cinny/src/app/hooks/useReminders.ts

import { useCallback } from 'react';
import { useMatrixClient } from './useMatrixClient';
import { createAccountDataListStore } from './createAccountDataListStore';

export type Reminder = {
  roomId: string;
  eventId: string;
  timestamp: number;
  message: string;
};

const REMINDERS_KEY = 'io.lotus.reminders';

type RemindersContent = {
  reminders: Reminder[];
};

// Shared, concurrency-safe store. See createAccountDataListStore for why the
// snapshot + write queue must be module-scoped (writes are serialized to avoid
// lost updates, since setAccountData replaces the whole content with no merge).
const remindersStore = createAccountDataListStore<Reminder[], RemindersContent>({
  eventType: REMINDERS_KEY,
  read: (content) => content?.reminders ?? [],
  write: (reminders) => ({ reminders }),
});

export function useReminders(): {
  reminders: Reminder[];
  addReminder: (r: Reminder) => Promise<void>;
  removeReminder: (eventId: string, timestamp: number) => Promise<void>;
  getReminders: () => Reminder[];
} {
  const mx = useMatrixClient();
  const reminders = remindersStore.useValue(mx);

  const addReminder = useCallback(
    (r: Reminder) => remindersStore.enqueueWrite(mx, (current) => [...current, r]),
    [mx],
  );

  const removeReminder = useCallback(
    (eventId: string, timestamp: number) =>
      remindersStore.enqueueWrite(mx, (current) =>
        current.filter((r) => !(r.eventId === eventId && r.timestamp === timestamp)),
      ),
    [mx],
  );

  const getReminders = useCallback(() => remindersStore.getLatest(mx), [mx]);

  return { reminders, addReminder, removeReminder, getReminders };
}