PacketStation/frontend/src/auth/useEvents.ts

import { useEffect, useRef, useState } from "react";
import type { PresenceUser } from "./types";

interface EventHandlers {
  /** Called when the server revokes this browser's own session. */
  onRevoked: () => void;
  /** Called for every `changed` event. Later phases refresh their data from it. */
  onChanged?: (payload: unknown) => void;
}

function parse(data: unknown): unknown {
  if (typeof data !== "string") return null;
  try {
    return JSON.parse(data) as unknown;
  } catch {
    return null;
  }
}

/**
 * Opens /api/events with EventSource while `sessionId` is set.
 * A `session` event with this session id and action "revoked" calls onRevoked.
 * `presence` is kept in state for later phases.
 */
export function useEvents(sessionId: string | null, handlers: EventHandlers): PresenceUser[] {
  const [presence, setPresence] = useState<PresenceUser[]>([]);
  const ref = useRef(handlers);
  useEffect(() => {
    ref.current = handlers;
  });

  useEffect(() => {
    if (!sessionId || typeof EventSource === "undefined") return;
    const es = new EventSource("/api/events", { withCredentials: true });

    es.addEventListener("session", (ev) => {
      const p = parse((ev as MessageEvent).data);
      if (p && typeof p === "object") {
        const o = p as { session_id?: unknown; action?: unknown };
        if (o.session_id === sessionId && o.action === "revoked") ref.current.onRevoked();
      }
    });
    es.addEventListener("presence", (ev) => {
      const p = parse((ev as MessageEvent).data);
      if (p && typeof p === "object" && Array.isArray((p as { users?: unknown }).users)) {
        setPresence((p as { users: PresenceUser[] }).users);
      }
    });
    es.addEventListener("changed", (ev) => {
      ref.current.onChanged?.(parse((ev as MessageEvent).data));
    });
    // Phase 3: the worker finished a feed run. Fanned out with the changed events, marked event "feed".
    es.addEventListener("feed", (ev) => {
      const p = parse((ev as MessageEvent).data);
      ref.current.onChanged?.({ ...(p && typeof p === "object" ? p : {}), event: "feed" });
    });

    return () => {
      es.close();
      setPresence([]);
    };
  }, [sessionId]);

  return presence;
}