/* Copyright 2002-2021 CS GROUP
    * Licensed to CS GROUP (CS) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * CS licenses this file to You 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 org.orekit.propagation.events;
  
  import org.hipparchus.Field;
  import org.hipparchus.CalculusFieldElement;
  import org.orekit.bodies.FieldGeodeticPoint;
  import org.orekit.bodies.OneAxisEllipsoid;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.events.handlers.FieldEventHandler;
  import org.orekit.propagation.events.handlers.FieldStopOnIncreasing;
  
  /** Detector for geographic latitude crossing.
   * <p>This detector identifies when a spacecraft crosses a fixed
   * latitude with respect to a central body.</p>
   * @author Luc Maisonobe
   * @author Evan Ward
   * @since 9.3
   */
  public class FieldLatitudeCrossingDetector <T extends CalculusFieldElement<T>>
          extends FieldAbstractDetector<FieldLatitudeCrossingDetector<T>, T> {
  
      /** Body on which the latitude is defined. */
      private OneAxisEllipsoid body;
  
      /** Fixed latitude to be crossed. */
      private final double latitude;
  
      /** Build a new detector.
       * <p>The new instance uses default values for maximal checking interval
       * ({@link #DEFAULT_MAXCHECK}) and convergence threshold ({@link
       * #DEFAULT_THRESHOLD}).</p>
       * @param field the type of numbers to use.
       * @param body body on which the latitude is defined
       * @param latitude latitude to be crossed
       */
      public FieldLatitudeCrossingDetector(final Field<T> field,
                                           final OneAxisEllipsoid body,
                                           final double latitude) {
          this(field.getZero().add(DEFAULT_MAXCHECK),
                  field.getZero().add(DEFAULT_THRESHOLD),
                  body,
                  latitude);
      }
  
      /** Build a detector.
       * @param maxCheck maximal checking interval (s)
       * @param threshold convergence threshold (s)
       * @param body body on which the latitude is defined
       * @param latitude latitude to be crossed
       */
      public FieldLatitudeCrossingDetector(final T maxCheck,
                                           final T threshold,
                                           final OneAxisEllipsoid body,
                                           final double latitude) {
          this(maxCheck, threshold, DEFAULT_MAX_ITER, new FieldStopOnIncreasing<>(),
               body, latitude);
      }
  
      /** Private constructor with full parameters.
       * <p>
       * This constructor is private as users are expected to use the builder
       * API with the various {@code withXxx()} methods to set up the instance
       * in a readable manner without using a huge amount of parameters.
       * </p>
       * @param maxCheck maximum checking interval (s)
       * @param threshold convergence threshold (s)
       * @param maxIter maximum number of iterations in the event time search
       * @param handler event handler to call at event occurrences
       * @param body body on which the latitude is defined
       * @param latitude latitude to be crossed
       */
      private FieldLatitudeCrossingDetector(
              final T maxCheck,
              final T threshold,
              final int maxIter,
              final FieldEventHandler<? super FieldLatitudeCrossingDetector<T>, T> handler,
              final OneAxisEllipsoid body,
              final double latitude) {
          super(maxCheck, threshold, maxIter, handler);
          this.body     = body;
          this.latitude = latitude;
      }
  
      /** {@inheritDoc} */
     @Override
     protected FieldLatitudeCrossingDetector<T> create(
             final T newMaxCheck,
             final T newThreshold,
             final int newMaxIter,
             final FieldEventHandler<? super FieldLatitudeCrossingDetector<T>, T> newHandler) {
         return new FieldLatitudeCrossingDetector<>(
                 newMaxCheck, newThreshold, newMaxIter, newHandler, body, latitude);
     }
 
     /** Get the body on which the geographic zone is defined.
      * @return body on which the geographic zone is defined
      */
     public OneAxisEllipsoid getBody() {
         return body;
     }
 
     /** Get the fixed latitude to be crossed (radians).
      * @return fixed latitude to be crossed (radians)
      */
     public double getLatitude() {
         return latitude;
     }
 
     /** Compute the value of the detection function.
      * <p>
      * The value is the spacecraft latitude minus the fixed latitude to be crossed.
      * It is positive if the spacecraft is northward and negative if it is southward
      * with respect to the fixed latitude.
      * </p>
      * @param s the current state information: date, kinematics, attitude
      * @return spacecraft latitude minus the fixed latitude to be crossed
      */
     public T g(final FieldSpacecraftState<T> s) {
 
         // convert state to geodetic coordinates
         final FieldGeodeticPoint<T> gp = body.transform(
                 s.getPVCoordinates().getPosition(),
                 s.getFrame(),
                 s.getDate());
 
         // latitude difference
         return gp.getLatitude().subtract(latitude);
 
     }
 
 }