Facade

Provides a simplified interface to a complex subsystem.

Context

Your app needs to use 5 services to "publish a post": validate, save, index, notify, audit. The controller ends up knowing about all of them.

Problem

You couple the transport layer to a bunch of internal services. Any change breaks many points.

Solution

A Facade class offers a PublishPost(...) method and orchestrates the services. The client only knows the facade.

#Example in C#

public class PostPublisher
{
    private readonly IPostValidator _val;
    private readonly IPostRepository _repo;
    private readonly ISearchIndexer _idx;
    private readonly INotifier _notify;

    public PostPublisher(IPostValidator v, IPostRepository r, ISearchIndexer i, INotifier n)
        => (_val, _repo, _idx, _notify) = (v, r, i, n);

    public async Task PublishAsync(Post post)
    {
        _val.Validate(post);
        await _repo.SaveAsync(post);
        await _idx.IndexAsync(post);
        await _notify.NotifySubscribersAsync(post);
    }
}

When NOT to use it

If the facade becomes a God Object that knows too much: split it.

Tradeoffs

Pro	Con
Reduces client coupling	Can hide subsystem flexibility

#structural #gof #api