package au.gov.amsa.geo.model;
   
   import java.io.Serializable;
   
   import au.gov.amsa.risky.format.HasPosition;
   
   import com.google.common.base.Optional;
   
   /**
   * A latitude longitude rectangle bordered by rhumb lines east-west and
   * north-south. The rectangle is equal in degrees in width and height (but in
   * terms of distance this can of course vary depending on the location of the
   * cell on the earth).
   */
  public class Cell implements Serializable {
  
      private static final long serialVersionUID = 5489135874617545438L;
      private static final double radiusEarthKm = 6371.01;
      private static final double KM_PER_NM = 1.852;
  
      private final long latIndex;
      private final long lonIndex;
      private final int hashCode;
  
      /**
       * Constructor.
       * 
       * @param latIndex
       * @param lonIndex
       */
      Cell(long latIndex, long lonIndex) {
          this.latIndex = latIndex;
          this.lonIndex = lonIndex;
          hashCode = calculateHashCode();
      }
  
      public static Optional<Cell> cellAt(HasPosition p, Options options) {
          return cellAt(p.lat(), p.lon(), options);
      }
  
      public static Optional<Cell> cellAt(double lat, double lon, Options options) {
          return options.getGrid().cellAt(lat, lon);
      }
  
      public double leftEdgeLongitude(Options options) {
          return options.getGrid().leftEdgeLongitude(this);
      }
  
      public double rightEdgeLongitude(Options options) {
          return options.getGrid().rightEdgeLongitude(this);
      }
  
      public double topEdgeLatitude(Options options) {
          return options.getGrid().topEdgeLatitude(this);
      }
  
      public double bottomEdgeLatitude(Options options) {
          return options.getGrid().bottomEdgeLatitude(this);
      }
  
      public long getLatIndex() {
          return latIndex;
      }
  
      public long getLonIndex() {
          return lonIndex;
      }
  
      public double getCentreLon(Options options) {
          return options.getGrid().centreLon(lonIndex);
      }
  
      public double getCentreLat(Options options) {
          return options.getGrid().centreLat(latIndex);
      }
  
      /**
       * From http://mathforum.org/library/drmath/view/63767.html
       * 
       * @param options
       * @return
       */
      public double areaNauticalMiles(Options options) {
          double topLatRads = Math.toRadians(topEdgeLatitude(options));
          double bottomLatRads = Math.toRadians(bottomEdgeLatitude(options));
  
          return Math.PI / 180 * radiusEarthKm * radiusEarthKm
                  * Math.abs(Math.sin(topLatRads) - Math.sin(bottomLatRads))
                  * options.getCellSizeDegreesAsDouble() / (KM_PER_NM * KM_PER_NM);
      }
  
      @Override
      public int hashCode() {
          return hashCode;
      }
  
      private int calculateHashCode() {
          final int prime = 31;
          int result = 1;
         result = prime * result + (int) (latIndex ^ (latIndex >>> 32));
         result = prime * result + (int) (lonIndex ^ (lonIndex >>> 32));
         return result;
     }
 
     @Override
     public boolean equals(Object obj) {
         if (this == obj)
             return true;
         if (obj == null)
             return false;
         if (getClass() != obj.getClass())
             return false;
         Cell other = (Cell) obj;
         if (latIndex != other.latIndex)
             return false;
         if (lonIndex != other.lonIndex)
             return false;
         return true;
     }
 
     @Override
     public String toString() {
         return "Cell [latIndex=" + latIndex + ", lonIndex=" + lonIndex + "]";
     }
 
 }