void Scrollbar::startTimerIfNeeded(double delay)
{
    // Don't do anything for the thumb.
    if (m_pressedPart == ThumbPart)
        return;

    // Handle the track.  We halt track scrolling once the thumb is level
    // with us.
    if ((m_pressedPart == BackTrackPart || m_pressedPart == ForwardTrackPart) && thumbUnderMouse(this)) {
        theme()->invalidatePart(this, m_pressedPart);
        setHoveredPart(ThumbPart);
        return;
    }

    // We can't scroll if we've hit the beginning or end.
    ScrollDirection dir = pressedPartScrollDirection();
    if (dir == ScrollUp || dir == ScrollLeft) {
        if (m_currentPos == 0)
            return;
    } else {
        if (m_currentPos == maximum())
            return;
    }

    m_scrollTimer.startOneShot(delay);
}

bool Scrollbar::mouseDown(const PlatformMouseEvent& evt)
{
    // Early exit for right click
    if (evt.button() == RightButton)
        return true; // FIXME: Handled as context menu by Qt right now.  Should just avoid even calling this method on a right click though.

    setPressedPart(theme()->hitTest(this, evt));
    int pressedPos = (orientation() == HorizontalScrollbar ? convertFromContainingWindow(evt.pos()).x() : convertFromContainingWindow(evt.pos()).y());
    
    if ((m_pressedPart == BackTrackPart || m_pressedPart == ForwardTrackPart) && theme()->shouldCenterOnThumb(this, evt)) {
        setHoveredPart(ThumbPart);
        setPressedPart(ThumbPart);
        m_dragOrigin = m_currentPos;
        int thumbLen = theme()->thumbLength(this);
        int desiredPos = pressedPos;
        // Set the pressed position to the middle of the thumb so that when we do the move, the delta
        // will be from the current pixel position of the thumb to the new desired position for the thumb.
        m_pressedPos = theme()->trackPosition(this) + theme()->thumbPosition(this) + thumbLen / 2;
        moveThumb(desiredPos);
        return true;
    } else if (m_pressedPart == ThumbPart)
        m_dragOrigin = m_currentPos;
    
    m_pressedPos = pressedPos;

    autoscrollPressedPart(theme()->initialAutoscrollTimerDelay());
    return true;
}

bool Scrollbar::mouseDown(const PlatformMouseEvent& evt)
{
    ScrollbarPart pressedPart = theme().hitTest(*this, evt.position());
    auto action = theme().handleMousePressEvent(*this, evt, pressedPart);
    if (action == ScrollbarButtonPressAction::None)
        return true;

    m_scrollableArea.mouseIsDownInScrollbar(this, true);
    setPressedPart(pressedPart);

    int pressedPosition = (orientation() == HorizontalScrollbar ? convertFromContainingWindow(evt.position()).x() : convertFromContainingWindow(evt.position()).y());
    if (action == ScrollbarButtonPressAction::CenterOnThumb) {
        setHoveredPart(ThumbPart);
        setPressedPart(ThumbPart);
        m_dragOrigin = m_currentPos;
        // Set the pressed position to the middle of the thumb so that when we do the move, the delta
        // will be from the current pixel position of the thumb to the new desired position for the thumb.
        m_pressedPos = theme().trackPosition(*this) + theme().thumbPosition(*this) + theme().thumbLength(*this) / 2;
        moveThumb(pressedPosition);
        return true;
    }

    m_pressedPos = pressedPosition;

    if (action == ScrollbarButtonPressAction::StartDrag)
        m_dragOrigin = m_currentPos;

    if (action == ScrollbarButtonPressAction::Scroll)
        autoscrollPressedPart(theme().initialAutoscrollTimerDelay());

    return true;
}

bool Scrollbar::mouseExited()
{
    if (m_scrollableArea)
        m_scrollableArea->mouseExitedScrollbar(this);
    setHoveredPart(NoPart);
    return true;
}

void Scrollbar::mouseMoved(const PlatformMouseEvent& evt)
{
    if (m_pressedPart == ThumbPart) {
        moveThumb(m_orientation == HorizontalScrollbar ?
                  convertFromContainingView(evt.position()).x() :
                  convertFromContainingView(evt.position()).y());
        return;
    }

    if (m_pressedPart != NoPart)
        m_pressedPos = orientation() == HorizontalScrollbar ? convertFromContainingView(evt.position()).x() : convertFromContainingView(evt.position()).y();

    // FIXME(sky): Cleanup this code now that part is always NoPart.
    ScrollbarPart part = NoPart;
    if (part != m_hoveredPart) {
        if (m_pressedPart != NoPart) {
            if (part == m_pressedPart) {
                // The mouse is moving back over the pressed part.  We
                // need to start up the timer action again.
                startTimerIfNeeded(autoscrollTimerDelay());
                invalidatePart(m_pressedPart);
            } else if (m_hoveredPart == m_pressedPart) {
                // The mouse is leaving the pressed part.  Kill our timer
                // if needed.
                stopTimerIfNeeded();
                invalidatePart(m_pressedPart);
            }
        }

        setHoveredPart(part);
    }

    return;
}

void Scrollbar::autoscrollPressedPart(double delay)
{
    // Don't do anything for the thumb or if nothing was pressed.
    if (m_pressedPart == ThumbPart || m_pressedPart == NoPart)
        return;

    // Handle the track.
    if ((m_pressedPart == BackTrackPart || m_pressedPart == ForwardTrackPart) && thumbWillBeUnderMouse()) {
        setHoveredPart(ThumbPart);
        return;
    }

    // Handle the arrows and track.
    if (m_scrollableArea && m_scrollableArea->userScroll(pressedPartScrollGranularity(), toScrollDelta(pressedPartScrollDirectionPhysical(), 1)).didScroll())
        startTimerIfNeeded(delay);
}

bool Scrollbar::mouseMoved(const PlatformMouseEvent& evt)
{
    if (m_pressedPart == ThumbPart) {
        if (theme()->shouldSnapBackToDragOrigin(this, evt)) {
            if (m_scrollableArea)
                m_scrollableArea->scrollToOffsetWithoutAnimation(m_orientation, m_dragOrigin);
        } else {
            moveThumb(m_orientation == HorizontalScrollbar ? 
                      convertFromContainingWindow(evt.pos()).x() :
                      convertFromContainingWindow(evt.pos()).y(), theme()->shouldDragDocumentInsteadOfThumb(this, evt));
        }
        return true;
    }

    if (m_pressedPart != NoPart)
        m_pressedPos = (orientation() == HorizontalScrollbar ? convertFromContainingWindow(evt.pos()).x() : convertFromContainingWindow(evt.pos()).y());

    ScrollbarPart part = theme()->hitTest(this, evt);    
    if (part != m_hoveredPart) {
        if (m_pressedPart != NoPart) {
            if (part == m_pressedPart) {
                // The mouse is moving back over the pressed part.  We
                // need to start up the timer action again.
                startTimerIfNeeded(theme()->autoscrollTimerDelay());
                theme()->invalidatePart(this, m_pressedPart);
            } else if (m_hoveredPart == m_pressedPart) {
                // The mouse is leaving the pressed part.  Kill our timer
                // if needed.
                stopTimerIfNeeded();
                theme()->invalidatePart(this, m_pressedPart);
            }
        } 
        
        setHoveredPart(part);
    } 

    return true;
}

bool Scrollbar::mouseExited()
{
    setHoveredPart(NoPart);
    return true;
}

void Scrollbar::mouseExited()
{
    if (m_scrollableArea)
        m_scrollableArea->mouseExitedScrollbar(this);
    setHoveredPart(NoPart);
}