import React, { useEffect, useRef, useState } from 'react';
import { NavigationContainer } from '@react-navigation/native';
import { createBottomTabNavigator } from '@react-navigation/bottom-tabs';
import { StatusBar, Alert, AppState, AppStateStatus } from 'react-native';
import { Ionicons } from '@expo/vector-icons';
import { theme } from './theme';
import TodayScreen from './screens/TodayScreen';
import CalendarScreen from './screens/CalendarScreen';
import * as Notifications from 'expo-notifications';
import { getEvents } from './api';
import { computeUpcomingReminders, EventForReminder } from './utils/recurrence';

const Tab = createBottomTabNavigator();
const WINDOW_MS = 2 * 60 * 1000; // 2 分钟容错窗口

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

export default function App() {
  const notifiedKeysRef = useRef<Set<string>>(new Set());
  const scheduledNotificationIdsRef = useRef<Set<string>>(new Set());
  const heartbeatTimerRef = useRef<NodeJS.Timeout | null>(null);
  const appStateRef = useRef<AppStateStatus>(AppState.currentState);

  useEffect(() => {
    requestNotificationPermissions();
    initializeNotifications();
    
    // 监听应用状态变化
    const subscription = AppState.addEventListener('change', handleAppStateChange);
    
    return () => {
      subscription.remove();
      cleanup();
    };
  }, []);

  const requestNotificationPermissions = async () => {
    const { status } = await Notifications.requestPermissionsAsync();
    if (status !== 'granted') {
      Alert.alert('提示', '需要通知权限才能发送提醒');
    }
  };

  const initializeNotifications = async () => {
    await loadAndScheduleReminders();
    startReminderHeartbeat();
  };

  const handleAppStateChange = (nextAppState: AppStateStatus) => {
    if (appStateRef.current.match(/inactive|background/) && nextAppState === 'active') {
      // 应用从后台回到前台，重新检查提醒
      loadAndScheduleReminders();
    }
    appStateRef.current = nextAppState;
  };

  const cleanup = () => {
    if (heartbeatTimerRef.current) {
      clearInterval(heartbeatTimerRef.current);
    }
    // 取消所有已安排的通知
    scheduledNotificationIdsRef.current.forEach(async (id) => {
      try {
        await Notifications.cancelScheduledNotificationAsync(id);
      } catch (e) {
        console.error('取消通知失败:', e);
      }
    });
  };

  const loadAndScheduleReminders = async () => {
    try {
      const now = Date.now();
      const next24h = now + 24 * 3600 * 1000;
      
      // 加载事件（覆盖当前月和前后各一个月）
      const currentDate = new Date();
      const events = await getEvents(currentDate);
      
      // 取消之前的所有通知
      scheduledNotificationIdsRef.current.forEach(async (id) => {
        try {
          await Notifications.cancelScheduledNotificationAsync(id);
        } catch (e) {
          console.error('取消通知失败:', e);
        }
      });
      scheduledNotificationIdsRef.current.clear();
      
      // 补偿通知：检查过去 2 分钟内到期的提醒
      catchUpNotifications(events, now);
      
      // 安排未来 24 小时的通知
      scheduleNotifications(events, now, next24h);
    } catch (e) {
      console.error('加载提醒失败:', e);
    }
  };

  const catchUpNotifications = (events: EventForReminder[], now: number) => {
    const since = now - WINDOW_MS;
    events.forEach((e) => {
      if (e.completed || e.deleted) return;
      const windowReminders = computeUpcomingReminders(e, since, now);
      windowReminders.forEach((remindIso) => {
        const key = `${e.id}|${remindIso}`;
        if (!notifiedKeysRef.current.has(key)) {
          triggerNotify(e, remindIso);
          notifiedKeysRef.current.add(key);
        }
      });
    });
  };

  const scheduleNotifications = async (
    events: EventForReminder[],
    now: number,
    next24h: number
  ) => {
    for (const e of events) {
      if (e.completed || e.deleted) continue;
      const upcoming = computeUpcomingReminders(e, now, next24h);
      for (const remindIso of upcoming) {
        const ts = new Date(remindIso).getTime();
        const delay = ts - now;
        if (delay > 0) {
          const key = `${e.id}|${remindIso}`;
          if (notifiedKeysRef.current.has(key)) continue;
          
          try {
            const notificationId = await Notifications.scheduleNotificationAsync({
              content: {
                title: '提醒',
                body: e.title,
                sound: true,
              },
              trigger: {
                type: Notifications.SchedulableTriggerInputTypes.TIME_INTERVAL,
                seconds: delay / 1000,
              } as any,
            });
            scheduledNotificationIdsRef.current.add(notificationId);
            console.log('已安排通知:', e.title, '在', new Date(ts).toLocaleString());
          } catch (e) {
            console.error('安排通知失败:', e);
          }
        }
      }
    }
  };

  const triggerNotify = (e: EventForReminder, remindIso: string) => {
    Notifications.scheduleNotificationAsync({
      content: {
        title: '提醒',
        body: e.title,
        sound: true,
      },
      trigger: null, // 立即触发
    });
  };

  const startReminderHeartbeat = () => {
    if (heartbeatTimerRef.current) {
      clearInterval(heartbeatTimerRef.current);
    }
    
    // 每分钟检查一次，捕捉睡眠/时间漂移导致的错过提醒
    heartbeatTimerRef.current = setInterval(async () => {
      const now = Date.now();
      const since = now - WINDOW_MS;
      
      try {
        const events = await getEvents(new Date());
        events.forEach((e: EventForReminder) => {
          if (e.completed || e.deleted) return;
          const windowReminders = computeUpcomingReminders(e, since, now);
          windowReminders.forEach((remindIso) => {
            const key = `${e.id}|${remindIso}`;
            if (!notifiedKeysRef.current.has(key)) {
              triggerNotify(e, remindIso);
              notifiedKeysRef.current.add(key);
            }
          });
        });
      } catch (e) {
        console.error('心跳检查失败:', e);
      }
    }, 60 * 1000);
  };

  return (
    <NavigationContainer>
      <StatusBar barStyle="light-content" backgroundColor={theme.colors.background} />
      <Tab.Navigator
        screenOptions={{
          tabBarActiveTintColor: theme.colors.primary,
          tabBarInactiveTintColor: theme.colors.textSecondary,
          tabBarStyle: {
            backgroundColor: theme.colors.surface,
            borderTopColor: theme.colors.border,
            paddingTop: 8,
            paddingBottom: 24,
            height: 70,
          },
          headerStyle: {
            backgroundColor: theme.colors.background,
          },
          headerTintColor: theme.colors.text,
          headerTitleStyle: {
            fontWeight: 'bold',
          },
        }}
      >
        <Tab.Screen
          name="Today"
          component={TodayScreen}
          options={{
            title: '今日',
            tabBarIcon: ({ color, size }) => (
              <Ionicons name="today" size={size} color={color} />
            ),
          }}
        />
        <Tab.Screen
          name="Calendar"
          component={CalendarScreen}
          options={{
            title: '日历',
            tabBarIcon: ({ color, size }) => (
              <Ionicons name="calendar" size={size} color={color} />
            ),
          }}
        />
      </Tab.Navigator>
    </NavigationContainer>
  );
}