/*
Copyright (c) 2023-forever Douglas Malnati. All rights reserved.

See the /faq/tos page for details.
    
(If this generated header is stamped on a file which is a 3rd party file or under a different license or copyright, then ignore this copyright statement and use that file's terms.)
*/

// Adapted from https://github.com/mwgg/GreatCircle

export let GreatCircle = {

    validateRadius: function(unit) {
        let r = {'M': 6371009, 'KM': 6371.009, 'MI': 3958.761, 'NM': 3440.070, 'YD': 6967420, 'FT': 20902260};
        if ( unit in r ) return r[unit];
        else return unit;
    },

    distance: function(lat1, lon1, lat2, lon2, unit) {
        if ( unit === undefined ) unit = 'KM';
        let r = this.validateRadius(unit); 
        lat1 *= Math.PI / 180;
        lon1 *= Math.PI / 180;
        lat2 *= Math.PI / 180;
        lon2 *= Math.PI / 180;
        let lonDelta = lon2 - lon1;
        let a = Math.pow(Math.cos(lat2) * Math.sin(lonDelta) , 2) + Math.pow(Math.cos(lat1) * Math.sin(lat2) - Math.sin(lat1) * Math.cos(lat2) * Math.cos(lonDelta) , 2);
        let b = Math.sin(lat1) * Math.sin(lat2) + Math.cos(lat1) * Math.cos(lat2) * Math.cos(lonDelta);
        let angle = Math.atan2(Math.sqrt(a) , b);
        
        return angle * r;
    },
    
    bearing: function(lat1, lon1, lat2, lon2) {
        lat1 *= Math.PI / 180;
        lon1 *= Math.PI / 180;
        lat2 *= Math.PI / 180;
        lon2 *= Math.PI / 180;
        let lonDelta = lon2 - lon1;
        let y = Math.sin(lonDelta) * Math.cos(lat2);
        let x = Math.cos(lat1) * Math.sin(lat2) - Math.sin(lat1) * Math.cos(lat2) * Math.cos(lonDelta);
        let brng = Math.atan2(y, x);
        brng = brng * (180 / Math.PI);
        
        if ( brng < 0 ) { brng += 360; }
        
        return brng;
    },
    
    destination: function(lat1, lon1, brng, dt, unit) {
        if ( unit === undefined ) unit = 'KM';
        let r = this.validateRadius(unit);
        lat1 *= Math.PI / 180;
        lon1 *= Math.PI / 180;
        let lat3 = Math.asin(Math.sin(lat1) * Math.cos(dt / r) + Math.cos(lat1) * Math.sin(dt / r) * Math.cos( brng * Math.PI / 180 ));
        let lon3 = lon1 + Math.atan2(Math.sin( brng * Math.PI / 180 ) * Math.sin(dt / r) * Math.cos(lat1) , Math.cos(dt / r) - Math.sin(lat1) * Math.sin(lat3));
        
        return {
            'LAT': lat3 * 180 / Math.PI,
            'LON': lon3 * 180 / Math.PI
        };
    }

};