// 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.Reactive.Disposables;
using System.Threading.Tasks;

namespace System.Reactive.Linq
{
    public static partial class AsyncObservable
    {
        public static IAsyncObservable<T> Create<T>(Func<IAsyncObserver<T>, Task<IAsyncDisposable>> subscribeAsync)
        {
            if (subscribeAsync == null)
                throw new ArgumentNullException(nameof(subscribeAsync));

            return new AnonymousAsyncObservable<T>(subscribeAsync);
        }

        public static Task<IAsyncDisposable> SubscribeSafeAsync<T>(this IAsyncObservable<T> source, IAsyncObserver<T> observer)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (observer == null)
                throw new ArgumentNullException(nameof(observer));

            return CoreAsync();

            async Task<IAsyncDisposable> CoreAsync()
            {
                try
                {
                    return await source.SubscribeAsync(observer);
                }
                catch (Exception ex)
                {
                    await observer.OnErrorAsync(ex).ConfigureAwait(false);

                    return AsyncDisposable.Nop;
                }
            }
        }

        private sealed class AnonymousAsyncObservable<T> : AsyncObservableBase<T>
        {
            private readonly Func<IAsyncObserver<T>, Task<IAsyncDisposable>> _subscribeAsync;

            public AnonymousAsyncObservable(Func<IAsyncObserver<T>, Task<IAsyncDisposable>> subscribeAsync)
            {
                _subscribeAsync = subscribeAsync;
            }

            protected override Task<IAsyncDisposable> SubscribeAsyncCore(IAsyncObserver<T> observer) => _subscribeAsync(observer);
        }
    }
}