"use client";

/**
 * usePresenceAnnouncer (TASK-0093, spec R5) — the polite live region for a
 * page's presence: "Ana is editing this page" / "Ana left" / "Ana joined",
 * rate-limited to ≤ 1 announcement per second, STATE CHANGES ONLY (a peer
 * typing fires cursor frames at ~8/s — those never announce).
 *
 * The pure state machine (the rate limiter + the join/edit/leave state
 * detection) is {@link PresenceAnnouncer} (lib/presence-announcer) — this
 * hook only owns the DOM: the `role=status` live-region text, fed from the
 * store's roster (others only), flushed on an idle tick so a change that
 * lands inside the 1 s window is still delivered (not lost).
 *
 * Returns the current announcement text (the component renders it in the
 * live region).
 */
import { useEffect, useRef, useState } from "react";
import { PresenceAnnouncer } from "@/lib/presence-announcer";
import { useBlockPatchStore } from "@/stores/block-patch-store";
import type { Presence } from "@/lib/types";

const EMPTY_PRESENCE: Record<string, Presence> = {};
const FLUSH_INTERVAL_MS = 1000;

export function usePresenceAnnouncer(pageId: string | null, selfUserId?: string | null): string {
  const [text, setText] = useState("");
  const announcerRef = useRef<PresenceAnnouncer | null>(null);

  useEffect(() => {
    if (pageId === null) return;
    const announcer = new PresenceAnnouncer();
    announcerRef.current = announcer;

    const emit = (a: { text: string } | null): void => {
      if (a !== null) setText(a.text);
    };

    const feed = (state: { presence: Record<string, Record<string, Presence>> }): void => {
      const roster = Object.values(state.presence[pageId] ?? EMPTY_PRESENCE);
      emit(announcer.update(selfUserId ? roster.filter((p) => p.userId !== selfUserId) : roster));
    };
    feed(useBlockPatchStore.getState());
    const off = useBlockPatchStore.subscribe(feed);

    // Flush a change that was queued inside the 1 s window (so it is
    // delivered, not lost) — the announcer emits at most once per window.
    const id = window.setInterval(() => emit(announcer.flush()), FLUSH_INTERVAL_MS);
    return () => {
      off();
      window.clearInterval(id);
      announcerRef.current = null;
      announcer.reset();
      setText("");
    };
  }, [pageId, selfUserId]);

  return text;
}