/* Copyright 2002-2025 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.forces.drag;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.stream.Stream;
  
  import org.hipparchus.CalculusFieldElement;
  import org.hipparchus.Field;
  import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  import org.hipparchus.geometry.euclidean.threed.Vector3D;
  import org.hipparchus.util.MathArrays;
  import org.orekit.annotation.DefaultDataContext;
  import org.orekit.frames.Frame;
  import org.orekit.models.earth.atmosphere.Atmosphere;
  import org.orekit.propagation.FieldSpacecraftState;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.events.DateDetector;
  import org.orekit.propagation.events.EventDetector;
  import org.orekit.propagation.events.FieldDateDetector;
  import org.orekit.propagation.events.FieldEventDetector;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.FieldAbsoluteDate;
  import org.orekit.time.TimeScale;
  import org.orekit.time.TimeScalesFactory;
  import org.orekit.utils.ParameterDriver;
  import org.orekit.utils.ParameterDriversProvider;
  import org.orekit.utils.TimeSpanMap;
  import org.orekit.utils.TimeSpanMap.Span;
  import org.orekit.utils.TimeSpanMap.Transition;
  
  
  /** Time span atmospheric drag force model.
   *  <p>
   *  This class is closely related to {@link org.orekit.forces.drag.DragForce DragForce} class.<br>
   *  The difference is that it has a {@link TimeSpanMap} of {@link DragSensitive} objects as attribute
   *  instead of a single {@link DragSensitive} object. <br>
   *  The idea behind this model is to allow the user to design a drag force model that can see its physical parameters
   *  (drag coefficient and lift ratio) change with time, at dates chosen by the user. <br>
   *  </p>
   *  <p>
   *  This is a behavior that can be sought in operational orbit determination.<br>
   *  Indeed the solar activity has a strong influence on the local atmospheric density, and thus on the drag force effect.<br>
   *  Solar activity is a physical phenomenon that is difficult to model and predict. <br>
   *  The errors induced by this incomplete modeling can be estimated through the drag coefficients.<br>
   *  Being able to define and estimate drag coefficients depending on user-chosen dates in a piecewise fashion allows for
   *  a better  modeling of solar activity uncertainties.
   *  </p>
   *  <p>
   *  A typical operational use case is to have a daily solar activity with three-hourly magnetic indexes provided by an
   *  international organization (NOAA for example).<br>
   *  Given this input, a user can define a piecewise drag force model with daily or three-hourly drag coefficients.<br>
   *  Each timed coefficient will absorb a part of the uncertainties in the solar activity and will allow for a more accurate
   *  orbit determination
   *  </p>
   *  <b>Usage</b>:<ul>
   *  <li><u>Construction</u>: constructor takes an atmospheric model and a DragSensitive model.<br>
   *  This last model will be your initial DragSensitive model and it will be initially valid for the whole time line.<br>
   *  The real validity of this first entry will be truncated as other DragSensitive models are added.
   *  <li><u>Time spans</u>: DragSensitive models are added using methods {@link #addDragSensitiveValidAfter(DragSensitive, AbsoluteDate)}
   *   or {@link #addDragSensitiveValidBefore(DragSensitive, AbsoluteDate)}.<br>
   *   Recommendations are the same than the ones in {@link TimeSpanMap}, meaning: <ul>
   *   <li>As an entry is added, it truncates the validity of the neighboring entries already present in the map;
   *   <li><b>The transition dates should be entered only once</b>. Repeating a transition date will lead to unexpected result and is not supported;
   *   <li>It is advised to order your DragSensitive models chronologically when adding them to avoid any confusion.
   *   </ul>
   *   <li><u>Naming the parameter drivers</u>: It is strongly advised to give a custom name to the {@link ParameterDriver}(s)
