import 'dart:async';
import 'dart:convert';
import 'dart:io';
import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:wakelock_plus/wakelock_plus.dart';
import 'package:flutter_epub_viewer/flutter_epub_viewer.dart';
import 'package:go_router/go_router.dart';
import 'package:worldhopper/config/constants.dart';
import 'package:worldhopper/models/enhanced_metadata.dart';
import 'package:worldhopper/models/opds_entry.dart';
import 'package:worldhopper/models/reading_progress.dart';
import 'package:worldhopper/providers/publication_cache_provider.dart';
import 'package:worldhopper/providers/reading_progress_provider.dart';
import 'package:worldhopper/providers/server_provider.dart';
import 'package:worldhopper/providers/connectivity_provider.dart';
import 'package:worldhopper/services/epub_download_service.dart';
import 'package:uuid/uuid.dart';

/// EPUB reader screen using flutter_epub_viewer with Epub.js integration
/// Provides integrated reading experience with CFI-based position tracking
class EpubReaderScreen extends ConsumerStatefulWidget {
  final OPDSEntry entry;
  final String serverId;

  const EpubReaderScreen({
    super.key,
    required this.entry,
    required this.serverId,
  });

  @override
  ConsumerState<EpubReaderScreen> createState() => _EpubReaderScreenState();
}

class _EpubReaderScreenState extends ConsumerState<EpubReaderScreen> {
  EpubController? _epubController;
  bool _isLoading = true;
  double _loadingProgress = 0.0;
  String _loadingStatus = 'Preparing...';
  String? _errorMessage;
  File? _epubFile;
  String? _initialCfi;
  List<EpubChapter>? _chapters;
  String? _viewerKey; // Unique key to force widget recreation
  EpubLocation? _lastLocation; // Track last location for saving on dispose
  bool _showAppBar = false; // Hidden by default for immersive reading
  Timer? _appBarAutoHideTimer; // Auto-hide timer (5 seconds)

  // Gesture tracking for tap vs swipe detection
  Offset? _pointerDownPosition;
  DateTime? _pointerDownTime;
  bool _isSwipe = false;

  // Thresholds
  static const double _swipeThreshold = 15.0; // pixels - movement beyond this = swipe
  static const Duration _tapMaxDuration = Duration(milliseconds: 500); // taps complete quickly

  @override
  void initState() {
    super.initState();
    // Create a new controller for each instance to avoid state retention
    _epubController = EpubController();
    _loadEpub();

    // Keep screen awake while reading
    WakelockPlus.enable();
  }

  Future<void> _loadEpub() async {
    try {
      setState(() {
        _isLoading = true;
        _loadingProgress = 0.0;
        _loadingStatus = 'Preparing...';
        _errorMessage = null;
      });

      final server = await ref.read(serverProvider(widget.serverId).future);

      if (server == null) {
        setState(() {
          _errorMessage = 'Server not found';
          _isLoading = false;
        });
        return;
      }

      // Check if file is cached first
      final epubService = EpubDownloadService();
      final isCached = await epubService.isEpubCached(widget.entry);

      if (isCached) {
        setState(() {
          _loadingStatus = 'Loading from cache...';
          _loadingProgress = 0.5;
        });
      }

      // Download or get cached EPUB file with progress tracking
      final file = await epubService.downloadEpub(
        widget.entry,
        server,
        onProgress: (progress) {
          setState(() {
            _loadingProgress = progress * 0.8; // Reserve 0.8-1.0 for processing
            _loadingStatus = isCached
                ? 'Loading from cache...'
                : 'Downloading... ${(progress * 100).toInt()}%';
          });
        },
      );

      setState(() {
        _loadingProgress = 0.85;
        _loadingStatus = 'Processing EPUB...';
      });

      // Cache the publication
      await ref.read(publicationCacheProvider.notifier).cachePublication(
        serverId: widget.serverId,
        entry: widget.entry,
        metadata: const EnhancedMetadata.empty(),
        downloadImages: true,
      );

      // Load saved progress to get initial CFI location
      final progressKey = ProgressKey(
        publicationId: widget.entry.id,
        serverId: widget.serverId,
      );
      final savedProgress = await ref.read(readingProgressProvider(progressKey).future);

