#include "haversine.h"
#include <math.h>

#define PI 3.14159265358979323845
#define SQUARE(X) ((X) * (X))

double radians(double degrees);

double haversine_of_degrees(double x0, double y0, double x1, double y1,
                            double radius) {
  double dy = radians(y1 - y0);
  double dx = radians(x1 - x0);
  y0 = radians(y0);
  y1 = radians(y1);

  double root_term =
      SQUARE(sin(dy / 2.0)) + cos(y0) * cos(y1) * SQUARE(sin(dx / 2.0));

  double result = 2.0 * radius * asin(sqrt(root_term));

  return result;
}

double radians(double degrees) { return (degrees * PI) / 180.0; }