import React, { useState, useEffect, useCallback } from 'react';
import {
  StyleSheet, View, Text, ActivityIndicator, ScrollView, RefreshControl,
} from 'react-native';
import { useFocusEffect } from '@react-navigation/native';
import { useTheme } from '../services/ThemeContext';
import DatabaseService from '../services/DatabaseService';
import DeviceMediaService from '../services/DeviceMediaService';
import GoogleAUTH from '../AUTH/GoogleAUTH';
import NASAUTH from '../AUTH/NASAUTH';
import { File } from 'expo-file-system';
import TopBar from '../components/TopBar';
import PhotoGrid from '../components/PhotoGrid';
import MediaViewer from '../components/MediaViewer';
import { logError } from '../services/ErrorHandler';
import { TouchableOpacity } from 'react-native';

/**
 * Merge media items from different services.
 * Items with the same filename (title) are merged into a single entry
 * with a `sources` array listing every service it appears in.
 * The best local_path is kept (prefer file:// from DEVICE over a cached
 * Picker download, since device URIs are always fresh).
 */
const mergeMediaAcrossServices = (items) => {
  // First pass: group by normalised filename
  const byFilename = new Map();
  const noFilename = [];

  for (const item of items) {
    const key = item.title?.toLowerCase().trim();
    if (!key || key === 'untitled') {
      noFilename.push({ ...item, sources: [item.source_service] });
      continue;
    }

    if (byFilename.has(key)) {
      const existing = byFilename.get(key);
      // Add this service to the sources list
      if (!existing.sources.includes(item.source_service)) {
        existing.sources.push(item.source_service);
      }
      // Prefer a local device path over a cached download
      if (item.source_service === 'DEVICE' && item.local_path) {
        existing.local_path = item.local_path;
      }
      // Keep the best local_path if the existing one is missing
      if (!existing.local_path && item.local_path) {
        existing.local_path = item.local_path;
      }
    } else {
      byFilename.set(key, { ...item, sources: [item.source_service] });
    }
  }

  // Second pass: also deduplicate by source_id for items with different titles
  const bySourceId = new Map();
  for (const item of [...byFilename.values(), ...noFilename]) {
    const key = item.source_id || item.id || item.local_path || Math.random().toString();
    if (bySourceId.has(key)) {
      const existing = bySourceId.get(key);
      for (const src of (item.sources || [])) {
        if (!existing.sources.includes(src)) existing.sources.push(src);
      }
      if (!existing.local_path && item.local_path) existing.local_path = item.local_path;
    } else {
      bySourceId.set(key, item);
    }
  }

  return Array.from(bySourceId.values());
};

const HomeScreen = ({ navigation, route }) => {
  const userId = route?.params?.userId;
  const { theme } = useTheme();
  const [currentUser, setCurrentUser] = useState(null);
  const [linkedAccounts, setLinkedAccounts] = useState([]);
  const [allMedia, setAllMedia] = useState([]);
  const [filteredMedia, setFilteredMedia] = useState([]);
  const [selectedFilter, setSelectedFilter] = useState('all');
  const [loading, setLoading] = useState(true);
  const [refreshing, setRefreshing] = useState(false);
  const [selectedMedia, setSelectedMedia] = useState(null);
  const [viewerVisible, setViewerVisible] = useState(false);
  const [deviceEndCursor, setDeviceEndCursor] = useState(null);
  const [deviceHasMore, setDeviceHasMore] = useState(false);
  const [googleNextPage, setGoogleNextPage] = useState(null);
  const [googleSessionId, setGoogleSessionId] = useState(null);
  const [loadingMore, setLoadingMore] = useState(false);
  const [importing, setImporting] = useState(false);

  useFocusEffect(
    useCallback(() => {
      if (userId) loadUserData();
    }, [userId])
  );

  useEffect(() => {
    if (currentUser) loadAllMedia();
  }, [currentUser]);

  useEffect(() => { filterMedia(); }, [selectedFilter, allMedia]);

  const loadUserData = async () => {
    try {
      const user = await DatabaseService.getUserById(userId);
      setCurrentUser(user);
      const accounts = await DatabaseService.getLinkedAccounts(userId);
      setLinkedAccounts(accounts);
    } catch (err) {
      console.error('Error loading user data:', err);
    }
  };

  const loadAllMedia = async () => {
    if (!loading) setLoading(true);
    try {
      const newMedia = [];

