// 摘自 MediatR 14.2.0 的 Mediator.cs，仅保留通知功能。
 // 许可声明与修改记录见 LICENSE.md 和 UPSTREAM.md。
 using System.Collections.Concurrent;
 using MAX.Notification.NotificationPublishers;
 using MAX.Notification.Wrappers;

 namespace MAX.Notification;

 public class NotificationPublisher : IPublisher
 {
     private readonly IServiceProvider _serviceProvider;
     private readonly INotificationPublisher _publisher;
     private static readonly ConcurrentDictionary<Type, NotificationHandlerWrapper> _notificationHandlers = new();

     public NotificationPublisher(IServiceProvider serviceProvider)
         : this(serviceProvider, new ForeachAwaitPublisher()) { }

     public NotificationPublisher(IServiceProvider serviceProvider, INotificationPublisher publisher)
     {
         ArgumentNullException.ThrowIfNull(serviceProvider);
         ArgumentNullException.ThrowIfNull(publisher);
         _serviceProvider = serviceProvider;
         _publisher = publisher;
     }
    public Task Publish<TNotification>(TNotification notification, CancellationToken cancellationToken = default)
        where TNotification : INotification
    {
        if (notification == null)
        {
            throw new ArgumentNullException(nameof(notification));
        }

        return PublishNotification(notification, cancellationToken);
    }

    public Task Publish(object notification, CancellationToken cancellationToken = default) =>
        notification switch
        {
            null => throw new ArgumentNullException(nameof(notification)),
            INotification instance => PublishNotification(instance, cancellationToken),
            _ => throw new ArgumentException($"{nameof(notification)} does not implement ${nameof(INotification)}")
        };

    /// <summary>
    /// 在派生类中重写此方法可控制任务的等待方式。默认调用 <see cref="INotificationPublisher"/>。
    /// </summary>
    /// <param name="handlerExecutors">封装各通知处理器实例及其调用委托的执行器集合。</param>
    /// <param name="notification">要发布的通知。</param>
    /// <param name="cancellationToken">取消令牌。</param>
    /// <returns>表示本次处理器分发操作的任务。</returns>
    protected virtual Task PublishCore(IEnumerable<NotificationHandlerExecutor> handlerExecutors, INotification notification, CancellationToken cancellationToken) 
        => _publisher.Publish(handlerExecutors, notification, cancellationToken);

    private Task PublishNotification(INotification notification, CancellationToken cancellationToken = default)
    {
        var handler = _notificationHandlers.GetOrAdd(notification.GetType(), static notificationType =>
        {
            var wrapperType = typeof(NotificationHandlerWrapperImpl<>).MakeGenericType(notificationType);
            var wrapper = Activator.CreateInstance(wrapperType) ?? throw new InvalidOperationException($"Could not create wrapper for type {notificationType}");
            return (NotificationHandlerWrapper)wrapper;
        });

        return handler.Handle(notification, _serviceProvider, PublishCore, cancellationToken);
    }


}