// 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;

namespace System.Reactive.Linq.ObservableImpl
{
    internal sealed class Using<TSource, TResource> : Producer<TSource, Using<TSource, TResource>._>
        where TResource : IDisposable
    {
        private readonly Func<TResource> _resourceFactory;
        private readonly Func<TResource, IObservable<TSource>> _observableFactory;

        public Using(Func<TResource> resourceFactory, Func<TResource, IObservable<TSource>> observableFactory)
        {
            _resourceFactory = resourceFactory;
            _observableFactory = observableFactory;
        }

        protected override _ CreateSink(IObserver<TSource> observer) => new _(observer);

        protected override void Run(_ sink) => sink.Run(this);

        internal sealed class _ : IdentitySink<TSource>
        {
            public _(IObserver<TSource> observer)
                : base(observer)
            {
            }

            private IDisposable _disposable;

            public void Run(Using<TSource, TResource> parent)
            {
                var source = default(IObservable<TSource>);
                try
                {
                    var resource = parent._resourceFactory();
                    if (resource != null)
                        Disposable.SetSingle(ref _disposable, resource);
                    source = parent._observableFactory(resource);
                }
                catch (Exception exception)
                {
                    SetUpstream(Observable.Throw<TSource>(exception).SubscribeSafe(this));

                    return;
                }

                base.Run(source);
            }

            protected override void Dispose(bool disposing)
            {
                if (disposing)
                {
                    Disposable.TryDispose(ref _disposable);
                }
                base.Dispose(disposing);
            }
        }
    }
}