/******************************************************************************
 * QSkinny - Copyright (C) 2016 Uwe Rathmann
 *           SPDX-License-Identifier: BSD-3-Clause
 *****************************************************************************/

#include "QskScrollBox.h"
#include "QskAnimationHint.h"
#include "QskEvent.h"
#include "QskFlickAnimator.h"
#include "QskGesture.h"
#include "QskPanGestureRecognizer.h"
#include "QskQuick.h"

QSK_QT_PRIVATE_BEGIN
#include <private/qquickwindow_p.h>
QSK_QT_PRIVATE_END

static inline constexpr qreal qskViewportPadding()
{
    return 10.0; // should be from the skin, TODO ...
}

static inline bool qskIsScrollable(
    const QskScrollBox* scrollBox, Qt::Orientations orientations )
{
    if ( orientations )
    {
        const QSizeF viewSize = scrollBox->viewContentsRect().size();
        const QSizeF& scrollableSize = scrollBox->scrollableSize();

        if ( orientations & Qt::Vertical )
        {
            if ( viewSize.height() < scrollableSize.height() )
                return true;
        }

        if ( orientations & Qt::Horizontal )
        {
            if ( viewSize.width() < scrollableSize.width() )
                return true;
        }
    }

    return false;
}

namespace
{
    class FlickAnimator final : public QskFlickAnimator
    {
      public:
        FlickAnimator()
        {
            // skin hints: TODO
            setDuration( 1000 );
            setEasingCurve( QEasingCurve::OutCubic );
        }

        void setScrollBox( QskScrollBox* scrollBox )
        {
            m_scrollBox = scrollBox;
        }

        void translate( qreal dx, qreal dy ) override
        {
            const QPointF pos = m_scrollBox->scrollPos();
            m_scrollBox->setScrollPos( pos - QPointF( dx, -dy ) );
        }

      private:
        QskScrollBox* m_scrollBox;
    };

    class ScrollAnimator final : public QskAnimator
    {
      public:
        ScrollAnimator()
            : m_scrollBox( nullptr )
        {
        }

        void setScrollBox( QskScrollBox* scrollBox )
        {
            m_scrollBox = scrollBox;
        }

        void scroll( const QPointF& from, const QPointF& to )
        {
            if ( isRunning() )
            {
                m_to = to;
                return;
            }

            if ( from == to || m_scrollBox == nullptr )
            {
                return;
            }

            m_from = from;
            m_to = to;

            const auto hint = m_scrollBox->flickHint();

            setDuration( hint.duration );
            setEasingCurve( hint.type );
            setWindow( m_scrollBox->window() );

            start();
        }

      protected:
        void advance( qreal value ) override
        {
            qreal x = m_from.x() + ( m_to.x() - m_from.x() ) * value;
            qreal y = m_from.y() + ( m_to.y() - m_from.y() ) * value;

            m_scrollBox->setScrollPos( QPointF( x, y ) );
        }

      private:
        QskScrollBox* m_scrollBox;

        QPointF m_from;
        QPointF m_to;
    };

    class PanRecognizer final : public QskPanGestureRecognizer
    {
        using Inherited = QskPanGestureRecognizer;

      public:
        PanRecognizer( QObject* parent = nullptr )
            : QskPanGestureRecognizer( parent )
        {
            setOrientations( Qt::Horizontal | Qt::Vertical );
        }

        bool isAcceptedPos( const QPointF& pos ) const override
        {
            if ( auto scrollBox = qobject_cast< const QskScrollBox* >( watchedItem() ) )
            {
                if ( qskIsScrollable( scrollBox, orientations() ) )
                    return scrollBox->viewContentsRect().contains( pos );
            }

            return false;
        }
    };
}

class QskScrollBox::PrivateData
{
  public:
    QPointF scrollPos;
    QSizeF scrollableSize = QSize( 0.0, 0.0 );

    PanRecognizer panRecognizer;

    FlickAnimator flicker;
    ScrollAnimator scroller;

    bool autoScrollFocusItem = true;
};