      // Extract CFI from saved progress if available
      String? cfi;
      if (savedProgress?.epubLocation != null && savedProgress!.epubLocation!.isNotEmpty) {
        try {
          final locationData = jsonDecode(savedProgress.epubLocation!);
          cfi = locationData['startCfi'] as String?;
        } catch (e) {
          debugPrint('Error parsing saved CFI: $e');
        }
      }

      setState(() {
        _loadingProgress = 1.0;
        _loadingStatus = 'Opening reader...';
        _epubFile = file;
        _initialCfi = cfi;
        // Generate a unique key to force widget recreation and reset viewport
        _viewerKey = 'epub-${widget.entry.id}-${file.path}-${DateTime.now().millisecondsSinceEpoch}';
        _isLoading = false;
      });
    } catch (e) {
      setState(() {
        _errorMessage = 'Error loading EPUB: $e';
        _isLoading = false;
      });
    }
  }

  /// Handle page navigation - save progress with CFI
  void _handleRelocated(EpubLocation location) {
    _lastLocation = location;
    // Save progress asynchronously (fire and forget, but we'll save on dispose too)
    _saveProgress(location);
  }

  /// Handle chapters loaded
  void _handleChaptersLoaded(List<EpubChapter> chapters) {
    setState(() {
      _chapters = chapters;
    });
  }

  /// Save reading progress with CFI-based location
  Future<void> _saveProgress(EpubLocation location) async {
    final progressKey = ProgressKey(
      publicationId: widget.entry.id,
      serverId: widget.serverId,
    );

    final existingProgress = await ref.read(
      readingProgressProvider(progressKey).future
    );

    // Calculate current/total pages from location percentage
    final percentage = location.progress;
    final currentPage = (percentage * 100).round();
    const totalPages = 100;
    
    debugPrint('EPUB Progress - Location: ${location.progress * 100}%, Page: $currentPage/$totalPages, CFI: ${location.startCfi}');

    // Store full location data as JSON
    final locationJson = jsonEncode({
      'startCfi': location.startCfi,
      'endCfi': location.endCfi,
      'progress': location.progress,
    });

    // Get cached publication
    final cachedPub = await ref.read(cachedPublicationProvider(widget.serverId, widget.entry.id).future);

    final progress = existingProgress?.copyWith(
      currentPage: currentPage,
      totalPages: totalPages,
      epubLocation: locationJson,
      lastReadAt: DateTime.now(),
      publicationCacheId: cachedPub?.id ?? existingProgress.publicationCacheId,
    ) ?? ReadingProgress(
      id: const Uuid().v4(),
      publicationId: widget.entry.id,
      serverId: widget.serverId,
      currentPage: currentPage,
      totalPages: totalPages,
      epubLocation: locationJson,
      lastReadAt: DateTime.now(),
      publicationCacheId: cachedPub?.id,
    );

    await ref
        .read(readingProgressNotifierProvider.notifier)
        .saveProgress(progress);

    ref.invalidate(readingProgressProvider(progressKey));
    ref.invalidate(recentlyReadProvider);
  }

  /// Build display settings based on orientation
  EpubDisplaySettings _buildDisplaySettings(Orientation orientation) {
    debugPrint('🔧 _buildDisplaySettings: orientation=$orientation, width=${MediaQuery.of(context).size.width}');

    final brightness = Theme.of(context).brightness;
    final isDarkMode = brightness == Brightness.dark;
    final colorScheme = Theme.of(context).colorScheme;

    final epubTheme = EpubTheme.custom(
      backgroundDecoration: BoxDecoration(
        color: isDarkMode ? colorScheme.surface : Colors.white,
      ),
      foregroundColor: colorScheme.onSurface,
      customCss: {
        'body': '''
          color: ${_colorToHex(colorScheme.onSurface)} !important;
          line-height: 1.6 !important;
          font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif !important;
        ''',
        'p': '''
          color: ${_colorToHex(colorScheme.onSurface)} !important;
          line-height: 1.6 !important;
        ''',
        'h1, h2, h3, h4, h5, h6': '''
          color: ${_colorToHex(colorScheme.onSurface)} !important;
        ''',
        'a': '''
          color: ${_colorToHex(colorScheme.primary)} !important;
        ''',
        'span, div': '''
          color: ${_colorToHex(colorScheme.onSurface)} !important;
        ''',
      },
    );

