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

namespace BITKit
{
    public sealed class CacheList<T> : IList<T>
    {
        private readonly IList<T> _listImplementation = new List<T>();
        private T[] _array = Array.Empty<T>();
        private bool _isDirty = true;

        public IEnumerator<T> GetEnumerator()
        {
            CheckChanges();
            return _listImplementation.GetEnumerator();
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            CheckChanges();
            return ((IEnumerable)_listImplementation).GetEnumerator();
        }

        public void Add(T item)
        {
            //CheckChanges();
            _listImplementation.Add(item);
        }

        public void Clear()
        {
            CheckChanges();
            _listImplementation.Clear();
        }

        public bool Contains(T item)
        {
            CheckChanges();
            return _listImplementation.Contains(item);
        }

        public void CopyTo(T[] array, int arrayIndex)
        {
            CheckChanges();
            _listImplementation.CopyTo(array, arrayIndex);
        }

        public bool Remove(T item)
        {
            //CheckChanges();
            return _listImplementation.Remove(item);
        }

        public int Count
        {

            get
            {
                CheckChanges();
                return _listImplementation.Count;
            }
        }

        public bool IsReadOnly
        {
            get
            {
                CheckChanges();
                return _listImplementation.IsReadOnly;
            }
        }

        public int IndexOf(T item)
        {
            CheckChanges();
            return _listImplementation.IndexOf(item);
        }

        public void Insert(int index, T item)
        {
            CheckChanges();
            _listImplementation.Insert(index, item);
        }

        public void RemoveAt(int index)
        {
            CheckChanges();
            _listImplementation.RemoveAt(index);
        }

        public T this[int index]
        {
            get
            {
                CheckChanges();
                return _listImplementation[index];
            }
            set
            {
                _listImplementation[index] = value;
                CheckChanges();
            }
        }

        private void CheckChanges()
        {
            if (!_isDirty) return;
            _array = new T[_listImplementation.Count];
            _listImplementation.CopyTo(_array, 0);
            _isDirty = false;
        }
    }

    public static partial class Extensions
    {
        public static IDictionary<TKey, TValue> CreateOrAddIfEmety<TKey, TValue>(this IDictionary<TKey, TValue> self, TKey key, Func<TValue> createFactory)
        {
            if (self.ContainsKey(key) is false)
            {
                self.Add(key, createFactory.Invoke());
            }
            return self;
        }
    }
}