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// Generic interfaces, covariance, and interface segregation

// Generic repository interface
public interface IRepository<T> where T : class
{
    T?           GetById(int id);
    IList<T>     GetAll();
    void         Add(T entity);
    void         Remove(int id);
}

// Covariant interface — T can only appear as output (out)
public interface IProducer<out T>
{
    T Produce();
}

// Contravariant interface — T can only appear as input (in)
public interface IConsumer<in T>
{
    void Consume(T item);
}

// Demonstrating covariance assignment
public class AnimalProducer : IProducer<string>
{
    public string Produce() => "Cat";
}

IProducer<string> stringProducer = new AnimalProducer();
IProducer<object> objectProducer = stringProducer;  // covariance — works!
Console.WriteLine(objectProducer.Produce());         // "Cat"

// Interface segregation — split large interface
public interface IReadable<T>  { T Read(int id); }
public interface IWritable<T>  { void Write(T item); }
public interface IReadWrite<T> : IReadable<T>, IWritable<T> { }

// A read-only view can depend on just IReadable
public class ReportGenerator<T>
{
    private readonly IReadable<T> _store;
    public ReportGenerator(IReadable<T> store) => _store = store;
    public void Generate(int id) => Console.WriteLine(_store.Read(id)?.ToString());
}