/*
 * This file is based on
 *   http://www.unicode.org/Public/PROGRAMS/CVTUTF/ConvertUTF.c
 *
 * The original parts have the following copyright
 * ---------------------------------------------------------------------
 * Copyright 2001-2004 Unicode, Inc.
 *
 * Disclaimer
 *
 * This source code is provided as is by Unicode, Inc. No claims are
 * made as to fitness for any particular purpose. No warranties of any
 * kind are expressed or implied. The recipient agrees to determine
 * applicability of information provided. If this file has been
 * purchased on magnetic or optical media from Unicode, Inc., the
 * sole remedy for any claim will be exchange of defective media
 * within 90 days of receipt.
 *
 * Limitations on Rights to Redistribute This Code
 *
 * Unicode, Inc. hereby grants the right to freely use the information
 * supplied in this file in the creation of products supporting the
 * Unicode Standard, and to make copies of this file in any form
 * for internal or external distribution as long as this notice
 * remains attached.
 * ---------------------------------------------------------------------
 *
 * The modifications and additions have the following copyright
 *
 * Copyright (C) 2005, 2007 Ronald Lamprecht
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

#include "ecl_utf.hh"

#define UNI_SUR_HIGH_START (UTF32)0xD800
#define UNI_SUR_HIGH_END (UTF32)0xDBFF
#define UNI_SUR_LOW_START (UTF32)0xDC00
#define UNI_SUR_LOW_END (UTF32)0xDFFF
#define false 0
#define true 1

namespace ecl {
static const int halfShift = 10; /* used for shifting by 10 bits */

static const UTF32 halfBase = 0x0010000UL;
static const UTF32 halfMask = 0x3FFUL;

/**
 * Index into the table below with the first byte of a UTF-8 sequence to
 * get the number of trailing bytes that are supposed to follow it.
 * Note that *legal* UTF-8 values can't have 4 or 5-bytes. The table is
 * left as-is for anyone who may want to do such conversion, which was
 * allowed in earlier algorithms.
 */
static const char trailingBytesForUTF8[256] = {
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
    2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 5};

/*
 * Once the bits are split out into bytes of UTF-8, this is a mask OR-ed
 * into the first byte, depending on how many bytes follow.  There are
 * as many entries in this table as there are UTF-8 sequence types.
 * (I.e., one byte sequence, two byte... etc.). Remember that sequencs
 * for *legal* UTF-8 will be 4 or fewer bytes total.
 */
static const UTF8 firstByteMark[7] = {0x00, 0x00, 0xC0, 0xE0, 0xF0, 0xF8, 0xFC};

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

/* The interface converts a whole buffer to avoid function-call overhead.
 * Constants have been gathered. Loops & conditionals have been removed as
 * much as possible for efficiency, in favor of drop-through switches.
 * (See "Note A" at the bottom of the file for equivalent code.)
 * If your compiler supports it, the "isLegalUTF8" call can be turned
 * into an inline function.
 */

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

ConversionResult ConvertUTF16toUTF8(const UTF16** sourceStart, const UTF16* sourceEnd,
                                    UTF8** targetStart, UTF8* targetEnd, ConversionFlags flags) {
    ConversionResult result = conversionOK;
    const UTF16* source = *sourceStart;
    UTF8* target = *targetStart;
    while (source < sourceEnd) {
        UTF32 ch;
        unsigned short bytesToWrite = 0;
        const UTF32 byteMask = 0xBF;
        const UTF32 byteMark = 0x80;
        const UTF16* oldSource =
            source; /* In case we have to back up because of target overflow. */
        ch = *source++;
        /* If we have a surrogate pair, convert to UTF32 first. */
        if (ch >= UNI_SUR_HIGH_START && ch <= UNI_SUR_HIGH_END) {
            /* If the 16 bits following the high surrogate are in the source buffer... */
            if (source < sourceEnd) {
                UTF32 ch2 = *source;
                /* If it's a low surrogate, convert to UTF32. */
                if (ch2 >= UNI_SUR_LOW_START && ch2 <= UNI_SUR_LOW_END) {
                    ch = ((ch - UNI_SUR_HIGH_START) << halfShift) + (ch2 - UNI_SUR_LOW_START) +
                         halfBase;
                    ++source;
                } else if (flags == strictConversion) { /* it's an unpaired high surrogate */
                    --source;                           /* return to the illegal value itself */
                    result = sourceIllegal;
                    break;
                }
            } else {      /* We don't have the 16 bits following the high surrogate. */
                --source; /* return to the high surrogate */
                result = sourceExhausted;
                break;
            }
        } else if (flags == strictConversion) {
            /* UTF-16 surrogate values are illegal in UTF-32 */
            if (ch >= UNI_SUR_LOW_START && ch <= UNI_SUR_LOW_END) {
                --source; /* return to the illegal value itself */
                result = sourceIllegal;
                break;
            }
        }
        /* Figure out how many bytes the result will require */
        if (ch < (UTF32)0x80) {
            bytesToWrite = 1;
        } else if (ch < (UTF32)0x800) {
            bytesToWrite = 2;
        } else if (ch < (UTF32)0x10000) {
            bytesToWrite = 3;
        } else if (ch < (UTF32)0x110000) {
            bytesToWrite = 4;
        } else {
            bytesToWrite = 3;
            ch = UNI_REPLACEMENT_CHAR;
        }

        target += bytesToWrite;
        if (target > targetEnd) {
            source = oldSource; /* Back up source pointer! */
            target -= bytesToWrite;
            result = targetExhausted;
            break;
        }
        switch (bytesToWrite) { /* note: everything falls through. */
        case 4: *--target = (UTF8)((ch | byteMark) & byteMask); ch >>= 6;
        case 3: *--target = (UTF8)((ch | byteMark) & byteMask); ch >>= 6;
        case 2: *--target = (UTF8)((ch | byteMark) & byteMask); ch >>= 6;
        case 1: *--target = (UTF8)(ch | firstByteMark[bytesToWrite]);
        }
        target += bytesToWrite;
    }
    *sourceStart = source;
    *targetStart = target;
    return result;
}

void utf8CharSizes(const std::string& utf8String, std::vector<unsigned char>& sizes) {
    int length = utf8String.size();

    for (int i = 0; i < length;) {
        unsigned char c = utf8String[i];
        int charSize = trailingBytesForUTF8[c] + 1;
        sizes.push_back(charSize);
        i += charSize;
    }
}

int utf8NextCharSize(const std::string& utf8String) {
    unsigned char c = utf8String[0];
    int len = 1;  // num of bytes that represents one real character
    if ((c & 0xC0) == 0x80) {
        // a spurious follow up byte
        len = 0;
    } else if ((c & 0xE0) == 0xC0) {
        len = 2;
    } else if ((c & 0xF0) == 0xE0) {
        len = 3;
    } else if ((c & 0xF8) == 0xF0) {
        len = 4;
    }
    return len;
}
}  // namespace ecl
