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    * contributor license agreements.  See the NOTICE file distributed with
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    * 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
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    *
    *   http://www.apache.org/licenses/LICENSE-2.0
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   * Unless required by applicable law or agreed to in writing, software
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  package org.orekit.models.earth.atmosphere.data;
  
  import java.util.ArrayList;
  import java.util.List;
  import java.util.stream.Collectors;
  
  import org.hipparchus.analysis.UnivariateFunction;
  import org.hipparchus.analysis.interpolation.LinearInterpolator;
  import org.hipparchus.util.FastMath;
  import org.orekit.annotation.DefaultDataContext;
  import org.orekit.data.DataContext;
  import org.orekit.data.DataProvidersManager;
  import org.orekit.data.DataSource;
  import org.orekit.models.earth.atmosphere.data.MarshallSolarActivityFutureEstimationLoader.LineParameters;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.time.DateComponents;
  import org.orekit.time.DateTimeComponents;
  import org.orekit.time.TimeComponents;
  import org.orekit.time.TimeScale;
  import org.orekit.time.TimeStampedDouble;
  import org.orekit.utils.Constants;
  import org.orekit.utils.GenericTimeStampedCache;
  import org.orekit.utils.OrekitConfiguration;
  import org.orekit.utils.TimeStampedGenerator;
  
  /**
   * This class provides solar activity data needed by atmospheric models: F107 solar flux, Ap and Kp indexes.
   * <p>
   * Data comes from the NASA Marshall Solar Activity Future Estimation (MSAFE) as estimates of monthly F10.7
   * Mean solar flux and Ap geomagnetic parameter
   * (see <a href="https://www.nasa.gov/solar-cycle-progression-and-forecast"> Marshall Solar Activity website</a>).
   *
   * <p>Data can be retrieved at the NASA
   * <a href="https://www.nasa.gov/solar-cycle-progression-and-forecast/archived-forecast/"> Marshall Solar Activity archived forecast</a>.
   * Here Kp indices are deduced from Ap indexes, which in turn are tabulated equivalent of retrieved Ap values.
   *
   * <p> If several MSAFE files are available, some dates may appear in several files (for example August 2007 is in all files from
   * the first one published in March 1999 to the February 2008 file). In this case, the data from the most recent file is used
   * and the older ones are discarded. The date of the file is assumed to be 6 months after its first entry (which explains why
   * the file having August 2007 as its first entry is the February 2008 file). This implies that MSAFE files must <em>not</em>
   * be edited to change their time span, otherwise this would break the old entries overriding mechanism.
   *
   * <p>With these data, the {@link #getInstantFlux(AbsoluteDate)} and {@link #getMeanFlux(AbsoluteDate)} methods return the same
   * values and the {@link #get24HoursKp(AbsoluteDate)} and {@link #getThreeHourlyKP(AbsoluteDate)} methods return the same
   * values.
   *
   * <p>Conversion from Ap index values in the MSAFE file to Kp values used by atmosphere models is done using Jacchia's equation
   * in [1].
   *
   * <p>With these data, the {@link #getAp(AbsoluteDate date)} method returns an array of seven times the same daily Ap value,
   * i.e. it is suited to be used only with the {@link org.orekit.models.earth.atmosphere.NRLMSISE00 NRLMSISE00} atmospheric
   * model where the switch #9 is set to 1.
   *
   * <h2>References</h2>
   *
   * <ol> <li> Jacchia, L. G. "CIRA 1972, recent atmospheric models, and improvements in
   * progress." COSPAR, 21st Plenary Meeting. Vol. 1. 1978. </li> </ol>
   *
   * @author Bruno Revelin
   * @author Luc Maisonobe
   * @author Evan Ward
   * @author Pascal Parraud
   * @author Vincent Cucchietti
   */
  public class MarshallSolarActivityFutureEstimation
          extends AbstractSolarActivityData<LineParameters, MarshallSolarActivityFutureEstimationLoader> {
  
