import type { LocalNotificationSchema } from '@capacitor/local-notifications';
import { isNativePlatform } from '@/lib/platform';
import { getNotificationPermission, numericId } from '@/lib/osNotify';

/**
 * Scheduled, future OS reminders — the only kind of notification that still
 * fires when the app is **fully closed**, because the OS holds the alarm. No
 * server, no background process, no network call: the app hands the OS a title,
 * a time and an in-app path, and the OS does the rest.
 *
 * Native (Android/iOS) only — the web has no scheduler. On web every function
 * here is a quiet no-op.
 *
 * We track the ids we handed out in localStorage so a reminder that no longer
 * applies (RSVP withdrawn, event passed) can be cancelled without disturbing
 * the one-off notifications fired elsewhere.
 */

export interface Reminder {
  /** Stable key. Reusing it reschedules in place; dropping it cancels. */
  key: string;
  title: string;
  body: string;
  /** In-app path to open when tapped. */
  path: string;
  /** Fire time, ms since epoch. */
  at: number;
}

const REMINDER_IDS_KEY = 'skatespots:notifications:reminders';

type ReminderIdMap = Record<string, number>;

function loadIds(): ReminderIdMap {
  try {
    const raw = localStorage.getItem(REMINDER_IDS_KEY);
    if (!raw) return {};
    const parsed = JSON.parse(raw) as unknown;
    if (parsed && typeof parsed === 'object') return parsed as ReminderIdMap;
  } catch {
    // Corrupt/blocked storage — start clean.
  }
  return {};
}

function saveIds(map: ReminderIdMap): void {
  try {
    localStorage.setItem(REMINDER_IDS_KEY, JSON.stringify(map));
  } catch {
    // Ignore — reminders still work for this session.
  }
}

async function cancelNative(ids: number[]): Promise<void> {
  if (ids.length === 0) return;
  const { LocalNotifications } = await import('@capacitor/local-notifications');
  await LocalNotifications.cancel({ notifications: ids.map((id) => ({ id })) });
}

/** Cancel every reminder we scheduled (used when turning notifications off). */
export async function cancelAllScheduledReminders(): Promise<void> {
  const ids = Object.values(loadIds());
  saveIds({});
  if (!isNativePlatform() || ids.length === 0) return;
  try {
    await cancelNative(ids);
  } catch (err) {
    console.warn('[reminders] cancel failed', err);
  }
}

/**
 * Make the OS's pending reminders match `reminders` exactly: cancel the ones we
 * previously scheduled that are no longer wanted, schedule the new ones, and
 * leave already-scheduled ones alone (re-scheduling would only churn).
 */
export async function syncScheduledReminders(reminders: Reminder[]): Promise<void> {
  if (!isNativePlatform()) return;

  const now = Date.now();
  const desired = new Map(reminders.filter((r) => r.at > now).map((r) => [r.key, r]));

  // Don't touch the OS at all without permission.
  const permission = await getNotificationPermission();
  if (permission !== 'granted') return;

  try {
    const { LocalNotifications } = await import('@capacitor/local-notifications');
    const previous = loadIds();

    const stale = Object.entries(previous)
      .filter(([key]) => !desired.has(key))
      .map(([, id]) => id);
    await cancelNative(stale);

    const next: ReminderIdMap = {};
    const toSchedule: LocalNotificationSchema[] = [];
    for (const [key, reminder] of desired) {
      const id = previous[key] ?? numericId(`reminder:${key}`);
      next[key] = id;
      if (previous[key] === undefined) {
        toSchedule.push({
          id,
          title: reminder.title,
          body: reminder.body,
          schedule: { at: new Date(reminder.at), allowWhileIdle: true },
          extra: { path: reminder.path },
        });
      }
    }

    if (toSchedule.length > 0) {
      await LocalNotifications.schedule({ notifications: toSchedule });
    }
    saveIds(next);
  } catch (err) {
    console.warn('[reminders] sync failed', err);
  }
}