using System;
using System.Collections.Generic;

namespace Chernobyl.DesignPatterns.Extension
{
    /// <summary>
    /// An <see cref="IExtension{TExtended}"/> that takes a list of 
    /// <see cref="IExtension{TExtended}"/> and attaches them to 
    /// another instance of some type specified by the 
    /// <typeparamref name="ExtendedType"/> generic argument. The instance to be 
    /// extended is received through the <see cref="AttachTo"/> method. 
    /// Basically, this class attaches and detaches extensions from a single 
    /// instance when requested by either an event (using the 
    /// <see cref="Attach(object, EventArgs)"/>) or just a method (using the 
    /// <see cref="Attach()"/>) method. When <see cref="Detach()"/> or 
    /// <see cref="Detach(object, EventArgs)"/> is called, this class detaches
    /// all of the extensions from the extended instance.
    /// </summary>
    /// <typeparam name="ExtendedType">The type of the instance that will be 
    /// extended. Note that, this instance must be reference type.</typeparam>
    public class Extender<ExtendedType> : Extension<ExtendedType> where ExtendedType : class
    {
        /// <summary>
        /// Constructor.
        /// </summary>
        /// <param name="extensions">The extensions to attach and detach to/from  
        /// the <typeparamref name="ExtendedType"/> when requested by 
        /// <see cref="Attach()"/> or <see cref="Attach(object, EventArgs)"/>
        /// (for attaching) and <see cref="Detach()"/> or 
        /// <see cref="Detach(object, EventArgs)"/> (for detaching).</param>
        public Extender(List<IExtension<ExtendedType>> extensions)
        {
            Extensions = extensions;
        }

        /// <summary>
        /// When invoked, this method will attach all the extensions in 
        /// <see cref="Extensions"/> to the extended object received in the 
        /// <see cref="AttachTo"/> method.
        /// </summary>
        public void Attach()
        {
            ExtendedType extended = Extended;
            foreach (IExtension<ExtendedType> extension in Extensions)
                extension.Extended = extended;
        }

        /// <summary>
        /// An event handler that can be attached to an event. When invoked, this
        /// method will attach all the extensions in <see cref="Extensions"/> to
        /// the extended object received in the <see cref="AttachTo"/> method.
        /// </summary>
        /// <param name="sender">The sender of the event.</param>
        /// <param name="e">The event's arguments.</param>
        public void Attach(object sender, EventArgs e)
        {
            Attach();
        }

        /// <summary>
        /// When invoked, this method will detach all the extensions in 
        /// <see cref="Extensions"/> from the extended object received in the 
        /// <see cref="AttachTo"/> method.
        /// </summary>
        public void Detach()
        {
            ExtendedType extended = Extended;
            foreach (IExtension<ExtendedType> extension in Extensions)
                extension.Extended = null;
        }

        /// <summary>
        /// An event handler that can be attached to an event. When invoked, this
        /// method will detach all the extensions in <see cref="Extensions"/> from
        /// the extended object received in the <see cref="AttachTo"/> method.
        /// </summary>
        /// <param name="sender">The sender of the event.</param>
        /// <param name="e">The event's arguments.</param>
        public void Detach(object sender, EventArgs e)
        {
            Detach();
        }

        /// <summary>
        /// Attaches this extension to the passed in object so that is can be
        /// extended.
        /// </summary>
        /// <param name="extended">The object to extend.</param>
        protected override void AttachTo(ExtendedType extended) { /*no-op*/ }

        /// <summary>
        /// Removes the decorator from an object so that it is no longer extended.
        /// </summary>
        /// <param name="extended">The object to remove the extension from.</param>
        protected override void DetachFrom(ExtendedType extended) { /*no-op*/ }

        /// <summary>
        /// The extensions to attach and detach to/from the 
        /// <typeparamref name="ExtendedType"/> when requested by 
        /// <see cref="Attach()"/> or <see cref="Attach(object, EventArgs)"/>
        /// (for attaching) and <see cref="Detach()"/> or 
        /// <see cref="Detach(object, EventArgs)"/> (for detaching).
        /// </summary>
        public List<IExtension<ExtendedType>> Extensions { get; private set; }
    }
}