + buffer.position();
    //             // int to = from + buffer.remaining();
    //             // ot.put(array[from .. to]);
    //             // buffer.position = buffer.position() + buffer.remaining();

    //             writeTo(buffer, ot);
    //         }
    //         return ot.data;
    //     } catch (IOException e) {
    //         return null;
    //     }
    // }

    // static ByteBuffer toDirectBuffer(ByteBuffer buf) {
    //     if (buf.isDirect()) {
    //         return buf;
    //     } else {
    //         ByteBuffer directBuf = ByteBuffer.allocateDirect(buf.remaining());
    //         directBuf.put(buf.slice()).flip();
    //         return directBuf;
    //     }
    // }

    static ByteBuffer toHeapBuffer(ByteBuffer buf) {
        if (buf.isDirect()) {
            ByteBuffer heapBuffer = allocate(buf.remaining());
            heapBuffer.put(buf.slice()).flip();
            return heapBuffer;
        } else {
            return buf;
        }
    }

    static ByteBuffer clone(ByteBuffer buf) {
        byte[] bytes = buf.getRemaining();
        ByteBuffer heapBuffer = new HeapByteBuffer(bytes.dup, 0, cast(int)bytes.length);
        return heapBuffer;

    }
}