   *   of each DragSensitive model that is added to the object. This will allow you keeping track of the evolution of your models.<br>
   *   Different names are mandatory to differentiate the different drivers.<br>
   *   If you do not specify a name, a default name will be chosen. Example for the drag coefficient:<ul>
   *   <li>Initial DragSensitive model: the driver's default name is "{@link DragSensitive#DRAG_COEFFICIENT}";
   *   <li>Using {@link #addDragSensitiveValidAfter(DragSensitive, AbsoluteDate)}: the driver's default name is
   *   "{@link DragSensitive#DRAG_COEFFICIENT} + {@link #DATE_AFTER} + date.toString()"
   *   <li>Using {@link #addDragSensitiveValidBefore(DragSensitive, AbsoluteDate)}: the driver's default name is
   *   "{@link DragSensitive#DRAG_COEFFICIENT} + {@link #DATE_BEFORE} + date.toString()"
   *   </ul>
   *   </ul>
   *  <b>Example following previous recommendations</b>:<ul>
   *  <li>Given:
   *  <ul>
   *  <li><code>atmosphere</code>: an {@link Atmosphere atmospheric model};
   *  <li><code>isotropicDrag0, 1 and 2</code>: three {@link org.orekit.forces.drag.IsotropicDrag IsotropicDrag} models;
   *  <li><code>date</code>: an {@link AbsoluteDate}.
   *  </ul>
  *  <li>Name the drivers:<br>
  *  <code>isotropicDrag0.getDragParametersDrivers()[0].setName = "Cd0";</code><br>
  *  <code>isotropicDrag1.getDragParametersDrivers()[0].setName = "Cd1";</code><br>
  *  <code>isotropicDrag2.getDragParametersDrivers()[0].setName = "Cd2";</code><br>
  *  <li>Initialize the model: <br>
  *  <code>TimeSpanDragForce force = new TimeSpanDragForce(atmosphere, isotropicDrag0);</code>
  *  <li>Set the second and third model one Julian day apart each:<br>
  *  <code>force.addDragSensitiveValidAfter(isotropicDrag1, date.shiftedBy(Constants.JULIAN_DAY));</code><br>
  *  <code>force.addDragSensitiveValidAfter(isotropicDrag2, date.shiftedBy(2 * Constants.JULIAN_DAY));</code><br>
  *  <li>With this, your model will have the following properties:
  *  <ul>
  *  <li>t in ]-∞, date + 1 day [ / Cd = Cd0
  *  <li>t in [date + 1 day, date + 2days [ / Cd = Cd1
  *  <li>t in [date + 2 days, +∞ [ / Cd = Cd2
  *  </ul>
  *  </ul>
  *  <p>
  *  <b>Warning</b>:<br> The TimeSpanDragForce model is versatile and you could end up with non-physical modeling.<br>
  *  For example you could add 2 {@link org.orekit.forces.drag.IsotropicDrag IsotropicDrag} models with different areas,
  *  or one {@link org.orekit.forces.drag.IsotropicDrag IsotropicDrag} model and then one
  *  {@link org.orekit.forces.BoxAndSolarArraySpacecraft BoxAndSolarArraySpacecraft} model.<br>
  *  It is up to you to ensure that your models are consistent with each other, Orekit will not perform any check for that.
  *  </p>
  * @author Maxime Journot
  * @since 10.2
  */
 public class TimeSpanDragForce extends AbstractDragForceModel {
 
     /** Prefix for dates before in the parameter drivers' name. */
     public static final String DATE_BEFORE = " - Before ";
 
     /** Prefix for dates after in the parameter drivers' name. */
     public static final String DATE_AFTER = " - After ";
 
     /** TimeSpanMap of DragSensitive objects. */
     private final TimeSpanMap<DragSensitive> dragSensitiveTimeSpanMap;
 
     /** Time scale used for the default names of the drag parameter drivers. */
     private final TimeScale timeScale;
 
     /** Constructor with default UTC time scale for the default names of the drag parameter drivers.
      * @param atmosphere atmospheric model
      * @param spacecraft Time scale used for the default names of the drag parameter drivers
      */
     @DefaultDataContext
     public TimeSpanDragForce(final Atmosphere atmosphere,
                              final DragSensitive spacecraft) {
         super(atmosphere);
         this.dragSensitiveTimeSpanMap = new TimeSpanMap<>(spacecraft);
         this.timeScale = TimeScalesFactory.getUTC();
     }
 
