main.ts

import { serveDir } from "serveDir";
import * as Y from "yjs";

const PORT = 8000;
const SAVE_FILE = "yjs_state.bin";

const doc = new Y.Doc();
const connections = new Set<WebSocket>();

try {
  const saved = await Deno.readFile(SAVE_FILE);
  Y.applyUpdate(doc, saved);
} catch (_) {
  // This just means no note has been created yet, we don't care.
}

doc.on("update", async (update: Uint8Array, origin) => {
  for (const socket of connections) {
    if (socket !== origin && socket.readyState === WebSocket.OPEN) {
      socket.send(update);
    }
  }
  const fullState = Y.encodeStateAsUpdate(doc);
  await Deno.writeFile(SAVE_FILE, fullState);
});

function handleWebSocket(req: Request): Response {
  const { socket, response } = Deno.upgradeWebSocket(req);
  connections.add(socket);
  const sendState = () => {
    if (socket.readyState === WebSocket.OPEN) {
      socket.send(Y.encodeStateAsUpdate(doc));
    }
  };
  if (socket.readyState === WebSocket.OPEN) {
    sendState();
  } else {
    socket.addEventListener("open", sendState, { once: true });
  }
  socket.onmessage = (event: MessageEvent) => {
    if (typeof event.data !== "string") {
      const update = new Uint8Array(event.data as ArrayBuffer);
      Y.applyUpdate(doc, update, socket);
    }
  };
  const cleanup = () => connections.delete(socket);
  socket.onclose = cleanup;
  socket.onerror = cleanup;
  return response;
}

const handler = (req: Request) => {
  const { pathname } = new URL(req.url);
  if (pathname === "/ws") {
    return handleWebSocket(req);
  }
  return serveDir(req, { fsRoot: "public", quiet: true });
};

Deno.serve({ port: PORT }, handler);