using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.IO;

using System.Linq;

​

public class Program

{  

    public static void Main()

    { 

        var sw = new Stopwatch();

        Console.WriteLine("******************************************************");

        Console.WriteLine("Example WITH multiple enumerations of the data source.");

        Console.WriteLine("******************************************************\n");

        //Mock data source that takes some time to retrieve data from

        var dataSource = DataSource.DataPoints;

​

        sw.Start();

​

        var result = dataSource.Step1().Step2(1).Step3(5).Step4(1); //Forces query validation SEVERAL TIMES

​

        sw.Stop();

​

        Console.WriteLine($"First item: {result.First()}"); //Forces query validation because of .First()

        Console.WriteLine($"It took {sw.Elapsed.Milliseconds} ms to execute the pipeline.");

        Console.WriteLine("\n\n*********************************************************");

        Console.WriteLine("Example WITHOUT multiple enumerations of the data source.");

        Console.WriteLine("*********************************************************\n\n");

​

        var anotherDataSource = DataSource.DataPoints; 

​

        sw.Restart();

​

        var fasterResult = anotherDataSource.BetterStep1().BetterStep2(1).BetterStep3(5).BetterStep4(1);

​

        sw.Stop(); 

        Console.WriteLine($"First item: {fasterResult.First()}"); //Forces query validation FOR THE FIRST TIME because of .First()

        Console.WriteLine($"It took {sw.Elapsed.Milliseconds} ms to execute the pipeline.");

    } 

}

​

public static class MyBadPipeline

{

    public static IEnumerable<int> Step1(this IEnumerable<int> data)

    {

        if (data.Any()) //forces query evaluation

        {

            return data;

        }

        else

        {

            //It's bad design to throw an Exception like this

            //The correct way would be to throw a custom exception

            //This is just to make a a point.

            throw new Exception("Failed");

        }

    }

    public static IEnumerable<int> Step2(this IEnumerable<int> data, int filterBottomThreshold)

    {

        return data.Where(t => t > filterBottomThreshold).ToList(); //forces query evaluation

    }

    public static IEnumerable<int> Step3(this IEnumerable<int> data, int filterTopThreshold)

    {

        return data.Where(t => t < filterTopThreshold).ToList(); //forces query evaluation

    }

​

    public static IEnumerable<int> Step4(this IEnumerable<int> data, int page)

    {

        var pageSize = 1000;

        return data.Skip(pageSize * page).Take(pageSize).ToList();

    }

}

​

public static class ABetterPipeline

{

    public static IEnumerable<int> BetterStep1(this IEnumerable<int> data)

    {

        //There is no point in verifying if data exists at the cost of having to access all the data

        return data;

    }

    public static IEnumerable<int> BetterStep2(this IEnumerable<int> data, int filterBottomThreshold)

    {

        return data?.Where(t => t > filterBottomThreshold); //forces query evaluation

    }

    public static IEnumerable<int> BetterStep3(this IEnumerable<int> data, int filterTopThreshold)

    {

        return data?.Where(t => t < filterTopThreshold); //forces query evaluation

    }

​

    public static IEnumerable<int> BetterStep4(this IEnumerable<int> data, int page)

    {

        var pageSize = 1000;

        return data?.Skip(pageSize * page).Take(pageSize);

    }

}

​

//This is to simulate a request to a datasource

public static class DataSource

{

    private const string FILEPATH = "datadump.txt";

    private const int DATASOURCE_SIZE = 100000;

    public static IEnumerable<int> DataPoints

    {

        get

        { 

            return GetDataPoints();

        }

    }

    private static IEnumerable<int> GetDataPoints()

    {

        Console.WriteLine("\nRetrieving data...\n");

        GenerateData();

        return File.ReadAllLines(FILEPATH).Select(int.Parse);

    }

​

    private static void GenerateData()

    {

        var rand = new Random();

        var data = Enumerable.Range(0, DATASOURCE_SIZE).Select(r => rand.Next(10).ToString());

        File.WriteAllLines(FILEPATH, data);

    } 

}