import { readLines } from "https://deno.land/std@0.157.0/io/buffer.ts";

const PORT = 5588;
console.log(`Starting TCP listener on on 0.0.0.0:${PORT}`);

const clients = new Map<Deno.Conn, string>();

const tEnc = new TextEncoder();

async function chatSession(conn: Deno.Conn) {
  try {
    let myNick: string | null = null;
    await sendPrompt(conn);
    for await (const line of readLines(conn)) {
      console.debug("Received line:", line);
      const message = line.trim();
      if (myNick == null) {
        if (isLegalNick(message)) {
          myNick = message;
          await join(myNick, conn);
        } else {
          console.error("Illegal nick:", message);
          break;
        }
      } else {
        const conns: Deno.Conn[] = [];
        for (const themConn of clients.keys()) {
          if (themConn != conn) conns.push(themConn);
        }
        await send(conns, `[${myNick}] ${message}`);
      }
    }
  } finally {
    if (clients.has(conn)) {
      try {
        await disconnect(conn);
      } catch (err) {
        console.error("Failed to disconnect:", err);
      }
    }
    try {
      if (conn.writable) {
        send(conn, "You are being disconnected...");
      }
    } catch (err) {
      console.error("Failed to send disconnect notice:", err);
    }
  }
  try {
    conn.close();
  } catch (err) {
    console.error("Failed to close connection:", err);
  }
}

async function send(
  connsArg: Deno.Conn | Array<Deno.Conn>,
  text: string,
) {
  const conns = !Array.isArray(connsArg) ? [connsArg] : connsArg;
  const messages: Promise<number>[] = [];
  const bytes = tEnc.encode(text + "\n");
  conns.forEach((conn) => messages.push(conn.write(bytes)));
  return await Promise.all(messages);
}

const broadcast = async (text: string) => await send([...clients.keys()], text);

const LEGAL_NICK_REGEXP = /^[a-z0-9]+$/i;
const isLegalNick = (nick: string) => {
  console.debug(
    `Checking nick: ${nick} (Bytes: ${tEnc.encode(nick)})`,
  );
  return LEGAL_NICK_REGEXP.exec(nick) != null;
};

const sendPrompt = async (conn: Deno.Conn) => {
  console.debug("Sending prompt...");
  return await send(conn, "Who you be?");
};

async function join(myNick: string, conn: Deno.Conn) {
  const userList: string[] = [];
  clients.forEach((nick, _) => userList.push(nick));
  await broadcast(`* ${myNick} joined`);
  clients.set(conn, myNick);
  await send(conn, `* users: ${userList.join(", ")}`);
}

async function disconnect(conn: Deno.Conn) {
  const myNick = clients.get(conn);
  clients.delete(conn);
  await broadcast(`* ${myNick} left`);
}

for await (const conn of Deno.listen({ port: PORT })) {
  console.log("Connection established:", conn.remoteAddr);
  try {
    chatSession(conn);
  } catch (e) {
    console.error(
      "Exception occurred during chat session:",
      conn.remoteAddr,
      e,
    );
  }
  console.log("Connection closed:", conn.remoteAddr);
}