/*
    Copyright (C) 2010 Henry de Valence <hdevalence@gmail.com>

    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation; either version 2 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License along
    with this program; if not, write to the Free Software Foundation, Inc.,
    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.

*/

#ifndef PROJECTOR_H
#define PROJECTOR_H

#include <Eigen/Core>
USING_PART_OF_NAMESPACE_EIGEN

#include <math.h>

#include <QPointF>

#include "skyobjects/skypoint.h"
#include "skymap.h"

class KStarsData;

/** This is just a container that holds infromation needed to do projections. */
class ViewParams
{
public:
    float width, height;
    float zoomFactor;
    bool useRefraction;
    bool useAltAz;
    bool fillGround; ///<If the ground is filled, then points below horizon are invisible
    SkyPoint *focus;
};

/** This class serves as an interface to handle projections. */
class Projector
{
public:
    /** Constructor.
      * @param p the ViewParams for this projection
      */
    Projector( const ViewParams& p );

    virtual ~Projector();

    /** Update cached values for projector */
    void setViewParams( const ViewParams& p );

    /** Return the type of this projection */
    virtual SkyMap::Projection type() const = 0;

    /** Return the FOV of this projection */
    double fov() const;

    /**Check if the current point on screen is a valid point on the sky. This is needed
        *to avoid a crash of the program if the user clicks on a point outside the sky (the
        *corners of the sky map at the lowest zoom level are the invalid points).
        *@param p the screen pixel position
        */
    virtual bool unusablePoint( const QPointF &p ) const;
    
    /**Given the coordinates of the SkyPoint argument, determine the
     * pixel coordinates in the SkyMap.
     *
     * Since most of the projections used by KStars are very similar,
     * if this function were to be reimplemented in each projection subclass
     * we would end up changing maybe 5 or 6 lines out of 150.
     * Instead, we have a default implementation that uses the projectionK
     * and projectionL functions to take care of the differences between
     * e.g. Orthographic and Stereographic. There is also the cosMaxFieldAngle
     * function, which is used for testing whether a point is on the visible
     * part of the projection, and the radius function which gives the radius of
     * the projection in screen coordinates.
     *
     * While this seems ugly, it is less ugly than duplicating 150 loc to change 5.
     *
     * @return Vector2f containing screen pixel x, y coordinates of SkyPoint.
     * @param o pointer to the SkyPoint for which to calculate x, y coordinates.
     * @param useRefraction true = use Options::useRefraction() value.
     *   false = do not use refraction.  This argument is only needed
     *   for the Horizon, which should never be refracted.
     * @param onVisibleHemisphere pointer to a bool to indicate whether the point is
     *   on the visible part of the Celestial Sphere.
     */
    virtual Vector2f toScreenVec( SkyPoint *o,
                                  bool oRefract = true,
                                  bool* onVisibleHemisphere = 0) const;

    /** This is exactly the same as toScreenVec but it returns a QPointF.
        It just calls toScreenVec and converts the result.
        @see toScreenVec()
      */
    QPointF toScreen( SkyPoint *o,
                      bool oRefract = true,
                      bool* onVisibleHemisphere = 0) const;

    /**@short Determine RA, Dec coordinates of the pixel at (dx, dy), which are the
     * screen pixel coordinate offsets from the center of the Sky pixmap.
     * @param the screen pixel position to convert
     * @param LST pointer to the local sidereal time, as a dms object.
     * @param lat pointer to the current geographic laitude, as a dms object
     */
    virtual SkyPoint fromScreen( const QPointF &p, dms *LST, const dms *lat ) const;


    /**ASSUMES *p1 did not clip but *p2 did.  Returns the QPointF on the line
     * between *p1 and *p2 that just clips.
     */
    QPointF clipLine( SkyPoint *p1, SkyPoint *p2 ) const;

    /**ASSUMES *p1 did not clip but *p2 did.  Returns the Vector2f on the line
     * between *p1 and *p2 that just clips.
     */
    Vector2f clipLineVec( SkyPoint *p1, SkyPoint *p2 ) const;

    /** Check whether the projected point is on-screen */
    bool onScreen( const QPointF& p ) const;
    bool onScreen( const Vector2f& p ) const;

