[4/3/2012] Challenge #35 [difficult]

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

namespace ListOfStrings
{
    class Program
    {
        private static readonly List<string> LMainList = new List<string>();
        private static readonly Stack<UserAction> SActionsDone = new Stack<UserAction>();
        private static readonly Stack<UserAction> SUndoneActions = new Stack<UserAction>();

        static void Main()
        {
            while (true)
            {
                Console.Write("Enter command ('A'dd, 'E'dit, 'D'elete, 'U'ndo, 'R'edo, 'Q'uit): ");
                var command = Console.ReadLine();
                string input;
                string strIndex;

                switch (command)
                {
                    case "A":
                        Console.Write("Enter text to add: ");
                        input = Console.ReadLine();

                        AddToList(input);
                        break;

                    case "E":
                        Console.Write("Enter index to edit: ");
                        strIndex = Console.ReadLine();
                        int index;
                        Console.Write("Enter text to edit: ");
                        input = Console.ReadLine();

                        if (int.TryParse(strIndex, out index))
                        {
                            var usAction2 = new UserAction { ListValue = LMainList.ElementAt(index), Command = EditList, Index = index };
                            SActionsDone.Push(usAction2);

                            EditList(input, index);
                        }
                        else
                            Console.WriteLine("{0} is not an integer.", strIndex);
                        break;

                    case "D":
                        Console.Write("Enter index to delete: ");
                        strIndex = Console.ReadLine();

                        if (int.TryParse(strIndex, out index))
                        {
                            var usAction3 = new UserAction { ListValue = LMainList.ElementAt(index), Index = index, Command = DeleteEntry };
                            SActionsDone.Push(usAction3);
                            DeleteEntry("", index);
                        }
                        else
                            Console.WriteLine("{0} is not an integer.", strIndex);
                        break;

                    case "U":
                        UndoAction();
                        break;

                    case "R":
                        RedoAction();
                        break;

                    case "Q":
                        return;

                    default:
                        Console.WriteLine("Not a valid command.");
                        break;
                }

                foreach (var entry in LMainList)
                {
                    Console.WriteLine(entry);
                }
            }
        }

        private static void RedoAction()
        {
            if (SUndoneActions.Count == 0)
                return;

            var action = SUndoneActions.Pop();

            action.Command(action.ListValue, action.Index);
        }

        private static void UndoAction()
        {
            if (SActionsDone.Count == 0)
                return;

            var action = SActionsDone.Pop();

            if (action.Command == DeleteEntry)
            {
                SUndoneActions.Push(action);
                AddToList(action.ListValue, action.Index);
            }
            else if (action.Command == AddToList)
            {
                SUndoneActions.Push(action);
                DeleteEntry(action.ListValue, action.Index);
            }
            else if (action.Command == EditList)
            {
                var temp = action.ListValue;
                action.ListValue = LMainList[action.Index];
                EditList(temp, action.Index);
                SUndoneActions.Push(action);
            }
        }

        private static void DeleteEntry(string input, int index = 0)
        {
            if (LMainList.Count == 0 || index >= LMainList.Count || index <  0)
                return;

            LMainList.RemoveAt(index);
        }

        private static void EditList(string input, int index = 0)
        {
            if (LMainList.Count == 0 || index >= LMainList.Count || index < 0)
                return;

            LMainList[index] = input;
        }

        private static void AddToList(string input, int index = 0)
        {
            if ( index == 0 )
                index = LMainList.Count;

            var usAction1 = new UserAction { ListValue = input, Command = AddToList, Index = index };
            SActionsDone.Push(usAction1);

            LMainList.Insert(index, input);
        }
    }

    class UserAction
    {
        public string ListValue { get; set; }
        public int Index { get; set; }
        public Action<string,int> Command { get; set; }
    }
}