"use client";

import { useEffect, useState } from "react";

export interface PresenceParticipant {
  id: number;
  name: string;
  lastSeen: string;
}

interface PresenceEvent {
  channel?: string;
  action?: "snapshot" | "join" | "update" | "leave";
  participants?: PresenceParticipant[];
  participant?: PresenceParticipant;
  participantId?: number;
}

const HEARTBEAT_MS = 15_000;

export function useRealtimePresence(channel: string, active: boolean, observe = true): PresenceParticipant[] {
  const [participants, setParticipants] = useState<PresenceParticipant[]>([]);

  useEffect(() => {
    if (!observe) {
      setParticipants([]);
      return;
    }

    let cancelled = false;
    const endpoint = `/api/realtime/presence?channel=${encodeURIComponent(channel)}`;
    const send = (method: "POST" | "DELETE") => {
      void fetch(endpoint, { method, keepalive: method === "DELETE" }).catch(() => undefined);
    };
    const source = new EventSource(`/api/realtime?channel=${encodeURIComponent(channel)}`);
    const onPresence = (event: MessageEvent<string>) => {
      if (cancelled) return;
      let detail: PresenceEvent;
      try {
        detail = JSON.parse(event.data) as PresenceEvent;
      } catch {
        return;
      }
      if (detail.channel !== channel) return;
      if (detail.action === "snapshot") setParticipants(detail.participants ?? []);
      if ((detail.action === "join" || detail.action === "update") && detail.participant) {
        setParticipants((current) => [
          ...current.filter((item) => item.id !== detail.participant!.id),
          detail.participant!,
        ]);
      }
      if (detail.action === "leave" && detail.participantId !== undefined) {
        setParticipants((current) => current.filter((item) => item.id !== detail.participantId));
      }
    };
    source.addEventListener("presence", onPresence);
    if (active) send("POST");
    const heartbeat = active ? window.setInterval(() => send("POST"), HEARTBEAT_MS) : undefined;

    return () => {
      cancelled = true;
      if (heartbeat) window.clearInterval(heartbeat);
      source.removeEventListener("presence", onPresence);
      source.close();
      if (active) send("DELETE");
    };
  }, [channel, active, observe]);

  return participants;
}