    /**@short Determine if the skypoint p is likely to be visible in the display
     * window.
     *
     * checkVisibility() is an optimization function.  It determines whether an object
     * appears within the bounds of the skymap window, and therefore should be drawn.
     * The idea is to save time by skipping objects which are off-screen, so it is
     * absolutely essential that checkVisibility() is significantly faster than
     * the computations required to draw the object to the screen.
     *
     * If the ground is to be filled, the function first checks whether the point is
     * below the horizon, because they will be covered by the ground anyways.
     * Importantly, it does not call the expensive EquatorialToHorizontal function.
     * This means that the horizontal coordinates MUST BE CORRECT! The vast majority
     * of points are already synchronized, so recomputing the horizontal coordinates is
     * a waste.
     *
     * The function then checks the difference between the Declination/Altitude
     * coordinate of the Focus position, and that of the point p.  If the absolute
     * value of this difference is larger than fov, then the function returns false.
     * For most configurations of the sky map window, this simple check is enough to
     * exclude a large number of objects.
     *
     * Next, it determines if one of the poles of the current Coordinate System
     * (Equatorial or Horizontal) is currently inside the sky map window.  This is
     * stored in the member variable 'bool SkyMap::isPoleVisible, and is set by the
     * function SkyMap::setMapGeometry(), which is called by SkyMap::paintEvent().
     * If a Pole is visible, then it will return true immediately.  The idea is that
     * when a pole is on-screen it is computationally expensive to determine whether
     * a particular position is on-screen or not: for many valid Dec/Alt values, *all*
     * values of RA/Az will indeed be onscreen, but for other valid Dec/Alt values,
     * only *most* RA/Az values are onscreen.  It is cheaper to simply accept all
     * "horizontal" RA/Az values, since we have already determined that they are
     * on-screen in the "vertical" Dec/Alt coordinate.
     *
     * Finally, if no Pole is onscreen, it checks the difference between the Focus
     * position's RA/Az coordinate and that of the point p.  If the absolute value of
     * this difference is larger than XMax, the function returns false.  Otherwise,
     * it returns true.
     *
     * @param p pointer to the skypoint to be checked.
     * @return true if the point p was found to be inside the Sky map window.
     * @see SkyMap::setMapGeometry()
     * @see SkyMap::fov()
     * @note If you are creating skypoints using equatorial coordinates, then
     * YOU MUST CALL EQUATORIALTOHORIZONTAL BEFORE THIS FUNCTION!
     */
    bool checkVisibility( SkyPoint *p ) const;

    /**Determine the on-screen position angle of a SkyObject.  This is the sum
     * of the object's sky position angle (w.r.t. North), and the position angle
     * of "North" at the position of the object (w.r.t. the screen Y-axis).
     * The latter is determined by constructing a test point with the same RA but
     * a slightly increased Dec as the object, and calculating the angle w.r.t. the
     * Y-axis of the line connecing the object to its test point.
     */
    double findPA( SkyObject *o, float x, float y ) const;


    /** Get the ground polygon
        @param labelpoint This point will be set to something suitable for attaching a label
        @param drawLabel this tells whether to draw a label.
        @return the ground polygon
        */
    virtual QVector<Vector2f> groundPoly( SkyPoint* labelpoint = 0, bool* drawLabel = 0 ) const;

protected:
    /** Get the radius of this projection's sky circle.
        @return the radius in radians
        */
    virtual double radius() const { return 2*M_PI; }

    /** This function handles some of the projection-specific code.
        @see toScreen()
        */
    virtual double projectionK(double x) const { return x; }

    /** This function handles some of the projection-specific code.
        @see toScreen()
        */
    virtual double projectionL(double x) const { return x; }

    /** This function returns the cosine of the maximum field angle,
        i.e., the maximum angular distance from the focus for
        which a point should be projected.
        Default is 0, i.e., 90 degrees.
        */
    virtual double cosMaxFieldAngle() const { return 0; }

    /** Helper function for drawing ground.
        @return the point with Alt = 0, az = @p az
        */
    static SkyPoint pointAt(double az, KStarsData* data);
    
    KStarsData *m_data;
    ViewParams m_vp;
    double m_sinY0, m_cosY0;
    double m_fov;
private:
    //Used by CheckVisibility
    double m_xrange;
    bool m_isPoleVisible;
};

#endif // PROJECTOR_H
