/* Copyright 2000 Charles G. Wright
 * This software may be distributed under the terms of the
 * GNU General Public License.
 *
 * $Id: SOLlocation.java,v 1.1 2000-06-15 10:15:00-05 chuckles Exp chuckles $
 */

import java.math.*;
import java.util.*;

/** <p>This class represents a location on the surface of planet Earth.
 * Its class variables define a position on Earth and its time zone.
 * Methods for this class deal with solar time and the position
 * of the sun in the sky at this location.</p>
 * <p>At this location can be defined one or more orientations,
 * defined by the SOLorientation object, of surfaces exposed to the sun. 
 * These are all contained the linked list "orientations" attached to
 * this location object.
 */

public class SOLlocation implements CWmonitorable{

  /** Values accessible using the getValue() method.*/

  public static final String[] fields = {"Solar Altitude", 
					 "Solar Azimuth"};
  public static final int[] field_types = {UnitConverter.NOTHING,
					   UnitConverter.NOTHING};
  // Constant:
  private static final double FEET_PER_METER = 3.2808389850;
  // locale
  /** Latitude of the surface, in degrees. */
  public double latitude;
  /** Longitude of the surface, in degrees. */
  public double longitude;
  /** Longitude of the standard time zone in degrees. */
  public int time_zone;
  /** Elevation at this location, in meters. */
  public double elevation;
  /** Name of this location. */
  public String name;

  /** List of orientations associated with this location.*/
  public Vector orientations;

  public TMYdata tmystuff;

  //--------------------  Constructor  -----------------------------
  /** <p>Create an SOLlocation object, which represents a location on the 
   * surface of planet Earth. The parameters defining the location
   * are its:</p><ul><li>latitude, in degrees - North is positive 
   * <li>longitude, in degrees - West is positive
   * <li>standard time zone, in degrees - West is positive
   * <li>elevation, in meters
   * </ul>
  */

  public SOLlocation(double latitude,
		     double longitude,
		     int time_zone,
		     double elevation,
		     String name){

    this.latitude = latitude;
    this.longitude = longitude;
    this.time_zone = time_zone;
    this.elevation = elevation;
    this.name = name;
    orientations = new Vector();
    CWmonitoredElements.addElements(this);
  }

  //-------------------  Methods  ------------------------------------

  //---- utility methods ------
  static public double toRadians(double angle){
    return(angle * 0.0174532925);
  }
  static public double toDegrees(double angle){
    return(angle / 0.0174532925);
  }
  //-----------------------------

  /** Returns the latitude of the location station. */

  public double getLatitude(){
    return latitude;
  }


  /** Returns the longitude of the location. */

  public double getLongitude(){
    return longitude;
  }

  /** Returns the time zone of the data location, in degrees
   * (longitude of standard meridian). */

  public int getTimeZone(){
    return time_zone;
  }


  /** Returns the elevation of the location. */
  public double getElevation(){
      return (double)elevation;
  }


  public String getName(){
    return(name);
  }

  /** Returns the list of monitorable fields. Part of the CWmonitorable
   * interface.*/

  public String[] getFields(){
    return fields;
  }

  /** Returns the list of types of the monitorable fields. Part of the CWmonitorable
   * interface. Used for unit conversions. Types are defined in class UnitConverter.*/

  public int[] getFieldTypes(){
    return(field_types);
  }


  //---------------------- Solar Declination ------------------------
  /** Returns solar declination, in degrees (angle between
   * ecliptic and equator), given a day number.
   */
  public double getDeclination(int daynum){
    return 23.45 * Math.sin(toRadians((360 * (284 + daynum))/ 365));
  }

  //------------------ Equation of time -----------------------------
  /** Returns local solar time, in seconds, given the day number (in the year) and the
  * local standard time (in seconds). */

  public int getSolarTime(int daynum, int standard_time){

    // convert daynum to radians
    int solar_time;
    double D = 2 * Math.PI * daynum / 365;
    double eot = -1 *
      ((445 * Math.sin(D)) - (15.4 * Math.cos(D)) + (554 * Math.sin(2 * D)) + (217.0 * Math.cos(2 * D)));
    solar_time = (int)(standard_time + (240.0 * (time_zone - longitude)) + eot);
    //System.out.println("[getSolarTime]: standard_time = " + standard_time + "solar_time = " + solar_time);
    return solar_time;
  }

  //------------------------- HMS to Sec ----------------------------
  /** Returns time of day in seconds. Inputs are the hour of the day (0-23),
   * the minute of the hour (0-59), and second of the minute (0-59). 
  */

  public int timeInSeconds(int hour, int minute, int second){
    return (((hour) * 3600) + ((minute) * 60) + (second));
  }

  //------------------------ Hour Angle -----------------------------
  /** Returns Hour Angle, in degrees. Input is the local solar time, in seconds.
   */
  public double getHourAngle(int solar_time){
    return(15.0 * ((solar_time / 3600.0) - 12.0));
  }

  //--------------------------   Solar Altitude ---------------------
  /** Returns solar altitude, in degrees, given solar time and declination.
   */
  public double getSolarAltitude(double decl, int solar_time){
    double hourAngle = getHourAngle(solar_time);
    // Calculate sine of altitude
    //    System.out.println("[getSolarAltitude]: decl="+decl+" hourAngle="+hourAngle);
    double sinAlt =  (Math.cos(toRadians(latitude)) 
		      * Math.cos(toRadians(decl))
		      * Math.cos(toRadians(hourAngle)))
      + (Math.sin(toRadians(latitude)) * Math.sin(toRadians(decl)));

    double alt = Math.max(0.0, toDegrees(Math.asin(sinAlt)));
    return alt;
  }

  /** Returns solar altitude, in degrees, given solar time and day number.
   */
  public double getSolarAltitude(int daynum, int solar_time){
    double decl = getDeclination(daynum);
    return(getSolarAltitude(decl, solar_time));
  }

  //---------------------------- Solar Azimuth ------------------------
  /** Returns solar azimuth, in degrees, given solar time and declination.
   */
  public double getSolarAzimuth(double decl, int solar_time){
    double alt = getSolarAltitude(decl, solar_time);
    // Calculate cosine of solar azimuth
    double cosAzi = 
      ((Math.sin(toRadians(alt)) * Math.sin(toRadians(latitude))) - Math.sin(toRadians(decl)))
			    / (Math.cos(toRadians(alt)) * Math.cos(toRadians(latitude)));
    double result = toDegrees(Math.acos(cosAzi));
    if (solar_time < 43200) result *= -1.0;

    //  System.out.println("[getSolarAzimuth]: decl="+decl+" alt="+alt+" latitude="+latitude+" azi="+result+" solar_time="+solar_time);
    
    return(result);
  }

  /** Returns solar azimuth, in degrees, given solar time and day number.
   */
  public double getSolarAzimuth(int daynum, int solar_time){
    double decl = getDeclination(daynum);
    return(getSolarAzimuth(decl, solar_time));
  }

  /** Provides access to this classes methods in common getValue() format. */
  public double getValue(int month, int day, int hour, int fieldnum) {
    double result = 0.0;
    int daynum = TMYdata.dayOfYear(month, day);
    int solar_time = getSolarTime(daynum, timeInSeconds(hour-1, 0, 0));
    switch (fieldnum){
    case 0: result = getSolarAltitude(daynum, solar_time); break;
    case 1: result = getSolarAzimuth(daynum, solar_time); break;
    }
    return(result);  
  }
}