/// Case-insensitive product name matching and duplicate grouping.
library;

import '../models/product.dart';

String normalizeProductName(String name) =>
    name.trim().toUpperCase().replaceAll(RegExp(r'\s+'), ' ');

String normalizeSupermarket(String? supermarket) =>
    supermarket?.trim().toUpperCase() ?? '';

String productConflictKey({
  required String name,
  required String? supermarket,
}) => '${normalizeSupermarket(supermarket)}|${normalizeProductName(name)}';

String mergeGroupKey(List<Product> products, String? supermarket) {
  final ids = products.map((product) => product.id).toList()..sort();
  return 'merge:${normalizeSupermarket(supermarket)}:'
      '${normalizeProductName(products.first.name)}:${ids.join(',')}';
}

String spellingVariantKey(int productId, String? supermarket) =>
    'spelling:$productId:${normalizeSupermarket(supermarket)}';

List<List<Product>> nameConflictGroups(Iterable<Product> products) {
  final groups = <String, List<Product>>{};
  for (final product in products) {
    final key = productConflictKey(
      name: product.name,
      supermarket: product.supermarket,
    );
    if (normalizeProductName(product.name).isEmpty) continue;
    (groups[key] ??= []).add(product);
  }
  return [
    for (final group in groups.values)
      if (group.length > 1) group,
  ];
}

Set<int> nameConflictIds(Iterable<Product> products) {
  return {
    for (final group in nameConflictGroups(products))
      for (final product in group) product.id,
  };
}

/// Separate catalog products with the same name at the same store.
class ProductMergeGroup {
  const ProductMergeGroup({
    required this.products,
    required this.supermarket,
    required this.key,
  });

  final List<Product> products;
  final String? supermarket;
  final String key;
}

/// One catalog product bought under multiple spellings at one store.
class ProductSpellingVariant {
  const ProductSpellingVariant({
    required this.product,
    required this.supermarket,
    required this.variants,
    required this.key,
  });

  final Product product;
  final String? supermarket;
  final List<String> variants;
  final String key;
}

/// Builds merge groups from catalog names and trip lines at the same store.
List<ProductMergeGroup> buildNameConflictGroups({
  required Iterable<Product> products,
  required Iterable<({int productId, String name, String supermarket})>
  shopLines,
}) {
  final productById = {for (final product in products) product.id: product};
  final idsByKey = <String, Set<int>>{};
  final supermarketByKey = <String, String>{};

  void add(int productId, String name, String? supermarket) {
    final key = productConflictKey(name: name, supermarket: supermarket);
    if (normalizeProductName(name).isEmpty) return;
    final trimmed = supermarket?.trim();
    if (trimmed != null && trimmed.isNotEmpty) {
      supermarketByKey.putIfAbsent(key, () => trimmed);
    }
    (idsByKey[key] ??= {}).add(productId);
  }

  for (final product in products) {
    add(product.id, product.name, product.supermarket);
  }
  for (final line in shopLines) {
    add(line.productId, line.name, line.supermarket);
  }

  final groups = <ProductMergeGroup>[];
  for (final entry in idsByKey.entries) {
    if (entry.value.length < 2) continue;
    final productsInGroup = [
      for (final id in entry.value)
        if (productById.containsKey(id)) productById[id]!,
    ];
    if (productsInGroup.length < 2) continue;

    productsInGroup.sort(
      (a, b) => a.name.toLowerCase().compareTo(b.name.toLowerCase()),
    );
    final supermarketLabel = supermarketByKey[entry.key];
    groups.add(
      ProductMergeGroup(
        products: productsInGroup,
        supermarket: supermarketLabel,
        key: mergeGroupKey(productsInGroup, supermarketLabel),
      ),
    );
  }

  groups.sort(
    (a, b) =>
        productConflictKey(
          name: a.products.first.name,
          supermarket: a.supermarket,
        ).compareTo(
          productConflictKey(
            name: b.products.first.name,
            supermarket: b.supermarket,
          ),
        ),
  );
  return groups;
}