     /** Constructor.
      * @param atmosphere atmospheric model
      * @param spacecraft the initial object physical and geometric information
      * @param timeScale Time scale used for the default names of the drag parameter drivers
      */
     public TimeSpanDragForce(final Atmosphere atmosphere,
                              final DragSensitive spacecraft,
                              final TimeScale timeScale) {
         super(atmosphere);
         this.dragSensitiveTimeSpanMap = new TimeSpanMap<>(spacecraft);
         this.timeScale = timeScale;
     }
 
     /** Add a DragSensitive entry valid before a limit date.<br>
      * Using <code>addDragSensitiveValidBefore(entry, t)</code> will make <code>entry</code>
      * valid in ]-∞, t[ (note the open bracket).
      * @param dragSensitive DragSensitive entry
      * @param latestValidityDate date before which the entry is valid
      * (must be different from <b>all</b> dates already used for transitions)
      */
     public void addDragSensitiveValidBefore(final DragSensitive dragSensitive, final AbsoluteDate latestValidityDate) {
         dragSensitiveTimeSpanMap.addValidBefore(changeDragParameterDriversNames(dragSensitive,
                                                                                 latestValidityDate,
                                                                                 DATE_BEFORE),
                                                 latestValidityDate, false);
     }
 
     /** Add a DragSensitive entry valid after a limit date.<br>
      * Using <code>addDragSensitiveValidAfter(entry, t)</code> will make <code>entry</code>
      * valid in [t, +∞[ (note the closed bracket).
      * @param dragSensitive DragSensitive entry
      * @param earliestValidityDate date after which the entry is valid
      * (must be different from <b>all</b> dates already used for transitions)
      */
     public void addDragSensitiveValidAfter(final DragSensitive dragSensitive, final AbsoluteDate earliestValidityDate) {
         dragSensitiveTimeSpanMap.addValidAfter(changeDragParameterDriversNames(dragSensitive,
                                                                                earliestValidityDate,
                                                                                DATE_AFTER),
                                                earliestValidityDate, false);
     }
 
     /** Get the {@link DragSensitive} model valid at a date.
      * @param date the date of validity
      * @return the DragSensitive model valid at date
      */
     public DragSensitive getDragSensitive(final AbsoluteDate date) {
         return dragSensitiveTimeSpanMap.get(date);
     }
 
     /** Get the {@link DragSensitive} {@link Span} containing a specified date.
      * @param date date belonging to the desired time span
      * @return the DragSensitive time span containing the specified date
      */
     public Span<DragSensitive> getDragSensitiveSpan(final AbsoluteDate date) {
         return dragSensitiveTimeSpanMap.getSpan(date);
     }
 
     /** Extract a range of the {@link DragSensitive} map.
      * <p>
      * The object returned will be a new independent instance that will contain
      * only the transitions that lie in the specified range.
      * </p>
      * See the {@link TimeSpanMap#extractRange TimeSpanMap.extractRange method} for more.
      * @param start earliest date at which a transition is included in the range
      * (may be set to {@link AbsoluteDate#PAST_INFINITY} to keep all early transitions)
      * @param end latest date at which a transition is included in the r
      * (may be set to {@link AbsoluteDate#FUTURE_INFINITY} to keep all late transitions)
      * @return a new TimeSpanMap instance of DragSensitive with all transitions restricted to the specified range
      */
     public TimeSpanMap<DragSensitive> extractDragSensitiveRange(final AbsoluteDate start, final AbsoluteDate end) {
         return dragSensitiveTimeSpanMap.extractRange(start, end);
     }
 
     /** Get the first {@link Span time span} of the drag sensitive time span map.
      * @return the first {@link Span time span} of the drag sensitive time span map
      * @since 11.1
      */
     public Span<DragSensitive> getFirstSpan() {
         return dragSensitiveTimeSpanMap.getFirstSpan();
     }
 
     /** {@inheritDoc} */
     @Override
     public Vector3D acceleration(final SpacecraftState s, final double[] parameters) {
 
         // Local atmospheric density
         final AbsoluteDate date     = s.getDate();
         final Frame        frame    = s.getFrame();
         final Vector3D     position = s.getPosition();
         final double rho    = getAtmosphere().getDensity(date, position, frame);
 