      /**
       * Default regular expression for the supported name that work with all officially published files.
       *
       * @since 10.0
       */
      public static final String DEFAULT_SUPPORTED_NAMES =
              "\\p{Alpha}\\p{Lower}\\p{Lower}\\p{Digit}\\p{Digit}\\p{Digit}\\p{Digit}(?:f|F)10(?:[-_]prd)?\\.(?:txt|TXT)";
  
      /** Serializable UID. */
      private static final long serialVersionUID = -5212198874900835369L;
  
      /** Selected strength level of activity. */
      private final StrengthLevel strengthLevel;
  
      /** Cache dedicated to average flux. */
      private final transient GenericTimeStampedCache<TimeStampedDouble> averageFluxCache;
 
     /**
      * Simple constructor. This constructor uses the {@link DataContext#getDefault() default data context}.
      * <p>
      * The original file names used by NASA Marshall space center are of the form: may2019f10_prd.txt or Oct1999F10.TXT. So a
      * recommended regular expression for the supported name that work with all published files is:
      * {@link #DEFAULT_SUPPORTED_NAMES}.
      * <p>
      * It provides a default configuration for the thread safe cache :
      * <ul>
      *     <li>Number of slots : {@code OrekitConfiguration.getCacheSlotsNumber()}</li>
      *     <li>Max span : {@code Constants.JULIAN_YEAR}</li>
      *     <li>Max span interval : {@code 0}</li>
      * </ul>
      *
      * @param supportedNames regular expression for supported files names
      * @param strengthLevel selected strength level of activity
      *
      * @see #MarshallSolarActivityFutureEstimation(String, StrengthLevel, DataProvidersManager, TimeScale)
      */
     @DefaultDataContext
     public MarshallSolarActivityFutureEstimation(final String supportedNames,
                                                  final StrengthLevel strengthLevel) {
         this(supportedNames, strengthLevel,
              DataContext.getDefault().getDataProvidersManager(),
              DataContext.getDefault().getTimeScales().getUTC());
     }
 
     /**
      * Constructor that allows specifying the source of the MSAFE auxiliary data files.
      * <p>
      * It provides a default configuration for the thread safe cache :
      * <ul>
      *     <li>Number of slots : {@code OrekitConfiguration.getCacheSlotsNumber()}</li>
      *     <li>Max span : {@code 31 * Constants.JULIAN_DAY}</li>
      *     <li>Max interval : {@code 0}</li>
      *     <li>Minimum step: {@code 27 * Constants.JULIAN_DAY}</li>
      * </ul>
      *
      * @param supportedNames regular expression for supported files names
      * @param strengthLevel selected strength level of activity
      * @param dataProvidersManager provides access to auxiliary data files.
      * @param utc UTC time scale.
      *
      * @since 10.1
      */
     public MarshallSolarActivityFutureEstimation(final String supportedNames,
                                                  final StrengthLevel strengthLevel,
                                                  final DataProvidersManager dataProvidersManager,
                                                  final TimeScale utc) {
         this(supportedNames, strengthLevel, dataProvidersManager, utc, OrekitConfiguration.getCacheSlotsNumber(),
              Constants.JULIAN_DAY * 31, 0, Constants.JULIAN_DAY * 27);
     }
 
     /**
      * Constructor that allows specifying the source of the MSAFE auxiliary data files and customizable thread safe cache
      * configuration.
      *
      * @param supportedNames regular expression for supported files names
      * @param strengthLevel selected strength level of activity
      * @param dataProvidersManager provides access to auxiliary data files.
      * @param utc UTC time scale.
      * @param maxSlots maximum number of independent cached time slots in the
      * {@link GenericTimeStampedCache time-stamped cache}
      * @param maxSpan maximum duration span in seconds of one slot in the {@link GenericTimeStampedCache time-stamped cache}
      * @param maxInterval time interval above which a new slot is created in the
      * {@link GenericTimeStampedCache time-stamped cache}
      * @param minimumStep overriding minimum step designed for non-homogeneous tabulated values. To be used for example when
      * caching monthly tabulated values. May be null.
      *
      * @since 10.1
      */
     public MarshallSolarActivityFutureEstimation(final String supportedNames,
                                                  final StrengthLevel strengthLevel,
                                                  final DataProvidersManager dataProvidersManager,
                                                  final TimeScale utc,
                                                  final int maxSlots,
                                                  final double maxSpan,
                                                  final double maxInterval,
                                                  final double minimumStep) {
         super(supportedNames, new MarshallSolarActivityFutureEstimationLoader(strengthLevel, utc),
               dataProvidersManager, utc, maxSlots, maxSpan, maxInterval, minimumStep);
 
