/*
 *  virt_mbrtowc.c
 *
 *  $Id$
 *  
 *  This file is part of the OpenLink Software Virtuoso Open-Source (VOS)
 *  project.
 *  
 *  Copyright (C) 1998-2024 OpenLink Software
 *  
 *  This project 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; only version 2 of the License, dated June 1991.
 *  
 *  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 St, Fifth Floor, Boston, MA 02110-1301 USA
 *  
 *  
*/

#include "libutil.h"


size_t
virt_mbrtowc (wchar_t *pwc, const unsigned char *s, size_t n, virt_mbstate_t *ps)
{
  size_t used = 0;
  static virt_mbstate_t internal;

  if (ps == NULL)
    ps = &internal;

  if (s == NULL)
    {
      /* See first paragraph of description in 7.16.6.3.2.  */
      pwc = NULL;
      s = (unsigned char *) "";
      n = 1;
    }

  if (n > 0)
    {
      if (ps->count == 0)
	{
	  unsigned char byte = (unsigned char) *s++;
	  ++used;

	  /* We must look for a possible first byte of a UTF8 sequence.  */
	  if (byte < 0x80)
	    {
	      /* One byte sequence.  */
	      if (pwc != NULL)
		*pwc = (wchar_t) byte;
	      return byte ? used : 0;
	    }

	  if ((byte & 0xc0) == 0x80 || (byte & 0xfe) == 0xfe)
	    {
	      /* Oh, oh.  An encoding error.  */
	      /* errno = (EILSEQ); */
	      return (size_t) -1;
	    }

	  if ((byte & 0xe0) == 0xc0)
	    {
	      /* We expect two bytes.  */
	      ps->count = 1;
	      ps->value = byte & 0x1f;
	    }
	  else if ((byte & 0xf0) == 0xe0)
	    {
	      /* We expect three bytes.  */
	      ps->count = 2;
	      ps->value = byte & 0x0f;
	    }
	  else if ((byte & 0xf8) == 0xf0)
	    {
	      /* We expect four bytes.  */
	      ps->count = 3;
	      ps->value = byte & 0x07;
	    }
	  else if ((byte & 0xfc) == 0xf8)
	    {
	      /* We expect five bytes.  */
	      ps->count = 4;
	      ps->value = byte & 0x03;
	    }
	  else
	    {
	      /* We expect six bytes.  */
	      ps->count = 5;
	      ps->value = byte & 0x01;
	    }
	}

      /* We know we have to handle a multibyte character and there are
	 some more bytes to read.  */
      while (used < n)
	{
	  /* The second to sixths byte must be of the form 10xxxxxx.  */
	  unsigned char byte = (unsigned char) *s++;
	  ++used;

	  if ((byte & 0xc0) != 0x80)
	    {
	      /* Oh, oh.  An encoding error.  */
	      /* errno = (EILSEQ); */
	      return (size_t) -1;
	    }

	  ps->value <<= 6;
	  ps->value |= byte & 0x3f;

	  if (--ps->count == 0)
	    {
	      /* The character is finished.  */
	      if (pwc != NULL)
		*pwc = (wchar_t) ps->value;
	      return ps->value ? used : 0;
	    }
	}
    }

  return (size_t) -2;
}
