package ru.olamedia.astronomy;

/*
 *  Copyright 2011 Brad Parks
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
//package com.bradsbrain.simpleastronomy;

import java.util.Calendar;

public class SunPosition {
	// some handy constants
	private double EPOCH = 2447891.5; // 1990 January 0.0
	private double ECLIPTIC_LONGITUDE_OF_PERIGREE = 282.768422;
	private double ECLIPTIC_LONGITUDE_AT_EPOCH_1990 = 279.403303;
	private double ECCENTRICITY_OF_ORBIT = 0.016713;

	/**
	 * The geocentric ecliptic longitude. <br>
	 * Calculation is good to 3 decimal places <br>
	 * me: 337.44406603442917, book: 337.444194
	 */
	private double geoEclipticLongitude = 0; // oft represented as a lambda with
												// little circle+dot
	/**
	 * The mean anomaly
	 */
	private double meanAnomaly = 0; // oft represented as capital M with little
									// circle+dot

	public SunPosition(Calendar cal) {
		Calendar myCal = BaseUtils.getSafeLocalCopy(cal.getTimeInMillis());

		double daysSince = BaseUtils.exactDaysSince(myCal, EPOCH);

		double N = (360 / 365.242191 * daysSince) % 360;
		if (N < 0) {
			N += 360;
		}

		meanAnomaly = computeMeanAnomaly(N);
		geoEclipticLongitude = computeGeoEclipticLongitude(N);
	}

	private double computeGeoEclipticLongitude(double nValue) {
		double Ec = (360.0 / Math.PI) * ECCENTRICITY_OF_ORBIT
				* Math.sin(Math.toRadians(meanAnomaly));
		double preliminaryLongitude = nValue + Ec
				+ ECLIPTIC_LONGITUDE_AT_EPOCH_1990;
		if (preliminaryLongitude > 360) {
			preliminaryLongitude -= 360;
		}
		return preliminaryLongitude;
	}

	private double computeMeanAnomaly(double nValue) {
		double someMean = nValue + ECLIPTIC_LONGITUDE_AT_EPOCH_1990
				- ECLIPTIC_LONGITUDE_OF_PERIGREE;
		return someMean < 0 ? someMean + 360 : someMean;
	}

	/**
	 * TODO: implement this someday
	 */
	public RightAscension getRightAscension() {
		return null;
	}

	/**
	 * TODO: implement this someday
	 */
	public Declination getDeclination() {
		return null;
	}

	public double getEclipticLongitude() {
		return geoEclipticLongitude;
	}

	public double getMeanAnomaly() {
		return meanAnomaly;
	}

}