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import static java.lang.Math.acos;
import static java.lang.Math.cos;
import static java.lang.Math.sin;

/**
 * Calculate distance between coordinates.
 */
public class DistanceCalculator {
  static double PI_RAD = Math.PI / 180.0;

  /**
   * Use Great Circle distance formula to calculate distance between 2 coordinates in meters.
   */
  public double greatCircleInFeet(LatLng latLng1, LatLng latLng2) {
    return greatCircleInKilometers(latLng1.latitude, latLng1.longitude, latLng2.latitude,
        latLng2.longitude) * 3280.84;
  }

  /**
   * Use Great Circle distance formula to calculate distance between 2 coordinates in meters.
   */
  public double greatCircleInMeters(LatLng latLng1, LatLng latLng2) {
    return greatCircleInKilometers(latLng1.latitude, latLng1.longitude, latLng2.latitude,
        latLng2.longitude) * 1000;
  }

  /**
   * Use Great Circle distance formula to calculate distance between 2 coordinates in kilometers.
   * https://software.intel.com/en-us/blogs/2012/11/25/calculating-geographic-distances-in-location-aware-apps
   */
  public double greatCircleInKilometers(double lat1, double long1, double lat2, double long2) {
    double phi1 = lat1 * PI_RAD;
    double phi2 = lat2 * PI_RAD;
    double lam1 = long1 * PI_RAD;
    double lam2 = long2 * PI_RAD;

    return 6371.01 * acos(sin(phi1) * sin(phi2) + cos(phi1) * cos(phi2) * cos(lam2 - lam1));
  }
}