// License: GPL. For details, see LICENSE file.
package org.openstreetmap.josm.data.projection;

import org.openstreetmap.josm.data.Bounds;
import org.openstreetmap.josm.data.ProjectionBounds;
import org.openstreetmap.josm.data.coor.EastNorth;
import org.openstreetmap.josm.data.coor.LatLon;
import org.openstreetmap.josm.data.projection.datum.Datum;
import org.openstreetmap.josm.data.projection.proj.Proj;

/**
 * Implementation of the Projection interface that represents a coordinate reference system and delegates
 * the real projection and datum conversion to other classes.
 *
 * It handles false easting and northing, central meridian and general scale factor before calling the
 * delegate projection.
 *
 * Forwards lat/lon values to the real projection in units of radians.
 *
 * The fields are named after Proj.4 parameters.
 *
 * Subclasses of AbstractProjection must set ellps and proj to a non-null value.
 * In addition, either datum or nadgrid has to be initialized to some value.
 */
public abstract class AbstractProjection implements Projection {

    protected Ellipsoid ellps;
    protected Datum datum;
    protected Proj proj;
    protected double x0;       /* false easting (in meters) */
    protected double y0;       /* false northing (in meters) */
    protected double lon0;     /* central meridian */
    protected double pm;       /* prime meridian */
    protected double k0 = 1.0; /* general scale factor */

    private volatile ProjectionBounds projectionBoundsBox;

    public final Ellipsoid getEllipsoid() {
        return ellps;
    }

    public final Datum getDatum() {
        return datum;
    }

    /**
     * Replies the projection (in the narrow sense)
     * @return The projection object
     */
    public final Proj getProj() {
        return proj;
    }

    public final double getFalseEasting() {
        return x0;
    }

    public final double getFalseNorthing() {
        return y0;
    }

    public final double getCentralMeridian() {
        return lon0;
    }

    public final double getScaleFactor() {
        return k0;
    }

    @Override
    public EastNorth latlon2eastNorth(LatLon ll) {
        ll = datum.fromWGS84(ll);
        double[] en = proj.project(Math.toRadians(ll.lat()), Math.toRadians(ll.lon() - lon0 - pm));
        return new EastNorth(ellps.a * k0 * en[0] + x0, ellps.a * k0 * en[1] + y0);
    }

    @Override
    public LatLon eastNorth2latlon(EastNorth en) {
        double[] latlon_rad = proj.invproject((en.east() - x0) / ellps.a / k0, (en.north() - y0) / ellps.a / k0);
        LatLon ll = new LatLon(Math.toDegrees(latlon_rad[0]), Math.toDegrees(latlon_rad[1]) + lon0 + pm);
        return datum.toWGS84(ll);
    }

    @Override
    public double getDefaultZoomInPPD() {
        // this will set the map scaler to about 1000 m
        return 10;
    }

    /**
     * @return The EPSG Code of this CRS, null if it doesn't have one.
     */
    public abstract Integer getEpsgCode();

    /**
     * Default implementation of toCode().
     * Should be overridden, if there is no EPSG code for this CRS.
     */
    @Override
    public String toCode() {
        return "EPSG:" + getEpsgCode();
    }

    protected static final double convertMinuteSecond(double minute, double second) {
        return (minute/60.0) + (second/3600.0);
    }

    protected static final double convertDegreeMinuteSecond(double degree, double minute, double second) {
        return degree + (minute/60.0) + (second/3600.0);
    }

    @Override
    public final ProjectionBounds getWorldBoundsBoxEastNorth() {
        ProjectionBounds result = projectionBoundsBox;
        if (result == null) {
            synchronized (this) {
                result = projectionBoundsBox;
                if (result == null) {
                    Bounds b = getWorldBoundsLatLon();
                    // add 4 corners
                    result = new ProjectionBounds(latlon2eastNorth(b.getMin()));
                    result.extend(latlon2eastNorth(b.getMax()));
                    result.extend(latlon2eastNorth(new LatLon(b.getMinLat(), b.getMaxLon())));
                    result.extend(latlon2eastNorth(new LatLon(b.getMaxLat(), b.getMinLon())));
                    // and trace along the outline
                    double dLon = (b.getMaxLon() - b.getMinLon()) / 1000;
                    double dLat = (b.getMaxLat() - b.getMinLat()) / 1000;
                    for (double lon=b.getMinLon(); lon<b.getMaxLon(); lon += dLon) {
                        result.extend(latlon2eastNorth(new LatLon(b.getMinLat(), lon)));
                        result.extend(latlon2eastNorth(new LatLon(b.getMaxLat(), lon)));
                    }
                    for (double lat=b.getMinLat(); lat<b.getMaxLat(); lat += dLat) {
                        result.extend(latlon2eastNorth(new LatLon(lat, b.getMinLon())));
                        result.extend(latlon2eastNorth(new LatLon(lat, b.getMaxLon())));
                    }
                    projectionBoundsBox = result;
                }
            }
        }
        return projectionBoundsBox;
    }
}