"use client";

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

// Use same origin — Next.js rewrites /api/* to backend

export function useSSE(path: string, maxEvents: number = 30) {
  const [events, setEvents] = useState<ActivityEvent[]>([]);
  const retryTimeout = useRef<ReturnType<typeof setTimeout> | null>(null);

  useEffect(() => {
    let es: EventSource | null = null;

    function connect() {
      es = new EventSource(path);

      // Backend sends "init" with the full batch and "update" with new events
      es.addEventListener("init", (e: MessageEvent) => {
        try {
          const batch: ActivityEvent[] = JSON.parse(e.data);
          setEvents(batch.slice(0, maxEvents));
        } catch {
          // ignore malformed events
        }
      });

      es.addEventListener("update", (e: MessageEvent) => {
        try {
          const batch: ActivityEvent[] = JSON.parse(e.data);
          setEvents((prev) => [...batch, ...prev].slice(0, maxEvents));
        } catch {
          // ignore malformed events
        }
      });

      es.onerror = () => {
        es?.close();
        retryTimeout.current = setTimeout(connect, 5000);
      };
    }

    connect();

    return () => {
      es?.close();
      if (retryTimeout.current) clearTimeout(retryTimeout.current);
    };
  }, [path, maxEvents]);

  return events;
}