import Toybox.Lang;
import Toybox.Math;

// Great-circle distance between two WGS84 coordinates, in meters.
module Haversine {

    const EARTH_RADIUS_M = 6371000.0;

    function distance(lat1 as Float, lon1 as Float, lat2 as Float, lon2 as Float) as Float {
        var dLat = _toRad(lat2 - lat1);
        var dLon = _toRad(lon2 - lon1);
        var rLat1 = _toRad(lat1);
        var rLat2 = _toRad(lat2);

        var a = Math.sin(dLat / 2) * Math.sin(dLat / 2)
              + Math.cos(rLat1) * Math.cos(rLat2)
              * Math.sin(dLon / 2) * Math.sin(dLon / 2);
        var c = 2 * Math.asin(Math.sqrt(a));
        return (EARTH_RADIUS_M * c).toFloat();
    }

    function _toRad(deg as Float) as Float {
        return (deg * Math.PI / 180.0).toFloat();
    }
}