An improved example for asynchronous pipeline code. See blog post for more info: https://blog.jermdavis.dev/posts/2021/a-second-pass-at-async-pipelines

AsyncPipelineExample-v2.cs

async Task Main()
{
	var pipeline = new ExampleAsyncPipeline();
	var uri = new Uri("https://news.bbc.co.uk/");

	var tempFile = await pipeline.ProcessAsync(uri);

	Console.WriteLine($"{uri} saved to {tempFile}");
}

public interface IAsyncPipelineStep<TIn, TOut>
{
	Task<TOut> ProcessAsync(TIn Input);
}

public abstract class AsyncPipeline<TIn, TOut> : IAsyncPipelineStep<TIn, TOut>
{
	public Func<TIn, Task<TOut>> _pipelineSteps { get; protected set; }

	public Task<TOut> ProcessAsync(TIn Input)
	{
		return _pipelineSteps(Input);
	}
}

public static class AsyncPipelineStepExtensions
{
	public async static Task<TOut> Step<TIn, TOut>(this Task<TIn> Input, IAsyncPipelineStep<TIn, TOut> Step)
	{
		Console.WriteLine($"Awaiting input for {Step.GetType().Name}");
		var input = await Input;
		Console.WriteLine($"Got input for {Step.GetType().Name}");
		
		return await Step.ProcessAsync(input);
	}

	public async static Task<TOut> Step<TIn, TOut>(this TIn Input, IAsyncPipelineStep<TIn, TOut> Step)
	{
		Console.WriteLine($"Got input for {Step.GetType().Name}");
		return await Step.ProcessAsync(Input);
	}
}

public class HttpFetchAsyncStep : IAsyncPipelineStep<Uri, string>
{
	private static readonly HttpClient _client = new HttpClient();

	public async Task<string> ProcessAsync(Uri Input)
	{
		Console.WriteLine("Entering HttpFetchAsyncStep #1");
		
		Console.WriteLine("Leaving HttpFetchAsyncStep #1");
		
		return await _client.GetStringAsync(Input);
	}
}

public class ModifyTextAsyncStep : IAsyncPipelineStep<string, string>
{
	public async Task<string> ProcessAsync(string Input)
	{
		Console.WriteLine("Entering ModifyTextAsyncStep #2");

		var output = Input.Replace("BBC", "Not the BBC");

		Console.WriteLine("Leaving ModifyTextAsyncStep #2");

		return output;
	}
}

public class DiskWriteAsyncStep : IAsyncPipelineStep<string, string>
{
	public async Task<string> ProcessAsync(string Input)
	{
		Console.WriteLine("Entering DiskWriteAsyncStep #3");
		
		var desktopFolder = System.Environment.GetFolderPath(Environment.SpecialFolder.Desktop);
		var fileName =  System.IO.Path.Combine(desktopFolder, "test.txt");

		await System.IO.File.WriteAllTextAsync(fileName, Input);

		Console.WriteLine("Leaving DiskWriteAsyncStep #3");

		return fileName;
	}
}

public class ExampleAsyncPipeline : AsyncPipeline<Uri, string>
{
	public ExampleAsyncPipeline()
	{
		_pipelineSteps = input => input
			.Step(new HttpFetchAsyncStep())
			.Step(new ModifyTextAsyncStep())
			.Step(new DiskWriteAsyncStep());

	}
}