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

namespace System.Reactive.Linq.ObservableImpl
{
    internal static class Timeout<TSource>
    {
        internal sealed class Relative : Producer<TSource, Relative._>
        {
            private readonly IObservable<TSource> _source;
            private readonly TimeSpan _dueTime;
            private readonly IObservable<TSource> _other;
            private readonly IScheduler _scheduler;

            public Relative(IObservable<TSource> source, TimeSpan dueTime, IObservable<TSource> other, IScheduler scheduler)
            {
                _source = source;
                _dueTime = dueTime;
                _other = other;
                _scheduler = scheduler;
            }

            protected override _ CreateSink(IObserver<TSource> observer, IDisposable cancel) => new _(this, observer, cancel);

            protected override IDisposable Run(_ sink) => sink.Run(_source);

            internal sealed class _ : IdentitySink<TSource>
            {
                private readonly TimeSpan _dueTime;
                private readonly IObservable<TSource> _other;
                private readonly IScheduler _scheduler;

                long _index;

                IDisposable _mainDisposable;
                IDisposable _otherDisposable;
                IDisposable _timerDisposable;

                public _(Relative parent, IObserver<TSource> observer, IDisposable cancel)
                    : base(observer, cancel)
                {
                    _dueTime = parent._dueTime;
                    _other = parent._other;
                    _scheduler = parent._scheduler;
                }

                public IDisposable Run(IObservable<TSource> source)
                {

                    CreateTimer(0L);

                    Disposable.SetSingle(ref _mainDisposable, source.SubscribeSafe(this));

                    return this;
                }

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

                private void CreateTimer(long idx)
                {
                    if (Disposable.TrySetMultiple(ref _timerDisposable, null))
                    {

                        var d = _scheduler.Schedule((idx, instance: this), _dueTime, (_, state) => { state.instance.Timeout(state.idx); return Disposable.Empty; });

                        Disposable.TrySetMultiple(ref _timerDisposable, d);
                    }
                }

                private void Timeout(long idx)
                {
                    if (Volatile.Read(ref _index) == idx && Interlocked.CompareExchange(ref _index, long.MaxValue, idx) == idx)
                    {
                        Disposable.TryDispose(ref _mainDisposable);

                        var d = _other.Subscribe(GetForwarder());

                        Disposable.SetSingle(ref _otherDisposable, d);
                    }
                }

                public override void OnNext(TSource value)
                {
                    var idx = Volatile.Read(ref _index);
                    if (idx != long.MaxValue && Interlocked.CompareExchange(ref _index, idx + 1, idx) == idx)
                    {
                        // Do not swap in the BooleanDisposable.True here
                        // As we'll need _timerDisposable to store the next timer
                        // BD.True would cancel it immediately and break the operation
                        Volatile.Read(ref _timerDisposable)?.Dispose();

                        ForwardOnNext(value);

                        CreateTimer(idx + 1);
                    }
                }

                public override void OnError(Exception error)
                {
                    if (Interlocked.Exchange(ref _index, long.MaxValue) != long.MaxValue)
                    {
                        Disposable.TryDispose(ref _timerDisposable);

                        ForwardOnError(error);
                    }
                }

                public override void OnCompleted()
                {
                    if (Interlocked.Exchange(ref _index, long.MaxValue) != long.MaxValue)
                    {
                        Disposable.TryDispose(ref _timerDisposable);

                        ForwardOnCompleted();
                    }
                }
            }
        }

        internal sealed class Absolute : Producer<TSource, Absolute._>
        {
            private readonly IObservable<TSource> _source;
            private readonly DateTimeOffset _dueTime;
            private readonly IObservable<TSource> _other;
            private readonly IScheduler _scheduler;

            public Absolute(IObservable<TSource> source, DateTimeOffset dueTime, IObservable<TSource> other, IScheduler scheduler)
            {
                _source = source;
                _dueTime = dueTime;
                _other = other;
                _scheduler = scheduler;
            }

            protected override _ CreateSink(IObserver<TSource> observer, IDisposable cancel) => new _(_other, observer, cancel);

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

            internal sealed class _ : IdentitySink<TSource>
            {
                private readonly IObservable<TSource> _other;

                private readonly object _gate = new object();
                private readonly SerialDisposable _subscription = new SerialDisposable();

                public _(IObservable<TSource> other, IObserver<TSource> observer, IDisposable cancel)
                    : base(observer, cancel)
                {
                    _other = other;
                }

                private bool _switched;

                public IDisposable Run(Absolute parent)
                {
                    var original = new SingleAssignmentDisposable();

                    _subscription.Disposable = original;