         // Spacecraft relative velocity with respect to the atmosphere
         final Vector3D vAtm = getAtmosphere().getVelocity(date, position, frame);
         final Vector3D relativeVelocity = vAtm.subtract(s.getPVCoordinates().getVelocity());
 
         // Extract the proper parameters valid at date from the input array
         final double[] extractedParameters = extractParameters(parameters, date);
 
         // Compute and return drag acceleration
         return getDragSensitive(date).dragAcceleration(s, rho, relativeVelocity, extractedParameters);
 
     }
 
     /** {@inheritDoc} */
     @Override
     public <T extends CalculusFieldElement<T>> FieldVector3D<T> acceleration(final FieldSpacecraftState<T> s,
                                                                              final T[] parameters) {
         // Density and its derivatives
         final T rho = getFieldDensity(s);
 
         // Spacecraft relative velocity with respect to the atmosphere
         final FieldAbsoluteDate<T> date     = s.getDate();
         final Frame                frame    = s.getFrame();
         final FieldVector3D<T>     position = s.getPosition();
         final FieldVector3D<T> vAtm = getAtmosphere().getVelocity(date, position, frame);
         final FieldVector3D<T> relativeVelocity = vAtm.subtract(s.getPVCoordinates().getVelocity());
 
         // Extract the proper parameters valid at date from the input array
         final T[] extractedParameters = extractParameters(parameters, date);
 
         // Compute and return drag acceleration
         return getDragSensitive(date.toAbsoluteDate()).dragAcceleration(s, rho, relativeVelocity, extractedParameters);
     }
 
     /**{@inheritDoc}
      * <p>
      * A date detector is used to cleanly stop the propagator and reset
      * the state derivatives at transition dates.
      * </p>
      */
     @Override
     public Stream<EventDetector> getEventDetectors() {
 
         // Get the transitions' dates from the TimeSpanMap
         final AbsoluteDate[] transitionDates = getTransitionDates();
 
         // create detector and return it in Stream
         final DateDetector detector = getDateDetector(transitionDates);
         return Stream.of(detector);
     }
 
     /** {@inheritDoc}
      * <p>
      * A date detector is used to cleanly stop the propagator and reset
      * the state derivatives at transition dates.
      * </p>
      */
     @Override
     public <T extends CalculusFieldElement<T>> Stream<FieldEventDetector<T>> getFieldEventDetectors(final Field<T> field) {
 
         // Get the transitions' dates from the TimeSpanMap
         final AbsoluteDate[] transitionDates = getTransitionDates();
 
         // create detector and return it in Stream
         final FieldDateDetector<T> detector = getFieldDateDetector(field, transitionDates);
         return Stream.of(detector);
     }
 
     /** {@inheritDoc}
      * <p>
      * All the parameter drivers of all DragSensitive models are returned in an array.
      * Models are ordered chronologically.
      * </p>
      */
     @Override
     public List<ParameterDriver> getParametersDrivers() {
 
         // Get all transitions from the TimeSpanMap
         final List<ParameterDriver> listParameterDrivers = new ArrayList<>();
 
         // Loop on the spans
         for (Span<DragSensitive> span = getFirstSpan(); span != null; span = span.next()) {
             // Add all the parameter drivers of the span
             for (ParameterDriver driver : span.getData().getDragParametersDrivers()) {
                 // Add the driver only if the name does not exist already
                 if (!findByName(listParameterDrivers, driver.getName())) {
                     listParameterDrivers.add(driver);
                 }
             }
         }
 
         // Return an array of parameter drivers with no duplicated name
         return listParameterDrivers;
 
     }
 
     /** Extract the proper parameter drivers' values from the array in input of the
      * {@link #acceleration(SpacecraftState, double[]) acceleration} method.
      *  Parameters are filtered given an input date.
      * @param parameters the input parameters array
      * @param date the date
      * @return the parameters given the date
      */
     public double[] extractParameters(final double[] parameters, final AbsoluteDate date) {
 
         // Get the drag parameter drivers of the date
         final List<ParameterDriver> dragParameterDriver = getDragSensitive(date).getDragParametersDrivers();
 
