** special case, if it ends with a period then a pointer to the
** terminating NUL byte is returned.
*/
const char * file_extension(const char *zFileName){
  const char * zExt = zFileName ? strrchr(zFileName, '.') : 0;
  return zExt ? &zExt[1] : 0;
}

/*
** Returns true if the given filename ends with any of fossil's
** checkout database filenames: _FOSSIL_ or .fslckout. Specifically,
** it returns 1 if it's an exact match and 2 if it's the tail match
** on a longer input.
**
** zFilename must, for efficiency's sake, be a
** canonicalized/normalized name, e.g. using only '/' as directory
** separators.
**
** nFilename must be the strlen of zFilename. If it is negative,
** strlen() is used to calculate it.
*/
int filename_is_ckout_db(const char *zFilename, int nFilename){
  const char *zEnd;  /* one-after-the-end of zFilename */
  int gotSuffix = 0; /* length of suffix (-wal, -shm, -journal) */

  assert(zFilename && "API misuse");
  if(nFilename<0) nFilename = (int)strlen(zFilename);
  if(nFilename<8/*strlen _FOSSIL_*/) return 0;
  zEnd = zFilename + nFilename;
  if(nFilename>=12/*strlen _FOSSIL_-(shm|wal)*/){
    /* Check for (-wal, -shm, -journal) suffixes, with an eye towards
    ** runtime speed. */
    if('-'==zEnd[-4]){
      if(fossil_stricmp("wal", &zEnd[-3])
         && fossil_stricmp("shm", &zEnd[-3])){
        return 0;
      }
      gotSuffix = 4;
    }else if(nFilename>=16/*strlen _FOSSIL_-journal*/ && '-'==zEnd[-8]){
      if(fossil_stricmp("journal",&zEnd[-7])){
        return 0;
      }
      gotSuffix = 8;
    }
    if(gotSuffix){
      assert(4==gotSuffix || 8==gotSuffix);
      zEnd -= gotSuffix;
      nFilename -= gotSuffix;
      gotSuffix = 1;
    }
    assert(nFilename>=8 && "strlen _FOSSIL_");
    assert(gotSuffix==0 || gotSuffix==1);
  }
  switch(zEnd[-1]){
    case '_': {
      return fossil_strnicmp("_FOSSIL_", &zEnd[-8], 8)
        ? 0 : (8==nFilename
               ? 1
               : ('/'==zEnd[-9] ? 2 : gotSuffix));
    }
    case 't': {
      return (nFilename<9
              || '.'!=zEnd[-9]
              || fossil_strnicmp(".fslckout", &zEnd[-9], 9))
        ? 0 : (9==nFilename
               ? 1
               : ('/'==zEnd[-10] ? 2 : gotSuffix));
    }
    default: {
      return 0;
    }
  }
}

/*
** COMMAND: test-is-ckout-db
**
** Usage: %fossil test-is-ckout-db FILENAMES...
**
** Passes each given name to filename_is_ckout_db() and outputs one
** line per file: the result value of that function followed by the
** name.
*/
void test_is_ckout_name_cmd(void){
  int i;

  if(g.argc<3){
    usage("FILENAME_1 [...FILENAME_N]");
  }
  for( i = 2; i < g.argc; ++i ){
    const int check = filename_is_ckout_db(g.argv[i], -1);
    fossil_print("%d %s\n", check, g.argv[i]);
  }
}