import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:dio/dio.dart';
import 'package:geolocator/geolocator.dart';
import '../../models/document_model.dart';
import '../../core/location/location_service.dart';
import '../../core/network/api_client.dart';
import '../../core/network/api_exception.dart';
import '../../core/storage/local_storage.dart';
import '../../config/app_config.dart';
import '../../main.dart';

enum PendingDocumentStatus { uploading, processing, success, error, syncFailed }

class PendingDocument {
  final String id;
  final String imagePath;
  final PendingDocumentStatus status;
  final DocumentModel? document;
  final double? latitude;
  final double? longitude;
  final String? errorMessage;
  final DateTime createdAt;

  PendingDocument({
    required this.id,
    required this.imagePath,
    this.status = PendingDocumentStatus.uploading,
    this.document,
    this.latitude,
    this.longitude,
    this.errorMessage,
    DateTime? createdAt,
  }) : createdAt = createdAt ?? DateTime.now();

  PendingDocument copyWith({
    PendingDocumentStatus? status,
    DocumentModel? document,
    double? latitude,
    double? longitude,
    String? errorMessage,
  }) {
    return PendingDocument(
      id: id,
      imagePath: imagePath,
      status: status ?? this.status,
      document: document ?? this.document,
      latitude: latitude ?? this.latitude,
      longitude: longitude ?? this.longitude,
      errorMessage: errorMessage,
      createdAt: createdAt,
    );
  }

  /// Round-trips with [fromJson] so the queue survives an OS-level app kill
  /// instead of living in memory only (`LocalStorage.savePendingDocument`).
  Map<String, dynamic> toJson() {
    return {
      'id': id,
      'image_path': imagePath,
      'status': status.name,
      'document': document?.toJson(),
      'latitude': latitude,
      'longitude': longitude,
      'error_message': errorMessage,
      'created_at': createdAt.toIso8601String(),
    };
  }

  factory PendingDocument.fromJson(Map<String, dynamic> json) {
    PendingDocumentStatus status;
    try {
      status = PendingDocumentStatus.values.byName(json['status'] as String? ?? '');
    } catch (_) {
      status = PendingDocumentStatus.error;
    }

    final rawDocument = json['document'];

    return PendingDocument(
      id: json['id'] as String,
      imagePath: json['image_path'] as String,
      status: status,
      document: rawDocument is Map
          ? DocumentModel.fromJson(Map<String, dynamic>.from(rawDocument))
          : null,
      latitude: (json['latitude'] as num?)?.toDouble(),
      longitude: (json['longitude'] as num?)?.toDouble(),
      errorMessage: json['error_message'] as String?,
      createdAt: json['created_at'] != null ? DateTime.parse(json['created_at'] as String) : null,
    );
  }
}

class PendingDocumentsNotifier extends StateNotifier<List<PendingDocument>> {
  PendingDocumentsNotifier(this._ref) : super([]) {
    hydrate();
  }

  final Ref _ref;

  LocalStorage get _storage => _ref.read(localStorageProvider);

  /// Loads the queue persisted by a previous app run and resumes anything that
  /// didn't reach a terminal state before the app was killed. Safe to resume
  /// blindly: the upload endpoint dedupes by file hash server-side, so
  /// re-uploading an item that actually finished before the kill just returns
  /// the existing document instead of creating a duplicate.
  Future<void> hydrate() async {
    List<Map<String, dynamic>> persisted;
    try {
      persisted = _storage.getAllPendingDocuments();
    } catch (_) {
      // No persisted queue to resume (e.g. storage not yet initialized) -
      // fall back to starting empty rather than crashing provider setup.
      return;
    }
    if (persisted.isEmpty) return;

    final docs = persisted.map(PendingDocument.fromJson).toList()
      ..sort((a, b) => b.createdAt.compareTo(a.createdAt));
    state = docs;

    for (final doc in docs) {
      if (doc.status == PendingDocumentStatus.uploading) {
        // `retrySync`'s own transient flip to `uploading` is never persisted
        // (see `_updateItemInMemory`), so a persisted `uploading` status only
        // ever means "upload/process from scratch" - from `addDocument` or a
        // `retryUpload` that got interrupted mid-flight.
        _uploadAndProcess(doc.id, doc.imagePath, latitude: doc.latitude, longitude: doc.longitude);
      } else if (doc.status == PendingDocumentStatus.processing && doc.document != null) {
        _resumePolling(doc.id, doc.document!);
      }
    }
  }

