/**
 * Sonnenterminatur: Echtzeit Tag/Nacht-Grenze als Linie + Nachtflaeche.
 */
const TerminatorLayer = {
    _viewer: null,
    _entity: null,
    _line: null,
    _interval: null,
    _count: 0,

    start(viewer) {
        if (this._entity) return;
        this._viewer = viewer;
        this._render();
        this._count = 1;
        var self = this;
        this._interval = setInterval(function() { self._render(); }, 60000);
    },

    stop() {
        if (this._interval) { clearInterval(this._interval); this._interval = null; }
        if (this._entity && this._viewer) { this._viewer.entities.remove(this._entity); this._entity = null; }
        if (this._line && this._viewer) { this._viewer.entities.remove(this._line); this._line = null; }
        this._count = 0;
    },

    _calcTerminator() {
        // Sonnenposition berechnen
        var now = new Date();
        var dayOfYear = Math.floor((now - new Date(now.getFullYear(), 0, 0)) / 86400000);
        var declination = -23.45 * Math.cos((360 / 365) * (dayOfYear + 10) * Math.PI / 180);
        var decRad = declination * Math.PI / 180;

        // Stunden seit Mitternacht UTC
        var utcHours = now.getUTCHours() + now.getUTCMinutes() / 60 + now.getUTCSeconds() / 3600;
        var sunLon = -(utcHours - 12) * 15; // Sonnen-Laengengrad

        // Terminatur-Punkte berechnen (Polygon um die Nachtseite)
        var points = [];
        var linePoints = [];
        for (var i = 0; i <= 360; i += 2) {
            var lon = i - 180;
            var lonRad = (lon - sunLon) * Math.PI / 180;
            var lat = Math.atan(-Math.cos(lonRad) / Math.tan(decRad)) * 180 / Math.PI;
            linePoints.push(lon, lat);
        }

        // Nacht-Polygon: Terminatur-Linie + Pole
        var nightPolygon = [];
        // Oberer Rand (Nordpol oder Suedpol je nach Jahreszeit)
        var topLat = declination > 0 ? -90 : 90;
        nightPolygon.push(-180, topLat);
        for (var j = 0; j < linePoints.length; j += 2) {
            nightPolygon.push(linePoints[j], linePoints[j + 1]);
        }
        nightPolygon.push(180, topLat);

        return { line: linePoints, night: nightPolygon };
    },

    _render() {
        if (!this._viewer) return;
        var data = this._calcTerminator();

        // Alte Entities entfernen
        if (this._entity) this._viewer.entities.remove(this._entity);
        if (this._line) this._viewer.entities.remove(this._line);

        // Nachtflaeche (dunkel, halbtransparent)
        var nightPositions = Cesium.Cartesian3.fromDegreesArray(data.night);
        this._entity = this._viewer.entities.add({
            polygon: {
                hierarchy: new Cesium.PolygonHierarchy(nightPositions),
                material: Cesium.Color.BLACK.withAlpha(0.35),
                height: 0,
                outline: false,
            },
        });

        // Terminatur-Linie (leuchtend)
        var linePositions = Cesium.Cartesian3.fromDegreesArray(data.line);
        this._line = this._viewer.entities.add({
            polyline: {
                positions: linePositions,
                width: 2,
                material: Cesium.Color.fromCssColorString('#ff8800').withAlpha(0.6),
                clampToGround: true,
            },
        });
    },
};