/* Copyright (C) 2011-2025 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library 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
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <assert.h>
#include <dlfcn.h>
#include <errno.h>
#include <gconv.h>
#include <uchar.h>
#include <wcsmbsload.h>

#include <pointer_guard.h>

#ifndef EILSEQ
# define EILSEQ EINVAL
#endif


/* This is the private state used if PS is NULL.  */
static mbstate_t state;

size_t
mbrtoc16 (char16_t *pc16, const char *s, size_t n, mbstate_t *ps)
{
  if (ps == NULL)
    ps = &state;

  /* The standard text does not say that S being NULL means the state
     is reset even if the second half of a surrogate still have to be
     returned.  In fact, the error code description indicates
     otherwise.  Therefore always first try to return a second
     half.  */
  if (ps->__count & 0x80000000)
    {
      /* We have to return the second word for a surrogate.  */
      ps->__count &= 0x7fffffff;
      *pc16 = ps->__value.__wch;
      ps->__value.__wch = L'\0';
      return (size_t) -3;
    }

  wchar_t wc;
  struct __gconv_step_data data;
  int status;
  size_t result;
  size_t dummy;
  const unsigned char *inbuf, *endbuf;
  unsigned char *outbuf = (unsigned char *) &wc;
  const struct gconv_fcts *fcts;

  /* Set information for this step.  */
  data.__invocation_counter = 0;
  data.__internal_use = 1;
  data.__flags = __GCONV_IS_LAST;
  data.__statep = ps;

  /* A first special case is if S is NULL.  This means put PS in the
     initial state.  */
  if (s == NULL)
    {
      pc16 = NULL;
      s = "";
      n = 1;
    }

  if (n == 0)
    return (size_t) -2;

  /* Tell where we want the result.  */
  data.__outbuf = outbuf;
  data.__outbufend = outbuf + sizeof (wchar_t);

  /* Get the conversion functions.  */
  fcts = get_gconv_fcts (_NL_CURRENT_DATA (LC_CTYPE));

  /* Do a normal conversion.  */
  inbuf = (const unsigned char *) s;
  endbuf = inbuf + n;
  if (__glibc_unlikely (endbuf < inbuf))
    {
      endbuf = (const unsigned char *) ~(uintptr_t) 0;
      if (endbuf == inbuf)
	goto ilseq;
    }
  __gconv_fct fct = fcts->towc->__fct;
  if (fcts->towc->__shlib_handle != NULL)
    PTR_DEMANGLE (fct);

  status = DL_CALL_FCT (fct, (fcts->towc, &data, &inbuf, endbuf,
			      NULL, &dummy, 0, 1));

  /* There must not be any problems with the conversion but illegal input
     characters.  The output buffer must be large enough, otherwise the
     definition of MB_CUR_MAX is not correct.  All the other possible
     errors also must not happen.  */
  assert (status == __GCONV_OK || status == __GCONV_EMPTY_INPUT
	  || status == __GCONV_ILLEGAL_INPUT
	  || status == __GCONV_INCOMPLETE_INPUT
	  || status == __GCONV_FULL_OUTPUT);

  if (status == __GCONV_OK || status == __GCONV_EMPTY_INPUT
      || status == __GCONV_FULL_OUTPUT)
    {
      result = inbuf - (const unsigned char *) s;

      if (wc < 0x10000)
	{
	  if (pc16 != NULL)
	    *pc16 = wc;

	  if (data.__outbuf != outbuf && wc == L'\0')
	    {
	      /* The converted character is the NUL character.  */
	      assert (__mbsinit (data.__statep));
	      result = 0;
	    }
	}
      else
	{
	  /* This is a surrogate.  */
	  if (pc16 != NULL)
	    *pc16 = 0xd7c0 + (wc >> 10);

	  ps->__count |= 0x80000000;
	  ps->__value.__wch = 0xdc00 + (wc & 0x3ff);
	}
    }
  else if (status == __GCONV_INCOMPLETE_INPUT)
    result = (size_t) -2;
  else
    {
    ilseq:
      result = (size_t) -1;
      __set_errno (EILSEQ);
    }

  return result;
}