QskScrollBox::QskScrollBox( QQuickItem* parent )
    : Inherited( parent )
    , m_data( new PrivateData() )
{
    m_data->flicker.setScrollBox( this );
    m_data->scroller.setScrollBox( this );

    m_data->panRecognizer.setWatchedItem( this );

    setAcceptedMouseButtons( Qt::LeftButton );
    setFiltersChildMouseEvents( true );

    setWheelEnabled( true );
    setFocusPolicy( Qt::StrongFocus );

    connectWindow( window(), true );
}

QskScrollBox::~QskScrollBox()
{
}

void QskScrollBox::setAutoScrollFocusedItem( bool on )
{
    if ( m_data->autoScrollFocusItem != on )
    {
        m_data->autoScrollFocusItem = on;
        connectWindow( window(), true );
        Q_EMIT autoScrollFocusedItemChanged( on );
    }
}

bool QskScrollBox::autoScrollFocusItem() const
{
    return m_data->autoScrollFocusItem;
}

void QskScrollBox::onFocusItemChanged()
{
    if ( window() )
    {
#if QT_VERSION >= QT_VERSION_CHECK( 6, 1, 0 )
        auto wd = QQuickWindowPrivate::get( window() )->deliveryAgentPrivate();
#else
        auto wd = QQuickWindowPrivate::get( window() );
#endif
        auto reason = wd->lastFocusReason;
        if ( reason == Qt::TabFocusReason || reason == Qt::BacktabFocusReason )
            ensureFocusItemVisible();
    }
}

void QskScrollBox::ensureFocusItemVisible()
{
    if ( window() == nullptr )
        return;

    if ( const auto focusItem = window()->activeFocusItem() )
        ensureItemVisible( focusItem );
}

void QskScrollBox::setFlickRecognizerTimeout( int timeout )
{
    if ( timeout < 0 )
        timeout = -1;

    m_data->panRecognizer.setTimeout( timeout );
}

int QskScrollBox::flickRecognizerTimeout() const
{
    return m_data->panRecognizer.timeout();
}

void QskScrollBox::setFlickableOrientations( Qt::Orientations orientations )
{
    if ( m_data->panRecognizer.orientations() != orientations )
    {
        m_data->panRecognizer.setOrientations( orientations );
        Q_EMIT flickableOrientationsChanged();
    }
}

Qt::Orientations QskScrollBox::flickableOrientations() const
{
    return m_data->panRecognizer.orientations();
}

void QskScrollBox::setScrollPos( const QPointF& pos )
{
    const QPointF boundedPos = boundedScrollPos( pos );
    if ( boundedPos != m_data->scrollPos )
    {
        m_data->scrollPos = boundedPos;
        update();

        Q_EMIT scrollPosChanged();
        Q_EMIT scrolledTo( boundedPos );
    }
}

QPointF QskScrollBox::scrollPos() const
{
    return m_data->scrollPos;
}

void QskScrollBox::scrollTo( const QPointF& pos )
{
    m_data->scroller.scroll( scrollPos(), pos );
}

void QskScrollBox::setScrollableSize( const QSizeF& size )
{
    const QSizeF boundedSize = size.expandedTo( QSizeF( 0, 0 ) );

    if ( boundedSize != m_data->scrollableSize )
    {
        m_data->scrollableSize = boundedSize;
        Q_EMIT scrollableSizeChanged( m_data->scrollableSize );

        setScrollPos( m_data->scrollPos ); // scroll pos might need to be re-bounded

        update();
    }
}

QSizeF QskScrollBox::scrollableSize() const
{
    return m_data->scrollableSize;
}

void QskScrollBox::ensureItemVisible( const QQuickItem* item )
{
    if ( qskIsAncestorOf( this, item ) )
    {
        auto pos = scrollPos() - viewContentsRect().topLeft();
        pos += mapFromItem( item, QPointF() );

        ensureVisible( QRectF( pos.x(), pos.y(), item->width(), item->height() ) );
    }
}

void QskScrollBox::ensureVisible( const QPointF& pos )
{
    const qreal margin = qskViewportPadding();

    QRectF r( scrollPos(), viewContentsRect().size() );
    r.adjust( margin, margin, -margin, -margin );

    qreal x = r.x();
    qreal y = r.y();

    if ( pos.x() < r.left() )
    {
        x = pos.x();
    }
    else if ( pos.x() > r.right() )
    {
        x = pos.x() - r.width();
    }

    if ( pos.y() < r.top() )
    {
        y = pos.y();
    }
    else if ( y > r.right() )
    {
        y = pos.y() - r.height();
    }

    const QPoint newPos( x - margin, y - margin );

    if( isInitiallyPainted() && window() )
        scrollTo( newPos );
    else
        setScrollPos( newPos );
}

void QskScrollBox::ensureVisible( const QRectF& itemRect )
{
    const qreal margin = qskViewportPadding();

