**
** 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.
**
** TODO: https://fossil-scm.org/sec2020/info/972cf9c302f5413f
** TL;DR: check for the -wal, -shm, -journal suffix forms of the db
** names.
*/
int filename_is_ckout_db(const char *zFilename, int nFilename){
  const char *zEnd;
  const char *zEnd;  /* one-after-the-end of zFilename */
  int gotSuffix = 0; /* length of suffix (-wal, -shm, -journal) */

  if(nFilename>=0 && nFilename<8/*strlen _FOSSIL_*/) return 0;
  else if(nFilename<0) nFilename = (int)strlen(zFilename);
  if(nFilename<8) return 0;
  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_strcmp("_FOSSIL_", &zEnd[-8])
        ? 0 : (8==nFilename ? 1 : ('/'==zEnd[-9] ? 2 : 0));
      return fossil_strnicmp("_FOSSIL_", &zEnd[-8], 8)
        ? 0 : (8==nFilename
               ? 1
               : ('/'==zEnd[-9] ? 2 : gotSuffix));
    }
    case 't': {
      return (nFilename<9
              || '.'!=zEnd[-9]
              || fossil_strcmp(".fslckout", &zEnd[-9]))
        ? 0 : (9==nFilename ? 1 : ('/'==zEnd[-10] ? 2 : 0));
              || fossil_strnicmp(".fslckout", &zEnd[-9], 9))
        ? 0 : (9==nFilename
               ? 1
               : ('/'==zEnd[-10] ? 2 : gotSuffix));
    }
    default:
    default: {
      return 0;
    }
  }
}

/*
** COMMAND: test-is-ckout-db
**
** Usage: %fossil test-is-ckout-db FILENAMES...