         // Initialise fields
         this.strengthLevel    = strengthLevel;
         this.averageFluxCache = new GenericTimeStampedCache<>(N_NEIGHBORS, OrekitConfiguration.getCacheSlotsNumber(),
                                                               Constants.JULIAN_DAY, 0, new AverageFluxGenerator());
     }
 
     /**
      * Simple constructor which use the {@link DataContext#getDefault() default data context}.
      * <p>
      * It provides a default configuration for the thread safe cache :
      * <ul>
      *     <li>Number of slots : {@code OrekitConfiguration.getCacheSlotsNumber()}</li>
      *     <li>Max span : {@code 31 * Constants.JULIAN_DAY}</li>
      *     <li>Max interval : {@code 0}</li>
      *     <li>Minimum step: {@code 27 * Constants.JULIAN_DAY}</li>
      * </ul>
      *
      * @param source source for the data
      * @param strengthLevel selected strength level of activity
      *
      * @since 12.0
      */
     @DefaultDataContext
     public MarshallSolarActivityFutureEstimation(final DataSource source,
                                                  final StrengthLevel strengthLevel) {
         this(source, strengthLevel, DataContext.getDefault().getTimeScales().getUTC());
     }
 
     /**
      * Simple constructor.
      * <p>
      * It provides a default configuration for the thread safe cache :
      * <ul>
      *     <li>Number of slots : {@code OrekitConfiguration.getCacheSlotsNumber()}</li>
      *     <li>Max span : {@code 31 * Constants.JULIAN_DAY}</li>
      *     <li>Max interval : {@code 0}</li>
      *     <li>Minimum step: {@code 27 * Constants.JULIAN_DAY}</li>
      * </ul>
      *
      * @param source source for the data
      * @param strengthLevel selected strength level of activity
      * @param utc UTC time scale
      *
      * @since 12.0
      */
     public MarshallSolarActivityFutureEstimation(final DataSource source,
                                                  final StrengthLevel strengthLevel,
                                                  final TimeScale utc) {
         this(source, strengthLevel, utc, OrekitConfiguration.getCacheSlotsNumber(),
              Constants.JULIAN_DAY * 31, 0, Constants.JULIAN_DAY * 27);
     }
 
     /**
      * Constructor with customizable thread safe cache configuration.
      *
      * @param source source for the data
      * @param strengthLevel selected strength level of activity
      * @param utc UTC time scale
      * @param maxSlots maximum number of independent cached time slots in the
      * {@link GenericTimeStampedCache time-stamped cache}
      * @param maxSpan maximum duration span in seconds of one slot in the {@link GenericTimeStampedCache time-stamped cache}
      * @param maxInterval time interval above which a new slot is created in the
      * {@link GenericTimeStampedCache time-stamped cache}
      * @param minimumStep overriding minimum step designed for non-homogeneous tabulated values. To be used for example when
      * caching monthly tabulated values. Use {@code Double.NaN} otherwise.
      *
      * @since 12.0
      */
     public MarshallSolarActivityFutureEstimation(final DataSource source,
                                                  final StrengthLevel strengthLevel,
                                                  final TimeScale utc,
                                                  final int maxSlots,
                                                  final double maxSpan,
                                                  final double maxInterval,
                                                  final double minimumStep) {
         super(source, new MarshallSolarActivityFutureEstimationLoader(strengthLevel, utc), utc,
               maxSlots, maxSpan, maxInterval, minimumStep);
         this.strengthLevel    = strengthLevel;
         this.averageFluxCache = new GenericTimeStampedCache<>(N_NEIGHBORS, OrekitConfiguration.getCacheSlotsNumber(),
                                                               Constants.JULIAN_DAY, 0, new AverageFluxGenerator());
     }
 
