import { useEffect, useState } from "react";
import { BASE } from "../api/client";
import { joinBackendPath } from "../api/runtime-config";
import { useSessionStore } from "../store/sessionStore";
import type { StreamEvent } from "../api/types";

export function useSessionStream(sessionId: string | null) {
  const [connected, setConnected] = useState(false);
  const applyEvent = useSessionStore((s) => s.applyEvent);

  useEffect(() => {
    if (!sessionId) return;

    const es = new EventSource(joinBackendPath(BASE, `/sessions/${sessionId}/events`));
    es.onopen = () => setConnected(true);
    es.onerror = () => setConnected(false);

    const handle = (ev: MessageEvent) => {
      try {
        applyEvent(JSON.parse(ev.data) as StreamEvent);
      } catch {
        /* ignore malformed */
      }
    };

    // onmessage catches unnamed events; addEventListener catches named events
    // (the backend sends event: ui_request, event: text_delta, etc.)
    es.onmessage = handle;
    const namedEvents = ["ui_request", "text_delta", "info", "system_event"] as const;
    for (const name of namedEvents) es.addEventListener(name, handle);

    return () => {
      for (const name of namedEvents) es.removeEventListener(name, handle);
      es.close();
      setConnected(false);
    };
  }, [sessionId, applyEvent]);

  return { connected };
}