import 'package:drift/drift.dart';
import 'package:uuid/uuid.dart';

import '../database/app_database.dart';
import '../database/catalog_queries.dart';
import '../database/stock_queries.dart';
import '../models/product.dart';
import '../models/tab_event.dart';

export '../database/stock_queries.dart' show ProductNotFoundException;

abstract class ProductService {
  /// Active products, re-emitted whenever the products table changes.
  Stream<List<Product>> watchProducts();

  Future<List<Product>> getProducts();

  Future<Product?> getProductById(String id);

  Future<void> createProduct({
    required String name,
    required String category,
    required int stockQuantity,
    required int lowStockThreshold,
    bool infiniteStock = false,
    required int priceInCents,
    required String? imagePath,
  });

  Future<void> updateProduct(Product product);

  Future<void> deleteProduct(String id);

  Future<void> decreaseStock(String productId, int amount);

  Future<void> increaseStock(String productId, int amount);
}

class DriftProductService implements ProductService {
  final AppDatabase database;
  final TabEventFactory eventFactory;
  final _uuid = const Uuid();

  DriftProductService({required this.database, TabEventFactory? eventFactory})
    : eventFactory = eventFactory ?? TabEventFactory();

  Product _mapRowToProduct(ProductRow row) {
    return Product(
      id: row.id,
      name: row.name,
      category: row.category,
      stockQuantity: row.stockQuantity,
      lowStockThreshold: row.lowStockThreshold,
      infiniteStock: row.infiniteStock,
      priceInCents: row.priceInCents,
      imagePath: row.imagePath,
      active: row.active,
    );
  }

  SimpleSelectStatement<$ProductsTable, ProductRow> _activeProductsQuery() {
    return database.select(database.products)
      ..where((product) => product.active.equals(true))
      ..orderBy([(product) => OrderingTerm.asc(product.name)]);
  }

  @override
  Stream<List<Product>> watchProducts() {
    return _activeProductsQuery().map(_mapRowToProduct).watch();
  }

  @override
  Future<List<Product>> getProducts() {
    return _activeProductsQuery().map(_mapRowToProduct).get();
  }

  @override
  Future<Product?> getProductById(String id) async {
    final query = database.select(database.products)
      ..where((product) => product.id.equals(id));

    final row = await query.getSingleOrNull();

    if (row == null) {
      return null;
    }

    return _mapRowToProduct(row);
  }

  /// Queues the new product for the server (which takes this tablet's id), its
  /// starting stock as a count, and its picture for upload.
  @override
  Future<void> createProduct({
    required String name,
    required String category,
    required int stockQuantity,
    required int lowStockThreshold,
    bool infiniteStock = false,
    required int priceInCents,
    required String? imagePath,
  }) async {
    final id = _uuid.v4();

    await database.transaction(() async {
      await database
          .into(database.products)
          .insert(
            ProductsCompanion.insert(
              id: id,
              name: name,
              category: category,
              stockQuantity: stockQuantity,
              lowStockThreshold: lowStockThreshold,
              infiniteStock: Value(infiniteStock),
              priceInCents: priceInCents,
              imagePath: Value(imagePath),
            ),
          );
      await database.queueEvent(
        eventFactory.productCreated(
          productId: id,
          fields: {
            'name': name,
            'category': _serverCategory(category),
            'priceInCents': priceInCents,
            'lowStockThreshold': lowStockThreshold,
          },
        ),
      );
      // The server starts a product it doesn't know as untracked
      if (!infiniteStock) {
        await database.queueEvent(
          eventFactory.stockSet(productId: id, quantity: stockQuantity),
        );
      }
      if (imagePath != null) await database.queueImageUpload(id, imagePath);
    });
  }

  /// Queues what changed for the server: the changed fields, a changed stock
  /// or tracking as a count, and a new picture for upload.
  @override
  Future<void> updateProduct(Product product) async {
    await database.transaction(() async {
      final current = await (database.select(
        database.products,
      )..where((row) => row.id.equals(product.id))).getSingleOrNull();

      await (database.update(
        database.products,
      )..where((row) => row.id.equals(product.id))).write(
        ProductsCompanion(
          name: Value(product.name),
          category: Value(product.category),
          stockQuantity: Value(product.stockQuantity),
          lowStockThreshold: Value(product.lowStockThreshold),
          infiniteStock: Value(product.infiniteStock),
          priceInCents: Value(product.priceInCents),
          imagePath: Value(product.imagePath),
          active: Value(product.active),
        ),
      );

      if (current == null) return;
      final fields = <String, Object?>{
        if (current.name != product.name) 'name': product.name,
        if (current.category != product.category)
          'category': _serverCategory(product.category),
        if (current.priceInCents != product.priceInCents)
          'priceInCents': product.priceInCents,
        if (current.lowStockThreshold != product.lowStockThreshold)
          'lowStockThreshold': product.lowStockThreshold,
      };
      if (fields.isNotEmpty) {
        await database.queueEvent(
          eventFactory.productUpdated(productId: product.id, fields: fields),
        );
      }

      final stockChanged = product.infiniteStock
          ? !current.infiniteStock
          : current.infiniteStock ||
                current.stockQuantity != product.stockQuantity;
      if (stockChanged) {
        await database.queueEvent(
          eventFactory.stockSet(
            productId: product.id,
            quantity: product.infiniteStock ? null : product.stockQuantity,
          ),
        );
      }

      final picture = product.imagePath;
      if (picture != null && picture != current.imagePath) {
        await database.queueImageUpload(product.id, picture);
      }
    });
  }

  /// Only hidden, since open tabs and history still refer to it; the server
  /// archives it for every tablet.
  @override
  Future<void> deleteProduct(String id) async {
    await database.transaction(() async {
      await (database.update(database.products)
            ..where((product) => product.id.equals(id)))
          .write(const ProductsCompanion(active: Value(false)));
      await database.queueEvent(eventFactory.productArchived(productId: id));
    });
  }

  /// The server has no category for an empty one.
  static String? _serverCategory(String category) {
    final trimmed = category.trim();
    return trimmed.isEmpty ? null : trimmed;
  }

  @override
  Future<void> decreaseStock(String productId, int amount) {
    return database.decreaseStock(productId, amount);
  }

  @override
  Future<void> increaseStock(String productId, int amount) {
    return database.increaseStock(productId, amount);
  }
}