using System;
using System.IO;
using System.Threading;
using System.Text;
using System.Diagnostics;
namespace sharp.extensions
{
	public class LockFile
	{
		public string LockFileName { get; private set; }
		public bool IsLocked { get; private set; }

		public int LockCount { get; private set; }

		public LockFile(string filename)
		{
			this.LockFileName = filename;
			this.LockCount = 0;
		}

		public void Lock()
		{
			if (IsLocked){
				LockCount++;
				return;
			}

			int retries = 3;

			Console.WriteLine("wait on lock file {0}", LockFileName);

			for (; retries > 0; retries--)
			{
				while (File.Exists(LockFileName))
				{
					Thread.Sleep(250);
				}
				try
				{
					FileStream ls = new FileStream(LockFileName, FileMode.CreateNew);
					byte[] pid = Encoding.UTF8.GetBytes(Process.GetCurrentProcess().Id.ToString());
					ls.Write(pid, 0, pid.Length);
					ls.Close();
					IsLocked = true;
					LockCount = 1;

					Console.WriteLine("lock acquired");
					return;
				}
				catch (IOException ioe)
				{
				}
			}
			ThrowIfUnlocked();
		}

		public void Unlock()
		{
			if (IsLocked)
			{
				LockCount--;

				if (LockCount == 0)
				{
					File.Delete(LockFileName);
					IsLocked = false;
				}
			}
		}

		public void ThrowIfUnlocked(){
			if (!IsLocked){
				throw new Exception("Lockfile is not locked");
			}
		}

	}
}