    // Determine spread based on available width, not orientation
    final screenWidth = MediaQuery.of(context).size.width;
    const minWidthForDualPage = 768.0;
    final spread = screenWidth >= minWidthForDualPage
        ? EpubSpread.always
        : EpubSpread.none;

    debugPrint('🔧 _buildDisplaySettings: returning spread=$spread (width=$screenWidth)');

    return EpubDisplaySettings(
      flow: EpubFlow.paginated,
      snap: true,
      useSnapAnimationAndroid: false,
      theme: epubTheme,
      spread: spread,
    );
  }

  @override
  Widget build(BuildContext context) {
    if (_isLoading) {
      return Scaffold(
        backgroundColor: Colors.black,
        appBar: AppBar(
          title: Text(widget.entry.title),
          backgroundColor: Colors.black,
          foregroundColor: Colors.white,
        ),
        body: Center(
          child: Padding(
            padding: const EdgeInsets.symmetric(horizontal: 48),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                CircularProgressIndicator(
                  value: _loadingProgress > 0 ? _loadingProgress : null,
                  color: Colors.white,
                ),
                const SizedBox(height: 24),
                LinearProgressIndicator(
                  value: _loadingProgress > 0 ? _loadingProgress : null,
                  backgroundColor: Colors.white24,
                  valueColor: const AlwaysStoppedAnimation<Color>(Colors.white),
                  minHeight: 4,
                  borderRadius: BorderRadius.circular(2),
                ),
                const SizedBox(height: 16),
                Text(
                  _loadingStatus,
                  style: const TextStyle(
                    color: Colors.white,
                    fontSize: 16,
                  ),
                ),
                if (_loadingProgress > 0 && _loadingProgress < 1.0)
                  Padding(
                    padding: const EdgeInsets.only(top: 8),
                    child: Text(
                      '${(_loadingProgress * 100).toInt()}%',
                      style: TextStyle(
                        color: Colors.white.withOpacity(0.7),
                        fontSize: 14,
                      ),
                    ),
                  ),
              ],
            ),
          ),
        ),
      );
    }

    if (_errorMessage != null) {
      return Scaffold(
        appBar: AppBar(
        ),
        body: Center(
          child: Padding(
            padding: const EdgeInsets.all(24.0),
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: [
                Text(
                  _errorMessage!,
                  style: const TextStyle(color: Colors.red),
                  textAlign: TextAlign.center,
                ),
                const SizedBox(height: 16),
                ElevatedButton(
                  onPressed: () => Navigator.pop(context),
                  child: const Text('Go Back'),
                ),
              ],
            ),
          ),
        ),
      );
    }

    // Render integrated EPUB viewer
    if (_epubController == null || _epubFile == null || _viewerKey == null) {
      return const Scaffold(
        body: Center(child: CircularProgressIndicator()),
      );
    }

    return PopScope(
      canPop: true,
      onPopInvoked: (bool didPop) {
        if (didPop) {
          // Save progress one final time when popping
          if (_lastLocation != null) {
            _saveProgress(_lastLocation!);
          }
        }
      },
      child: Scaffold(
        body: Listener(
          behavior: HitTestBehavior.translucent,
          onPointerDown: (event) {
            // Record initial touch position and time
            _pointerDownPosition = event.position;
            _pointerDownTime = DateTime.now();
            _isSwipe = false;
          },
          onPointerMove: (event) {
            // Track movement to detect swipes
            if (_pointerDownPosition != null) {
              final delta = (event.position - _pointerDownPosition!).distance;

              // If movement exceeds threshold, mark as swipe (not a tap)
              if (delta > _swipeThreshold) {
                _isSwipe = true;
              }
            }
          },
          onPointerUp: (event) {
            // Only toggle on tap (not swipe)
            if (_pointerDownTime != null && _pointerDownPosition != null) {
              final duration = DateTime.now().difference(_pointerDownTime!);

              // Check if this was a tap (minimal movement, quick release)
              if (!_isSwipe && duration < _tapMaxDuration) {
                // Apply existing position check for app bar exclusion
                if (_showAppBar) {
                  final appBarHeight = MediaQuery.of(context).padding.top + 56;
                  if (event.position.dy < appBarHeight) {
                    return; // Tap on app bar, don't toggle
                  }
                }

