/*
Copyright (c) 2016-2021 Timur Gafarov

Boost Software License - Version 1.0 - August 17th, 2003

Permission is hereby granted, free of charge, to any person or organization
obtaining a copy of the software and accompanying documentation covered by
this license (the "Software") to use, reproduce, display, distribute,
execute, and transmit the Software, and to prepare derivative works of the
Software, and to permit third-parties to whom the Software is furnished to
do so, all subject to the following:

The copyright notices in the Software and this entire statement, including
the above license grant, this restriction and the following disclaimer,
must be included in all copies of the Software, in whole or in part, and
all derivative works of the Software, unless such copies or derivative
works are solely in the form of machine-executable object code generated by
a source language processor.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
DEALINGS IN THE SOFTWARE.
*/

/**
 * UTF-16 decoder and encoder
 *
 * Copyright: Timur Gafarov 2016-2021.
 * License: $(LINK2 boost.org/LICENSE_1_0.txt, Boost License 1.0).
 * Authors: Timur Gafarov, Roman Chistokhodov
 */
module dlib.text.utf16;

import core.stdc.stdio;
import dlib.core.memory;
import dlib.container.array;
import dlib.text.utf8;
import dlib.text.utils;
import dlib.text.common;

enum ushort UTF16_HI_SURROGATE = 0xD800;
enum ushort UTF16_LO_SURROGATE = 0xDC00;
enum ushort UTF16_BOM_LE = 0xfeff;
enum ushort UTF16_BOM_BE = 0xfffe;

/**
 * UTF-16 LE decoder to use with dlib.text.encodings.transcode
 */
struct UTF16LEDecoder
{
    // TODO: byte order
    public:

    /// Input string. Set it before decoding
    string input;

    /// Current index in an input string
    size_t index = 0;

    /// Current character index
    int character = 0;

    /**
     * Decode next character.
     * Returns: decoded code point, or UTF8_ERROR if error occured, or UTF8_END if input has no more characters.
     */
    int decodeNext()
    {
        if (index >= input.length)
            return index == input.length ? DECODE_END : DECODE_ERROR;
        character++;
        wchar c = *cast(wchar*)(&input[index]);
        index += 2;
        return c;
    }

    /**
     * Check if decoder is in the end of input.
     */
    bool eos()
    {
        return (index >= input.length);
    }

    /**
     * Range interface.
     */
    auto decode(string s)
    {
        input = s;

        static struct ByDchar
        {
            private:
            UTF16LEDecoder _decoder;
            dchar _lastRead;

            public:
            this(UTF16LEDecoder decoder) {
                _decoder = decoder;
                _lastRead = cast(dchar)_decoder.decodeNext();
            }

            bool empty() {
                return _lastRead == DECODE_END || _lastRead == DECODE_ERROR;
            }

            dchar front() {
                return _lastRead;
            }

            void popFront() {
                _lastRead = cast(dchar)_decoder.decodeNext();
            }

            auto save() {
                return this;
            }
        }

        return ByDchar(this);
    }

    /// ditto
    auto decode()
    {
        return decode(input);
    }
}

/**
 * UTF-16 LE encoder to use with dlib.text.encodings.transcode
 */
struct UTF16LEEncoder
{
    /**
     * Encodes a Unicode code point to UTF-16 LE into user-provided buffer.
     * Returns number of bytes written, or 0 at error.
     */
    size_t encode(uint ch, char[] buffer)
    {
        wchar[] wbuffer = cast(wchar[])buffer;
        if (ch > 0xFFFF)
        {
            wchar x = cast(wchar)ch;
            wchar vh = cast(wchar)(UTF16_HI_SURROGATE | ((((ch >> 16) & ((1 << 5) - 1)) - 1) << 6) | (x >> 10));
            wchar vl = cast(wchar)(UTF16_LO_SURROGATE | (x & ((1 << 10) - 1)));
            wbuffer[0] = vh;
            wbuffer[1] = vl;
            return 4;
        }
        else
        {
            wbuffer[0] = cast(wchar)ch;
            return 2;
        }
    }
}

/**
 * Converts UTF-8 to UTF-16
 * Will be deprecated soon, use transcode!(UTF8Decoder, UTF16LEEncoder) instead
 */
wchar[] convertUTF8toUTF16(string s, bool nullTerm = false)
{
    Array!wchar array;
    wchar[] output;

    UTF8Decoder dec = UTF8Decoder(s);

    while (!dec.eos)
    {
        int code = dec.decodeNext();

        if (code == UTF8_ERROR)
        {
            array.free();
            return output;
        }

        dchar ch = cast(dchar)code;

        if (ch > 0xFFFF)
        {
            // Split ch up into a surrogate pair as it is over 16 bits long.
            wchar x = cast(wchar)ch;
            auto vh = UTF16_HI_SURROGATE | ((((ch >> 16) & ((1 << 5) - 1)) - 1) << 6) | (x >> 10);
            auto vl = UTF16_LO_SURROGATE | (x & ((1 << 10) - 1));
            array.append(cast(wchar)vh);
            array.append(cast(wchar)vl);
        }
        else
        {
            array.append(cast(wchar)ch);
        }
    }

    if (nullTerm)
    {
        array.append(0);
    }

    output = copy(array.data);
    array.free();
    return output;
}

/**
 * Converts UTF-16 zero-terminated string to UTF-8
 */
char[] convertUTF16ztoUTF8(wchar* s, bool nullTerm = false)
{
    Array!char array;
    char[] output;
    wchar* utf16 = s;

    wchar utf16char;
    do
    {
        utf16char = *utf16;
        utf16++;

        if (utf16char)
        {
            if (utf16char < 0x80)
            {
                array.append((utf16char >> 0 & 0x7F) | 0x00);
            }
            else if (utf16char < 0x0800)
            {
                array.append((utf16char >> 6 & 0x1F) | 0xC0);
                array.append((utf16char >> 0 & 0x3F) | 0x80);
            }
            else if (utf16char < 0x010000)
            {
                array.append((utf16char >> 12 & 0x0F) | 0xE0);
                array.append((utf16char >> 6 & 0x3F) | 0x80);
                array.append((utf16char >> 0 & 0x3F) | 0x80);
            }
            else if (utf16char < 0x110000)
            {
                array.append((utf16char >> 18 & 0x07) | 0xF0);
                array.append((utf16char >> 12 & 0x3F) | 0x80);
                array.append((utf16char >> 6 & 0x3F) | 0x80);
                array.append((utf16char >> 0 & 0x3F) | 0x80);
            }
        }
    }
    while (utf16char);

    if (nullTerm)
    {
        array.append(0);
    }

    output = copy(array.data);
    array.free();
    return output;
}