using System;
using System.Collections.Generic;

namespace Open.RandomizationExtensions;

class DeferredHashSet<T> : HashSet<T>, IDisposable
{
	public DeferredHashSet(IEnumerator<T> source)
		=> Source = source ?? throw new ArgumentNullException(nameof(source));

	public DeferredHashSet(IEnumerable<T> source)
		: this((source ?? throw new ArgumentNullException(nameof(source))).GetEnumerator()) { }

	private readonly IEnumerator<T> Source;

	public new bool Contains(T item)
	{
		if (base.Contains(item))
			return true;

		while (Source.MoveNext())
		{
			var i = Source.Current;
			_ = Add(i);
			if (item is null ? i is null : item.Equals(i))
				return true;
		}

		return false;
	}

	public void Dispose()
	{
		Source.Dispose();
		Clear();
	}
}