ChatApp with Bots

Implement a small in-memory chat application that supports multiple channels and extensible bots.

Each channel maintains its own message history and any bot state associated with that channel.

Process a list of commands in order:

• REGISTER botName1 [botName2 ...] — Register one or more bots by name. Multiple REGISTER commands accumulate; re-registering an already-registered bot has no effect. Two built-in bot types exist:
  • EchoBot — replies with the exact message text it receives, for every message.
  • HelpBot — replies with the string available commands: ... only when the entire message text is exactly help (case-sensitive).
• SEND channelId userId text... — Append a user message entry (userId: <text>) to the named channel's history, where text is all tokens after userId joined with a single space. Then, in registration order, check each registered bot: the first bot whose trigger condition matches the message text appends its reply (botName: <reply>) to that channel's history. At most one bot replies per SEND.
• PRINT channelId — Emit the full message history for that channel. The first line emitted is channel=channelId, followed by each history entry in insertion order, one per line. A PRINT on a channel with no prior messages emits only the header line channel=channelId.

The return value is the concatenation of all lines produced by all PRINT commands, in order. When multiple PRINT commands are issued, the output blocks are separated by a single empty string "" between consecutive blocks (i.e., after every block except the last).