**
** An input of "tip" returns the most recent check-in.
**
** Memory to hold the returned string comes from malloc() and needs to
** be freed by the caller.
*/
char *tag_to_uuid(const char *zTag){
  int vid;
  char *zUuid = 
    db_text(0,
       "SELECT blob.uuid"
       "  FROM tag, tagxref, event, blob"
       " WHERE tag.tagname='sym-'||%Q "
       "   AND tagxref.tagid=tag.tagid AND tagxref.tagtype>0 "
       "   AND event.objid=tagxref.rid "

      zUuid = db_text(0,
        "SELECT blob.uuid"
        "  FROM event, blob"
        " WHERE event.type='ci'"
        "   AND blob.rid=event.objid"
        " ORDER BY event.mtime DESC"
      );
    }
    if( zUuid==0 && g.localOpen && (vid=db_lget_int("checkout",0))!=0 ){
      if( strcmp(zTag, "ckout")==0 ){
        zUuid = db_text(0, "SELECT uuid FROM blob WHERE rid=%d", vid);
      }else if( strcmp(zTag, "prev")==0 ){
        zUuid = db_text(0, "SELECT uuid FROM blob WHERE rid="
                           "(SELECT pid FROM plink WHERE cid=%d AND isprim)",
                           vid);
      }else if( strcmp(zTag, "next")==0 ){
        zUuid = db_text(0, "SELECT uuid FROM blob WHERE rid="
                           "(SELECT cid FROM plink WHERE pid=%d AND isprim"
                           "  ORDER BY mtime DESC)",
                           vid);
      }
    }
  }
  return zUuid;
}

/*
** Convert a date/time string into a UUID.