import { Platform } from "react-native";
import * as Notifications from "expo-notifications";

import type { BirthdayEntry } from "@/context/birthdays-context";

const CHANNEL_ID = "birthdays";
const NOTIFICATION_HOUR = 9;
const NOTIFICATION_MINUTE = 0;
const IDENTIFIER_PREFIX = "birthday-";

Notifications.setNotificationHandler({
  handleNotification: async () => ({
    shouldPlaySound: true,
    shouldSetBadge: false,
    shouldShowBanner: true,
    shouldShowList: true,
  }),
});

function getNotificationIdentifier(id: string) {
  return `${IDENTIFIER_PREFIX}${id}`;
}

function parseBirthdayDate(date: string) {
  return new Date(`${date}T00:00:00`);
}

async function configureAndroidChannel() {
  if (Platform.OS !== "android") {
    return;
  }

  await Notifications.setNotificationChannelAsync(CHANNEL_ID, {
    name: "Birthdays",
    description: "Birthday reminders",
    importance: Notifications.AndroidImportance.DEFAULT,
  });
}

async function hasNotificationPermissionAsync() {
  const settings = await Notifications.getPermissionsAsync();

  return (
    settings.granted ||
    settings.ios?.status === Notifications.IosAuthorizationStatus.PROVISIONAL
  );
}

async function ensureNotificationPermissionAsync() {
  await configureAndroidChannel();

  if (await hasNotificationPermissionAsync()) {
    return true;
  }

  const settings = await Notifications.requestPermissionsAsync({
    ios: {
      allowAlert: true,
      allowBadge: false,
      allowSound: true,
    },
  });

  return (
    settings.granted ||
    settings.ios?.status === Notifications.IosAuthorizationStatus.PROVISIONAL
  );
}

async function clearStaleBirthdayNotifications(birthdays: BirthdayEntry[]) {
  const validIdentifiers = new Set(
    birthdays.map((birthday) => getNotificationIdentifier(birthday.id))
  );
  const scheduledNotifications =
    await Notifications.getAllScheduledNotificationsAsync();

  await Promise.all(
    scheduledNotifications
      .filter(
        (notification) =>
          notification.identifier.startsWith(IDENTIFIER_PREFIX) &&
          !validIdentifiers.has(notification.identifier)
      )
      .map((notification) =>
        Notifications.cancelScheduledNotificationAsync(notification.identifier)
      )
  );
}

async function scheduleBirthdayNotification(birthday: BirthdayEntry) {
  const parsedDate = parseBirthdayDate(birthday.date);
  const month = parsedDate.getMonth();
  const day = parsedDate.getDate();

  await Notifications.cancelScheduledNotificationAsync(
    getNotificationIdentifier(birthday.id)
  );

  await Notifications.scheduleNotificationAsync({
    identifier: getNotificationIdentifier(birthday.id),
    content: {
      title: `Today is ${birthday.name}'s birthday`,
      body: `Wish ${birthday.name} a happy birthday!`,
      sound: true,
    },
    trigger: {
      type: Notifications.SchedulableTriggerInputTypes.YEARLY,
      channelId: Platform.OS === "android" ? CHANNEL_ID : undefined,
      month,
      day,
      hour: NOTIFICATION_HOUR,
      minute: NOTIFICATION_MINUTE,
    },
  });
}

export async function syncBirthdayNotifications(birthdays: BirthdayEntry[]) {
  if (Platform.OS === "web") {
    return;
  }

  const permissionGranted = await ensureNotificationPermissionAsync();
  if (!permissionGranted) {
    return;
  }

  await clearStaleBirthdayNotifications(birthdays);
  await Promise.all(birthdays.map(scheduleBirthdayNotification));
}