         // Find out the indexes of the parameters in the whole array of parameters
         final List<ParameterDriver> allParameters = getParametersDrivers();
         final double[] outParameters = new double[dragParameterDriver.size()];
         int index = 0;
         for (int i = 0; i < allParameters.size(); i++) {
             final String driverName = allParameters.get(i).getName();
             for (ParameterDriver dragDriver : dragParameterDriver) {
                 if (dragDriver.getName().equals(driverName)) {
                     outParameters[index++] = parameters[i];
                 }
             }
         }
         return outParameters;
     }
 
     /** Extract the proper parameter drivers' values from the array in input of the
      * {@link #acceleration(FieldSpacecraftState, CalculusFieldElement[]) acceleration} method.
      *  Parameters are filtered given an input date.
      * @param parameters the input parameters array
      * @param date the date
      * @param <T> extends CalculusFieldElement
      * @return the parameters given the date
      */
     public <T extends CalculusFieldElement<T>> T[] extractParameters(final T[] parameters,
                                                                  final FieldAbsoluteDate<T> date) {
 
         // Get the drag parameter drivers of the date
         final List<ParameterDriver> dragPD = getDragSensitive(date.toAbsoluteDate()).getDragParametersDrivers();
 
         // Find out the indexes of the parameters in the whole array of parameters
         final List<ParameterDriver> allParameters = getParametersDrivers();
         final T[] outParameters = MathArrays.buildArray(date.getField(), dragPD.size());
         int index = 0;
         for (int i = 0; i < allParameters.size(); i++) {
             final String driverName = allParameters.get(i).getName();
             for (ParameterDriver dragDriver : dragPD) {
                 if (dragDriver.getName().equals(driverName)) {
                     outParameters[index++] = parameters[i];
                 }
             }
         }
         return outParameters;
     }
 
     /** Find if a parameter driver with a given name already exists in a list of parameter drivers.
      * @param driversList the list of parameter drivers
      * @param name the parameter driver's name to filter with
      * @return true if the name was found, false otherwise
      */
     private boolean findByName(final List<ParameterDriver> driversList, final String name) {
         return ParameterDriversProvider.findByName(driversList, name);
     }
 
     /** Get the dates of the transitions for the drag sensitive models {@link TimeSpanMap}.
      * @return dates of the transitions for the drag sensitive models {@link TimeSpanMap}
      */
     private AbsoluteDate[] getTransitionDates() {
 
         // Get all transitions
         final List<AbsoluteDate> listDates = new ArrayList<>();
 
         // Extract all the transitions' dates
         for (Transition<DragSensitive> transition = getFirstSpan().getEndTransition(); transition != null; transition = transition.next()) {
             listDates.add(transition.getDate());
         }
         // Return the array of transition dates
         return listDates.toArray(new AbsoluteDate[0]);
     }
 
     /** Change the parameter drivers names of a {@link DragSensitive} model, if needed.
      * <p>
      * This is done to avoid that several parameter drivers have the same name.<br>
      * It is done only if the user hasn't modify the DragSensitive parameter drivers default names.
      * </p>
      * @param dragSensitive the DragSensitive model
      * @param date the date used in the parameter driver's name
      * @param datePrefix the date prefix used in the parameter driver's name
      * @return the DragSensitive with its drivers' names changed
      */
     private DragSensitive changeDragParameterDriversNames(final DragSensitive dragSensitive,
                                                           final AbsoluteDate date,
                                                           final String datePrefix) {
         // Loop on the parameter drivers of the DragSensitive model
         for (ParameterDriver driver: dragSensitive.getDragParametersDrivers()) {
             final String driverName = driver.getName();
 
             // If the name is the default name for DragSensitive parameter drivers
             // Modify the name to add the prefix and the date
             if (driverName.equals(DragSensitive.GLOBAL_DRAG_FACTOR) ||
                 driverName.equals(DragSensitive.DRAG_COEFFICIENT) ||
                 driverName.equals(DragSensitive.LIFT_RATIO)) {
                 driver.setName(driverName + datePrefix + date.toString(timeScale));
             }
         }
         return dragSensitive;
     }
 
 }