"use client";

/**
 * usePresenceToasts (TASK-0093, spec R5) — the join/leave TOASTS for a
 * page's presence (the live region is the a11y channel; the toasts are the
 * visual one). Controlled by the `presenceToastsEnabled` setting (ON by
 * default) in the ui store.
 *
 *  - Join: "{name} joined" (a peer newly present — a `presence` frame for
 *    a userId not in the prior roster).
 *  - Leave: "{name} left" (a `presence-leave`, or a peer dropped from the
 *    roster — the 90 s prune surfaces as their frame not re-asserting;
 *    we key on the store roster diff, so the prune toast fires too).
 *  - Edit START/STOP are NOT toasted (the live region covers them; toasts
 *    for every start/stop would be noisy — the spec says toasts are
 *    join/leave).
 *
 * Deterministic (no timers — toasts auto-dismiss on their own duration).
 * Call once per page (the page view, next to `usePresenceAnnouncer`).
 */
import { useEffect, useRef } from "react";
import { toast, useUiStore } from "@/stores/ui-store";
import { useBlockPatchStore } from "@/stores/block-patch-store";
import type { Presence } from "@/lib/types";

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

export function usePresenceToasts(pageId: string | null, selfUserId?: string | null): void {
  const enabled = useUiStore((s) => s.presenceToastsEnabled);
  const prevRef = useRef<Map<string, string> | null>(null);

  useEffect(() => {
    if (pageId === null || !enabled) {
      prevRef.current = null;
      return;
    }
    const feed = (state: { presence: Record<string, Record<string, Presence>> }): void => {
      const roster = Object.values(state.presence[pageId] ?? EMPTY_PRESENCE);
      const now = new Map<string, string>();
      for (const p of roster) if (p.userId !== selfUserId) now.set(p.userId, p.name);
      const prev = prevRef.current;
      if (prev !== null) {
        for (const [userId, name] of now) {
          if (!prev.has(userId)) toast("info", `${name} joined`);
        }
        for (const [userId, name] of prev) {
          if (!now.has(userId)) toast("info", `${name} left`);
        }
      }
      prevRef.current = now;
    };
    feed(useBlockPatchStore.getState());
    const off = useBlockPatchStore.subscribe(feed);
    return () => {
      off();
      prevRef.current = null;
    };
  }, [pageId, enabled, selfUserId]);
}