import React, { useState, useCallback, useEffect } from 'react';
import {
  View,
  Text,
  StyleSheet,
  FlatList,
  TouchableOpacity,
  Alert,
  ActivityIndicator,
} from 'react-native';
import { Ionicons } from '@expo/vector-icons';
import { useNavigation, useFocusEffect } from '@react-navigation/native';
import { theme } from '../theme';
import { Event } from '../types';
import { eventApi } from '../api';
import EventModal from '../components/EventModal';
import EventCard from '../components/EventCard';
import { shouldShowEventOnDate, safeParseDate } from '../utils/recurrence';

const showError = (title: string, error: any) => {
  const message = error instanceof Error ? error.message : '加载事件失败';
  Alert.alert(title, message);
};

export default function TodayScreen() {
  const navigation = useNavigation();
  const [events, setEvents] = useState<Event[]>([]);
  const [loading, setLoading] = useState(true);
  const [modalVisible, setModalVisible] = useState(false);
  const [selectedEvent, setSelectedEvent] = useState<Event | null>(null);
  const [saving, setSaving] = useState(false);

  const loadEvents = useCallback(async () => {
    try {
      setLoading(true);
      const today = new Date();
      const allEvents = await eventApi.getEvents(today.getFullYear(), today.getMonth() + 1);
      const todayEvents = allEvents.filter(event => {
        if (event.deleted) return false;
        return shouldShowEventOnDate(event, today);
      }).sort((a, b) => safeParseDate(a.start).getTime() - safeParseDate(b.start).getTime());
      setEvents(todayEvents);
    } catch (error) {
      showError('加载失败', error);
    } finally {
      setLoading(false);
    }
  }, []);

  useFocusEffect(
    useCallback(() => {
      loadEvents();
    }, [loadEvents])
  );

  const handleAddEvent = () => {
    setSelectedEvent(null);
    setModalVisible(true);
  };

  const handleEditEvent = (event: Event) => {
    setSelectedEvent(event);
    setModalVisible(true);
  };

  const handleToggleComplete = async (event: Event) => {
    try {
      setSaving(true);
      await eventApi.updateEvent(event.id, { completed: !event.completed });
      await loadEvents();
    } catch (error) {
      showError('更新失败', error);
    } finally {
      setSaving(false);
    }
  };

  const handleDeleteEvent = async (event: Event) => {
    Alert.alert(
      '确认删除',
      '确定要删除这个事件吗？',
      [
        { text: '取消', style: 'cancel' },
        {
          text: '删除',
          style: 'destructive',
          onPress: async () => {
            try {
              await eventApi.deleteEvent(event.id);
              await loadEvents();
            } catch (error) {
              showError('删除失败', error);
            }
          },
        },
      ]
    );
  };

  const handleSaveEvent = async (eventData: Partial<Event>) => {
    try {
      setSaving(true);
      if (selectedEvent) {
        await eventApi.updateEvent(selectedEvent.id, eventData);
      } else {
        await eventApi.createEvent({
          ...eventData,
          createdAt: new Date().toISOString(),
          updatedAt: new Date().toISOString(),
          deleted: false,
        } as Event);
      }
      setModalVisible(false);
      await loadEvents();
    } catch (error) {
      showError('保存失败', error);
    } finally {
      setSaving(false);
    }
  };

  const getGreeting = () => {
    const hour = new Date().getHours();
    if (hour < 12) return '早上好';
    if (hour < 18) return '下午好';
    return '晚上好';
  };

  const pendingEvents = events.filter(e => !e.completed);
  const completedEvents = events.filter(e => e.completed);

  return (
    <View style={styles.container}>
      <View style={styles.header}>
        <View style={styles.headerLeft}>
          <Text style={styles.greeting}>{getGreeting()} 👋</Text>
          <Text style={styles.date}>
            {new Date().toLocaleDateString('zh-CN', {
              year: 'numeric',
              month: 'long',
              day: 'numeric',
            })}
          </Text>
        </View>
        <TouchableOpacity style={styles.addButton} onPress={handleAddEvent}>
          <Ionicons name="add" size={28} color={theme.colors.background} />
        </TouchableOpacity>
      </View>

      <View style={styles.statsContainer}>
        <View style={styles.statCard}>
          <Text style={styles.statNumber}>{pendingEvents.length}</Text>
          <Text style={styles.statLabel}>待完成</Text>
        </View>
        <View style={styles.statCard}>
          <Text style={styles.statNumber}>{completedEvents.length}</Text>
          <Text style={styles.statLabel}>已完成</Text>
        </View>
        <View style={styles.statCard}>
          <Text style={styles.statNumber}>{events.length}</Text>
          <Text style={styles.statLabel}>共计</Text>
        </View>
      </View>

      <Text style={styles.sectionTitle}>待完成</Text>

      {loading ? (
        <ActivityIndicator style={styles.loader} color={theme.colors.primary} />
      ) : (
        <FlatList
          data={pendingEvents}
          keyExtractor={(item) => item.id}
          renderItem={({ item }) => (
            <EventCard
              event={item}
              onEdit={handleEditEvent}
              onToggleComplete={handleToggleComplete}
              onDelete={handleDeleteEvent}
            />
          )}
          contentContainerStyle={styles.list}
          showsVerticalScrollIndicator={false}
          ListEmptyComponent={
            <View style={styles.emptyContainer}>
              <Text style={styles.emptyText}>今天没有待办事项 🎉</Text>
            </View>
          }
        />
      )}

      <EventModal
        visible={modalVisible}
        event={selectedEvent}
        onClose={() => setModalVisible(false)}
        onSave={handleSaveEvent}
      />
    </View>
  );
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: theme.colors.background,
    padding: theme.spacing.md,
  },
  header: {
    flexDirection: 'row',
    justifyContent: 'space-between',
    alignItems: 'flex-start',
    marginBottom: theme.spacing.lg,
  },
  headerLeft: {
    flex: 1,
  },
  greeting: {
    ...theme.typography.h1,
    color: theme.colors.text,
    marginBottom: theme.spacing.xs,
  },
  date: {
    ...theme.typography.bodySmall,
    color: theme.colors.textSecondary,
  },
  addButton: {
    backgroundColor: theme.colors.primary,
    width: 56,
    height: 56,
    borderRadius: 28,
    justifyContent: 'center',
    alignItems: 'center',
  },
  statsContainer: {
    flexDirection: 'row',
    gap: theme.spacing.sm,
    marginBottom: theme.spacing.lg,
  },
  statCard: {
    flex: 1,
    backgroundColor: theme.colors.surface,
    padding: theme.spacing.md,
    borderRadius: theme.borderRadius.lg,
    alignItems: 'center',
  },
  statNumber: {
    ...theme.typography.h2,
    color: theme.colors.primary,
  },
  statLabel: {
    ...theme.typography.bodySmall,
    color: theme.colors.textSecondary,
  },
  sectionTitle: {
    ...theme.typography.h3,
    color: theme.colors.text,
    marginBottom: theme.spacing.sm,
  },
  list: {
    paddingBottom: 20,
  },
  loader: {
    flex: 1,
    justifyContent: 'center',
  },
  emptyContainer: {
    padding: theme.spacing.xl,
    alignItems: 'center',
  },
  emptyText: {
    ...theme.typography.body,
    color: theme.colors.textSecondary,
    textAlign: 'center',
  },
});