using System;
using System.Reflection;
using System.Windows.Forms;
using JD.Kernel.StaticHelpers;

namespace JD.Threading.Dispatch
{
    /// <summary>
    /// Must be created on the destination UI thread to work.
    /// </summary>

    internal class WindowsFormsThreadDispatchStrategy : IThreadDispatchStrategy
    {
        #region Variables

        private readonly Control m_control;

        #endregion

        #region Constructor

        public WindowsFormsThreadDispatchStrategy()
        {
            // WindowsFormsSynchronizationContext manages a special control that is always available for marshalling
            // Works around limitations of normal Control.Invoke (never knowing when the control is going to be disposed)
            // Sadly, it's not publicly available so we use reflection to get to it
            WindowsFormsSynchronizationContext syncContext = new WindowsFormsSynchronizationContext();
            m_control = (Control)syncContext.GetType().GetField("controlToSendTo", BindingFlags.Instance | BindingFlags.NonPublic).GetValue(syncContext);
            Throw.InvalidOperationIf(m_control == null, "Could not create WindowsFormsThreadDispatchStrategy");
        }

        #endregion

        #region Properties

        public bool InvokeRequired
        {
            get
            {
                return m_control.InvokeRequired;
            }
        }

        bool IThreadDispatchStrategy.LongOperationInvokeRequired
        {
            get { return InvokeRequired; }
        }

        #endregion

        #region Methods

        public void Dispatch(System.Action action)
        {
            if (InvokeRequired)
            {
                DoControlInvoke(action);
            }
            else
            {
                action();
            }
        }

        public void DispatchAsync(System.Action action, bool forceAsync)
        {
            if (InvokeRequired || forceAsync)
            {
                m_control.BeginInvoke(action);
            }
            else
            {
                action();
            }
        }

        public void DoLongOperation(System.Action action)
        {
            Dispatch(action);
        }

        public void DoLongOperationAsync(System.Action action)
        {
            DispatchAsync(action, false);
        }

        private void DoControlInvoke(System.Action action)
        {
            Exception ex = null;
            m_control.Invoke(new System.Action(() =>
            {
                try
                {
                    action();
                }
                catch (Exception e)
                {
                    ex = e;
                }
            }));

            if (ex != null)
            {
                throw new Exception("An exception occurred while invoking an action on the UI thread", ex);
            }
        }

        #endregion
    }
}