using System.Collections.Generic;

namespace Clones
{
    public class Clone
    {
        public StackForClone AddProgramm;
        public StackForClone RemoveProgramm;

        public Clone()
        {
            AddProgramm = new StackForClone();
            RemoveProgramm = new StackForClone();
        }

        public Clone(Clone baseClone)
        {
            AddProgramm = new StackForClone(baseClone.AddProgramm);
            RemoveProgramm = new StackForClone(baseClone.RemoveProgramm);
        }
    }

    public class StackFCItem
    {
        public string Command;
        public StackFCItem First;

        public StackFCItem(string value, StackFCItem first)
        {
            Command = value;
            First = first;
        }
    }

    public class StackForClone
    {
        public StackFCItem Last;

        public StackForClone()
        {
        }

        public StackForClone(StackForClone baseStack)
        {
            Last = baseStack.Last;
        }

        public void Push(string item)
        {
            Last = new StackFCItem(item, Last);
        }

        public string Pop()
        {
            var result = Last.Command;
            Last = Last.First;
            return result;
        }
    }

    public class CloneVersionSystem : ICloneVersionSystem
    {
        private List<Clone> cloneslist;

        public CloneVersionSystem()
        {
            cloneslist = new List<Clone>();
            cloneslist.Add(new Clone());
        }

        public string Execute(string query)
        {
            var input = query.Split(' ');
            var command = input[0];
            var cloneIndex = int.Parse(input[1]) - 1;
            return Commands(input, cloneIndex);
        }

        public string Commands(string[] command, int num)
        {
            var clone = cloneslist[num];

            if (command[0] == "learn")
            {
                clone.AddProgramm.Push(command[2]);
                clone.RemoveProgramm.Last = null;
            }
            if (command[0] == "rollback")
            {
                if (clone.AddProgramm.Last == null)
                    return null;
                var progRoll = clone.AddProgramm.Pop();
                clone.RemoveProgramm.Push(progRoll);
            }

            if (command[0] == "relearn")
            {
                if (clone.RemoveProgramm.Last == null)
                    return null;
                var progRelearn = clone.RemoveProgramm.Pop();
                clone.AddProgramm.Push(progRelearn);
            }

            if (command[0] ==  "clone")
            {
                cloneslist.Add(new Clone(cloneslist[num]));
            }
            if(command[0] ==  "check")
            {
                if (clone.AddProgramm.Last == null) return "basic";
                return clone.AddProgramm.Last.Command;
            }
            return null;
        }
    }
}