// 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. 

namespace System.Reactive
{
    /// <summary>
    /// Class to create an <see cref="IObserver{T}"/> instance from delegate-based implementations of the On* methods.
    /// </summary>
    /// <typeparam name="T">The type of the elements in the sequence.</typeparam>
    public sealed class AnonymousObserver<T> : ObserverBase<T>
    {
        private readonly Action<T> _onNext;
        private readonly Action<Exception> _onError;
        private readonly Action _onCompleted;

        /// <summary>
        /// Creates an observer from the specified OnNext, OnError, and OnCompleted actions.
        /// </summary>
        /// <param name="onNext">Observer's OnNext action implementation.</param>
        /// <param name="onError">Observer's OnError action implementation.</param>
        /// <param name="onCompleted">Observer's OnCompleted action implementation.</param>
        /// <exception cref="ArgumentNullException"><paramref name="onNext"/> or <paramref name="onError"/> or <paramref name="onCompleted"/> is null.</exception>
        public AnonymousObserver(Action<T> onNext, Action<Exception> onError, Action onCompleted)
        {
            if (onNext == null)
                throw new ArgumentNullException(nameof(onNext));
            if (onError == null)
                throw new ArgumentNullException(nameof(onError));
            if (onCompleted == null)
                throw new ArgumentNullException(nameof(onCompleted));

            _onNext = onNext;
            _onError = onError;
            _onCompleted = onCompleted;
        }

        /// <summary>
        /// Creates an observer from the specified OnNext action.
        /// </summary>
        /// <param name="onNext">Observer's OnNext action implementation.</param>
        /// <exception cref="ArgumentNullException"><paramref name="onNext"/> is null.</exception>
        public AnonymousObserver(Action<T> onNext)
            : this(onNext, Stubs.Throw, Stubs.Nop)
        {
        }

        /// <summary>
        /// Creates an observer from the specified OnNext and OnError actions.
        /// </summary>
        /// <param name="onNext">Observer's OnNext action implementation.</param>
        /// <param name="onError">Observer's OnError action implementation.</param>
        /// <exception cref="ArgumentNullException"><paramref name="onNext"/> or <paramref name="onError"/> is null.</exception>
        public AnonymousObserver(Action<T> onNext, Action<Exception> onError)
            : this(onNext, onError, Stubs.Nop)
        {
        }

        /// <summary>
        /// Creates an observer from the specified OnNext and OnCompleted actions.
        /// </summary>
        /// <param name="onNext">Observer's OnNext action implementation.</param>
        /// <param name="onCompleted">Observer's OnCompleted action implementation.</param>
        /// <exception cref="ArgumentNullException"><paramref name="onNext"/> or <paramref name="onCompleted"/> is null.</exception>
        public AnonymousObserver(Action<T> onNext, Action onCompleted)
            : this(onNext, Stubs.Throw, onCompleted)
        {
        }

        /// <summary>
        /// Calls the onNext action.
        /// </summary>
        /// <param name="value">Next element in the sequence.</param>
        protected override void OnNextCore(T value)
        {
            _onNext(value);
        }

        /// <summary>
        /// Calls the onError action.
        /// </summary>
        /// <param name="error">The error that has occurred.</param>
        protected override void OnErrorCore(Exception error)
        {
            _onError(error);
        }

        /// <summary>
        /// Calls the onCompleted action.
        /// </summary>
        protected override void OnCompletedCore()
        {
            _onCompleted();
        }

        internal IObserver<T> MakeSafe(IDisposable disposable)
        {
            return new AnonymousSafeObserver<T>(_onNext, _onError, _onCompleted, disposable);
        }
    }
}