Generic Repository Pattern

// Domain/Interfaces/IRepository.cs
// Note: interfaces are in Domain - no EF Core dependency here
public interface IRepository<T> where T : BaseEntity
{
    Task<T?> FindByIdAsync(Guid id, CancellationToken ct = default);
    Task<IReadOnlyList<T>> GetAllAsync(CancellationToken ct = default);
    Task<bool> ExistsAsync(Guid id, CancellationToken ct = default);
    void Add(T entity);
    void Update(T entity);
    void Remove(T entity);
}

// Domain-specific interface (Domain/Interfaces/IProductRepository.cs)
public interface IProductRepository : IRepository<Product>
{
    Task<Product?> FindBySlugAsync(string slug, CancellationToken ct = default);
    Task<IReadOnlyList<Product>> GetByCategoryAsync(Guid categoryId, CancellationToken ct = default);
    Task<bool> SlugExistsAsync(string slug, Guid? excludeId = null, CancellationToken ct = default);
    Task<CursorPage<Product>> GetPagedAsync(ProductPageQuery query, CancellationToken ct = default);
}

// Infrastructure/Repositories/BaseRepository.cs
public abstract class BaseRepository<T>(AppDbContext db) : IRepository<T>
    where T : BaseEntity
{
    protected readonly AppDbContext Db = db;
    protected readonly DbSet<T> Set = db.Set<T>();

    public virtual async Task<T?> FindByIdAsync(Guid id, CancellationToken ct = default) =>
        await Set.FindAsync([id], ct);

    public virtual async Task<IReadOnlyList<T>> GetAllAsync(CancellationToken ct = default) =>
        await Set.AsNoTracking().ToListAsync(ct);

    public virtual async Task<bool> ExistsAsync(Guid id, CancellationToken ct = default) =>
        await Set.AnyAsync(e => e.Id == id, ct);

    public virtual void Add(T entity) => Set.Add(entity);
    public virtual void Update(T entity) => Set.Update(entity);
    public virtual void Remove(T entity) => Set.Remove(entity);
}

// Infrastructure/Repositories/ProductRepository.cs
public class ProductRepository(AppDbContext db) : BaseRepository<Product>(db), IProductRepository
{
    public async Task<Product?> FindBySlugAsync(string slug, CancellationToken ct = default) =>
        await Set
            .Include(p => p.Category)
            .AsNoTracking()
            .FirstOrDefaultAsync(p => p.Slug == slug, ct);

    public async Task<IReadOnlyList<Product>> GetByCategoryAsync(Guid categoryId, CancellationToken ct = default) =>
        await Set
            .Where(p => p.CategoryId == categoryId)
            .AsNoTracking()
            .OrderBy(p => p.Name)
            .ToListAsync(ct);

    public async Task<bool> SlugExistsAsync(string slug, Guid? excludeId = null, CancellationToken ct = default) =>
        await Set.AnyAsync(p => p.Slug == slug && p.Id != excludeId, ct);

    public async Task<CursorPage<Product>> GetPagedAsync(ProductPageQuery query, CancellationToken ct = default)
    {
        var q = Set.Where(p => query.CategoryId == null || p.CategoryId == query.CategoryId);
        if (query.AfterDate.HasValue)
            q = q.Where(p => p.CreatedAt < query.AfterDate.Value);
        var items = await q.OrderByDescending(p => p.CreatedAt).Take(query.Limit + 1).ToListAsync(ct);
        var hasNext = items.Count > query.Limit;
        if (hasNext) items.RemoveAt(items.Count - 1);
        return new CursorPage<Product>([.. items], null, hasNext, query.Limit);
    }
}

record ProductPageQuery(Guid? CategoryId, DateTime? AfterDate, int Limit = 20);