import 'package:openfoodfacts/openfoodfacts.dart';

import '../../domain/entities/food_product.dart';
import 'remote_food_data_source.dart';

/// Client for the Open Food Facts crowdsourced product database.
///
/// Configures the shared [OpenFoodAPIConfiguration] with the app's user
/// agent (contact info + app identity, per the OFF API guidelines) and maps
/// raw [Product] records onto the nutrition feature's [FoodProduct] entity.
///
/// All lookups are wrapped by the search repository in a 4-second timeout so
/// a slow OFF backend degrades into the USDA FoodData Central fallback
/// instead of blocking the UI.
class OpenFoodFactsClient implements RemoteFoodDataSource {
  OpenFoodFactsClient() {
    configureUserAgent();
  }

  /// Identifies the app to the Open Food Facts API (politeness policy:
  /// include app name, version, and contact info so operators can reach the
  /// maintainer if traffic misbehaves).
  static void configureUserAgent() {
    OpenFoodAPIConfiguration.userAgent = UserAgent(
      name: 'GLP-1 Companion',
      version: '0.1.0',
      url: 'https://git.kellsupport.com/mtkell/glp-companion',
      comment: 'Nutrition lookup for GLP-1 therapy tracking; '
          'maintainer contact: mt.kell (at) kellsupport.com',
    );
  }

  /// Fields requested for every remote product so the mapper has everything
  /// it needs without pulling the entire OFF record.
  static const List<ProductField> _fields = [
    ProductField.BARCODE,
    ProductField.NAME,
    ProductField.GENERIC_NAME,
    ProductField.BRANDS,
    ProductField.SERVING_SIZE,
    ProductField.SERVING_QUANTITY,
    // ignore: deprecated_member_use
    ProductField.NUTRIMENTS,
    ProductField.IMAGE_FRONT_SMALL_URL,
    ProductField.IMAGE_FRONT_URL,
  ];

  /// Resolves a single UPC/EAN [barcode]; empty when OFF does not know the
  /// code.
  @override
  Future<List<FoodProduct>> lookupBarcode(String barcode) async {
    final trimmed = barcode.trim();
    if (trimmed.isEmpty) return const [];

    final configuration = ProductQueryConfiguration(
      trimmed,
      fields: _fields,
      version: ProductQueryVersion.latestVersion,
    );

    try {
      final result = await OpenFoodAPIClient.getProductV3(configuration);
      if (result.status != ProductResultV3.statusSuccess) return const [];
      final product = result.product;
      if (product == null) return const [];
      final mapped = _mapProduct(product);
      return mapped == null ? const [] : [mapped];
    } on TooManyRequestsException {
      rethrow;
    } catch (_) {
      // OFF throws HttpStatusException (and friends) for unknown barcodes;
      // treat every non-rate-limit failure as "not found" so the repository
      // can fall through to the USDA source.
      return const [];
    }
  }

  /// Free-text product search (e.g. "greek yogurt").
  @override
  Future<List<FoodProduct>> searchByText(String query) async {
    final trimmed = query.trim();
    if (trimmed.isEmpty) return const [];

    final configuration = ProductSearchQueryConfiguration(
      parametersList: [
        SearchTerms(terms: trimmed.split(RegExp(r'\s+'))),
      ],
      fields: _fields,
      version: ProductQueryVersion.latestVersion,
    );

    final result = await OpenFoodAPIClient.searchProducts(null, configuration);
    final products = result.products ?? const <Product>[];
    return products
        .map(_mapProduct)
        .whereType<FoodProduct>()
        .toList(growable: false);
  }

  /// Maps an OFF [Product] onto the domain entity; returns `null` when the
  /// record has no name or no usable energy value.
  FoodProduct? _mapProduct(Product product) {
    final name = _firstNonEmpty(product.productName, product.genericName);
    if (name == null) return null;

    final barcode = product.barcode?.trim();
    final brand = product.brands?.split(',').first.trim();

    final servingGrams = _resolveServingGrams(product);
    final perServing = servingGrams != null && servingGrams > 0;