  /// Applies [update] to the item with [id], both in in-memory state and on
  /// disk, so every status transition survives an app restart.
  void _updateItem(String id, PendingDocument Function(PendingDocument item) update) {
    final updated = _updateItemInMemory(id, update);
    if (updated != null) {
      _persistPendingDocument(updated);
    }
  }

  /// Best-effort disk write - a Hive/storage failure is a lost "resume after
  /// restart" affordance, not something that should break the in-progress
  /// upload/sync flow itself.
  void _persistPendingDocument(PendingDocument doc) {
    try {
      _storage.savePendingDocument(doc.toJson()).catchError((_) {});
    } catch (_) {}
  }

  void _removePersistedPendingDocument(String id) {
    try {
      _storage.removePendingDocument(id).catchError((_) {});
    } catch (_) {}
  }

  /// Same as [_updateItem] but doesn't touch disk - for transient, optimistic
  /// UI states that shouldn't change what a resumed app restart does (see
  /// `retrySync`).
  PendingDocument? _updateItemInMemory(String id, PendingDocument Function(PendingDocument item) update) {
    PendingDocument? updated;
    state = [
      for (final item in state)
        if (item.id == id)
          (updated = update(item))
        else
          item
    ];
    return updated;
  }

  void addDocument(String imagePath, {double? latitude, double? longitude}) {
    final id = DateTime.now().millisecondsSinceEpoch.toString();
    final newDoc = PendingDocument(
      id: id,
      imagePath: imagePath,
      latitude: latitude,
      longitude: longitude,
    );
    state = [newDoc, ...state];
    _persistPendingDocument(newDoc);

    _uploadAndProcess(id, imagePath, latitude: latitude, longitude: longitude);
  }

  Future<Position?> _determinePosition() async {
    return await LocationService.determinePosition();
  }

  Future<void> _uploadAndProcess(String id, String imagePath, {double? latitude, double? longitude}) async {
    double? lat = latitude;
    double? lng = longitude;

    if (lat == null || lng == null) {
      try {
        final position = await _determinePosition();
        if (position != null) {
          lat = position.latitude;
          lng = position.longitude;
          if (mounted) {
            _updateItem(id, (item) => item.copyWith(latitude: lat, longitude: lng));
          }
        }
      } catch (_) {
        // Gracefully continue without location tags if fetch fails
      }
    }

    try {
      // API call to upload and process
      final apiClient = _ref.read(apiClientProvider);
      final formData = FormData.fromMap({
        'image': await MultipartFile.fromFile(
          imagePath,
          filename: imagePath.split(RegExp(r'[/\\]')).last,
        ),
        if (lat != null) 'latitude': lat.toString(),
        if (lng != null) 'longitude': lng.toString(),
      });

      final response = await apiClient.client.post(
        AppConfig.uploadDocumentEndpoint,
        data: formData,
      );

      final doc = DocumentModel.fromJson(response.data['data']);

      if (!mounted) return;
      _updateItem(id, (item) => item.copyWith(status: PendingDocumentStatus.processing, document: doc));

      await _pollUntilParsed(id, doc);
    } catch (e) {
      if (!mounted) return;
      _updateItem(id, (item) => item.copyWith(status: PendingDocumentStatus.error, errorMessage: ApiException.from(e).displayMessage));
    }
  }

  /// Resumes polling for an item whose upload already completed (status
  /// `processing`) in a previous app run — never re-uploads the image.
  Future<void> _resumePolling(String id, DocumentModel doc) async {
    try {
      await _pollUntilParsed(id, doc);
    } catch (e) {
      if (!mounted) return;
      _updateItem(id, (item) => item.copyWith(status: PendingDocumentStatus.error, errorMessage: ApiException.from(e).displayMessage));
    }
  }

