using System;
using System.Collections.Generic;
using UnityEngine;

namespace BaseGames.Core.Events
{
    /// <summary>
    /// 单条订阅的 Disposable 句柄。Dispose() 自动取消注册。
    /// </summary>
    public readonly struct EventSubscription : IDisposable
    {
        private readonly Action _unsubscribe;

        public EventSubscription(Action unsubscribe)
            => _unsubscribe = unsubscribe;

        public void Dispose() => _unsubscribe?.Invoke();
    }

    /// <summary>
    /// 批量管理多条订阅，统一在 Dispose / Clear 时取消所有注册。
    /// 用法：OnEnable 调用 Subscribe，OnDisable 调用 Clear。
    /// </summary>
    public sealed class CompositeDisposable : IDisposable
    {
        private readonly List<IDisposable> _items = new();

        public void Add(IDisposable item) => _items.Add(item);

        public void Clear()
        {
            foreach (var item in _items) item.Dispose();
            _items.Clear();
        }

        public void Dispose() => Clear();
    }

    /// <summary>
    /// <see cref="EventSubscription"/> 扩展方法（架构 02 §8）。
    /// </summary>
    public static class EventSubscriptionExtensions
    {
        /// <summary>
        /// 将订阅句柄添加到集合中，统一生命周期管理。
        /// 用法：channel.Subscribe(Handler).AddTo(_subscriptions);
        /// </summary>
        public static EventSubscription AddTo(this EventSubscription subscription,
            ICollection<IDisposable> collection)
        {
            collection.Add(subscription);
            return subscription;
        }

        /// <summary>
        /// 将订阅句柄添加到 <see cref="CompositeDisposable"/> 中。
        /// </summary>
        public static EventSubscription AddTo(this EventSubscription subscription,
            CompositeDisposable compositeDisposable)
        {
            compositeDisposable.Add(subscription);
            return subscription;
        }
    }
}