using System;
#if NETSTANDARD1_3
using System.Reflection;
#endif

namespace Unosquare.Swan.Components {


  /// <summary>
  /// Represents an active subscription to a message.
  /// </summary>
  public sealed class MessageHubSubscriptionToken
      : IDisposable {
    private readonly WeakReference _hub;
    private readonly Type _messageType;

    /// <summary>
    /// Initializes a new instance of the <see cref="MessageHubSubscriptionToken"/> class.
    /// </summary>
    /// <param name="hub">The hub.</param>
    /// <param name="messageType">Type of the message.</param>
    /// <exception cref="System.ArgumentNullException">hub.</exception>
    /// <exception cref="System.ArgumentOutOfRangeException">messageType.</exception>
    public MessageHubSubscriptionToken(IMessageHub hub, Type messageType) {
      if(hub == null) {
        throw new ArgumentNullException(nameof(hub));
      }

      if(!typeof(IMessageHubMessage).IsAssignableFrom(messageType)) {
        throw new ArgumentOutOfRangeException(nameof(messageType));
      }

      this._hub = new WeakReference(hub);
      this._messageType = messageType;
    }

    /// <inheritdoc />
    public void Dispose() {
      if(this._hub.IsAlive && this._hub.Target is IMessageHub hub) {
        System.Reflection.MethodInfo unsubscribeMethod = typeof(IMessageHub).GetMethod(nameof(IMessageHub.Unsubscribe),
            new[] { typeof(MessageHubSubscriptionToken) });
        unsubscribeMethod = unsubscribeMethod.MakeGenericMethod(this._messageType);
        _ = unsubscribeMethod.Invoke(hub, new Object[] { this });
      }

      GC.SuppressFinalize(this);
    }
  }
}