using Chernobyl.Collections.Generic.Event;
using Chernobyl.DesignPatterns.Extension;
using Chernobyl.Game;

namespace Chernobyl.Interface.Game.StateMachine
{
    /// <summary>
    /// An <see cref="IExtension{TExtended}"/> that, when attached to an
    /// <see cref="IGame"/>, displays itself when that <see cref="IGame"/> enters
    /// into its paused state.
    /// </summary>
    public class PauseScreen : StateScreen
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="PauseScreen"/> class.
        /// </summary>
        /// <param name="services">The root <see cref="IEventCollection{T}"/> 
        /// instance that gives and takes services.</param>
        /// <param name="extended">The instance whose pause state is to be
        /// rendered to the screen.</param>
        public PauseScreen(IEventCollection<object> services, IGame extended)
            : base(services)
        {
            _services = services;
            Extended = extended;
        }

        /// <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(IGame extended)
        {
            extended.OfType<IEnableable>(service => PausedEnableable = service);
        }

        /// <summary>
        /// Removes this extension 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(IGame extended)
        {
            PausedEnableable = null;
        }

        /// <summary>
        /// The <see cref="IEnableable"/> instance retrieved from the extended
        /// <see cref="IGame"/> instance that indicates whether the 
        /// <see cref="IGame"/> is paused or not.
        /// </summary>
        IEnableable PausedEnableable
        {
            get { return _pausedEnableable; }
            set
            {
                IEnableable previousValue = _pausedEnableable;
                _pausedEnableable = value;

                if (previousValue != null)
                {
                    previousValue.Enabled.Entered -= OnOffDrawable.Enable;
                    previousValue.Enabled.Left -= OnOffDrawable.Disable;
                }

                if (_pausedEnableable != null)
                {
                    _pausedEnableable.Enabled.Entered += OnOffDrawable.Enable;
                    _pausedEnableable.Enabled.Left += OnOffDrawable.Disable;
                }
            }
        }

        /// <summary>
        /// The root <see cref="IEventCollection{T}"/> instance that gives and 
        /// takes services.
        /// </summary>
        IEventCollection<object> _services;

        /// <summary>
        /// The backing field to <see cref="PausedEnableable"/>.
        /// </summary>
        IEnableable _pausedEnableable;
    }
}