using System.Collections;

namespace System.Windows.Forms
{
    public partial class CheckedListBox
    {
        public new class ObjectCollection : CollectionBase
        {
            private CheckedListBox owner { get; }

            private IList items { get; }

            public object this[int index] => ((Item)items[index])?.Value;

            public new int Count => items.Count;

            public void Add(object obj, CheckState check)
            {
                var item = new Item(owner, obj);
                items.Add(item);
                item.SetState(check);
                owner.ClearCheckedItems();
            }

            public void Add(object obj, bool isChecked) => Add(obj, isChecked ? CheckState.Checked : CheckState.Unchecked);

            public void Add(object obj) => Add(obj, false);

            public void AddRange(object[] objects)
            {
                foreach (object obj in objects)
                    Add(obj);
            }

            public void Insert(int index, object obj)
            {
                var item = new Item(owner, obj);
                items.Insert(index, item);
                item.SetState(CheckState.Unchecked);
                owner.ClearCheckedItems();
            }

            public void Remove(object obj)
            {
                int index = IndexOf(obj);
                if (index != -1)
                    RemoveAt(index);
            }

            public new void RemoveAt(int index)
            {
                items.RemoveAt(index);
                owner.ClearCheckedItems();
            }

            public new void Clear()
            {
                items.Clear();
                owner.ClearCheckedItems();
            }

            public int IndexOf(object obj)
            {
                for (int i = 0; i < Count; i++)
                {
                    if (this[i] == obj)
                        return i;
                }
                return -1;
            }

            public bool Contains(object obj) => IndexOf(obj) != -1;

            internal int IndexOfItem(object item) => items.IndexOf(item);

            // the reason for this method is that enumerator must return Item.Value rather than Item itself
            public new IEnumerator GetEnumerator()
            {
                foreach (Item item in items)
                    yield return item.Value;
            }

            internal ObjectCollection(CheckedListBox owner, IList items)
            { 
                this.owner = owner;
                this.items = items;
            }
        }
    }
}