Ysurac / FlightAirMap

    Leaflet.Terminator.js, 

    (c) 2016, FCOO

    https://github.com/FCOO/Leaflet.Terminator

    https://github.com/FCOO

****************************************************************************/

(function (L/*, window, document, undefined*/) {

    "use strict";

    /* Terminator.js -- Overlay day/night region on a Leaflet map */

    /* Extending prototype of native object - don't do it

    Date.prototype.getJulian = function() {

    // Calculate the present UTC Julian Date. Function is valid after the beginning of the UNIX epoch 1970-01-01 and ignores leap seconds.

        return (this / 86400000) + 2440587.5;

    };

    */

    function getJulian( date ){

    // Calculate the present UTC Julian Date. Function is valid after the beginning of the UNIX epoch 1970-01-01 and ignores leap seconds.

        return (date / 86400000) + 2440587.5;

    }

    /* Extending prototype of native object - don't do it

    Date.prototype.getGMST = function() {

    // Calculate Greenwich Mean Sidereal Time according to http://aa.usno.navy.mil/faq/docs/GAST.php /

    var julianDay = this.getJulian();

    var d = julianDay - 2451545.0;

    // Low precision equation is good enough for our purposes.

    return (18.697374558 + 24.06570982441908 * d) % 24;

    };

    */

    function getGMST( date ){

    // Calculate Greenwich Mean Sidereal Time according to http://aa.usno.navy.mil/faq/docs/GAST.php /

    var julianDay = getJulian( date );

    var d = julianDay - 2451545.0;

    // Low precision equation is good enough for our purposes.

    return (18.697374558 + 24.06570982441908 * d) % 24;

    }

    L.Terminator = L.Polygon.extend({

        options: {

            color: '#00',

            opacity: 0.5,

            fillColor: '#00',

            fillOpacity: 0.5,

            resolution: 2

        },

        initialize: function(options) {

            this.VERSION = "1.0.1";

            this._R2D = 180 / Math.PI;

            this._D2R = Math.PI / 180;

            L.Util.setOptions(this, options);

            var latLng = this._compute(this.options.time || null);

            this.setLatLngs(latLng);

    },

    onAdd: function(map) {

            L.Polygon.prototype.onAdd.call(this, map);

            var that = this;

            // Subscribe to datetime updates

            map.on('datetimechange', function(evt) {

                var datetime = evt.datetime.split('T');

                var date = datetime[0].split('-');

                var time = datetime[1].split(':');

                datetime = new Date(Date.UTC(parseInt(date[0]), parseInt(date[1])-1, parseInt(date[2]), parseInt(time[0]), parseInt(time[1]), parseInt(time[2].replace('Z',''))));

                that.setTime(datetime);

            });

    },

    setTime: function(date) {

            this.options.time = date;

            var latLng = this._compute(date || null);

            this.setLatLngs(latLng);

    },

    _sunEclipticPosition: function(julianDay) {

        /* Compute the position of the Sun in ecliptic coordinates at

             julianDay.  Following

           http://en.wikipedia.org/wiki/Position_of_the_Sun */

            // Days since start of J2000.0

            var n = julianDay - 2451545.0;

            // mean longitude of the Sun

            var L = 280.460 + 0.9856474 * n;

            L %= 360;

            // mean anomaly of the Sun

            var g = 357.528 + 0.9856003 * n;

            g %= 360;

            // ecliptic longitude of Sun

            var lambda = L + 1.915 * Math.sin(g * this._D2R) + 0.02 * Math.sin(2 * g * this._D2R);

            // distance from Sun in AU

            var R = 1.00014 - 0.01671 * Math.cos(g * this._D2R) - 0.0014 * Math.cos(2 * g * this._D2R);

            return {"lambda": lambda, "R": R};

    },

    _sunEquatorialPosition: function(sunEclLng, eclObliq) {

            /* Compute the Sun's equatorial position from its ecliptic

             * position. Inputs are expected in degrees. Outputs are in

             * degrees as well. */

            var alpha = Math.atan(Math.cos(eclObliq * this._D2R) * Math.tan(sunEclLng * this._D2R)) * this._R2D;

            var delta = Math.asin(Math.sin(eclObliq * this._D2R) * Math.sin(sunEclLng * this._D2R)) * this._R2D;

            var lQuadrant  = Math.floor(sunEclLng / 90) * 90;

            var raQuadrant = Math.floor(alpha / 90) * 90;

            alpha = alpha + (lQuadrant - raQuadrant);

            return {"alpha": alpha, "delta": delta};

    },

    _hourAngle: function(lng, sunPos, gst) {

            /* Compute the hour angle of the sun for a longitude on

             * Earth. Return the hour angle in degrees. */

            var lst = gst + lng / 15;

            return lst * 15 - sunPos.alpha;

    },

    _latitude: function(ha, sunPos) {

            /* For a given hour angle and sun position, compute the

             * latitude of the terminator in degrees. */

            var lat = Math.atan(-Math.cos(ha * this._D2R) / 

                                Math.tan(sunPos.delta * this._D2R)) * this._R2D;

            return lat;

    },

    _compute: function(time) {

            var today = time === null ? new Date() : new Date(time),

                    julianDay = getJulian(today), //today.getJulian(),

                    gst = getGMST( today ), //today.getGMST(),

                    latLng = [],

                    ha, lat, lng,

                    sunEclPos = this._sunEclipticPosition(julianDay),

                    eclObliq = this._eclipticObliquity(julianDay),

                    sunEqPos = this._sunEquatorialPosition(sunEclPos.lambda, eclObliq);

            for (var i = 0; i <= 720 * this.options.resolution; i++) {

                lng = -360 + i / this.options.resolution;

              ha = this._hourAngle(lng, sunEqPos, gst);

              lat = this._latitude(ha, sunEqPos);

              latLng[i+1] = [lat, lng];

            }

            if (sunEqPos.delta < 0) {

              latLng[0] = [90, -360];

              latLng[latLng.length] = [90, 360];

            } else {

              latLng[0] = [-90, -360];

              latLng[latLng.length] = [-90, 360];

            }

            return latLng;

    }

    });

    L.terminator = function(options) {

    return new L.Terminator(options);

    };