#include <math.h>
#include <stdio.h>
#include <string.h>

#include <postgres.h>
#include <utils/geo_decls.h>	/* for Pt */
#include <utils/palloc.h>	/* for palloc */

/* Earth's radius is in statute miles. */
const EARTH_RADIUS = 3958.747716;
const TWO_PI = 2.0 * M_PI;

/******************************************************
 *
 * degtorad - convert degrees to radians
 *
 * arg:	double, angle in degrees
 *
 * returns:	double, same angle in radians
 ******************************************************/

static double
degtorad (double degrees) {
	return (degrees / 360.0) * TWO_PI;
}


/******************************************************
 *
 * geo_distance - distance between points
 *
 * args:
 *   a pair of points - for each point,
 *     x-coordinate is longitude in degrees west of Greenwich
 *     y-coordinate is latitude in degrees above equator
 *
 * returns:	double
 *   distance between the points in miles on earth's surface
 ******************************************************/

double *
geo_distance (Point *pt1, Point *pt2) {

	double long1, lat1, long2, lat2;
	double longdiff;
	double * resultp = palloc (sizeof(double));

	/* convert degrees to radians */

	long1 = degtorad (pt1->x);
	lat1 = degtorad (pt1->y);

	long2 = degtorad (pt2->x);
	lat2 = degtorad (pt2->y);

	/* compute difference in longitudes - want < 180 degrees */
	longdiff = fabs (long1 - long2);
	if (longdiff > M_PI)
		longdiff = TWO_PI - longdiff;

	* resultp = EARTH_RADIUS * acos
	  (sin (lat1) * sin (lat2) + cos (lat1) * cos (lat2) * cos (longdiff));

	return resultp;
}
