decorate.cs

    internal class MyModule : Module
    {
        readonly SourceSettings[] _settings =
        {
            new SourceSettings {FTPServerAddress = "ftp1.server1.lab", Filter = "ALL"},
            new SourceSettings {FTPServerAddress = "ftp2.server2.lab", Filter = "pdf;docx"},
            new SourceSettings {FTPServerAddress = "ftp3.server3.lab", Filter = "pdf"}
        };
        
        protected override void Load(ContainerBuilder builder)
        {
            foreach (var sourceSettings in _settings)
            {
                builder
                    .Register(c => new FTPDocumentSource(sourceSettings.FTPServerAddress))
                    .Named<IDocumentSource>(sourceSettings.Filter != "ALL" ? "do-not-decorate" : "decorate");
                
                builder.RegisterDecorator<IDocumentSource>((c, inner) => new DocumentSourceFilteringDecorator(inner), fromKey: "decorate");
            }

            builder.RegisterType<AggregatedDocumentSource>();
        }
    }