/**
 * Helper for Geo-Coordinates
 */
export class GeoHelper {
  /**
   * Earth-Radius
   * @return {number}
   */
  private static get R() {
    return 6371e3;
  }

  /**
     * Calculate Distance between two GPS Koordinates
     * @param {number} lat1
     * @param {number} lon1
     * @param {number} lat2
     * @param {number} lon2
     * @return {number} number
     */
  public static calculateDistance(
      lat1: number,
      lon1: number,
      lat2: number,
      lon2: number): number {
    const φ1 = lat1 * Math.PI/180; // φ, λ in radians
    const φ2 = lat2 * Math.PI/180;
    const Δφ = (lat2-lat1) * Math.PI/180;
    const Δλ = (lon2-lon1) * Math.PI/180;

    const a = Math.sin(Δφ/2) * Math.sin(Δφ/2) +
                Math.cos(φ1) * Math.cos(φ2) *
                Math.sin(Δλ/2) * Math.sin(Δλ/2);
    const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a));

    return this.R * c; // in metres
  }
}