using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Mail;
using System.Text;
using System.Threading.Tasks;

namespace Firebird2D.EventPipelines
{
    /// <summary>
    /// Eventpypeline which transports an event to every Subscyber
    /// </summary>
    /// <typeparam name="T">Event Arguments for the Pipeline event</typeparam>
    public class Pipeline <T> : I_Pipeline where T : EventArgs
    {
        /// <summary>
        /// Class witch owns the Pipeline and has the right to send events or delete the pipeline
        /// </summary>
        public object PipelineMaster { get; }

        //EventHandler to which the subscribers subribe.
        private event EventHandler<T>? OnEvent;

        /// <summary>
        /// Pipeline Constructor
        /// </summary>
        /// <param name="pipelineMaster">Every pipeline needs a Master which is able to send events or Destroy the pipeline</param>
        public Pipeline(object pipelineMaster)
        {
            PipelineMaster = pipelineMaster;
        }

        /// <summary>
        /// Check if no one subscribed to the event
        /// </summary>
        public bool IsEventEmpty { get {  return OnEvent != null; } }

        /// <summary>
        /// Subscribe to this event Pipeline
        /// </summary>
        /// <param name="handler">Handler witch should be Invoked when the event is send</param>
        public void Subscribe(Delegate handler)
        {
            OnEvent += (EventHandler<T>)handler;
        }

        /// <summary>
        /// Unsubscribe from this event Pipeline
        /// </summary>
        /// <param name="handler">Handler witch should be removed from the Pipeline</param>
        public void Unsubscribe(Delegate handler)
        {
            OnEvent -= (EventHandler<T>)handler;
        }

        /// <summary>
        /// Method to send an event through the pipeline
        /// </summary>
        /// <param name="sender">Sneder object must be Pipelinemaster or the Pipeline throws an exception</param>
        /// <param name="args">Arguments that should be sent</param>
        /// <exception cref="ArgumentNullException">Exception when sender or arguments ar null</exception>
        /// <exception cref="ArgumentException">Exception wehn Arguments are not equal the Pipeline type</exception>
        /// <exception cref="InvalidDataException">Exception when sender is not Pipeline master</exception>
        public void SendEvent(object sender, T args)
        {
            if (sender == null || args == null) throw new ArgumentNullException(nameof(sender));
            if (args is not T) throw new ArgumentException($"Invalid EventArgs type. Expected {typeof(T)}");
            if (sender.Equals(PipelineMaster)) throw new InvalidDataException("Only the pipeline master is allowed to send events through this pipeline.");

            OnEvent?.Invoke(sender, args);

        }
    }
}