IServiceDecorator

IServiceDecorator is an interface for objects that can decorate a service in some specific way.

/// <summary>Decorates <see cref="IService"/> in a specific way.</summary>
public interface IServiceDecorator
{
    /// <summary>Decorate <paramref name="service"/></summary>
    /// <returns>Decorated version of <paramref name="service"/>.</returns>
    IServiceBase Decorate(IServiceBase service);
}

IServiceDecoration is for service implementations that indicate that they are a decoration or type-cast.

/// <summary>Indicates that service implementation is decoration.</summary>
public interface IServiceDecoration : IServiceBase
{
    /// <summary>Is decoration</summary>
    bool IsServiceDecoration { get; }
    /// <summary>The underlying <see cref="IService"/> this decoration is derivation of.</summary>
    IServiceBase? DecorationSource { get; }
}

Decorator modifies service in a specific way.

// Create service
IService service = Services.Create(ServiceHandlers.Instance);
// Create decorator
IServiceDecorator decorator = new LoggerDecorator(System.Console.Out);
// Decorate to log
IServiceDecoration decoration = (IServiceDecoration)decorator.Decorate(service);
// Query request (is printed)
Type? type = ((IService)decoration).Get<TypeRequest, Type>("System.String"); 
// Prints: "Get(TypeRequest(System.String, Module=)) = System.String"

public class LoggerDecorator : IServiceDecorator
{
    TextWriter output;
    public LoggerDecorator(TextWriter output) => this.output = output;
    public IServiceBase Decorate(IServiceBase service) => new LoggerDecoration((IService)service, output);
}

public class LoggerDecoration : ServiceDecorationBase, IServiceDecoration
{
    TextWriter output;
    public LoggerDecoration(IService service, TextWriter output) : base(service) => this.output = output;

    public override Response Get<Request, Response>(
        in Request request, 
        CancellationToken cancelToken = default, 
        IDictionary<string, object>? context = null)
    {
        Response response = base.Get<Request, Response>(request, cancelToken, context)!;
        output.Write($"Get({request}) = {response}");
        return response;
    }
}

Full Example

Full example

using System;
using System.Collections.Generic;
using System.IO;
using System.Threading;
using Avalanche.Service;

public class service_decoration
{
    public static void Run()
    {
        {
            // <01>
            // Create service
            IService service = Services.Create(ServiceHandlers.Instance);
            // Create decorator
            IServiceDecorator decorator = new LoggerDecorator(System.Console.Out);
            // Decorate to log
            IServiceDecoration decoration = (IServiceDecoration)decorator.Decorate(service);
            // Query request (is printed)
            Type? type = ((IService)decoration).Get<TypeRequest, Type>("System.String"); 
            // Prints: "Get(TypeRequest(System.String, Module=)) = System.String"
            // </01>
        }
    }
    // <99>
    public class LoggerDecorator : IServiceDecorator
    {
        TextWriter output;
        public LoggerDecorator(TextWriter output) => this.output = output;
        public IServiceBase Decorate(IServiceBase service) => new LoggerDecoration((IService)service, output);
    }

    public class LoggerDecoration : ServiceDecorationBase, IServiceDecoration
    {
        TextWriter output;
        public LoggerDecoration(IService service, TextWriter output) : base(service) => this.output = output;

        public override Response Get<Request, Response>(
            in Request request, 
            CancellationToken cancelToken = default, 
            IDictionary<string, object>? context = null)
        {
            Response response = base.Get<Request, Response>(request, cancelToken, context)!;
            output.Write($"Get({request}) = {response}");
            return response;
        }
    }
    // </99>
}