                    _switched = false;

                    var timer = parent._scheduler.Schedule(this, parent._dueTime, (_, state) => state.Timeout());

                    original.Disposable = parent._source.SubscribeSafe(this);

                    return StableCompositeDisposable.Create(_subscription, timer);
                }

                private IDisposable Timeout()
                {
                    var timerWins = false;

                    lock (_gate)
                    {
                        timerWins = !_switched;
                        _switched = true;
                    }

                    if (timerWins)
                        _subscription.Disposable = _other.SubscribeSafe(GetForwarder());

                    return Disposable.Empty;
                }

                public override void OnNext(TSource value)
                {
                    lock (_gate)
                    {
                        if (!_switched)
                            ForwardOnNext(value);
                    }
                }

                public override void OnError(Exception error)
                {
                    var onErrorWins = false;

                    lock (_gate)
                    {
                        onErrorWins = !_switched;
                        _switched = true;
                    }

                    if (onErrorWins)
                    {
                        ForwardOnError(error);
                    }
                }

                public override void OnCompleted()
                {
                    var onCompletedWins = false;

                    lock (_gate)
                    {
                        onCompletedWins = !_switched;
                        _switched = true;
                    }

                    if (onCompletedWins)
                    {
                        ForwardOnCompleted();
                    }
                }
            }
        }
    }

    internal sealed class Timeout<TSource, TTimeout> : Producer<TSource, Timeout<TSource, TTimeout>._>
    {
        private readonly IObservable<TSource> _source;
        private readonly IObservable<TTimeout> _firstTimeout;
        private readonly Func<TSource, IObservable<TTimeout>> _timeoutSelector;
        private readonly IObservable<TSource> _other;

        public Timeout(IObservable<TSource> source, IObservable<TTimeout> firstTimeout, Func<TSource, IObservable<TTimeout>> timeoutSelector, IObservable<TSource> other)
        {
            _source = source;
            _firstTimeout = firstTimeout;
            _timeoutSelector = timeoutSelector;
            _other = other;
        }

        protected override _ CreateSink(IObserver<TSource> observer, IDisposable cancel) => new _(this, observer, cancel);

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

        internal sealed class _ : IdentitySink<TSource>
        {
            private readonly Func<TSource, IObservable<TTimeout>> _timeoutSelector;
            private readonly IObservable<TSource> _other;

            private readonly object _gate = new object();
            private readonly SerialDisposable _subscription = new SerialDisposable();
            private readonly SerialDisposable _timer = new SerialDisposable();

            public _(Timeout<TSource, TTimeout> parent, IObserver<TSource> observer, IDisposable cancel)
                : base(observer, cancel)
            {
                _timeoutSelector = parent._timeoutSelector;
                _other = parent._other;
            }

            private ulong _id;
            private bool _switched;

            public IDisposable Run(Timeout<TSource, TTimeout> parent)
            {
                var original = new SingleAssignmentDisposable();

                _subscription.Disposable = original;

                _id = 0UL;
                _switched = false;

                SetTimer(parent._firstTimeout);

                original.Disposable = parent._source.SubscribeSafe(this);

                return StableCompositeDisposable.Create(_subscription, _timer);
            }

            public override void OnNext(TSource value)
            {
                if (ObserverWins())
                {
                    ForwardOnNext(value);

                    var timeout = default(IObservable<TTimeout>);
                    try
                    {
                        timeout = _timeoutSelector(value);
                    }
                    catch (Exception error)
                    {
                        ForwardOnError(error);
                        return;
                    }

                    SetTimer(timeout);
                }
            }

            public override void OnError(Exception error)
            {
                if (ObserverWins())
                {
                    ForwardOnError(error);
                }
            }

            public override void OnCompleted()
            {
                if (ObserverWins())
                {
                    ForwardOnCompleted();
                }
            }

            private void SetTimer(IObservable<TTimeout> timeout)
            {
                var myid = _id;

                var d = new SingleAssignmentDisposable();
                _timer.Disposable = d;
                d.Disposable = timeout.SubscribeSafe(new TimeoutObserver(this, myid, d));
            }

            private sealed class TimeoutObserver : IObserver<TTimeout>
            {
                private readonly _ _parent;
                private readonly ulong _id;
                private readonly IDisposable _self;

                public TimeoutObserver(_ parent, ulong id, IDisposable self)
                {
                    _parent = parent;
                    _id = id;
                    _self = self;
                }

                public void OnNext(TTimeout value)
                {
                    if (TimerWins())
                        _parent._subscription.Disposable = _parent._other.SubscribeSafe(_parent.GetForwarder());

                    _self.Dispose();
                }

                public void OnError(Exception error)
                {
                    if (TimerWins())
                    {
                        _parent.ForwardOnError(error);
                    }
                }

                public void OnCompleted()
                {
                    if (TimerWins())
                        _parent._subscription.Disposable = _parent._other.SubscribeSafe(_parent.GetForwarder());
                }

                private bool TimerWins()
                {
                    var res = false;

                    lock (_parent._gate)
                    {
                        _parent._switched = (_parent._id == _id);
                        res = _parent._switched;
                    }

                    return res;
                }
            }

            private bool ObserverWins()
            {
                var res = false;

                lock (_gate)
                {
                    res = !_switched;
                    if (res)
                    {
                        _id = unchecked(_id + 1);
                    }
                }

                return res;
            }
        }
    }
}