// From LinkedIn Learning course: From the course: Async Programming in C#
// https://www.linkedin.com/learning/async-programming-in-c-sharp?u=2374954
// and from
// https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/async/using-async-for-file-access

//-// lines commented like this refer to MS-only sections of the code (ie. only works in Visual Studio)

using System;
using System.IO;
using System.Threading;
using System.Text;
using System.Collections.Generic;
using System.Net;
using System.Threading.Tasks;
// using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace Networking
{
    public class AsyncFiles
    {
      public async Task ProcessRead(string filePath)  
      {  
	// string filePath = @"temp.txt";  

	Console.WriteLine("ProcessRead: Begin");

	if (File.Exists(filePath) == false)  
	  {  
	    Console.WriteLine("file not found: " + filePath);  
	  }  
	else  
	  {  
	    try  
	      {  
		string text = await ReadTextAsync(filePath);  
		Console.WriteLine(text);  
	      }  
	    catch (Exception ex)  
	      {  
		Console.WriteLine(ex.Message);  
	      }  
	  }
	Console.WriteLine("ProcessRead: End");
      }  
      
      private async Task<string> ReadTextAsync(string filePath)  
      {  
	using (FileStream sourceStream = new FileStream(filePath,  
        FileMode.Open, FileAccess.Read, FileShare.Read,  
							bufferSize: 4096, useAsync: true))  
	  {  
	    StringBuilder sb = new StringBuilder();  
	    
	    byte[] buffer = new byte[0x1000];  
	    int numRead;  
	    while ((numRead = await sourceStream.ReadAsync(buffer, 0, buffer.Length)) != 0)  
	      {  
		string text = Encoding.Unicode.GetString(buffer, 0, numRead);  
		sb.Append(text);  
	      }  

	    // Thread.Sleep(5000);

	    return sb.ToString();  
	  }  
      }

      public async Task DoIt(params string[] strs){
	Task t;
	List<Task> tasks = new List<Task>();  
	foreach (string str in strs) {
	  t = ProcessRead(str);
	  tasks.Add(t);
	}
	await Task.WhenAll(tasks);
      }
    }

public class Tester {
	public static void Main(){
	  AsyncFiles afs = new AsyncFiles();
	  Console.WriteLine("Main: before ProcessRead()");
	  afs.DoIt("temp.txt", "tmp.txt");
	  Console.WriteLine("Main: after ProcessRead()");
	  //t.ProcessWriteMult();
	}
}

}