/*
 * Copyright 2009, Alexandre Deckner, alex@zappotek.com
 * Distributed under the terms of the MIT License.
 */

/*!
        \class DragTrackingFilter
        \brief A simple mouse drag detection filter
        *
        * A simple mouse filter that detects the start of a mouse drag over a
        * threshold distance and sends a message with the 'what' field of your
        * choice. Especially useful for drag and drop.
        * Allows you to free your code of encumbering mouse tracking details.
        *
        * It can detect fast drags spanning outside of a small view by temporarily
        * setting the B_POINTER_EVENTS flag on the view.
*/

#include <DragTrackingFilter.h>

#include <Message.h>
#include <Messenger.h>
#include <View.h>

static const int kSquaredDragThreshold = 9;

DragTrackingFilter::DragTrackingFilter(BView* targetView, uint32 messageWhat)
        : BMessageFilter(B_ANY_DELIVERY, B_ANY_SOURCE),
        fTargetView(targetView),
        fMessageWhat(messageWhat),
        fIsTracking(false),
        fClickButtons(0)
{
}


filter_result
DragTrackingFilter::Filter(BMessage* message, BHandler** /*_target*/)
{
        if (fTargetView == NULL)
                return B_DISPATCH_MESSAGE;

        switch (message->what) {
                case B_MOUSE_DOWN:
                        message->FindPoint("where", &fClickPoint);
                        message->FindInt32("buttons", (int32*)&fClickButtons);
                        fIsTracking = true;

                        fTargetView->SetMouseEventMask(B_POINTER_EVENTS);

                        return B_DISPATCH_MESSAGE;

                case B_MOUSE_UP:
                        fIsTracking = false;
                        return B_DISPATCH_MESSAGE;

                case B_MOUSE_MOVED:
                {
                        BPoint where;
                        message->FindPoint("be:view_where", &where);

                        // TODO: be more flexible about buttons and pass their state
                        //               in the message
                        if (fIsTracking && (fClickButtons & B_PRIMARY_MOUSE_BUTTON)) {

                                BPoint delta(fClickPoint - where);
                                float squaredDelta = (delta.x * delta.x) + (delta.y * delta.y);

                                if (squaredDelta >= kSquaredDragThreshold) {
                                        BMessage dragClickMessage(fMessageWhat);
                                        dragClickMessage.AddPoint("be:view_where", fClickPoint);
                                                // name it "be:view_where" since BView::DragMessage
                                                // positions the dragging frame/bitmap by retrieving the
                                                // current message and reading that field
                                        BMessenger messenger(fTargetView);
                                        messenger.SendMessage(&dragClickMessage);

                                        fIsTracking = false;
                                }
                        }
                        return B_DISPATCH_MESSAGE;
                }
                default:
                        break;
        }

        return B_DISPATCH_MESSAGE;
}