/* Case-mapping context of prefix UTF-8/UTF-16/UTF-32 string.
   Copyright (C) 2009-2018 Free Software Foundation, Inc.
   Written by Bruno Haible <bruno@clisp.org>, 2009.

   This program is free software: you can redistribute it and/or
   modify it under the terms of either:

     * the GNU Lesser General Public License as published by the Free
       Software Foundation; either version 3 of the License, or (at your
       option) any later version.

   or

     * 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.

   or both in parallel, as here.
   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
   Lesser General Public License for more details.

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

casing_prefix_context_t
FUNC1 (const UNIT *s, size_t n)
{
  return FUNC2 (s, n, unicase_empty_prefix_context);
}

casing_prefix_context_t
FUNC2 (const UNIT *s, size_t n, casing_prefix_context_t a_context)
{
#if 0
  /* Forward iteration.  Slow for long strings.  */
  casing_prefix_context_t context = a_context;
  const UNIT *s_end = s + n;

  while (s < s_end)
    {
      ucs4_t uc;
      int count = U_MBTOUC_UNSAFE (&uc, s, s_end - s);

      if (!uc_is_case_ignorable (uc))
        context.last_char_except_ignorable = uc;

      {
        int ccc = uc_combining_class (uc);
        if (ccc == UC_CCC_A || ccc == UC_CCC_NR)
          context.last_char_normal_or_above = uc;
      }

      s += count;
    }

  return context;
#else
  /* Iterate backwards, only as far as needed.  */
  casing_prefix_context_t context;
  ucs4_t last_char_except_ignorable = (ucs4_t)(-1);
  ucs4_t last_char_normal_or_above = (ucs4_t)(-1);
  const UNIT *p = s + n;

  for (;;)
    {
      ucs4_t uc;
      p = U_PREV (&uc, p, s);
      if (p == NULL)
        break;

      if (last_char_except_ignorable == (ucs4_t)(-1))
        {
          if (!uc_is_case_ignorable (uc))
            last_char_except_ignorable = uc;
        }

      if (last_char_normal_or_above == (ucs4_t)(-1))
        {
          int ccc = uc_combining_class (uc);
          if (ccc == UC_CCC_A || ccc == UC_CCC_NR)
            last_char_normal_or_above = uc;
        }

      if (last_char_except_ignorable != (ucs4_t)(-1)
          && last_char_normal_or_above != (ucs4_t)(-1))
        break;
    }
  context.last_char_except_ignorable =
    (last_char_except_ignorable != (ucs4_t)(-1)
     ? last_char_except_ignorable
     : a_context.last_char_except_ignorable);
  context.last_char_normal_or_above =
    (last_char_normal_or_above != (ucs4_t)(-1)
     ? last_char_normal_or_above
     : a_context.last_char_normal_or_above);

  return context;
#endif
}
