import { useState } from 'react';
import {
  ActivityIndicator,
  ScrollView,
  StyleSheet,
  Text,
  TextInput,
  TouchableOpacity,
  View,
} from 'react-native';
import type { NativeStackNavigationProp } from '@react-navigation/native-stack';
import type { RouteProp } from '@react-navigation/native';
import { api } from '../services/api';
import { fetchNativeEvents } from '../services/calendar';
import { addEvent, loadEvents } from '../store/eventStore';
import type { Event as CalendarEvent } from '@timetoleave/core';
import type { RootStack } from '../types/navigation';
import { useColors } from '../hooks/useColors';

type ScreenProps = {
  navigation: NativeStackNavigationProp<RootStack, 'CalendarImport'>;
  route: RouteProp<RootStack, 'CalendarImport'>;
};

/**
 * Screen for importing events from either an ICS calendar URL or the device's
 * native calendar. Deduplicates against already-imported events by ID.
 */
export function CalendarImportScreen({ navigation }: ScreenProps) {
  const colors = useColors();
  const [url, setUrl] = useState('');
  const [loading, setLoading] = useState(false);
  const [error, setError] = useState<string | null>(null);
  const [count, setCount] = useState<number | null>(null);

  const handleImport = async () => {
    if (!url.trim()) {
      setError('Bitte ICS-URL eingeben');
      return;
    }

    setLoading(true);
    setError(null);
    setCount(null);

    try {
      const [events, existing] = await Promise.all([
        api.fetchCalendar(url.trim()),
        loadEvents(),
      ]);
      const existingIds = new Set(existing.map((e) => e.id));
      let added = 0;
      for (const evt of events) {
        if (!existingIds.has(evt.id)) {
          const localEvent: CalendarEvent = {
            id: evt.id,
            title: evt.title,
            destination: evt.destination,
            eventTime: new Date(evt.eventTime),
            source: `calendar:${url.trim().slice(0, 40)}`,
          };
          await addEvent(localEvent);
          added++;
        }
      }
      setCount(added);
    } catch (err) {
      setError(err instanceof Error ? err.message : 'Import fehlgeschlagen');
    } finally {
      setLoading(false);
    }
  };

  const handleSyncNative = async () => {
    setLoading(true);
    setError(null);
    setCount(null);

    try {
      // Fetch events from the next 30 days
      const now = new Date();
      const thirtyDaysLater = new Date(now.getTime() + 30 * 24 * 60 * 60 * 1000);

      const nativeEvents = await fetchNativeEvents(now, thirtyDaysLater);

      // Load existing events to avoid duplicates
      const existing = await loadEvents();
      const existingIds = new Set(existing.map((e) => e.id));

      let added = 0;
      for (const evt of nativeEvents) {
        if (!existingIds.has(evt.id)) {
          await addEvent(evt);
          added++;
        }
      }

      setCount(added);
    } catch (err) {
      setError(err instanceof Error ? err.message : 'Sync fehlgeschlagen');
    } finally {
      setLoading(false);
    }
  };

  return (
    <ScrollView style={[styles.container, { backgroundColor: colors.background }]}>
      <View style={styles.content}>
        <Text style={[styles.heading, { color: colors.text }]}>Kalender-Import</Text>
        <Text style={[styles.description, { color: colors.subtext }]}>
          Importiere Termine über eine ICS-URL oder sync mit dem Geräte-Kalender.
        </Text>

        <View style={styles.section}>
          <Text style={[styles.sectionTitle, { color: colors.text }]}>ICS-URL Import</Text>

          <TextInput
            style={[styles.input, { backgroundColor: colors.card, color: colors.text, borderColor: colors.border }]}
            placeholder="https://calendar.google.com/calendar/ical/..."
            placeholderTextColor={colors.subtext}
            value={url}
            onChangeText={setUrl}
            autoCapitalize="none"
            keyboardType="url"
          />

          <TouchableOpacity
            style={[styles.importBtn, loading && styles.importBtnDisabled]}
            onPress={handleImport}
            disabled={loading}
          >
            {loading ? (
              <ActivityIndicator color="#fff" />
            ) : (
              <Text style={styles.importBtnText}>ICS Importieren</Text>
            )}
          </TouchableOpacity>
        </View>

        <View style={styles.section}>
          <Text style={[styles.sectionTitle, { color: colors.text }]}>Geräte-Kalender Sync</Text>
          <Text style={[styles.sectionDesc, { color: colors.subtext }]}>
            Hole Termine der nächsten 30 Tage aus den Kalendern auf deinem Gerät.
          </Text>

          <TouchableOpacity
            style={[styles.importBtn, { backgroundColor: colors.purple }, loading && styles.importBtnDisabled]}
            onPress={handleSyncNative}
            disabled={loading}
          >
            <Text style={styles.importBtnText}>📅 Kalender Sync</Text>
          </TouchableOpacity>
        </View>

        {error && (
          <View style={[styles.errorBanner, { backgroundColor: colors.error }]}>
            <Text style={styles.errorText}>{error}</Text>
          </View>
        )}

        {count !== null && (
          <View style={[styles.successBanner, { backgroundColor: colors.success }]}>
            <Text style={styles.successText}>
              ✓ {count} Termin(e) erfolgreich importiert!
            </Text>
          </View>
        )}

        <TouchableOpacity
          style={styles.backBtn}
          onPress={() => navigation.goBack()}
        >
          <Text style={[styles.backBtnText, { color: colors.accent }]}>← Zurück</Text>
        </TouchableOpacity>
      </View>
    </ScrollView>
  );
}

const styles = StyleSheet.create({
  container: { flex: 1 },
  content: { padding: 20 },
  heading: { fontSize: 22, fontWeight: '700', marginBottom: 4 },
  description: { fontSize: 14, marginBottom: 20, lineHeight: 20 },
  section: { marginBottom: 24 },
  sectionTitle: { fontSize: 16, fontWeight: '600', marginBottom: 8 },
  sectionDesc: { fontSize: 13, marginBottom: 12, lineHeight: 18 },
  input: {
    borderRadius: 10,
    paddingHorizontal: 14,
    paddingVertical: 12,
    fontSize: 16,
    borderWidth: 1,
    marginBottom: 12,
  },
  errorBanner: { borderRadius: 8, padding: 12, marginBottom: 12 },
  errorText: { color: '#fff', fontSize: 14 },
  successBanner: { borderRadius: 8, padding: 12, marginBottom: 12 },
  successText: { color: '#fff', fontSize: 14 },
  importBtn: {
    backgroundColor: '#8B5CF6',
    paddingVertical: 14,
    borderRadius: 12,
    alignItems: 'center',
  },
  importBtnDisabled: { opacity: 0.6 },
  importBtnText: { color: '#fff', fontSize: 16, fontWeight: '600' },
  backBtn: {
    paddingVertical: 10,
    alignItems: 'center',
  },
  backBtnText: { fontSize: 15 },
});