using System;

namespace UniRx.Operators
{
    internal class TakeObservable<T> : OperatorObservableBase<T>
    {
        private readonly int count;
        private readonly TimeSpan duration;
        internal readonly IScheduler scheduler; // public for optimization check
        private readonly IObservable<T> source;

        public TakeObservable(IObservable<T> source, int count)
            : base(source.IsRequiredSubscribeOnCurrentThread())
        {
            this.source = source;
            this.count = count;
        }

        public TakeObservable(IObservable<T> source, TimeSpan duration, IScheduler scheduler)
            : base(scheduler == Scheduler.CurrentThread || source.IsRequiredSubscribeOnCurrentThread())
        {
            this.source = source;
            this.duration = duration;
            this.scheduler = scheduler;
        }

        // optimize combiner

        public IObservable<T> Combine(int count)
        {
            // xs = 6
            // xs.Take(5) = 5         | xs.Take(3) = 3
            // xs.Take(5).Take(3) = 3 | xs.Take(3).Take(5) = 3

            // use minimum one
            return this.count <= count
                ? this
                : new TakeObservable<T>(source, count);
        }

        public IObservable<T> Combine(TimeSpan duration)
        {
            // xs = 6s
            // xs.Take(5s) = 5s          | xs.Take(3s) = 3s
            // xs.Take(5s).Take(3s) = 3s | xs.Take(3s).Take(5s) = 3s

            // use minimum one
            return this.duration <= duration
                ? this
                : new TakeObservable<T>(source, duration, scheduler);
        }

        protected override IDisposable SubscribeCore(IObserver<T> observer, IDisposable cancel)
        {
            if (scheduler == null) return source.Subscribe(new Take(this, observer, cancel));

            return new Take_(this, observer, cancel).Run();
        }

        private class Take : OperatorObserverBase<T, T>
        {
            private int rest;

            public Take(TakeObservable<T> parent, IObserver<T> observer, IDisposable cancel) : base(observer, cancel)
            {
                rest = parent.count;
            }

            public override void OnNext(T value)
            {
                if (rest > 0)
                {
                    rest -= 1;
                    observer.OnNext(value);
                    if (rest == 0)
                    {
                        try
                        {
                            observer.OnCompleted();
                        }
                        finally
                        {
                            Dispose();
                        }

                        ;
                    }
                }
            }

            public override void OnError(Exception error)
            {
                try
                {
                    observer.OnError(error);
                }
                finally
                {
                    Dispose();
                }
            }

            public override void OnCompleted()
            {
                try
                {
                    observer.OnCompleted();
                }
                finally
                {
                    Dispose();
                }
            }
        }

        private class Take_ : OperatorObserverBase<T, T>
        {
            private readonly object gate = new();
            private readonly TakeObservable<T> parent;

            public Take_(TakeObservable<T> parent, IObserver<T> observer, IDisposable cancel) : base(observer, cancel)
            {
                this.parent = parent;
            }

            public IDisposable Run()
            {
                var d1 = parent.scheduler.Schedule(parent.duration, Tick);
                var d2 = parent.source.Subscribe(this);

                return StableCompositeDisposable.Create(d1, d2);
            }

            private void Tick()
            {
                lock (gate)
                {
                    try
                    {
                        observer.OnCompleted();
                    }
                    finally
                    {
                        Dispose();
                    }

                    ;
                }
            }

            public override void OnNext(T value)
            {
                lock (gate)
                {
                    observer.OnNext(value);
                }
            }

            public override void OnError(Exception error)
            {
                lock (gate)
                {
                    try
                    {
                        observer.OnError(error);
                    }
                    finally
                    {
                        Dispose();
                    }

                    ;
                }
            }

            public override void OnCompleted()
            {
                lock (gate)
                {
                    try
                    {
                        observer.OnCompleted();
                    }
                    finally
                    {
                        Dispose();
                    }

                    ;
                }
            }
        }
    }
}