namespace GalaSoft.MvvmLight.Messaging
{
    using System;

    /// <summary>
    /// Use this class to send a message when the busy state of an application changes.
    /// </summary>
    public class BusyMessage : MessageBase
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="BusyMessage"/> class.
        /// </summary>
        /// <param name="isBusy"><b>true</b> if the application is busy; otherwise, <b>false</b>.</param>
        /// <param name="userState">Optional. User state information to include with the message.</param>
        public BusyMessage(bool isBusy, object userState)
            : this(isBusy, userState, null)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="BusyMessage"/> class.
        /// </summary>
        /// <param name="isBusy"><b>true</b> if the application is busy; otherwise, <b>false</b>.</param>
        /// <param name="userState">Optional. User state information to include with the message.</param>
        /// <param name="sender">Optional. The message's original sender.</param>
        public BusyMessage(bool isBusy, object userState, object sender)
            : base(sender)
        {
            this.IsBusy = isBusy;
            this.UserState = userState;
        }

        /// <summary>
        /// Gets a value indicating whether the application is currently in a busy state.
        /// </summary>
        public bool IsBusy { get; private set; }
        
        /// <summary>
        /// Gets user state information to include with the message.
        /// </summary>
        public object UserState { get; private set; }
    }

}

namespace GalaSoft.MvvmLight.Threading
{
    using System;
    using System.Threading;
    using GalaSoft.MvvmLight.Messaging;

    /// <summary>
    /// Provides a thread-safe controller for managing the busy state of the application.
    /// </summary>
    public class BusyController : GalaSoft.MvvmLight.ObservableObject
    {
        private readonly object SyncRoot = new object();
        private int count;

        /// <summary>
        /// Initializes static members of the <see cref="BusyController"/> class.
        /// </summary>
        static BusyController()
        {
            _default = new BusyController();
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="BusyController"/> class.
        /// </summary>
        public BusyController()
            : this(Messenger.Default)
        {
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="BusyController"/> class.
        /// </summary>
        /// <param name="messenger">Optional. An <see cref="IMessenger"/> which will be used to send messages.</param>
        public BusyController(IMessenger messenger)
        {
            this.MessengerInstance = messenger;
        }

        private static BusyController _default;

        /// <summary>
        /// Gets the default busy controller instance.
        /// </summary>
        public static BusyController Default
        {
            get
            {
                return _default;
            }
        }

        private bool _isBusy;

        /// <summary>
        /// Gets a value indicating whether the controller is currently in the busy state.
        /// </summary>
        public bool IsBusy
        {
            get
            {
                return this._isBusy;
            }

            private set
            {
                if (this._isBusy != value)
                {
                    this._isBusy = value;
                    this.RaisePropertyChanged(() => this.IsBusy);
                }
            }
        }

        private IMessenger _messengerInstance;

        /// <summary>
        /// Gets the messenger instance used by the controller.
        /// </summary>
        protected IMessenger MessengerInstance
        {
            get
            {
                return this._messengerInstance;
            }

            set
            {
                if (this._messengerInstance != value)
                {
                    this._messengerInstance = value;
                    this.RaisePropertyChanged(() => this.MessengerInstance);
                }
            }
        }

        /// <summary>
        /// Resets the controller.
        /// </summary>
        public void Reset()
        {
            lock (this.SyncRoot)
            {
                this.IsBusy = false;
                this.count = 0;

                if (this.MessengerInstance != null)
                {
                    // Send the message indicating that the controller is no longer busy.
                    this.MessengerInstance.Send<BusyMessage>(new BusyMessage(this.IsBusy, null));
                }
            }
        }

        /// <summary>
        /// Sends the message.
        /// </summary>
        /// <param name="value"><b>true</b> if the application is busy; otherwise, <b>false</b> when the application is no longer busy.</param>        
        public void SendMessage(bool value)
        {
            this.SendMessage(value, null);
        }

        /// <summary>
        /// Sends the message.
        /// </summary>
        /// <param name="value"><b>true</b> if the application is busy; otherwise, <b>false</b> when the application is no longer busy.</param>
        /// <param name="state">Optional. User state data to include with the message if the controller transitions between busy states.</param>
        public void SendMessage(bool value, object userState)
        {
            lock (this.SyncRoot)
            {
                bool send = false;

                if (value)
                {
                    Interlocked.Increment(ref this.count);

                    if (this.count == 1)
                    {
                        this.IsBusy = true;

                        // The controller is now busy, send the message.
                        send = true;
                    }
                }
                else
                {
                    if (this.count > 0)
                    {
                        Interlocked.Decrement(ref this.count);

                        if (this.count == 0)
                        {
                            this.IsBusy = false;

                            // The controller is no longer busy, send the message.
                            send = true;
                        }
                    }
                }

                if (send && this.MessengerInstance != null)
                {
                    this.MessengerInstance.Send<BusyMessage>(new BusyMessage(this.IsBusy, userState, this));
                }
            }            
        }
    }
}