// The Repository Pattern is a design pattern commonly used in C# applications to separate the data access logic from the business logic. 
// This pattern aims to create a layer that isolates the database access, enabling a more modular, maintainable, and testable codebase. 
// Here's a basic example to demonstrate how to implement the Repository Pattern in C#.

public class Product
{
    public int Id { get; set; }
    public string Name { get; set; }
    public decimal Price { get; set; }
}

using System.Collections.Generic;

public interface IProductRepository
{
    IEnumerable<Product> GetAll();
    Product GetById(int id);
    void Add(Product product);
    void Update(Product product);
    void Delete(int id);
}

using System.Collections.Generic;
using System.Linq;
using Microsoft.EntityFrameworkCore;

public class ProductRepository : IProductRepository
{
    private readonly AppDbContext _context;

    public ProductRepository(AppDbContext context)
    {
        _context = context;
    }

    public IEnumerable<Product> GetAll()
    {
        return _context.Products.ToList();
    }

    public Product GetById(int id)
    {
        return _context.Products.Find(id);
    }

    public void Add(Product product)
    {
        _context.Products.Add(product);
        _context.SaveChanges();
    }

    public void Update(Product product)
    {
        _context.Products.Update(product);
        _context.SaveChanges();
    }

    public void Delete(int id)
    {
        var product = _context.Products.Find(id);
        if (product != null)
        {
            _context.Products.Remove(product);
            _context.SaveChanges();
        }
    }
}

using Microsoft.EntityFrameworkCore;

public class AppDbContext : DbContext
{
    public DbSet<Product> Products { get; set; }

    public AppDbContext(DbContextOptions<AppDbContext> options) : base(options)
    {
    }
}

public void ConfigureServices(IServiceCollection services)
{
    services.AddDbContext<AppDbContext>(options =>
        options.UseSqlServer(Configuration.GetConnectionString("DefaultConnection")));

    services.AddScoped<IProductRepository, ProductRepository>();

    services.AddControllersWithViews();
}

using Microsoft.AspNetCore.Mvc;
using System.Collections.Generic;

public class ProductsController : Controller
{
    private readonly IProductRepository _productRepository;

    public ProductsController(IProductRepository productRepository)
    {
        _productRepository = productRepository;
    }

    public IActionResult Index()
    {
        IEnumerable<Product> products = _productRepository.GetAll();
        return View(products);
    }

    public IActionResult Details(int id)
    {
        Product product = _productRepository.GetById(id);
        if (product == null)
        {
            return NotFound();
        }
        return View(product);
    }

    // Add other actions for Create, Update, and Delete operations
}

///// setup unit tests /////
dotnet add package Microsoft.EntityFrameworkCore.InMemory
dotnet add package Moq
dotnet add package xunit
dotnet add package xunit.runner.visualstudio
dotnet add package Microsoft.NET.Test.Sdk

using System.Collections.Generic;
using System.Linq;
using Microsoft.EntityFrameworkCore;
using Moq;
using Xunit;

public class ProductRepositoryTests
{
    private DbContextOptions<AppDbContext> _dbContextOptions;

    public ProductRepositoryTests()
    {
        _dbContextOptions = new DbContextOptionsBuilder<AppDbContext>()
            .UseInMemoryDatabase(databaseName: "TestDatabase")
            .Options;

        using (var context = new AppDbContext(_dbContextOptions))
        {
            context.Products.Add(new Product { Id = 1, Name = "Product1", Price = 10 });
            context.Products.Add(new Product { Id = 2, Name = "Product2", Price = 20 });
            context.SaveChanges();
        }
    }

    [Fact]
    public void GetAll_ReturnsAllProducts()
    {
        using (var context = new AppDbContext(_dbContextOptions))
        {
            var repository = new ProductRepository(context);

            var products = repository.GetAll().ToList();

            Assert.Equal(2, products.Count);
            Assert.Equal("Product1", products[0].Name);
            Assert.Equal("Product2", products[1].Name);
        }
    }

    [Fact]
    public void GetById_ReturnsCorrectProduct()
    {
        using (var context = new AppDbContext(_dbContextOptions))
        {
            var repository = new ProductRepository(context);

            var product = repository.GetById(1);

            Assert.NotNull(product);
            Assert.Equal("Product1", product.Name);
        }
    }

    [Fact]
    public void Add_AddsProductToDatabase()
    {
        using (var context = new AppDbContext(_dbContextOptions))
        {
            var repository = new ProductRepository(context);
            var newProduct = new Product { Id = 3, Name = "Product3", Price = 30 };

            repository.Add(newProduct);

            var product = repository.GetById(3);
            Assert.NotNull(product);
            Assert.Equal("Product3", product.Name);
        }
    }

    [Fact]
    public void Update_UpdatesExistingProduct()
    {
        using (var context = new AppDbContext(_dbContextOptions))
        {
            var repository = new ProductRepository(context);
            var product = repository.GetById(1);

            product.Name = "UpdatedProduct";
            repository.Update(product);

            var updatedProduct = repository.GetById(1);
            Assert.Equal("UpdatedProduct", updatedProduct.Name);
        }
    }

    [Fact]
    public void Delete_RemovesProductFromDatabase()
    {
        using (var context = new AppDbContext(_dbContextOptions))
        {
            var repository = new ProductRepository(context);

            repository.Delete(1);

            var product = repository.GetById(1);
            Assert.Null(product);
        }
    }
}