AJAX Progress Bar for ASP.NET

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace hmlib.Web.UI.Controls
{
	public partial class Progress
	{
		static List<Progress> _list = new List<Progress>();
		public static Progress Find(string id)
		{
			Progress.CleanUp();
			return _list.Find(a => a.ID == id);
		}
		public static Progress FindOrCreate(string id)
		{
			return Progress.Find(id) ?? new Progress(id);
		}
		public static object GetResponse(string progressId)
		{
			Progress item = Progress.Find(progressId);
			if (item == null) return null;
			if (item.NewLines.Count > 1000) throw new Exception("Too many lines");
			var result = new
			{
				value = item.Value,
				lines = item.NewLines.ToArray()
			};
			item.NewLines.Clear();
			return result;
		}
		internal static void CleanUp()
		{
			_list.RemoveAll(a => (DateTime.Now - a.CreatedOn).TotalDays > 1);
			//_list.RemoveAll(a => a.Value == 1 && (DateTime.Now - a.ChangedOn).TotalSeconds > 5);
		}
	}
}