                _toggleAppBarVisibility();
              }
            }

            // Reset tracking state
            _pointerDownPosition = null;
            _pointerDownTime = null;
            _isSwipe = false;
          },
          child: Stack(
            children: [
              OrientationBuilder(
                builder: (context, orientation) {
                  // Calculate spread mode to include in key for widget recreation
                  final screenWidth = MediaQuery.of(context).size.width;
                  const minWidthForDualPage = 768.0;
                  final shouldUseDualPage = screenWidth >= minWidthForDualPage;
                  
                  return EpubViewer(
                    key: ValueKey('$_viewerKey-${shouldUseDualPage ? "dual" : "single"}'), // Include spread in key to force recreation
                    epubController: _epubController!,
                    epubSource: EpubSource.fromFile(_epubFile!),
                    initialCfi: _initialCfi,
                    displaySettings: _buildDisplaySettings(orientation),
                    onEpubLoaded: () {
                      debugPrint('EPUB loaded successfully');
                    },
                    onChaptersLoaded: _handleChaptersLoaded,
                    onRelocated: _handleRelocated,
                    onTextSelected: (selection) {
                      // Future: Handle text selection for highlights/notes
                      debugPrint('Selected: ${selection.selectedText}');
                    },
                  );
                },
              ),
              // Conditional custom app bar overlay
              if (_showAppBar) _buildCustomAppBar(),
            ],
          ),
        ),
      ),
    );
  }

  /// Show chapter list dialog
  void _showChapterList(BuildContext context) {
    if (_chapters == null || _chapters!.isEmpty) return;

    showModalBottomSheet(
      context: context,
      builder: (context) => ListView.builder(
        itemCount: _chapters!.length,
        itemBuilder: (context, index) {
          final chapter = _chapters![index];
          return ListTile(
            title: Text(chapter.title),
            onTap: () {
              Navigator.pop(context);
              _epubController?.display(cfi: chapter.href);
              _hideAppBarOnNavigation();
            },
          );
        },
      ),
    );
  }

  /// Show search dialog
  void _showSearchDialog(BuildContext context) {
    String searchQuery = '';

    showDialog(
      context: context,
      builder: (context) => AlertDialog(
        title: const Text('Search'),
        content: TextField(
          autofocus: true,
          decoration: const InputDecoration(
            hintText: 'Enter search term...',
          ),
          onChanged: (value) => searchQuery = value,
          onSubmitted: (value) {
            if (value.isNotEmpty) {
              Navigator.pop(context);
              _performSearch(value);
            }
          },
        ),
        actions: [
          TextButton(
            onPressed: () => Navigator.pop(context),
            child: const Text('Cancel'),
          ),
          TextButton(
            onPressed: () {
              if (searchQuery.isNotEmpty) {
                Navigator.pop(context);
                _performSearch(searchQuery);
              }
            },
            child: const Text('Search'),
          ),
        ],
      ),
    );
  }

  /// Perform search and show results
  Future<void> _performSearch(String query) async {
    if (_epubController == null) return;
    try {
      final results = await _epubController!.search(query: query);

      if (!mounted) return;

      if (results.isEmpty) {
        ScaffoldMessenger.of(context).showSnackBar(
          const SnackBar(content: Text('No results found')),
        );
        return;
      }

      // Show search results in bottom sheet
      showModalBottomSheet(
        context: context,
        builder: (context) => Column(
          children: [
            Padding(
              padding: const EdgeInsets.all(16.0),
              child: Text(
                '${results.length} results for "$query"',
                style: Theme.of(context).textTheme.titleMedium,
              ),
            ),
            Expanded(
              child: ListView.builder(
                itemCount: results.length,
                itemBuilder: (context, index) {
                  final result = results[index];
                  return ListTile(
                    title: Text(
                      result.excerpt,
                      maxLines: 2,
                      overflow: TextOverflow.ellipsis,
                    ),
                    onTap: () {
                      Navigator.pop(context);
                      _epubController?.display(cfi: result.cfi);
                      _hideAppBarOnNavigation();
                    },
                  );
                },
              ),
            ),
          ],
        ),
      );
    } catch (e) {
      if (!mounted) return;
      ScaffoldMessenger.of(context).showSnackBar(
        SnackBar(content: Text('Search failed: $e')),
      );
    }
  }

