using System;
using System.Reactive.Disposables;
using UnityEngine;

namespace Chernobyl.Unity.Event
{
    /// <summary>
    /// Forwards events from a <see cref="EventSource"/> to one <see cref="EventSource"/> from a
    /// collection and then moves to the next <see cref="EventSource"/> in that collection in
    /// preparation for the next event.
    /// </summary>
    public class EventCarousel : MonoBehaviour
    {
        /// <summary>
        /// When an event is received from this input, it will be sent through the current item from
        /// <see cref="Outputs"/> and then the next item will be selected.
        /// </summary>
        [Tooltip("When an event is received from this input, it will be sent through the current " +
                 "item from Outputs and then the next item will be selected.")]
        public EventSource Input;

        /// <summary>
        /// The <see cref="EventSource"/> instances that are to receive events, one at a time.
        /// </summary>
        [Tooltip("The EventSources that are to receive events, one at a time.")]
        public EventSource[] Outputs = Array.Empty<EventSource>();

        /// <summary>See Unity docs for more info.</summary>
        public void Start()
        {
            Input.ThrowIfNull(nameof(Input));
            Outputs.ThrowIfEmptyOrNull(nameof(Outputs));
        }
        /// <summary>See Unity docs for more info.</summary>
        public void OnEnable() => _subscription = Input.Observable.Subscribe(OnNext);
        /// <summary>See Unity docs for more info.</summary>
        public void OnDisable() => _subscription.Dispose();
        /// <summary>See Unity docs for more info.</summary>
        public void OnDestroy() => _subscription.Dispose();

        void OnNext(object obj)
        {
            Outputs[_currentOutputIndex].Subject.OnNext(obj);

            _currentOutputIndex++;
            if (_currentOutputIndex >= Outputs.Length)
                _currentOutputIndex = 0;
        }

        IDisposable _subscription = Disposable.Empty;
        int _currentOutputIndex;
    }
}