      // ─── Device photos (local camera roll, screenshots, etc.) ───
      try {
        const deviceResult = await DeviceMediaService.getPhotos(100);
        if (deviceResult.mediaItems.length) {
          newMedia.push(...deviceResult.mediaItems);
        }
        setDeviceEndCursor(deviceResult.endCursor);
        setDeviceHasMore(deviceResult.hasNextPage);
      } catch (err) {
        console.error('Device media fetch error:', err);
      }

      // ─── Previously imported Google Photos (stored in DB) ───
      try {
        const googleMedia = await DatabaseService.getMediaByService(userId, 'GOOGLE_PHOTOS');
        if (googleMedia?.length) {
          // Validate cached files still exist — clear stale paths
          const validated = googleMedia.map((item) => {
            if (item.local_path) {
              try {
                const f = new File(item.local_path);
                if (!f.exists || f.size === 0) {
                  return { ...item, local_path: null };
                }
              } catch (_) {
                return { ...item, local_path: null };
              }
            }
            return item;
          });
          newMedia.push(...validated);
        }
      } catch (err) {
        console.error('DB Google media fetch error:', err);
      }

      // ─── NAS fetch ───
      const nasAccount = linkedAccounts.find((a) => a.service_type === 'NAS');
      if (nasAccount) {
        try {
          const nasAuth = new NASAUTH();
          const nasData = nasAccount.account_data;
          await nasAuth.authenticate(nasData.host, nasData.port, nasData.username, nasData.password, nasData.photoFolder);
          const nasPhotos = await nasAuth.getPhotos(nasData.photoFolder);
          if (nasPhotos?.mediaItems) newMedia.push(...nasPhotos.mediaItems);
          await nasAuth.revokeAccess();
        } catch (err) {
          console.error('NAS fetch error:', err);
        }
      }

      // ─── iCloud (placeholder) ───
      const iosAccount = linkedAccounts.find((a) => a.service_type === 'ICLOUD_PHOTOS');
      if (iosAccount) {
        console.log('iCloud: placeholder — would fetch photos here');
      }

      // ─── Merge & cross-reference across services ───
      // Match items across sources by filename so we can show "this photo
      // exists on Device AND Google Photos" etc.
      const merged = mergeMediaAcrossServices(newMedia);
      setAllMedia(merged);
    } catch (err) {
      console.error('Error loading media:', err);
    } finally {
      setLoading(false);
      setRefreshing(false);
    }
  };

  // ─── Import from Google Photos (opens picker in browser) ───
  const importGooglePhotos = async () => {
    const googleAccount = linkedAccounts.find((a) => a.service_type === 'GOOGLE_PHOTOS');
    if (!googleAccount) {
      console.warn('No Google account linked');
      return;
    }

    setImporting(true);
    try {
      const data = googleAccount.account_data || {};
      const googleAuth = new GoogleAUTH();
      googleAuth.accessToken = data.accessToken || null;
      googleAuth.refreshToken = data.refreshToken || null;
      googleAuth.expiresAt = data.expiresAt || 0;

      let result = await googleAuth.pickPhotos();

      // If 403 (stale scopes), auto re-auth and retry
      if (result?.error?.code === 403) {
        console.log('Stale token — re-authenticating…');
        await googleAuth.revokeAccess();
        const fresh = await googleAuth.authenticate();
        await DatabaseService.linkAccount(userId, 'GOOGLE_PHOTOS', {
          accessToken: fresh.accessToken,
          refreshToken: fresh.refreshToken || null,
          expiresAt: googleAuth.expiresAt,
          email: fresh.email || data.email || 'google-user',
        });
        result = await googleAuth.pickPhotos();
      }

      if (result?.error) {
        logError('Import Google Photos', result.error.message);
      } else if (result?.mediaItems?.length) {
        // Save imported items to DB so they persist across app restarts
        for (const item of result.mediaItems) {
          await DatabaseService.saveMediaItem(userId, item);
        }

        setGoogleNextPage(result.nextPageToken || null);
        setGoogleSessionId(result.sessionId || null);

