/****************************************************************************
**
** Copyright (C) 2016 The Qt Company Ltd.
** Contact: https://www.qt.io/licensing/
**
** This file is part of the demonstration applications of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:BSD$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and The Qt Company. For licensing terms
** and conditions see https://www.qt.io/terms-conditions. For further
** information use the contact form at https://www.qt.io/contact-us.
**
** BSD License Usage
** Alternatively, you may use this file under the terms of the BSD license
** as follows:
**
** "Redistribution and use in source and binary forms, with or without
** modification, are permitted provided that the following conditions are
** met:
**   * Redistributions of source code must retain the above copyright
**     notice, this list of conditions and the following disclaimer.
**   * Redistributions in binary form must reproduce the above copyright
**     notice, this list of conditions and the following disclaimer in
**     the documentation and/or other materials provided with the
**     distribution.
**   * Neither the name of The Qt Company Ltd nor the names of its
**     contributors may be used to endorse or promote products derived
**     from this software without specific prior written permission.
**
**
** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
**
** $QT_END_LICENSE$
**
****************************************************************************/

#include "flickable.h"

#include <QtCore>
#include <QtWidgets>

class FlickableTicker: QObject
{
public:
    FlickableTicker(Flickable *scroller) {
        m_scroller = scroller;
    }

    void start(int interval) {
        if (!m_timer.isActive())
            m_timer.start(interval, this);
    }

    void stop() {
        m_timer.stop();
    }

protected:
    void timerEvent(QTimerEvent *event) {
        Q_UNUSED(event);
        m_scroller->tick();
    }

private:
    Flickable *m_scroller;
    QBasicTimer m_timer;
};

class FlickablePrivate
{
public:
    typedef enum {
        Steady,
        Pressed,
        ManualScroll,
        AutoScroll,
        Stop
    } State;

    State state;
    int threshold;
    QPoint pressPos;
    QPoint offset;
    QPoint delta;
    QPoint speed;
    FlickableTicker *ticker;
    QElapsedTimer timeStamp;
    QWidget *target;
    QList<QEvent*> ignoreList;
};

Flickable::Flickable()
{
    d = new FlickablePrivate;
    d->state = FlickablePrivate::Steady;
    d->threshold = 10;
    d->ticker = new FlickableTicker(this);
    d->timeStamp.start();
    d->target = 0;
}

Flickable::~Flickable()
{
    delete d;
}

void Flickable::setThreshold(int th)
{
    if (th >= 0)
        d->threshold = th;
}

int Flickable::threshold() const
{
    return d->threshold;
}

void Flickable::setAcceptMouseClick(QWidget *target)
{
    d->target = target;
}

static QPoint deaccelerate(const QPoint &speed, int a = 1, int max = 64)
{
    int x = qBound(-max, speed.x(), max);
    int y = qBound(-max, speed.y(), max);
    x = (x == 0) ? x : (x > 0) ? qMax(0, x - a) : qMin(0, x + a);
    y = (y == 0) ? y : (y > 0) ? qMax(0, y - a) : qMin(0, y + a);
    return QPoint(x, y);
}

void Flickable::handleMousePress(QMouseEvent *event)
{
    event->ignore();

    if (event->button() != Qt::LeftButton)
        return;

    if (d->ignoreList.removeAll(event))
        return;

    switch (d->state) {

    case FlickablePrivate::Steady:
        event->accept();
        d->state = FlickablePrivate::Pressed;
        d->pressPos = event->pos();
        break;

    case FlickablePrivate::AutoScroll:
        event->accept();
        d->state = FlickablePrivate::Stop;
        d->speed = QPoint(0, 0);
        d->pressPos = event->pos();
        d->offset = scrollOffset();
        d->ticker->stop();
        break;

    default:
        break;
    }
}

void Flickable::handleMouseRelease(QMouseEvent *event)
{
    event->ignore();

    if (event->button() != Qt::LeftButton)
        return;

    if (d->ignoreList.removeAll(event))
        return;

    QPoint delta;

    switch (d->state) {

    case FlickablePrivate::Pressed:
        event->accept();
        d->state = FlickablePrivate::Steady;
        if (d->target) {
            QMouseEvent *event1 = new QMouseEvent(QEvent::MouseButtonPress,
                                                  d->pressPos, Qt::LeftButton,
                                                  Qt::LeftButton, Qt::NoModifier);
            QMouseEvent *event2 = new QMouseEvent(*event);
            d->ignoreList << event1;
            d->ignoreList << event2;
            QApplication::postEvent(d->target, event1);
            QApplication::postEvent(d->target, event2);
        }
        break;

    case FlickablePrivate::ManualScroll:
        event->accept();
        delta = event->pos() - d->pressPos;
        if (d->timeStamp.elapsed() > 100) {
            d->timeStamp.start();
            d->speed = delta - d->delta;
            d->delta = delta;
        }
        d->offset = scrollOffset();
        d->pressPos = event->pos();
        if (d->speed == QPoint(0, 0)) {
            d->state = FlickablePrivate::Steady;
        } else {
            d->speed /= 4;
            d->state = FlickablePrivate::AutoScroll;
            d->ticker->start(20);
        }
        break;

    case FlickablePrivate::Stop:
        event->accept();
        d->state = FlickablePrivate::Steady;
        d->offset = scrollOffset();
        break;

    default:
        break;
    }
}

void Flickable::handleMouseMove(QMouseEvent *event)
{
    event->ignore();

    if (!(event->buttons() & Qt::LeftButton))
        return;

    if (d->ignoreList.removeAll(event))
        return;

    QPoint delta;

    switch (d->state) {

    case FlickablePrivate::Pressed:
    case FlickablePrivate::Stop:
        delta = event->pos() - d->pressPos;
        if (delta.x() > d->threshold || delta.x() < -d->threshold ||
                delta.y() > d->threshold || delta.y() < -d->threshold) {
            d->timeStamp.start();
            d->state = FlickablePrivate::ManualScroll;
            d->delta = QPoint(0, 0);
            d->pressPos = event->pos();
            event->accept();
        }
        break;

    case FlickablePrivate::ManualScroll:
        event->accept();
        delta = event->pos() - d->pressPos;
        setScrollOffset(d->offset - delta);
        if (d->timeStamp.elapsed() > 100) {
            d->timeStamp.start();
            d->speed = delta - d->delta;
            d->delta = delta;
        }
        break;

    default:
        break;
    }
}

void Flickable::tick()
{
    if (d->state == FlickablePrivate:: AutoScroll) {
        d->speed = deaccelerate(d->speed);
        setScrollOffset(d->offset - d->speed);
        d->offset = scrollOffset();
        if (d->speed == QPoint(0, 0)) {
            d->state = FlickablePrivate::Steady;
            d->ticker->stop();
        }
    } else {
        d->ticker->stop();
    }
}