using System.Drawing;
using System.Windows.Forms;

namespace WeifenLuo.WinFormsUI.Docking {
  partial class DockPanel {
    /// <summary>
    /// DragHandlerBase is the base class for drag handlers. The derived class should:
    ///   1. Define its public method BeginDrag. From within this public BeginDrag method,
    ///      DragHandlerBase.BeginDrag should be called to initialize the mouse capture
    ///      and message filtering.
    ///   2. Override the OnDragging and OnEndDrag methods.
    /// </summary>
    private abstract class DragHandlerBase : NativeWindow, IMessageFilter {
      protected DragHandlerBase() {
      }

      protected abstract Control DragControl {
        get;
      }

      private Point m_startMousePosition = Point.Empty;
      protected Point StartMousePosition {
        get { return m_startMousePosition; }
        private set { m_startMousePosition = value; }
      }

      protected bool BeginDrag() {
        // Avoid re-entrance;
        lock (this) {
          if (DragControl == null)
            return false;

          StartMousePosition = Control.MousePosition;

          if (!NativeMethods.DragDetect(DragControl.Handle, StartMousePosition))
            return false;

          DragControl.FindForm().Capture = true;
          AssignHandle(DragControl.FindForm().Handle);
          Application.AddMessageFilter(this);
          return true;
        }
      }

      protected abstract void OnDragging();

      protected abstract void OnEndDrag(bool abort);

      private void EndDrag(bool abort) {
        ReleaseHandle();
        Application.RemoveMessageFilter(this);
        DragControl.FindForm().Capture = false;

        OnEndDrag(abort);
      }

      bool IMessageFilter.PreFilterMessage(ref Message m) {
        if (m.Msg == (int)Win32.Msgs.WM_MOUSEMOVE)
          OnDragging();
        else if (m.Msg == (int)Win32.Msgs.WM_LBUTTONUP)
          EndDrag(false);
        else if (m.Msg == (int)Win32.Msgs.WM_CAPTURECHANGED)
          EndDrag(true);
        else if (m.Msg == (int)Win32.Msgs.WM_KEYDOWN && (int)m.WParam == (int)Keys.Escape)
          EndDrag(true);

        return OnPreFilterMessage(ref m);
      }

      protected virtual bool OnPreFilterMessage(ref Message m) {
        return false;
      }

      protected sealed override void WndProc(ref Message m) {
        if (m.Msg == (int)Win32.Msgs.WM_CANCELMODE || m.Msg == (int)Win32.Msgs.WM_CAPTURECHANGED)
          EndDrag(true);

        base.WndProc(ref m);
      }
    }

    private abstract class DragHandler : DragHandlerBase {
      private DockPanel m_dockPanel;

      protected DragHandler(DockPanel dockPanel) {
        m_dockPanel = dockPanel;
      }

      public DockPanel DockPanel {
        get { return m_dockPanel; }
      }

      private IDragSource m_dragSource;
      protected IDragSource DragSource {
        get { return m_dragSource; }
        set { m_dragSource = value; }
      }

      protected sealed override Control DragControl {
        get { return DragSource == null ? null : DragSource.DragControl; }
      }

      protected sealed override bool OnPreFilterMessage(ref Message m) {
        if ((m.Msg == (int)Win32.Msgs.WM_KEYDOWN || m.Msg == (int)Win32.Msgs.WM_KEYUP) &&
            ((int)m.WParam == (int)Keys.ControlKey || (int)m.WParam == (int)Keys.ShiftKey))
          OnDragging();

        return base.OnPreFilterMessage(ref m);
      }
    }
  }
}