// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the Apache 2.0 License.
// See the LICENSE file in the project root for more information. 

using System.Collections.Generic;

namespace System.Linq
{
    public static partial class AsyncEnumerable
    {
        public static IAsyncEnumerable<TSource> Union<TSource>(this IAsyncEnumerable<TSource> first, IAsyncEnumerable<TSource> second, IEqualityComparer<TSource> comparer)
        {
            if (first == null)
            {
                throw new ArgumentNullException(nameof(first));
            }

            if (second == null)
            {
                throw new ArgumentNullException(nameof(second));
            }

            if (comparer == null)
            {
                throw new ArgumentNullException(nameof(comparer));
            }

            return first.Concat(second)
                        .Distinct(comparer);
        }

        public static IAsyncEnumerable<TSource> Union<TSource>(this IAsyncEnumerable<TSource> first, IAsyncEnumerable<TSource> second)
        {
            if (first == null)
            {
                throw new ArgumentNullException(nameof(first));
            }

            if (second == null)
            {
                throw new ArgumentNullException(nameof(second));
            }

            return first.Union(second, EqualityComparer<TSource>.Default);
        }
    }
}