/* Copyright (C) 2001-2023 Artifex Software, Inc.
   All Rights Reserved.

   This software is provided AS-IS with no warranty, either express or
   implied.

   This software is distributed under license and may not be copied,
   modified or distributed except as expressly authorized under the terms
   of the license contained in the file LICENSE in this distribution.

   Refer to licensing information at http://www.artifex.com or contact
   Artifex Software, Inc.,  39 Mesa Street, Suite 108A, San Francisco,
   CA 94129, USA, for further information.
*/


#include "gp_utf8.h"

static int
decode_utf8(const char **inp, unsigned int i)
{
    const char *in = *inp;
    unsigned char c;

    if (i < 0x80) {
    } else if ((i & 0xE0) == 0xC0) {
        i &= 0x1F;
        c = (unsigned char)*in++;
        if ((c & 0xC0) != 0x80)
            goto fail;
        i = (i<<6) | (c & 0x3f);
    } else if ((i & 0xF0) == 0xE0) {
        i &= 0xF;
        c = (unsigned char)*in++;
        if ((c & 0xC0) != 0x80)
            goto fail;
        i = (i<<6) | (c & 0x3f);
        c = (unsigned char)*in++;
        if ((c & 0xC0) != 0x80)
            goto fail;
        i = (i<<6) | (c & 0x3f);
    } else if ((i & 0xF8) == 0xF0) {
        i &= 0x7;
        c = (unsigned char)*in++;
        if ((c & 0xC0) != 0x80)
            goto fail;
        i = (i<<6) | (c & 0x3f);
        c = (unsigned char)*in++;
        if ((c & 0xC0) != 0x80)
            goto fail;
        i = (i<<6) | (c & 0x3f);
        c = (unsigned char)*in++;
        if ((c & 0xC0) != 0x80)
            goto fail;
        i = (i<<6) | (c & 0x3f);
    }
    if (0)
    {
        /* If we fail, unread the last one, and return the unicode replacement char. */
fail:
       in--;
       i = 0xfffd;
    }
    *inp = in;

    return i;
}

int gp_utf8_to_uint16(unsigned short *out, const char *in)
{
    unsigned int i;
    unsigned int len = 1;

    if (out) {
        while ((i = *(unsigned char *)in++) != 0) {
            /* Decode UTF-8 */
            i = decode_utf8(&in, i);

            /* Encode, allowing for surrogates. */
            if (i >= 0x10000 && i <= 0x10ffff)
            {
                i -= 0x10000;
                *out++ = 0xd800 + (i>>10);
                *out++ = 0xdc00 + (i & 0x3ff);
                len++;
            }
            else if (i > 0x10000)
            {
                return -1;
            }
            else
                *out++ = (unsigned short)i;
            len++;
        }
        *out = 0;
    } else {
        while ((i = *(unsigned char *)in++) != 0) {
            /* Decode UTF-8 */
            i = decode_utf8(&in, i);

            /* Encode, allowing for surrogates. */
            if (i >= 0x10000 && i <= 0x10ffff)
                len++;
            else if (i > 0x10000)
                return -1;
            len++;
        }
    }
    return len;
}

int gp_uint16_to_utf8(char *out, const unsigned short *in)
{
    unsigned int i;
    unsigned int len = 1;

    if (out) {
        while ((i = (unsigned int)*in++) != 0) {
            /* Decode surrogates */
            if (i >= 0xD800 && i <= 0xDBFF)
            {
                /* High surrogate. Must be followed by a low surrogate, or this is a failure. */
                int hi = i & 0x3ff;
                int j = (unsigned int)*in++;
                if (j == 0 || (j <= 0xDC00 || j >= 0xDFFF))
                {
                    /* Failure! Unicode replacement char! */
                    in--;
                    i = 0xfffd;
                } else {
                    /* Decode surrogates */
                    i = 0x10000 + (hi<<10) + (j & 0x3ff);
                }
            } else if (i >= 0xDC00 && i <= 0xDFFF)
            {
                /* Lone low surrogate. Failure. Unicode replacement char. */
                i = 0xfffd;
            }

            /* Encode output */
            if (i < 0x80) {
                *out++ = (char)i;
                len++;
            } else if (i < 0x800) {
                *out++ = 0xC0 | ( i>> 6        );
                *out++ = 0x80 | ( i      & 0x3F);
                len+=2;
            } else if (i < 0x10000) {
                *out++ = 0xE0 | ( i>>12        );
                *out++ = 0x80 | ((i>> 6) & 0x3F);
                *out++ = 0x80 | ( i      & 0x3F);
                len+=3;
            } else {
                *out++ = 0xF0 | ( i>>18        );
                *out++ = 0x80 | ((i>>12) & 0x3F);
                *out++ = 0x80 | ((i>> 6) & 0x3F);
                *out++ = 0x80 | ( i      & 0x3F);
                len+=4;
            }
        }
        *out = 0;
    } else {
        while ((i = (unsigned int)*in++) != 0) {
            /* Decode surrogates */
            if (i >= 0xD800 && i <= 0xDBFF)
            {
                /* High surrogate. Must be followed by a low surrogate, or this is a failure. */
                int hi = i & 0x3ff;
                int j = (unsigned int)*in++;
                if (j == 0 || (j <= 0xDC00 || j >= 0xDFFF))
                {
                    /* Failure! Unicode replacement char! */
                    in--;
                    i = 0xfffd;
                } else {
                    /* Decode surrogates */
                    i = 0x10000 + (hi<<10) + (j & 0x3ff);
                }
            } else if (i >= 0xDC00 && i <= 0xDFFF)
            {
                /* Lone low surrogate. Failure. Unicode replacement char. */
                i = 0xfffd;
            }

            if (i < 0x80) {
                len++;
            } else if (i < 0x800) {
                len += 2;
            } else if (i < 0x10000) {
                len += 3;
            } else {
                len += 4;
            }
        }
    }
    return len;
}