asclass DynServerAwareDiscordBot<A extends DynServerAwareDiscordBot.ByServer> extends DynDiscordHopper {
  new Map<Long, A> dataByServer;
  int guildCount;
  transient IF0<A> makeByServer; // mandatory
  
  class ByServer {
    bool isGuild;
    
    S answer(S s, Map map) { null; }

    bool setField(S name, O value) {
      if (set_trueIfChanged(this, name, value)) false;
      ret true with _change();
    }
    
    Member getSelfMember(Guild guild) {
      ret guild.getMember(getSelfUser());
    }
  }
  
  @Override S answer(S input, Map map) {
    try answer super.answer(input, map); // discord hopping
    
    long guildID = toLong(map.get('guildID));
    long id = guildID;
    print("Guild ID: " + guildID);
    if (id == 0) {
      id = toLong(map.get('userID));
      print("User ID: " + id);
    }
      
    // config by guild or user
    A data = getByServer(id, id == guildID);
    
    Message msg = cast map.get('msg);
    if (msg != null && nempty(msg.getAttachments()))
      ret data.answer(input, map);
    else // TODO: don't always go line by line
      ret mapEachLine_tlft_nempties(input, s -> {
        ret data.answer(s, map);
      });
  }
  
  A getByServer(long id, bool isGuild) {
    ret pairA(getByServer2(id, isGuild));
  }
  
  Pair<A, Bool> getByServer2(long id, bool isGuild) {
    A data, bool isNew = unpair syncGetOrCreate2(dataByServer, id, makeByServer);
    data.isGuild = isGuild;
    if (isNew) {
      if (data.isGuild) ++guildCount;
      change();
    }
    ret pair(data, isNew);
  }
  
  start {
    if (guildCount == 0)
      setField(guildCount := countValuesWhere_sync(dataByServer, isGuild := true));
  }
  
  int liveGuildCount() {
    ret l(discord.getGuilds());
  }
  
  long idForByServer(A bs) {
    ret bs == null ? 0 : toLong(keyForValue_sync(dataByServer, bs));
  }
}