手写简单责任链框架

public interface IStepContext
{
}

public class StepContext : IStepContext
{
}

using System.Threading.Tasks;

public delegate Task StepDelegate(IStepContext context);

using System.Threading.Tasks;

public interface IPipelineBuilder
{
    IPipelineBuilder Use(Func<IStepContext, Func<Task>, Task> step);
    IPipelineBuilder Use(Func<StepDelegate, StepDelegate> step);
    StepDelegate Build();
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

public class PipelineBuilder : IPipelineBuilder
{
    private readonly IList<Func<StepDelegate, StepDelegate>> _components = null;
    private bool _builded = false;

    public PipelineBuilder()
    {
        this._components = new List<Func<StepDelegate, StepDelegate>>();
    }

    public StepDelegate Build()
    {
        if (_builded) throw new InvalidOperationException("Build can only once");
        _builded = true;

        StepDelegate step = context => 
        {
            Console.WriteLine($"Warning: you didn't provide an endpoint on {DateTime.Now:yyyy/MM/dd HH:mm:ss.fff}"); ;
            return Task.CompletedTask;
        };

        foreach (var component in _components.Reverse())
        {
            step = component(step);
        }

        _components.Clear();

        return step;
    }

    public IPipelineBuilder Use(Func<IStepContext, Func<Task>, Task> step)
    {
        return Use(next =>
        {
            return context =>
            {
                Task nextTask() => next(context); // Task nextTask() { return next(context); };
                return step(context, nextTask);
            };
        });
    }

    public IPipelineBuilder Use(Func<StepDelegate, StepDelegate> step)
    {
        this._components.Add(step);
        return this;
    }
}

using System;
using System.Threading.Tasks;

class Program
{
    static void Main(string[] args)
    {
        IPipelineBuilder pipelineBuilder = new PipelineBuilder();
        IStepContext stepContext = new StepContext();

        pipelineBuilder.Use(async (context, next) => 
        {
            Console.WriteLine("第一步开始");
            await next();
            Console.WriteLine("第一步结束");
        });

        pipelineBuilder.Use(async (context, next) =>
        {
            Console.WriteLine("第二步开始");
            await next();
            Console.WriteLine("第二步结束");
        }).Use(async (context, next) =>
        {
            Console.WriteLine("第三步开始");
            await next();
            Console.WriteLine("第三步结束");
        });
        
        pipelineBuilder.Use((context, next) => 
        {
            Console.WriteLine("第四步终结点");
            return Task.CompletedTask;
        });

        var pipeline = pipelineBuilder.Build();
        pipeline(stepContext).Wait();
    }
}