/Samples/DragDrop/DragDrop.Model/CookieJar.cs

using System.Collections.Generic;

using System.ComponentModel;

using System.Linq;

using System.Windows;

using SharpFellows.Toolkit.Behaviours;



namespace DragDrop.Model

{

    /// <summary>

    /// Container for cookies 

    /// </summary>

    public class CookieJar : INotifyPropertyChanged

    {

        #region Constants

        private const int INITIAL_NUMBER_OF_COOKIES = 5;

        private const int JAR_CAPACITY = 10;

        #endregion



        #region Fields



        private readonly Stack<Cookie> _cookies = new Stack<Cookie>(JAR_CAPACITY);

        private IDragSource _source;

        private IDropTarget _target;



        #endregion



        /// <summary>

        /// Occurs when a property value changes.

        /// </summary>

        public event PropertyChangedEventHandler PropertyChanged;



        /// <summary>

        /// Initializes a new instance of the <see cref="CookieJar"/> class.

        /// </summary>

        /// <param name="numberOfCookies">The number of cookies to be placed in the jar</param>

        public CookieJar(int numberOfCookies)

        {

            for (int i = 0; i < numberOfCookies; i++)

                _cookies.Push(new Cookie { Jar = this });            

        }



        /// <summary>

        /// Initializes a new instance of the <see cref="CookieJar"/> class.

        /// </summary>

        public CookieJar() : this(INITIAL_NUMBER_OF_COOKIES)

        {

        }



        /// <summary>

        /// Gets the (drag) source of cookies.

        /// </summary>

        /// <value>The source of cookies.</value>

        public IDragSource SourceOfCookies

        {

            get

            {

                if (_source == null)

                    _source = new DragSource<CookieJar>(GetDragEffects, GetData);



                return _source;

            }

        }



        /// <summary>

        /// Gets the drop target for cookies.

        /// </summary>

        /// <value>The cookie sink.</value>

        public IDropTarget CookieSink

        {

            get

            {

                if (_target == null)

                    _target = new DropTarget<Cookie>(GetDropEffects, Drop);



                return _target;

            }

        }



        /// <summary>

        /// Gets the number of cookies in the jar.

        /// </summary>

        /// <value>The number of cookies.</value>

        public int NumberOfCookies

        {

            get

            {

                return _cookies.Count;

            }

        }



        private DragDropEffects GetDragEffects(CookieJar jar)

        {

            // Only allow the drag and drop to start if we have any cookies

            return _cookies.Any() ? DragDropEffects.Move : DragDropEffects.None;

        }



        private object GetData(CookieJar jar)

        {

            return _cookies.Peek();

        }



        private void Drop(Cookie cookie)

        {

            AddCookie(cookie);

            RaisePropertyChangedEvent("NumberOfCookies");

        }



        private void AddCookie(Cookie cookie)

        {

            cookie.Jar.PopOne();

            _cookies.Push(cookie);

            cookie.Jar = this;

        }



        private void PopOne()

        {

            _cookies.Pop();

            RaisePropertyChangedEvent("NumberOfCookies");

        }



        private DragDropEffects GetDropEffects(Cookie cookie)

        {

            // Do not allow our own cookies

            if (cookie.Jar == this)

                return DragDropEffects.None;

            // The cookie can be dropped if we are not exceeding the capacity of the jar

            return _cookies.Count >= JAR_CAPACITY ? DragDropEffects.None : DragDropEffects.Move;

        }



        public void RaisePropertyChangedEvent(string propertyName)

        {

            PropertyChangedEventHandler handler = PropertyChanged;



            if (handler != null)

                handler(this, new PropertyChangedEventArgs(propertyName));

        }

    }

}