The dependency rule and the four circles

// ╔══ QAYDAYI POZUR ══════════════════════════════════════╗
// fayl: lib/domain/product.dart
import 'package:http/http.dart';          // ❌ domain şəbəkəni tanıyır
import 'package:flutter/material.dart';   // ❌ domain UI-nı tanıyır

class Product {
  Product(this.title, this.priceCents);
  final String title;
  final int priceCents;

  // ❌ domain modeli özü sorğu atır
  static Future<Product> fetch(String id) async { /* http.get(...) */ }

  // ❌ domain modeli rəng qaytarır — bu, UI qərarıdır
  Color get badgeColor => priceCents > 10000 ? Colors.red : Colors.green;
}


// ╔══ QAYDAYI SAXLAYIR ═══════════════════════════════════╗
// fayl: lib/domain/models/product.dart  — təmiz Dart, import yoxdur
class Product {
  const Product({required this.id, required this.title, required this.price});
  final String id;
  final String title;
  final double price;      // artıq manatla: çevirmə mapper-də olub

  bool get isExpensive => price > 100;   // biznes qaydası — UI deyil
}

// fayl: lib/domain/repositories/product_repository.dart
// Yalnız müqavilə. Domain "necə" olduğunu bilmir, "nə" olduğunu bilir.
abstract class ProductRepository {
  Future<List<Product>> fetchActive();
  Future<Product> fetchById(String id);
}

// fayl: lib/data/repositories/product_repository_remote.dart
import 'package:my_app/domain/models/product.dart';            // ✅ data → domain
import 'package:my_app/domain/repositories/product_repository.dart';
import 'package:my_app/data/services/product_api_client.dart';

class ProductRepositoryRemote implements ProductRepository {
  ProductRepositoryRemote({required ProductApiClient apiClient})
      : _apiClient = apiClient;

  final ProductApiClient _apiClient;

  @override
  Future<List<Product>> fetchActive() async {
    final dtos = await _apiClient.getActiveProducts();
    return dtos.map((dto) => dto.toDomain()).toList();
  }

  @override
  Future<Product> fetchById(String id) async =>
      (await _apiClient.getProduct(id)).toDomain();
}