#nullable enable

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

namespace SharpGen.Platform
{
    public sealed class ObservableSet<T> : ObservableCollection<T>
    {
        private readonly HashSet<T> set;

        public ObservableSet(IEqualityComparer<T> equalityComparer) => set = new HashSet<T>(equalityComparer);

        public void AddRange(IEnumerable<T> items)
        {
            foreach (var item in items)
                Add(item);
        }

        protected override void InsertItem(int index, T item)
        {
            if (!set.Add(item))
                return;

            base.InsertItem(index, item);
        }

        protected override void ClearItems()
        {
            base.ClearItems();
            set.Clear();
        }

        protected override void RemoveItem(int index)
        {
            var item = this[index];
            set.Remove(item);
            base.RemoveItem(index);
        }

        protected override void SetItem(int index, T item)
        {
            if (!set.Add(item))
                return;

            var oldItem = this[index];
            set.Remove(oldItem);
            base.SetItem(index, item);
        }
    }
}