    // Values are read per-serving when OFF carries them, otherwise the
    // per-100 g figures are scaled onto the resolved serving size.
    final calories = _nutrient(product, Nutrient.energyKCal, perServing);
    if (calories == null) return null;

    final imageFront = product.imageFrontSmallUrl?.trim();
    final imageFull = product.imageFrontUrl?.trim();

    return FoodProduct(
      id: (barcode == null || barcode.isEmpty)
          // Offline-only OFF records still get a stable id.
          ? 'off:${product.barcode ?? product.productName}'
          : barcode,
      barcode: (barcode == null || barcode.isEmpty) ? null : barcode,
      productName: name,
      brand: (brand == null || brand.isEmpty) ? null : brand,
      servingSizeGrams: servingGrams ?? 100,
      servingSizeUnit: _unitFromServingSize(product.servingSize) ?? 'g',
      calories: calories,
      proteinGrams: _nutrient(product, Nutrient.proteins, perServing) ?? 0,
      carbsGrams: _nutrient(product, Nutrient.carbohydrates, perServing) ?? 0,
      fatGrams: _nutrient(product, Nutrient.fat, perServing) ?? 0,
      fiberGrams: _nutrient(product, Nutrient.fiber, perServing),
      sodiumMg: _sodiumMg(product, perServing),
      imageUrl: (imageFront?.isNotEmpty ?? false)
          ? imageFront
          : (imageFull?.isNotEmpty ?? false)
              ? imageFull
              : null,
      lastUpdated: DateTime.now(),
    );
  }

  /// Reads [nutrient] for the given size, preferring per-serving values and
  /// scaling per-100 g fallbacks onto the resolved serving size.
  // ignore: deprecated_member_use
  double? _nutrient(Product product, Nutrient nutrient, bool perServing) {
    // `Product.nutriments` and the `Nutriments` class are deprecated in
    // favor of the API v3.5 `nutrition` map, but the v3 map is not populated
    // by the search endpoint yet; the legacy accessor remains the reliable
    // read path.
    // ignore: deprecated_member_use
    final nutriments = product.nutriments;
    if (nutriments == null) return null;
    if (perServing) {
      // ignore: deprecated_member_use
      final serving = nutriments.getValue(nutrient, PerSize.serving);
      if (serving != null) return serving;
    }
    // ignore: deprecated_member_use
    final perHundred = nutriments.getValue(nutrient, PerSize.oneHundredGrams);
    if (perHundred == null) return null;
    return perServing ? _scaled(perHundred, product) : perHundred;
  }

  /// Scales a per-100 g value onto the product's serving size.
  double _scaled(double perHundred, Product product) {
    final grams = _resolveServingGrams(product);
    if (grams == null || grams <= 0) return perHundred;
    return perHundred * grams / 100;
  }

  /// Sodium is stored in mg; OFF reports grams.
  double? _sodiumMg(Product product, bool perServing) {
    final grams = _nutrient(product, Nutrient.sodium, perServing);
    return grams == null ? null : grams * 1000;
  }

  /// Resolves the serving weight in grams from `servingQuantity` or by
  /// parsing the human-readable `servingSize` string (e.g. "30 g").
  double? _resolveServingGrams(Product product) {
    final quantity = product.servingQuantity;
    if (quantity != null && quantity > 0) return quantity;
    return _parseGrams(product.servingSize);
  }

  /// Parses a leading number + mass unit from strings like "30 g" / "0.5 kg".
  static double? _parseGrams(String? servingSize) {
    if (servingSize == null) return null;
    final match = RegExp(
      r'(\d+(?:[.,]\d+)?)\s*(g|gram|grams|kg|kilogram|kilograms|oz|ounces?)',
      caseSensitive: false,
    ).firstMatch(servingSize);
    if (match == null) return null;
    final value = double.tryParse(match.group(1)!.replaceAll(',', '.'));
    if (value == null) return null;
    switch (match.group(2)!.toLowerCase()) {
      case 'kg':
      case 'kilogram':
      case 'kilograms':
        return value * 1000;
      case 'oz':
      case 'ounce':
      case 'ounces':
        return value * 28.3495;
      default:
        return value;
    }
  }

  /// Extracts the canonical pantry unit from a serving-size string.
  static String? _unitFromServingSize(String? servingSize) {
    if (servingSize == null) return null;
    final lower = servingSize.toLowerCase();
    if (RegExp(r'\bml\b|milliliter|millilitre').hasMatch(lower)) return 'ml';
    if (RegExp(r'\bl\b|liter|litre').hasMatch(lower)) return 'l';
    if (RegExp(r'\bg\b|gram|kg').hasMatch(lower)) return 'g';
    if (RegExp(r'\boz\b|ounce').hasMatch(lower)) return 'oz';
    return null;
  }

  static String? _firstNonEmpty(String? a, String? b) {
    if (a != null && a.trim().isNotEmpty) return a.trim();
    if (b != null && b.trim().isNotEmpty) return b.trim();
    return null;
  }
}