        // Merge into current view with cross-service matching
        setAllMedia((prev) => mergeMediaAcrossServices([...prev, ...result.mediaItems]));

        console.log(`Imported ${result.mediaItems.length} photos from Google`);
      }

      // Persist refreshed tokens
      if (googleAuth.accessToken && googleAuth.accessToken !== data.accessToken) {
        await DatabaseService.linkAccount(userId, 'GOOGLE_PHOTOS', {
          accessToken: googleAuth.accessToken,
          refreshToken: googleAuth.refreshToken || data.refreshToken,
          expiresAt: googleAuth.expiresAt,
          email: data.email || 'google-user',
        });
      }
    } catch (err) {
      logError('Import Google Photos', err);
    } finally {
      setImporting(false);
    }
  };

  const filterMedia = () => {
    let filtered = allMedia;
    if (selectedFilter !== 'all') {
      // Check both source_service and the sources array for cross-service items
      filtered = allMedia.filter((m) =>
        m.source_service === selectedFilter ||
        (m.sources && m.sources.includes(selectedFilter))
      );
    }
    filtered.sort((a, b) => new Date(b.created_date || 0) - new Date(a.created_date || 0));
    setFilteredMedia(filtered);
  };

  const loadMorePhotos = async () => {
    if (loadingMore) return;
    const canLoadDevice = deviceHasMore;
    const canLoadGoogle = !!googleNextPage && !!googleSessionId;
    if (!canLoadDevice && !canLoadGoogle) return;

    setLoadingMore(true);
    try {
      const moreMedia = [];

      if (canLoadDevice) {
        const result = await DeviceMediaService.getPhotos(100, deviceEndCursor);
        if (result.mediaItems.length) moreMedia.push(...result.mediaItems);
        setDeviceEndCursor(result.endCursor);
        setDeviceHasMore(result.hasNextPage);
      }

      if (canLoadGoogle) {
        const googleAccount = linkedAccounts.find((a) => a.service_type === 'GOOGLE_PHOTOS');
        if (googleAccount) {
          const data = googleAccount.account_data || {};
          const googleAuth = new GoogleAUTH();
          googleAuth.accessToken = data.accessToken || null;
          googleAuth.refreshToken = data.refreshToken || null;
          googleAuth.expiresAt = data.expiresAt || 0;

          const photos = await googleAuth.getMorePhotos(100, googleNextPage, googleSessionId);
          if (photos?.mediaItems?.length) {
            moreMedia.push(...photos.mediaItems);
            for (const item of photos.mediaItems) {
              await DatabaseService.saveMediaItem(userId, item);
            }
          }
          setGoogleNextPage(photos?.nextPageToken || null);
          if (photos?.sessionId) setGoogleSessionId(photos.sessionId);
        }
      }

      if (moreMedia.length) {
        setAllMedia((prev) => mergeMediaAcrossServices([...prev, ...moreMedia]));
      }
    } catch (err) {
      console.error('Error loading more photos:', err);
    } finally {
      setLoadingMore(false);
    }
  };

  const getServiceIcon = (type) => ({ DEVICE: '📱', GOOGLE_PHOTOS: '📷', ICLOUD_PHOTOS: '🍎', NAS: '💾' }[type] || '📱');
  const getServiceName = (type) => ({ DEVICE: 'On Device', GOOGLE_PHOTOS: 'Google Photos', ICLOUD_PHOTOS: 'iCloud', NAS: 'NAS' }[type] || type);

  const hasGoogleAccount = linkedAccounts.some((a) => a.service_type === 'GOOGLE_PHOTOS');

  if (loading && allMedia.length === 0) {
    return (
      <View style={[styles.centerContainer, { backgroundColor: theme.background }]}>
        <ActivityIndicator size="large" color={theme.primary} />
        <Text style={[styles.loadingText, { color: theme.textSecondary }]}>Loading photos...</Text>
      </View>
    );
  }

  // Build the list of available source filters
  const sourceFilters = [
    { key: 'DEVICE', icon: '📱', name: 'On Device' },
    ...linkedAccounts.map((acc) => ({
      key: acc.service_type,
      icon: getServiceIcon(acc.service_type),
      name: getServiceName(acc.service_type),
    })),
  ];

  const FilterChips = () => (
    <ScrollView horizontal showsHorizontalScrollIndicator={false} contentContainerStyle={styles.filterRow} style={styles.filterContainer}>
      <TouchableOpacity
        style={[styles.chip, { backgroundColor: selectedFilter === 'all' ? theme.chipActiveBg : theme.chipBg }]}
        onPress={() => setSelectedFilter('all')}
      >
        <Text style={[styles.chipText, selectedFilter === 'all' && { color: theme.primary, fontWeight: '600' }]}>All</Text>
      </TouchableOpacity>
      {sourceFilters.map((f) => (
        <TouchableOpacity
          key={f.key}
          style={[styles.chip, { backgroundColor: selectedFilter === f.key ? theme.chipActiveBg : theme.chipBg }]}
          onPress={() => setSelectedFilter(f.key)}
        >
          <Text style={styles.chipIcon}>{f.icon}</Text>
          <Text style={[styles.chipText, selectedFilter === f.key && { color: theme.primary, fontWeight: '600' }]}>
            {f.name}
          </Text>
        </TouchableOpacity>
      ))}
    </ScrollView>
  );

