using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace Clones
{
	public class CloneVersionSystem : ICloneVersionSystem
	{
		List<MyClone> Clones = new List<MyClone>(){new MyClone()};
		public string Execute(string query)
		{
			var parameters = query.Split();
			var act = parameters[0];
			var ci = int.Parse(parameters[1]);
			var pi = 0;
			if (parameters.Length > 2)
			{
				pi = int.Parse(parameters[2]);
			}

			switch (act)
			{
				case "learn":
					Clones[ci - 1].listLearned.AddLast(pi);
					return null;
				case "rollback":
					var tempDel = Clones[ci - 1].listLearned.Last();
					Clones[ci - 1].listLearned.RemoveLast();
					Clones[ci - 1].listRollbacked.AddLast(tempDel);
					return null;
				case "relearn":
					var tempRet = Clones[ci - 1].listRollbacked.Last();
					Clones[ci - 1].listRollbacked.RemoveLast();
					Clones[ci - 1].listLearned.AddLast(tempRet);
					return null;
				case "clone":
					Clones.Add(Clones[ci-1].Clone(Clones[ci-1]));
					return null;
				case "check":
					if (Clones[ci - 1].listLearned.Count == 0)
					{
						return "basic";
					}
					return Clones[ci-1].listLearned.Last().ToString();
				default:
					return null;
			}
		}
	}

	public class MyClone
	{
		public LinkedList<int> listLearned = new LinkedList<int>();
		public LinkedList<int> listRollbacked = new LinkedList<int>();
		public MyClone Clone(MyClone oldCl)
		{
			var newCl = new MyClone();
			newCl.listLearned = new LinkedList<int>(oldCl.listLearned);
			newCl.listRollbacked = new LinkedList<int>(oldCl.listRollbacked);
			return newCl;
		}
	}
}