/* ============================================================
 *
 * This file is a part of digiKam project
 * https://www.digikam.org
 *
 * Date        : 2023-05-15
 * Description : geolocation engine based on Marble.
 *               (c) 2007-2022 Marble Team
 *               https://invent.kde.org/education/marble/-/raw/master/data/credits_authors.html
 *
 * SPDX-FileCopyrightText: 2023-2026 by Gilles Caulier <caulier dot gilles at gmail dot com>
 *
 * SPDX-License-Identifier: LGPL-2.1-or-later
 *
 * ============================================================ */

#include "EquirectProjection.h"

// Qt includes

#include <QIcon>

// KDE includes

#include <klocalizedstring.h>

// Local includes

#include "ViewportParams.h"
#include "GeoDataLatLonAltBox.h"
#include "digikam_debug.h"

namespace Marble
{

EquirectProjection::EquirectProjection()
    : CylindricalProjection()
{
    setMinLat(minValidLat());
    setMaxLat(maxValidLat());
}

EquirectProjection::~EquirectProjection()
{
}

QString EquirectProjection::name() const
{
    return i18n("Flat Map");
}

QString EquirectProjection::description() const
{
    return i18n("<p><b>Equirectangular Projection</b> "
                "(\"Plate carrée\")</p><p>Applications: De facto standard for "
                "global texture data sets for computer software.</p>");
}

QIcon EquirectProjection::icon() const
{
    return QIcon::fromTheme(QStringLiteral("map-flat"));
}

bool EquirectProjection::screenCoordinates(const GeoDataCoordinates& geopoint,
                                           const ViewportParams* viewport,
                                           qreal& x, qreal& y, bool& globeHidesPoint) const
{
    globeHidesPoint = false;

    // Convenience variables
    int  radius = viewport->radius();
    int  width  = viewport->width();
    int  height = viewport->height();

    qreal  lon;
    qreal  lat;
    qreal  rad2Pixel = 2.0 * viewport->radius() / M_PI;

    const qreal centerLon = viewport->centerLongitude();
    const qreal centerLat = viewport->centerLatitude();

    geopoint.geoCoordinates(lon, lat);

    // Let (x, y) be the position on the screen of the geopoint.
    x = ((qreal)(viewport->width())  / 2.0 + rad2Pixel * (lon - centerLon));
    y = ((qreal)(viewport->height()) / 2.0 - rad2Pixel * (lat - centerLat));

    // Return true if the calculated point is inside the screen area,
    // otherwise return false.
    return ((0 <= y && y < height)
            && ((0 <= x && x < width)
                || (0 <= x - 4 * radius && x - 4 * radius < width)
                || (0 <= x + 4 * radius && x + 4 * radius < width)));
}

bool EquirectProjection::screenCoordinates(const GeoDataCoordinates& coordinates,
                                           const ViewportParams* viewport,
                                           qreal* x, qreal& y,
                                           int& pointRepeatNum,
                                           const QSizeF& size,
                                           bool& globeHidesPoint) const
{
    pointRepeatNum = 0;
    // On flat projections the observer's view onto the point won't be
    // obscured by the target planet itself.
    globeHidesPoint = false;

    // Convenience variables
    int  radius = viewport->radius();
    qreal  width  = (qreal)(viewport->width());
    qreal  height = (qreal)(viewport->height());

    // Let (itX, y) be the first guess for one possible position on screen.
    qreal itX;
    screenCoordinates(coordinates, viewport, itX, y);

    // Make sure that the requested point is within the visible y range:
    if (0 <= y + size.height() / 2.0 && y < height + size.height() / 2.0)
    {
        // For the repetition case the same geopoint gets displayed on
        // the map many times.across the longitude.

        int xRepeatDistance = 4 * radius;

        // Finding the leftmost positive x value
        if (itX + size.width() > xRepeatDistance)
        {
            const int repeatNum = (int)((itX + size.width()) / xRepeatDistance);
            itX = itX - repeatNum * xRepeatDistance;
        }

        if (itX + size.width() / 2.0 < 0)
        {
            itX += xRepeatDistance;
        }

        // The requested point is out of the visible x range:
        if (itX > width + size.width() / 2.0)
        {
            return false;
        }

        // Now iterate through all visible x screen coordinates for the point
        // from left to right.
        int itNum = 0;

        while (itX - size.width() / 2.0 < width)
        {
            *x = itX;
            ++x;
            ++itNum;
            itX += xRepeatDistance;
        }

        pointRepeatNum = itNum;

        return true;
    }

    // The requested point is out of the visible y range.
    return false;
}


bool EquirectProjection::geoCoordinates(const int x, const int y,
                                        const ViewportParams* viewport,
                                        qreal& lon, qreal& lat,
                                        GeoDataCoordinates::Unit unit) const
{
    const int radius = viewport->radius();
    const qreal pixel2Rad = M_PI / (2.0 * radius);