/// Finds receipt spellings that differ only by capitals at one store.
List<ProductSpellingVariant> findSpellingVariants({
  required Iterable<Product> products,
  required Iterable<({int productId, String name, String supermarket})>
  shopLines,
  Iterable<int> mergeProductIds = const [],
  Iterable<String> mergeGroupKeys = const [],
}) {
  final productById = {for (final product in products) product.id: product};
  final excludedProducts = mergeProductIds.toSet();
  final excludedGroups = mergeGroupKeys.toSet();
  final namesByProductStore = <String, Set<String>>{};
  final supermarketByKey = <String, String>{};

  void addName(int productId, String name, String supermarket) {
    final storeKey = normalizeSupermarket(supermarket);
    final bucketKey = '$productId|$storeKey';
    supermarketByKey[bucketKey] = supermarket;
    (namesByProductStore[bucketKey] ??= {}).add(name);
  }

  for (final line in shopLines) {
    addName(line.productId, line.name, line.supermarket);
  }
  for (final product in products) {
    final supermarket = product.supermarket;
    if (supermarket == null || supermarket.trim().isEmpty) continue;
    addName(product.id, product.name, supermarket);
  }

  final issues = <ProductSpellingVariant>[];
  for (final entry in namesByProductStore.entries) {
    final parts = entry.key.split('|');
    final productId = int.parse(parts.first);
    if (excludedProducts.contains(productId)) continue;

    final product = productById[productId];
    if (product == null) continue;

    final supermarket = supermarketByKey[entry.key];
    final byNormalized = <String, Set<String>>{};
    for (final name in entry.value) {
      final key = normalizeProductName(name);
      if (key.isEmpty) continue;
      (byNormalized[key] ??= {}).add(name);
    }

    for (final names in byNormalized.values) {
      if (names.length < 2) continue;
      final variants = names.toList()
        ..sort((a, b) => a.toLowerCase().compareTo(b.toLowerCase()));
      final issue = ProductSpellingVariant(
        product: product,
        supermarket: supermarket,
        variants: variants,
        key: spellingVariantKey(productId, supermarket),
      );
      if (excludedGroups.contains(issue.key)) continue;
      issues.add(issue);
    }
  }

  issues.sort(
    (a, b) =>
        productConflictKey(
          name: a.product.name,
          supermarket: a.supermarket,
        ).compareTo(
          productConflictKey(name: b.product.name, supermarket: b.supermarket),
        ),
  );
  return issues;
}

/// Catalog merges and receipt spelling variants for the Products screen.
class ProductNameIssues {
  const ProductNameIssues({
    required this.mergeGroups,
    required this.spellingVariants,
  });

  final List<ProductMergeGroup> mergeGroups;
  final List<ProductSpellingVariant> spellingVariants;

  bool get isEmpty => mergeGroups.isEmpty && spellingVariants.isEmpty;

  bool get isNotEmpty => !isEmpty;

  int get issueCount => mergeGroups.length + spellingVariants.length;

  Set<int> get productIds => {
    for (final group in mergeGroups)
      for (final product in group.products) product.id,
    for (final variant in spellingVariants) variant.product.id,
  };
}

ProductNameIssues buildProductNameIssues({
  required Iterable<Product> products,
  required Iterable<({int productId, String name, String supermarket})>
  shopLines,
  Set<String> dismissedKeys = const {},
}) {
  final mergeGroups = [
    for (final group in buildNameConflictGroups(
      products: products,
      shopLines: shopLines,
    ))
      if (!dismissedKeys.contains(group.key)) group,
  ];
  final mergeIds = {
    for (final group in mergeGroups)
      for (final product in group.products) product.id,
  };
  final mergeKeys = {for (final group in mergeGroups) group.key};
  final spellingVariants = [
    for (final variant in findSpellingVariants(
      products: products,
      shopLines: shopLines,
      mergeProductIds: mergeIds,
      mergeGroupKeys: mergeKeys,
    ))
      if (!dismissedKeys.contains(variant.key)) variant,
  ];
  return ProductNameIssues(
    mergeGroups: mergeGroups,
    spellingVariants: spellingVariants,
  );
}