using System;
using Chernobyl.Input.Controls;
using Chernobyl.Utility;

namespace Chernobyl.Interface.Input
{
    /// <summary>
    /// An <see cref="IControl"/> that provides interface control using an
    /// <see cref="IMouse"/>.
    /// </summary>
    public class MousePointerControl : IPointerControl
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="MousePointerControl"/> class.
        /// </summary>
        /// <param name="mouse">The instance that provides the interface control.</param>
        public MousePointerControl(IMouse mouse)
        {
            Mouse = mouse;
        }

        /// <summary>
        /// An event that is raised each time the control mechanism is pressed
        /// down. This mechanism can only be <see cref="PressedDown"/> once per
        /// mechanism's pointer. The mechanism must raise
        /// <see cref="LetUp"/> for a pointer prior to that pointer raising
        /// <see cref="PressedDown"/> again. For example, a mouse can only raise
        /// <see cref="PressedDown"/> once and then it must raise <see cref="LetUp"/>
        /// to allow <see cref="PressedDown"/> to be raised. A touch screen on
        /// the other hand can invoke <see cref="PressedDown"/> for each finger
        /// that touches the screen but must invoke <see cref="LetUp"/> for each
        /// finger.
        /// </summary>
        public event EventHandler<PointerEventArgs> PressedDown;

        /// <summary>
        /// An event that is raised each time the control mechanism is let up.
        /// See <see cref="PressedDown"/> for more information on this topic.
        /// </summary>
        public event EventHandler<PointerEventArgs> LetUp;

        /// <summary>
        /// The instance that provides the interface control.
        /// </summary>
        public IMouse Mouse
        {
            get { return _mouse; }
            private set
            {
                value.ThrowIfNull("value");
                IMouse previousValue = _mouse;
                _mouse = value;

                if(previousValue != null)
                {
                    previousValue.LeftButton.OnDown -= MouseLeftButtonOnDown;
                    previousValue.LeftButton.OnUp -= MouseLeftButtonOnUp;
                }

                if(_mouse != null)
                {
                    _mouse.LeftButton.OnDown += MouseLeftButtonOnDown;
                    _mouse.LeftButton.OnUp += MouseLeftButtonOnUp;
                }
            }
        }

        /// <summary>
        /// An event handler that is invoked when the 
        /// <see cref="IMouse.LeftButton"/> of <see cref="Mouse"/> has been let 
        /// up. This method raises the <see cref="LetUp"/> event on this instance.
        /// </summary>
        /// <param name="sender">The instance that generated the event.</param>
        /// <param name="e">The <see cref="EventArgs"/> instance containing the 
        /// event data.</param>
        void MouseLeftButtonOnUp(object sender, EventArgs e)
        {
            if(LetUp != null)
                LetUp(this, new PointerEventArgs(_mouse));
        }

        /// <summary>
        /// An event handler that is invoked when the 
        /// <see cref="IMouse.LeftButton"/> of <see cref="Mouse"/> has been  
        /// pressed down. This method raises the <see cref="PressedDown"/> event
        /// on this instance.
        /// </summary>
        /// <param name="sender">The instance that generated the event.</param>
        /// <param name="e">The <see cref="EventArgs"/> instance containing the
        /// event data.</param>
        void MouseLeftButtonOnDown(object sender, EventArgs e)
        {
            if(PressedDown != null)
                PressedDown(this, new PointerEventArgs(_mouse));
        }

        /// <summary>
        /// The backing field to <see cref="Mouse"/>.
        /// </summary>
        IMouse _mouse;
    }
}