/* ------------------------------------------------------------ */
/*
HTTrack Website Copier, Offline Browser for Windows and Unix
Copyright (C) 2013 Xavier Roche and other contributors

SPDX-License-Identifier: GPL-3.0-or-later

This program 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, either version 3 of the License, or
(at your option) any later version.

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, see <http://www.gnu.org/licenses/>.

Ethical use: we kindly ask that you NOT use this software to harvest email
addresses or to collect any other private information about people. Doing so
would dishonor our work and waste the many hours we have spent on it.

Please visit our Website: http://www.httrack.com
*/

/* ------------------------------------------------------------ */
/* File: Encoding conversion functions                          */
/* Author: Xavier Roche                                         */
/* ------------------------------------------------------------ */

#include <stdint.h>

#include "htscharset.h"
#include "htsencoding.h"
#include "htssafe.h"

/* static int decode_entity(const uint64_t hash, const size_t len);
 */
#include "htsentities.h"

/* 64-bit FNV-1a; must match htsentities.sh, which keys the entity table on it.
 */
#define HASH_INIT 0xcbf29ce484222325ULL
#define HASH_PRIME 0x100000001b3ULL
#define HASH_ADD(HASH, C)                                                      \
  do {                                                                         \
    (HASH) ^= (unsigned char) (C);                                             \
    (HASH) *= HASH_PRIME;                                                      \
  } while (0)

int hts_unescapeEntitiesWithCharset(const char *src, char *dest, const size_t max, const char *charset) {
  return hts_unescapeEntitiesWithCharsetSpecial(src, dest, max, charset, 0);
}

int hts_unescapeEntitiesWithCharsetSpecial(const char *src, char *dest,
                                           const size_t max,
                                           const char *charset,
                                           const int flags) {
  size_t i, j, ampStart, ampStartDest;
  int uc;
  int hex;
  uint64_t hash;

  assertf(max != 0);
  for (i = 0, j = 0, ampStart = (size_t) -1, ampStartDest = 0, uc = -1, hex = 0,
      hash = HASH_INIT;
       src[i] != '\0'; i++) {
    /* start of entity */
    if (src[i] == '&') {
      ampStart = i;
      ampStartDest = j;
      hash = HASH_INIT;
      uc = -1;
    }
    /* inside a potential entity */
    else if (ampStart != (size_t) -1) {
      /* &#..; entity */
      if (ampStart + 1 == i && src[ampStart + 1] == '#') {
        uc = 0;
        hex = 0;
      }
      /* &#x..; entity */
      else if (ampStart + 2 == i && src[ampStart + 1] == '#'
               && src[ampStart + 2] == 'x') {
        hex = 1;
      }
      /* end of entity */
      else if (src[i] == ';') {
        size_t len;
        
        /* decode entity */
        if (uc == -1) {
          /* &foo; */
          uc = decode_entity(hash, /*&src[ampStart + 1],*/
                             i - ampStart - 1);
          /* FIXME: TEMPORARY HACK FROM PREVIOUS VERSION TO BE INVESTIGATED */
          if (uc == 160) {
            uc = 32;
          }
        }
        
        /* end */
        ampStart = (size_t) -1;
        
        /* success ? */
        if (uc > 0) {
          const size_t maxOut = max - ampStartDest;
          /* write at position */
          if (charset != NULL && hts_isCharsetUTF8(charset)) {
            len = hts_writeUTF8(uc, &dest[ampStartDest], maxOut);
          } else {
            size_t ulen;
            char buffer[32];
            len = 0;
            if ( ( ulen = hts_writeUTF8(uc, buffer, sizeof(buffer)) ) != 0) {
              const hts_boolean urlQuery =
                  (flags & UNESCAPE_ENTITIES_URL_QUERY) != 0;
              char *s;
              buffer[ulen] = '\0';
              /* Strict for a query only: a substituted '?' must not pass for
                 the code point the document wrote. */
              if (urlQuery) {
                s = hts_convertStringFromUTF8Strict(buffer, strlen(buffer),
                                                    charset);
              } else {
                s = hts_convertStringFromUTF8(buffer, strlen(buffer), charset);
              }
              if (s != NULL) {
                const size_t sLen = strlen(s);
                if (sLen < maxOut) {
                  /* Do not copy \0. */
                  memcpy(&dest[ampStartDest], s, sLen);
                  len = sLen;
                }
                freet(s);
              } else if (urlQuery) {
                /* URL Standard: an unrepresentable code point is written
                   %26%23<decimal>%3B rather than left as source text. */
                char esc[32];
                const int escLen =
                    snprintf(esc, sizeof(esc), "%%26%%23%d%%3B", uc);

