using System;
using System.Collections.Generic;

namespace TodoApplication
{
    public class ListModel<TItem>
    {
        public List<TItem> Items { get; }
        public int Limit;
        public LimitedSizeStack<Tuple<string, TItem, int>> Stack;
        private string commandAddName;
        private string commandRemoveName;

        public ListModel(int limit)
        {
            Items = new List<TItem>();
            Limit = limit;
            Stack = new LimitedSizeStack<Tuple<string, TItem, int>>(limit);
            commandAddName = "AddItem";
            commandRemoveName = "RemoveItem";
        }

        public void AddItem(TItem item)
        {
            Items.Add(item);
            Stack.Push(Tuple.Create(commandAddName, item, Items.Count));
        }

        public void RemoveItem(int index)
        {
            Items.RemoveAt(index);
            Stack.Push(Tuple.Create(commandRemoveName, Items[index], index));
        }

        public bool CanUndo()
        {
            return Stack.Count > 0;
        }

        public void Undo()
        {
            if (CanUndo())
            {
                Tuple<string, TItem, int> tuple = Stack.Pop();
                string command = tuple.Item1;
                TItem stringValue = tuple.Item2;
                int index = tuple.Item3;
                if (command.Equals(commandAddName))
                    Items.RemoveAt(index);
                if (command.Equals(commandRemoveName))
                {
                    if (index == Items.Count)
                        Items.Add(stringValue);
                    else
                        Items.Insert(index, stringValue);
                }
            }
        }
    }
}