  Future<void> _pollUntilParsed(String id, DocumentModel doc) async {
    final apiClient = _ref.read(apiClientProvider);

    // Poll until the document is parsed on the server
    bool isParsed = false;
    DocumentModel? parsedDoc;
    int retries = 0;
    // Server's OCR pass can take up to 210s worst case (see
    // v1/documents/upload/route.ts), so poll comfortably past that instead
    // of giving up right as the backend might still be finishing.
    const maxRetries = 130; // ~4.3 minutes max polling (130 retries * 2s)

    while (!isParsed && retries < maxRetries && mounted) {
      await Future.delayed(const Duration(seconds: 2));
      if (!mounted) return;

      try {
        final getRes = await apiClient.client.get(AppConfig.fetchDocumentsEndpoint);
        if (getRes.statusCode == 200 && getRes.data['data'] is List) {
          final list = (getRes.data['data'] as List)
              .map((e) => DocumentModel.fromJson(Map<String, dynamic>.from(e)))
              .toList();

          final found = list.firstWhere(
            (element) => element.id == doc.id,
            orElse: () => doc,
          );

          if (found != doc) {
            isParsed = true;
            parsedDoc = found;
          }
        }
      } catch (_) {
        // Ignore network glitch during polling
      }
      retries++;
    }

    if (!mounted) return;

    if (isParsed && parsedDoc != null) {
      _updateItem(id, (item) => item.copyWith(status: PendingDocumentStatus.success, document: parsedDoc));
    } else {
      _updateItem(id, (item) => item.copyWith(
        status: PendingDocumentStatus.error,
        errorMessage: 'Gagal mengekstrak data dari dokumen (Timeout).',
      ));
    }
  }

  void removeDocument(String id) {
    state = state.where((item) => item.id != id).toList();
    _removePersistedPendingDocument(id);
  }

  /// Marks a pending item as failed to sync after an editor save, keeping the
  /// finalized [doc] so [retrySync] can resend it without re-running OCR.
  void markSyncFailed(String id, DocumentModel doc, String message) {
    _updateItem(id, (item) => item.copyWith(status: PendingDocumentStatus.syncFailed, document: doc, errorMessage: message));
  }

  /// Resends a previously-failed editor save. Unlike [retryUpload], this never
  /// re-uploads the image or re-runs OCR - it only retries the PUT with the
  /// already-corrected [PendingDocument.document].
  Future<void> retrySync(String id) async {
    final matches = state.where((item) => item.id == id);
    if (matches.isEmpty) return;
    final doc = matches.first.document;
    if (doc == null) return;

    // Transient/optimistic only - if the app is killed right here, a restart
    // should resend the PUT (still `syncFailed` on disk), not redo the whole
    // upload, so this particular flip is never persisted.
    _updateItemInMemory(id, (item) => item.copyWith(status: PendingDocumentStatus.uploading, errorMessage: null));

    try {
      final apiClient = _ref.read(apiClientProvider);
      await apiClient.client.put(
        '${AppConfig.fetchDocumentsEndpoint}/${doc.id}',
        data: doc.toPutPayload(),
      );
      if (!mounted) return;
      removeDocument(id);
    } catch (e) {
      if (!mounted) return;
      _updateItem(id, (item) => item.copyWith(
        status: PendingDocumentStatus.syncFailed,
        errorMessage: 'Gagal sinkronisasi ke server: ${ApiException.from(e).displayMessage}',
      ));
    }
  }

  void retryUpload(String id) {
    final doc = state.firstWhere((item) => item.id == id);
    final lat = doc.latitude;
    final lng = doc.longitude;
    _updateItem(id, (item) => item.copyWith(status: PendingDocumentStatus.uploading, errorMessage: null));
    _uploadAndProcess(id, doc.imagePath, latitude: lat, longitude: lng);
  }
}

final pendingDocumentsProvider = StateNotifierProvider<PendingDocumentsNotifier, List<PendingDocument>>((ref) {
  return PendingDocumentsNotifier(ref);
});