using System;

namespace Unosquare.Swan.Components {
  /// <summary>
  /// Base class for messages that provides weak reference storage of the sender.
  /// </summary>
  public abstract class MessageHubMessageBase
      : IMessageHubMessage {
    /// <summary>
    /// Store a WeakReference to the sender just in case anyone is daft enough to
    /// keep the message around and prevent the sender from being collected.
    /// </summary>
    private readonly WeakReference _sender;

    /// <summary>
    /// Initializes a new instance of the <see cref="MessageHubMessageBase"/> class.
    /// </summary>
    /// <param name="sender">The sender.</param>
    /// <exception cref="System.ArgumentNullException">sender.</exception>
    protected MessageHubMessageBase(Object sender) {
      if(sender == null) {
        throw new ArgumentNullException(nameof(sender));
      }

      this._sender = new WeakReference(sender);
    }

    /// <summary>
    /// The sender of the message, or null if not supported by the message implementation.
    /// </summary>
    public Object Sender => this._sender?.Target;
  }

  /// <summary>
  /// Generic message with user specified content.
  /// </summary>
  /// <typeparam name="TContent">Content type to store.</typeparam>
  public class MessageHubGenericMessage<TContent>
      : MessageHubMessageBase {
    /// <summary>
    /// Initializes a new instance of the <see cref="MessageHubGenericMessage{TContent}"/> class.
    /// </summary>
    /// <param name="sender">The sender.</param>
    /// <param name="content">The content.</param>
    public MessageHubGenericMessage(Object sender, TContent content)
        : base(sender) => this.Content = content;

    /// <summary>
    /// Contents of the message.
    /// </summary>
    public TContent Content {
      get; protected set;
    }
  }
}