                if (escLen > 0 && (size_t) escLen < maxOut) {
                  memcpy(&dest[ampStartDest], esc, (size_t) escLen);
                  len = (size_t) escLen;
                }
              }
            }
          }
          if (len > 0) {
            /* new dest position */
            j = ampStartDest + len;
            /* do not copy ; */
            continue;
          }
        }
      }
      /* numerical entity */
      else if (uc != -1) {
        /* decimal */
        if (!hex) {
          if (src[i] >= '0' && src[i] <= '9') {
            const int h = src[i] - '0';
            /* Guard before multiplying: a codepoint past the Unicode max
               (0x10FFFF) is invalid anyway, so stop rather than overflow uc. */
            if (uc > (0x10FFFF - h) / 10) {
              ampStart = (size_t) -1;
            } else {
              uc = uc * 10 + h;
            }
          } else {
            /* abandon */
            ampStart = (size_t) -1;
          }
        }
        /* hex */
        else {
          const int h = hts_ehexh(src[i]);
          if (h != -1) {
            if (uc > (0x10FFFF - h) / 16) {
              ampStart = (size_t) -1;
            } else {
              uc = uc * 16 + h;
            }
          } else {
            /* abandon */
            ampStart = (size_t) -1;
          }
        }
      }
      /* alphanumerical entity */
      else {
        /* alphanum, capped at the longest name
         * '&CounterClockwiseContourIntegral;' (31) */
        if (i <= ampStart + 31 && ((src[i] >= '0' && src[i] <= '9') ||
                                   (src[i] >= 'A' && src[i] <= 'Z') ||
                                   (src[i] >= 'a' && src[i] <= 'z'))) {
          /* compute hash */
          HASH_ADD(hash, (unsigned char) src[i]);
        } else {
          /* abandon */
          ampStart = (size_t) -1;
        }
      }
    }

    /* reserve one byte for the trailing NUL written after the loop */
    if (j + 1 >= max) {
      /* overflow */
      return -1;
    }
    if (src != dest || i != j) {
      dest[j] = src[i];
    }
    j++;
  }
  dest[j] = '\0';

  return 0;
}

int hts_unescapeEntities(const char *src, char *dest, const size_t max) {
  return hts_unescapeEntitiesWithCharset(src, dest, max, "UTF-8");
}

int hts_unescapeUrlSpecial(const char *src, char *dest, const size_t max,
                           const int flags) {
  size_t i, j, lastI, lastJ, k, utfBufferJ, utfBufferSize;
  int seenQuery = 0;
  char utfBuffer[32];

  assertf(src != dest);
  assertf(max != 0);

  for(i = 0, j = 0, k = 0, utfBufferJ = 0, utfBufferSize = 0,
      lastI = (size_t) -1, lastJ = (size_t) -1
      ; src[i] != '\0' ; i++) {
    char c = src[i];
    unsigned char cUtf = (unsigned char) c;

    /* Replacement for ' ' */
    if (c == '+' && seenQuery) {
      c = cUtf = ' ';
      k = 0;  /* cancel any sequence */
    }
    /* Escape sequence start */
    else if (c == '%') {
      /* last known position of % written on destination
         copy blindly c, we'll rollback later */
      lastI = i;
      lastJ = j;
    }
    /* End of sequence seen */
    else if (i >= 2 && i == lastI + 2) {
      const int a1 = hts_ehexh(src[lastI + 1]);
      const int a2 = hts_ehexh(src[lastI + 2]);
      if (a1 != -1 && a2 != -1) {
        const char ec = a1*16 + a2;  /* new character */
        cUtf = (unsigned char) ec;

        /* Shortcut for ASCII (do not unescape non-printable) */
        if (
            (cUtf < 0x80 && cUtf >= 32)
            && ( flags & UNESCAPE_URL_NO_ASCII ) == 0
            ) {
          /* Rollback new write position and character */
          j = lastJ;
          c = ec;
        }
      } else {
        k = 0;  /* cancel any sequence */
      }
    }
    /* ASCII (and not in %xx) */
    else if (cUtf < 0x80 && i != lastI + 1) {
      k = 0;  /* cancel any sequence */
      if (c == '?' && !seenQuery) {
        seenQuery = 1;
      }
    }
    
    /* UTF-8 sequence in progress (either a raw or a %xx character) */
    if (cUtf >= 0x80) {
      /* Leading UTF ? */
      if (HTS_IS_LEADING_UTF8(cUtf)) {
        k = 0;  /* cancel any sequence */
      }

      /* Copy */
      if (k < sizeof(utfBuffer)) {
        /* First character */
        if (k == 0) {
          /* New destination-centric offset of utf-8 buffer beginning */
          if (lastI != (size_t) -1 && i == lastI + 2) {  /* just read a %xx */
            utfBufferJ = lastJ;  /* position of % */
          } else {
            utfBufferJ = j;      /* current position otherwise */
          }

          /* Sequence length */
          utfBufferSize = hts_getUTF8SequenceLength(cUtf);
        }

        /* Copy */
        utfBuffer[k++] = cUtf;

        /* Flush UTF-8 buffer when completed. */
        if (k == utfBufferSize) {
          const size_t nRead = hts_readUTF8(utfBuffer, utfBufferSize, NULL);

          /* Reset UTF-8 buffer in all cases. */
          k = 0;

          /* Was the character read successfully ? */
          if (nRead == utfBufferSize) {
            /* the 'continue' below skips the NUL-reserve guard: re-check */
            if (utfBufferJ + utfBufferSize >= max) {
              return -1;
            }

            /* Rollback write position to sequence start write position */
            j = utfBufferJ;

            /* Copy full character sequence */
            memcpy(&dest[j], utfBuffer, utfBufferSize);
            j += utfBufferSize;

            /* Skip current character */
            continue;
          }
        }
      }
    }

    /* reserve one byte for the trailing NUL written after the loop */
    if (j + 1 >= max) {
      return -1;
    }

    /* Copy current */
    dest[j++] = c;
  }
  dest[j] = '\0';

  return 0;
}

int hts_unescapeUrl(const char *src, char *dest, const size_t max) {
  return hts_unescapeUrlSpecial(src, dest, max, 0);
}
