IHandlerDecoration

IHandlerDecoration indicates that handler is a decoration of another handler.

/// <summary>Indicates that handler is based on decorating another <see cref="IHandlerBase"/>.</summary>
public interface IHandlerDecoration : IHandlerBase
{
    /// <summary>Is decoration</summary>
    bool IsHandlerDecoration { get; }
    /// <summary>The underlying <see cref="IHandlerBase"/> this decoration is derivation of.</summary>
    IHandlerBase? DecorationSource { get; }
}

IHandlerDecorator decorates a handler in some specific way.

/// <summary>Decorates <see cref="IHandlerBase"/> in an specific way.</summary>
public interface IHandlerDecorator
{
    /// <summary>Decorate <paramref name="handler"/></summary>
    /// <param name="handler"></param>
    /// <returns>Decorated version of <paramref name="handler"/>. May or may not implement <see cref="IHandlerDecoration"/>.</returns>
    IHandlerBase Decorate(IHandlerBase handler);
}

Decorator applies a decoration to a handler.

// Create sum calculator
Action<IQuery<(int, int), int>> sumCalculator = q => q.Response.SetValue(q.Request.Item1 + q.Request.Item2);
// Cast to handler
IHandlerBase handler = Handlers.Action(sumCalculator);
// Create decorator
IHandlerDecorator decorator = new LoggingDecorator(Console.Out);
// Decorate handler to log 
handler = decorator.Decorate(handler);
// Create service
IService<(int, int), int> service = Services.CreateWithoutCache<(int, int), int>(handler);
// Query (logs with decorator)
int value = service.GetRequired((10, 20));
// The decoration prints: "(10, 20) = Entry<Object>(Value, 30, , Default)"

public class LoggingDecorator : IHandlerDecorator
{
    static ConstructorT2<IHandlerBase, TextWriter, IHandlerBase> ctor = new(typeof(LoggingDecoration<,>));
    TextWriter writer;
    public LoggingDecorator(TextWriter writer) => this.writer = writer;

    public IHandlerBase Decorate(IHandlerBase handler)
    {
        if (TypeUtilities.TryGetTypeArgumentOfCorrespondingDefinedType(handler.GetType(), typeof(IHandler<,>), 0, out Type requestType) &&
            TypeUtilities.TryGetTypeArgumentOfCorrespondingDefinedType(handler.GetType(), typeof(IHandler<,>), 1, out Type responseType))
        {
            IHandlerBase decoration = ctor.Create(requestType, responseType, handler, writer);
            return decoration;
        }
        else throw new NotSupportedException($"{handler.GetType()} is not supported.");
    }
}

public class LoggingDecoration<Request, Response> : IHandler<Request, Response>, IHandlerDecoration where Request : notnull
{
    public bool IsHandlerDecoration => true;
    public IHandlerBase? DecorationSource => source;

    IHandler<Request, Response> source;
    TextWriter writer;

    public LoggingDecoration(IHandlerBase source, TextWriter writer)
    {
        this.source = (IHandler<Request, Response>)source;
        this.writer = writer;
    }

    public void Handle(IQuery<Request, Response> query)
    {
        try
        {
            source.Handle(query);
        } finally
        {
            writer.WriteLine($"{query.Request} = {query.Response}");
        }
    }
}

Full Example

Full example

using System;
using System.IO;
using Avalanche.Service;
using Avalanche.Utilities;

public class handler_decoration
{
    public static void Run()
    {
        {
            // <01>
            // Create sum calculator
            Action<IQuery<(int, int), int>> sumCalculator = q => q.Response.SetValue(q.Request.Item1 + q.Request.Item2);
            // Cast to handler
            IHandlerBase handler = Handlers.Action(sumCalculator);
            // Create decorator
            IHandlerDecorator decorator = new LoggingDecorator(Console.Out);
            // Decorate handler to log 
            handler = decorator.Decorate(handler);
            // Create service
            IService<(int, int), int> service = Services.CreateWithoutCache<(int, int), int>(handler);
            // Query (logs with decorator)
            int value = service.GetRequired((10, 20));
            // The decoration prints: "(10, 20) = Entry<Object>(Value, 30, , Default)"
            // </01>
        }
    }

    // <98>
    public class LoggingDecorator : IHandlerDecorator
    {
        static ConstructorT2<IHandlerBase, TextWriter, IHandlerBase> ctor = new(typeof(LoggingDecoration<,>));
        TextWriter writer;
        public LoggingDecorator(TextWriter writer) => this.writer = writer;

        public IHandlerBase Decorate(IHandlerBase handler)
        {
            if (TypeUtilities.TryGetTypeArgumentOfCorrespondingDefinedType(handler.GetType(), typeof(IHandler<,>), 0, out Type requestType) &&
                TypeUtilities.TryGetTypeArgumentOfCorrespondingDefinedType(handler.GetType(), typeof(IHandler<,>), 1, out Type responseType))
            {
                IHandlerBase decoration = ctor.Create(requestType, responseType, handler, writer);
                return decoration;
            }
            else throw new NotSupportedException($"{handler.GetType()} is not supported.");
        }
    }
    // </98>

    // <99>
    public class LoggingDecoration<Request, Response> : IHandler<Request, Response>, IHandlerDecoration where Request : notnull
    {
        public bool IsHandlerDecoration => true;
        public IHandlerBase? DecorationSource => source;

        IHandler<Request, Response> source;
        TextWriter writer;

        public LoggingDecoration(IHandlerBase source, TextWriter writer)
        {
            this.source = (IHandler<Request, Response>)source;
            this.writer = writer;
        }

        public void Handle(IQuery<Request, Response> query)
        {
            try
            {
                source.Handle(query);
            } finally
            {
                writer.WriteLine($"{query.Request} = {query.Response}");
            }
        }
    }
    // </99>
}