  return (
    <View style={[styles.container, { backgroundColor: theme.background }]}>
      <TopBar
        currentUser={currentUser}
        onSearchPress={() => navigation.navigate('Search')}
        onProfilePress={() => navigation.navigate('Settings', { userId })}
        onMenuPress={() => navigation.navigate('Settings', { userId })}
      />

      <FilterChips />

      {/* Import from Google Photos button */}
      {hasGoogleAccount && (
        <TouchableOpacity
          style={[styles.importButton, { backgroundColor: theme.primary }]}
          onPress={importGooglePhotos}
          disabled={importing}
          activeOpacity={0.7}
        >
          {importing ? (
            <ActivityIndicator size="small" color="#fff" />
          ) : (
            <>
              <Text style={styles.importIcon}>📷</Text>
              <Text style={styles.importText}>Import from Google Photos</Text>
            </>
          )}
        </TouchableOpacity>
      )}

      {filteredMedia.length === 0 ? (
        <View style={styles.centerContainer}>
          <Text style={{ fontSize: 56, marginBottom: 16 }}>📸</Text>
          <Text style={[styles.emptyTitle, { color: theme.text }]}>No Photos Yet</Text>
          <Text style={[styles.emptyText, { color: theme.textSecondary }]}>
            {hasGoogleAccount
              ? 'Tap "Import from Google Photos" above to select cloud photos,\nor grant media library permission to see on-device photos.'
              : 'Grant media library permission or take some photos to get started'}
          </Text>
          <TouchableOpacity
            style={[styles.retryButton, { backgroundColor: theme.primary }]}
            onPress={() => { setRefreshing(true); loadAllMedia(); }}
          >
            <Text style={styles.retryButtonText}>Refresh</Text>
          </TouchableOpacity>
        </View>
      ) : (
        <PhotoGrid
          data={filteredMedia}
          onItemPress={(item) => { setSelectedMedia(item); setViewerVisible(true); }}
          onEndReached={loadMorePhotos}
          refreshControl={
            <RefreshControl refreshing={refreshing} onRefresh={() => { setRefreshing(true); loadAllMedia(); }} />
          }
          ListFooterComponent={loadingMore ? (
            <View style={{ padding: 16, alignItems: 'center' }}>
              <ActivityIndicator size="small" color={theme.primary} />
            </View>
          ) : null}
        />
      )}

      <MediaViewer
        visible={viewerVisible}
        media={selectedMedia}
        allMedia={filteredMedia}
        onClose={() => setViewerVisible(false)}
      />
    </View>
  );
};

const styles = StyleSheet.create({
  container: { flex: 1 },
  centerContainer: { flex: 1, justifyContent: 'center', alignItems: 'center', paddingHorizontal: 24 },
  loadingText: { marginTop: 12, fontSize: 14 },
  // Filter chips
  filterContainer: { maxHeight: 40 },
  filterRow: { paddingHorizontal: 12, paddingVertical: 6, gap: 6, alignItems: 'center' },
  chip: {
    flexDirection: 'row', alignItems: 'center', paddingHorizontal: 10, paddingVertical: 4,
    borderRadius: 16, gap: 4, height: 28,
  },
  chipIcon: { fontSize: 11 },
  chipText: { fontSize: 12, fontWeight: '500', color: '#3c4043' },
  // Import button
  importButton: {
    flexDirection: 'row', alignItems: 'center', justifyContent: 'center',
    marginHorizontal: 12, marginVertical: 6, paddingVertical: 10, paddingHorizontal: 16,
    borderRadius: 12, gap: 8, minHeight: 42,
  },
  importIcon: { fontSize: 16 },
  importText: { color: '#fff', fontSize: 14, fontWeight: '600' },
  // Empty
  emptyTitle: { fontSize: 18, fontWeight: '600', marginBottom: 6 },
  emptyText: { fontSize: 13, textAlign: 'center', marginBottom: 20, lineHeight: 20 },
  retryButton: { paddingHorizontal: 24, paddingVertical: 10, borderRadius: 20 },
  retryButtonText: { color: '#fff', fontSize: 14, fontWeight: '600' },
});

export default HomeScreen;