I’m developing a React Native Expo mobile app. Now I’m going to use expo-notifications library to show reminder push notifications. I want reminders to be displayed at a specific time (for example, 8 a.m.) if the user has not opened the app for more than 4 hours. I’ve already implemented showing notifications at a specific time. But I have a problem keeping track of when the app was last opened.

import Constants from "expo-constants";
import * as Device from "expo-device";
import { useFonts } from "expo-font";
import * as Notifications from "expo-notifications";
import * as SplashScreen from "expo-splash-screen";
import { StatusBar } from "expo-status-bar";
import React, { useCallback, useEffect } from "react";
import { View, Platform } from "react-native";
import { SafeAreaProvider } from "react-native-safe-area-context";
import { Provider } from "react-redux";
import { PersistGate } from "redux-persist/integration/react";

import Navigation from "./src/navigation";
import { store, persistor } from "./src/store";
import styles from "./styles";

SplashScreen.preventAutoHideAsync();

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

export default function App() {
  const [fontsLoaded, fontError] = useFonts({
    mainReg: require("./assets/fonts/DINReg.otf"),
    mainMed: require("./assets/fonts/DINMed.otf"),
    mainBold: require("./assets/fonts/DINBold.otf"),
  });

  const onLayoutRootView = useCallback(async () => {
    if (fontsLoaded || fontError) {
      await SplashScreen.hideAsync();
    }
  }, [fontsLoaded, fontError]);

  useEffect(() => {
    registerForPushNotificationsAsync();
    scheduleReminderNotification();
  }, []);

  async function scheduleReminderNotification() {
    const now = new Date();
    const trigger = new Date();
    trigger.setHours(8, 0, 0); // Set to 8:00 AM local time
    if (trigger <= now) {
      trigger.setDate(trigger.getDate() + 1); // If 8:00 AM has already passed today, set for tomorrow
    }

    await Notifications.scheduleNotificationAsync({
      content: {
        title: "Reminder",
        body: "You haven't opened the app for more than 4 hours. Check out now!",
      },
      trigger,
    });
  }

  if (!fontsLoaded && !fontError) {
    return null;
  }

  return (
    <Provider store={store}>
      <PersistGate loading={null} persistor={persistor}>
        <SafeAreaProvider>
          <View style={styles.container} onLayout={onLayoutRootView}>
            <Navigation />
            <StatusBar style="auto" />
          </View>
        </SafeAreaProvider>
      </PersistGate>
    </Provider>
  );
}

async function registerForPushNotificationsAsync() {
  let token;

  if (Platform.OS === "android") {
    await Notifications.setNotificationChannelAsync("default", {
      name: "default",
      importance: Notifications.AndroidImportance.MAX,
      vibrationPattern: [0, 250, 250, 250],
      lightColor: "#FF231F7C",
    });
  }

  if (Device.isDevice) {
    const { status: existingStatus } = await Notifications.getPermissionsAsync();
    let finalStatus = existingStatus;
    if (existingStatus !== "granted") {
      const { status } = await Notifications.requestPermissionsAsync();
      finalStatus = status;
    }
    if (finalStatus !== "granted") {
      alert("Failed to get push token for push notification!");
      return;
    }
    try {
      const projectId = Constants?.expoConfig?.extra?.eas?.projectId ?? Constants?.easConfig?.projectId;
      if (!projectId) {
        throw new Error("Project ID not found");
      }
      token = (
        await Notifications.getExpoPushTokenAsync({
          projectId,
        })
      ).data;
      console.log(token);
    } catch (e) {
      token = `${e}`;
    }
  } else {
    alert("Must use physical device for Push Notifications");
  }

  return token;
}