Hexdump console application to be refactored

hexdump.cs

using System;
using System.IO;
using System.Text;

namespace hexdump
{
	// source: "C# von Kopf bis Fuß", O'Reilly, see also https://app.box.com/s/a9n6kipfdonr5yeo44ha
	class MainClass
	{
		public static void Main (string[] args)
		{
			if (args.Length != 1) {
				Console.Error.WriteLine ("Usage: hexdump <dateiname>");
				Environment.Exit (1);
			}

			if (!File.Exists(args[0])) {
				Console.Error.WriteLine("No such file: {0}", args[0]);
				Environment.Exit(2);
			}

			using (var input = File.OpenRead (args [0])) {
				int position = 0;
				var buffer = new byte[16];

				while (position < input.Length) {
					var charsRead = input.Read (buffer, 0, buffer.Length);
					if (charsRead > 0) {
						Console.Write ("{0}: ", string.Format ("{0:x4}", position));
						position += charsRead;

						for (int i = 0; i < 16; i++) {
							if (i < charsRead) {
								var hex = string.Format ("{0:x2}", buffer [i]);
								Console.Write (hex + " ");
							} else {
								Console.Write ("  ");
							}

							if (i == 7) {
								Console.Write ("-- ");
							}

							if (buffer [i] < 32 || buffer [i] > 250) {
								buffer [i] = (byte)'.';
							}
						}

						var bufferContent = Encoding.ASCII.GetString (buffer);
						Console.WriteLine ("  " + bufferContent.Substring (0, charsRead));
					}
				}
			}
		}
	}
}