"use client";

import { useEffect, useRef } from "react";

/** One stream per board/thread; open replies refresh through the board revision. */
export function useCommentEvents(scope: { target: string } | { admin: true }, refresh: (changed: boolean) => Promise<unknown>) {
  const refreshRef = useRef(refresh);
  useEffect(() => { refreshRef.current = refresh; }, [refresh]);
  const query = "target" in scope ? `target=${encodeURIComponent(scope.target)}` : "scope=admin";
  useEffect(() => {
    let source: EventSource | null = null;
    let timer: ReturnType<typeof setTimeout> | undefined;
    let refreshing = false;
    let dirty = false;
    let pendingChange = false;
    let connectedBefore = false;
    let disposed = false;
    async function flush() {
      timer = undefined;
      if (disposed) return;
      if (refreshing) { dirty = true; return; }
      refreshing = true;
      const changed = pendingChange;
      pendingChange = false;
      try { await refreshRef.current(changed); }
      finally {
        refreshing = false;
        if (dirty && !disposed) { dirty = false; schedule(); }
      }
    }
    function schedule(changed = false) {
      pendingChange ||= changed;
      if (!timer && !disposed) timer = setTimeout(() => { void flush(); }, 250);
    }
    function connect() {
      source?.close(); source = null;
      if (document.visibilityState !== "visible") return;
      source = new EventSource(`/api/comments/events?${query}`);
      source.addEventListener("changed", () => schedule(true));
      // Catch updates between the initial page response and stream subscription,
      // and updates missed while disconnected. EventSource handles reconnects.
      source.addEventListener("open", () => {
        // A reconnect can have missed reply edits even if the root is unchanged.
        schedule(connectedBefore);
        connectedBefore = true;
      });
    }
    connect();
    document.addEventListener("visibilitychange", connect);
    return () => {
      disposed = true; source?.close();
      if (timer) clearTimeout(timer);
      document.removeEventListener("visibilitychange", connect);
    };
  }, [query]);
}