    QRectF r( scrollPos(), viewContentsRect().size() );
    r.adjust( margin, margin, -margin, -margin );

    qreal x = r.x();
    qreal y = r.y();

    if ( itemRect.width() > r.width() )
    {
        x = itemRect.left() + 0.5 * ( itemRect.width() - r.width() );
    }
    else if ( itemRect.right() > r.right() )
    {
        x = itemRect.right() - r.width();
    }
    else if ( itemRect.left() < r.left() )
    {
        x = itemRect.left();
    }

    if ( itemRect.height() > r.height() )
    {
        y = itemRect.top() + 0.5 * ( itemRect.height() - r.height() );
    }
    else if ( itemRect.bottom() > r.bottom() )
    {
        y = itemRect.bottom() - r.height();
    }
    else if ( itemRect.top() < r.top() )
    {
        y = itemRect.top();
    }

    const QPoint newPos( x - margin, y - margin );

    if( isInitiallyPainted() && window() )
        scrollTo( newPos );
    else
        setScrollPos( newPos );
}

void QskScrollBox::windowChangeEvent( QskWindowChangeEvent* event )
{
    Inherited::windowChangeEvent( event );

    connectWindow( event->oldWindow(), false );
    connectWindow( event->window(), true );
}

void QskScrollBox::geometryChangeEvent( QskGeometryChangeEvent* event )
{
    if ( event->isResized() )
        setScrollPos( scrollPos() );

    Inherited::geometryChangeEvent( event );
}

void QskScrollBox::gestureEvent( QskGestureEvent* event )
{
    if ( event->gesture()->type() == QskGesture::Pan )
    {
        const auto gesture = static_cast< const QskPanGesture* >( event->gesture().get() );

        switch ( gesture->state() )
        {
            case QskGesture::Updated:
            {
                setScrollPos( scrollPos() - gesture->delta() );
                break;
            }
            case QskGesture::Finished:
            {
                m_data->flicker.setWindow( window() );
                m_data->flicker.accelerate( gesture->angle(), gesture->velocity() );
                break;
            }
            case QskGesture::Canceled:
            {
                // what to do here: maybe going back to the origin of the gesture ??
                break;
            }
            default:
                break;
        }

        return;
    }

    Inherited::gestureEvent( event );
}

#ifndef QT_NO_WHEELEVENT

QPointF QskScrollBox::scrollOffset( const QWheelEvent* event ) const
{
    QPointF offset;

    const auto pos = qskWheelPosition( event );
    const auto viewRect = viewContentsRect();

    if ( viewRect.contains( pos ) )
    {
        offset = event->pixelDelta();
        if ( offset.isNull() )
            offset = event->angleDelta() / QWheelEvent::DefaultDeltasPerStep;

        offset.rx() *= viewRect.width();
        offset.ry() *= viewRect.height();
    }

    return offset;
}

void QskScrollBox::wheelEvent( QWheelEvent* event )
{
    const auto offset = scrollOffset( event );
    if ( !offset.isNull() )
        setScrollPos( m_data->scrollPos - offset );
}

#endif

QPointF QskScrollBox::boundedScrollPos( const QPointF& pos ) const
{
    const QRectF vr = viewContentsRect();

    const qreal maxX = qMax( 0.0, scrollableSize().width() - vr.width() );
    const qreal maxY = qMax( 0.0, scrollableSize().height() - vr.height() );

    return QPointF( qBound( 0.0, pos.x(), maxX ), qBound( 0.0, pos.y(), maxY ) );
}

void QskScrollBox::connectWindow( const QQuickWindow* window, bool on )
{
    if ( ( window == nullptr ) || ( on && !autoScrollFocusItem() ) )
        return;

    if ( on )
    {
        QObject::connect( window, &QQuickWindow::activeFocusItemChanged,
            this, &QskScrollBox::onFocusItemChanged, Qt::UniqueConnection );
    }
    else
    {
        QObject::disconnect( window, &QQuickWindow::activeFocusItemChanged,
            this, &QskScrollBox::onFocusItemChanged );
    }
}

#include "moc_QskScrollBox.cpp"