using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;
using System.Net;

namespace CheckUserNames
{
  class Program
  {

    static void Main(string[] args)
    {
      //Declare input and output file
      string InputFilePath = @"C:\b\input.txt";
      string OutputFilePath = @"C:\b\output.txt";


      //Read input file
      var input = new StreamReader(InputFilePath);
      string CurrentUsername;

      //Open output file for writing, overwrite if it already exists.
      //Change false to true to append instead of overwriting.
      var Output = new StreamWriter(OutputFilePath, false);

      Console.WriteLine("Reading users...");

      //Read every line of the input file.
      while (!input.EndOfStream)
      {
        CurrentUsername = input.ReadLine();

        //Check if username is available
        if (UserNameExists(CurrentUsername))
        {
          Console.WriteLine("Username {0} exists", CurrentUsername);
        }
        else
        {
          Console.WriteLine("Username {0} doesn't exist", CurrentUsername);

          //Output to file if it is
          Output.WriteLine(CurrentUsername);
        }

      }

      //Cleanup
      Output.Close();
      input.Close();
      Console.WriteLine("Done. Press Enter to exit...");
      Console.ReadLine();
    }

    /// <summary>
    /// Check to see if a username exists
    /// </summary>
    /// <param name="username">The username</param>
    /// <returns>True if the username exists. False if not.</returns>
    private static bool UserNameExists(string username)
    {
      try
      {
        string url = "http://www.reddit.com/user/" + username;
        HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
        request.Method = "HEAD";
        request.Timeout = 2000; // I've noticed it can take very long to get a timeout. So I set it to two seconds.
        HttpWebResponse response = request.GetResponse() as HttpWebResponse;
        return (response.StatusCode == HttpStatusCode.OK);
      }
      catch
      {
        return false;
      }
    }
  }
}