/*
 * Copyright (C) 2005, 2016 Free Software Foundation, Inc.
 * This file is part of the GNU LIBICONV Library.
 *
 * The GNU LIBICONV 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
 * of the License, or (at your option) any later version.
 *
 * The GNU LIBICONV 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 LIBICONV Library; see the file COPYING.LIB.
 * If not, see <https://www.gnu.org/licenses/>.
 */

/*
 * CP936
 */

/*
 * The IANA has CP936 as an alias of GBK. But GBK is an official Chinese
 * specification, whereas CP936 is de-facto maintained by Microsoft. And,
 * of course, Microsoft modified CP936 since 1999.
 *
 * The differences from GBK are:
 *
 * 1. A single character:
 *
 *    code   CP936.TXT
 *    0x80   0x20AC # EURO SIGN
 *
 * Some variants of CP936 (in JDK, Windows-2000, ICU) also add:
 *
 * 2. Private area mappings:
 *
 *              code                 Unicode
 *    0x{A1..A2}{40..7E,80..A0}  U+E4C6..U+E585
 *    0x{AA..AF,F8..FE}{A1..FE}  U+E000..U+E4C5
 *
 * We add them too because, although there are backward compatibility problems
 * when a character from a private area is moved to an official Unicode code
 * point, they are useful for some people in practice.
 */

static int
cp936_mbtowc (conv_t conv, ucs4_t *pwc, const unsigned char *s, size_t n)
{
  /* Try GBK first. */
  {
    int ret = ces_gbk_mbtowc(conv,pwc,s,n);
    if (ret != RET_ILSEQ)
      return ret;
  }
  /* Then handle the additional mappings. */
  {
    unsigned char c = *s;
    if (c == 0x80) {
      *pwc = 0x20ac;
      return 1;
    }
    /* User-defined characters */
    if (c >= 0xa1 && c <= 0xa2) {
      if (n < 2)
        return RET_TOOFEW(0);
      {
        unsigned char c2 = s[1];
        if ((c2 >= 0x40 && c2 < 0x7f) || (c2 >= 0x80 && c2 < 0xa1)) {
          *pwc = 0xe4c6 + 96 * (c - 0xa1) + (c2 - (c2 >= 0x80 ? 0x41 : 0x40));
          return 2;
        }
      }
    } else if ((c >= 0xaa && c < 0xb0) || (c >= 0xf8 && c < 0xff)) {
      if (n < 2)
        return RET_TOOFEW(0);
      {
        unsigned char c2 = s[1];
        if (c2 >= 0xa1 && c2 < 0xff) {
          *pwc = 0xe000 + 94 * (c - (c >= 0xf8 ? 0xf2 : 0xaa)) + (c2 - 0xa1);
          return 2;
        }
      }
    }
  }
  return RET_ILSEQ;
}

static int
cp936_wctomb (conv_t conv, unsigned char *r, ucs4_t wc, size_t n)
{
  /* Try GBK first. */
  {
    int ret = ces_gbk_wctomb(conv,r,wc,n);
    if (ret != RET_ILUNI)
      return ret;
  }
  /* Then handle the additional mappings. */
  if (wc >= 0xe000 && wc < 0xe586) {
    /* User-defined characters */
    if (n < 2)
      return RET_TOOFEW(0);
    if (wc < 0xe4c6) {
      unsigned int i = wc - 0xe000;
      unsigned int c1 = i / 94;
      unsigned int c2 = i % 94;
      r[0] = c1 + (c1 < 6 ? 0xaa : 0xf2);
      r[1] = c2 + 0xa1;
      return 2;
    } else {
      unsigned int i = wc - 0xe4c6;
      unsigned int c1 = i / 96;
      unsigned int c2 = i % 96;
      r[0] = c1 + 0xa1;
      r[1] = c2 + (c2 < 0x3f ? 0x40 : 0x41);
      return 2;
    }
  } else if (wc == 0x20ac) {
    r[0] = 0x80;
    return 1;
  }
  return RET_ILUNI;
}