    // Get the Lat and Lon of the center point of the screen.
    const qreal centerLon = viewport->centerLongitude();
    const qreal centerLat = viewport->centerLatitude();

    {
        const int halfImageWidth = viewport->width() / 2;
        const int xPixels = x - halfImageWidth;

        lon = + xPixels * pixel2Rad + centerLon;

        while (lon > M_PI)
        {
            lon -= 2.0 * M_PI;
        }

        while (lon < -M_PI)
        {
            lon += 2.0 * M_PI;
        }

        if (unit == GeoDataCoordinates::Degree)
        {
            lon *= RAD2DEG;
        }
    }

    {
        // Get yTop and yBottom, the limits of the map on the screen.
        const int halfImageHeight = viewport->height() / 2;
        const int yCenterOffset = (int)(centerLat * (qreal)(2 * radius) / M_PI);
        const int yTop          = halfImageHeight - radius + yCenterOffset;
        const int yBottom       = yTop + 2 * radius;

        // Return here if the y coordinate is outside the map
        if (yTop <= y && y < yBottom)
        {
            const int yPixels = y - halfImageHeight;
            lat = - yPixels * pixel2Rad + centerLat;

            if (unit == GeoDataCoordinates::Degree)
            {
                lat *= RAD2DEG;
            }

            return true;
        }
    }

    return false;
}

GeoDataLatLonAltBox EquirectProjection::latLonAltBox(const QRect& screenRect,
                                                     const ViewportParams* viewport) const
{
    qreal west;
    qreal north = 90 * DEG2RAD;
    geoCoordinates(screenRect.left(), screenRect.top(), viewport, west, north, GeoDataCoordinates::Radian);

    qreal east;
    qreal south = -90 * DEG2RAD;
    geoCoordinates(screenRect.right(), screenRect.bottom(), viewport, east, south, GeoDataCoordinates::Radian);

    // For the case where the whole viewport gets covered there is a
    // pretty dirty and generic detection algorithm:
    GeoDataLatLonAltBox latLonAltBox;
    latLonAltBox.setNorth(north, GeoDataCoordinates::Radian);
    latLonAltBox.setSouth(south, GeoDataCoordinates::Radian);
    latLonAltBox.setWest(west, GeoDataCoordinates::Radian);
    latLonAltBox.setEast(east, GeoDataCoordinates::Radian);
    latLonAltBox.setMinAltitude(-100000000.0);
    latLonAltBox.setMaxAltitude(100000000000000.0);

    // Convenience variables
    int  radius = viewport->radius();
    int  width  = viewport->width();

    // The remaining algorithm should be pretty generic for all kinds of
    // flat projections:

    int xRepeatDistance = 4 * radius;

    if (width >= xRepeatDistance)
    {
        latLonAltBox.setWest(-M_PI);
        latLonAltBox.setEast(+M_PI);
    }

    // Now we need to check whether maxLat (e.g. the north pole) gets displayed
    // inside the viewport.

    // We need a point on the screen at maxLat that definitely gets displayed:
    qreal averageLongitude = latLonAltBox.east();

    GeoDataCoordinates maxLatPoint(averageLongitude, maxLat(), 0.0, GeoDataCoordinates::Radian);
    GeoDataCoordinates minLatPoint(averageLongitude, minLat(), 0.0, GeoDataCoordinates::Radian);

    qreal dummyX, dummyY; // not needed

    if (screenCoordinates(maxLatPoint, viewport, dummyX, dummyY))
    {
        latLonAltBox.setEast(+M_PI);
        latLonAltBox.setWest(-M_PI);
    }

    if (screenCoordinates(minLatPoint, viewport, dummyX, dummyY))
    {
        latLonAltBox.setEast(+M_PI);
        latLonAltBox.setWest(-M_PI);
    }

    return latLonAltBox;
}

bool EquirectProjection::mapCoversViewport(const ViewportParams* viewport) const
{
    // Convenience variables
    int  radius          = viewport->radius();
    //int  width         = viewport->width();
    int  height          = viewport->height();
    int  halfImageHeight = viewport->height() / 2;

    // Get the Lat and Lon of the center point of the screen.
    const qreal centerLat = viewport->centerLatitude();

    // Calculate how many pixel are being represented per radians.
    const float rad2Pixel = (qreal)(2 * radius) / M_PI;

    // Get yTop and yBottom, the limits of the map on the screen.
    int yCenterOffset = (int)(centerLat * rad2Pixel);
    int yTop          = halfImageHeight - radius + yCenterOffset;
    int yBottom       = yTop + 2 * radius;

    return !(yTop >= 0 || yBottom < height);
}

} // namespace Marble