  /// Helper method to convert Flutter Color to CSS hex string
  String _colorToHex(Color color) {
    return '#${color.value.toRadixString(16).substring(2).toUpperCase()}';
  }

  /// Toggle app bar visibility
  void _toggleAppBarVisibility() {
    setState(() {
      _showAppBar = !_showAppBar;
    });

    if (_showAppBar) {
      _startAutoHideTimer();
    } else {
      _cancelAutoHideTimer();
    }
  }

  /// Start auto-hide timer
  void _startAutoHideTimer() {
    _cancelAutoHideTimer();
    _appBarAutoHideTimer = Timer(const Duration(seconds: 5), () {
      if (mounted) {
        setState(() {
          _showAppBar = false;
        });
      }
    });
  }

  /// Cancel auto-hide timer
  void _cancelAutoHideTimer() {
    _appBarAutoHideTimer?.cancel();
    _appBarAutoHideTimer = null;
  }

  /// Hide app bar when navigating
  void _hideAppBarOnNavigation() {
    _cancelAutoHideTimer();
    setState(() {
      _showAppBar = false;
    });
  }

  /// Build custom app bar overlay
  Widget _buildCustomAppBar() {
    final topPadding = MediaQuery.of(context).padding.top;

    return Positioned(
      top: 0,
      left: 0,
      right: 0,
      child: AnimatedOpacity(
        opacity: _showAppBar ? 1.0 : 0.0,
        duration: const Duration(milliseconds: 200),
        child: Container(
          padding: EdgeInsets.only(
            top: topPadding,
            left: 4,
            right: 4,
          ),
          decoration: BoxDecoration(
            gradient: LinearGradient(
              begin: Alignment.topCenter,
              end: Alignment.bottomCenter,
              colors: [
                Colors.black.withOpacity(0.7),
                Colors.black.withOpacity(0.0),
              ],
              stops: const [0.0, 1.0],
            ),
          ),
          child: Consumer(
            builder: (context, ref, _) {
              // Watch connectivity state
              final connectivityState = ref.watch(connectivityStateProvider);

              // Check if offline (default to online while loading)
              final isOffline = connectivityState.whenOrNull(
                    data: (isOnline) => !isOnline,
                  ) ??
                  false;

              return Row(
                children: [
                  IconButton(
                    icon: const Icon(Icons.arrow_back),
                    color: Colors.white,
                    onPressed: () => context.pop(),
                    tooltip: 'Back',
                  ),
                  Expanded(
                    child: Text(
                      widget.entry.title,
                      style: const TextStyle(
                        color: Colors.white,
                        fontSize: 18,
                        fontWeight: FontWeight.w500,
                      ),
                      maxLines: 1,
                      overflow: TextOverflow.ellipsis,
                    ),
                  ),
                  // Offline indicator
                  if (isOffline)
                    const Padding(
                      padding: EdgeInsets.only(right: 8),
                      child: Icon(
                        Icons.cloud_off,
                        color: Colors.redAccent,
                        semanticLabel: 'Offline',
                      ),
                    ),
                  // Chapter navigation button
                  if (_chapters != null && _chapters!.isNotEmpty)
                    IconButton(
                      icon: const Icon(Icons.list),
                      color: Colors.white,
                      onPressed: () {
                        _cancelAutoHideTimer();
                        _showChapterList(context);
                      },
                      tooltip: 'Chapters',
                    ),
                  // Search button
                  IconButton(
                    icon: const Icon(Icons.search),
                    color: Colors.white,
                    onPressed: () {
                      _cancelAutoHideTimer();
                      _showSearchDialog(context);
                    },
                    tooltip: 'Search',
                  ),
                ],
              );
            },
          ),
        ),
      ),
    );
  }

  @override
  void dispose() {
    // Cancel timers
    _appBarAutoHideTimer?.cancel();

    // Save progress one final time before disposing
    if (_lastLocation != null) {
      _saveProgress(_lastLocation!);
    }

    // Allow screen to sleep again
    WakelockPlus.disable();

    // Clean up WebView resources to prevent OOM crashes
    // The EpubController holds a reference to the InAppWebViewController
    // which needs to be properly disposed
    _epubController?.webViewController?.dispose();
    _epubController = null;
    super.dispose();
  }
}