     /** {@inheritDoc} */
     public double getInstantFlux(final AbsoluteDate date) {
         return getMeanFlux(date);
     }
 
     /** {@inheritDoc} */
     public double getMeanFlux(final AbsoluteDate date) {
         return getLinearInterpolation(date, LineParameters::getF107);
     }
 
     /** {@inheritDoc} */
     public double getThreeHourlyKP(final AbsoluteDate date) {
         return get24HoursKp(date);
     }
 
     /**
      * Get the date of the file from which data at the specified date comes from.
      * <p>
      * If several MSAFE files are available, some dates may appear in several files (for example August 2007 is in all files
      * from the first one published in March 1999 to the February 2008 file). In this case, the data from the most recent
      * file is used and the older ones are discarded. The date of the file is assumed to be 6 months after its first entry
      * (which explains why the file having August 2007 as its first entry is the February 2008 file). This implies that MSAFE
      * files must <em>not</em> be edited to change their time span, otherwise this would break the old entries overriding
      * mechanism.
      * </p>
      *
      * @param date date of the solar activity data
      *
      * @return date of the file
      */
     public DateComponents getFileDate(final AbsoluteDate date) {
         // Get the neighboring solar activity
         final LocalSolarActivity localSolarActivity = new LocalSolarActivity(date);
         final LineParameters     previousParam      = localSolarActivity.getPreviousParam();
         final LineParameters     currentParam       = localSolarActivity.getNextParam();
 
         // Choose which file date to return
         final double dtP = date.durationFrom(previousParam.getDate());
         final double dtC = currentParam.getDate().durationFrom(date);
         return (dtP < dtC) ? previousParam.getFileDate() : currentParam.getFileDate();
     }
 
     /**
      * The Kp index is derived from the Ap index.
      * <p>The method used is explained on <a
      * href="http://www.ngdc.noaa.gov/stp/GEOMAG/kp_ap.html"> NOAA website.</a> as follows:</p>
      * <p>The scale is 0 to 9 expressed in thirds of a unit, e.g. 5- is 4 2/3,
      * 5 is 5 and 5+ is 5 1/3. The ap (equivalent range) index is derived from the Kp index as follows:</p>
      * <table border="1">
      * <caption>Kp / Ap Conversion Table</caption>
      * <tbody>
      * <tr>
      * <td>Kp</td><td>0o</td><td>0+</td><td>1-</td><td>1o</td><td>1+</td><td>2-</td><td>2o</td><td>2+</td><td>3-</td><td>3o</td><td>3+</td><td>4-</td><td>4o</td><td>4+</td>
      * </tr>
      * <tr>
      * <td>ap</td><td>0</td><td>2</td><td>3</td><td>4</td><td>5</td><td>6</td><td>7</td><td>9</td><td>12</td><td>15</td><td>18</td><td>22</td><td>27</td><td>32</td>
      * </tr>
      * <tr>
      * <td>Kp</td><td>5-</td><td>5o</td><td>5+</td><td>6-</td><td>6o</td><td>6+</td><td>7-</td><td>7o</td><td>7+</td><td>8-</td><td>8o</td><td>8+</td><td>9-</td><td>9o</td>
      * </tr>
      * <tr>
      * <td>ap</td><td>39</td><td>48</td><td>56</td><td>67</td><td>80</td><td>94</td><td>111</td><td>132</td><td>154</td><td>179</td><td>207</td><td>236</td><td>300</td><td>400</td>
      * </tr>
      * </tbody>
      * </table>
      *
      * @param date date of the Kp data
      *
      * @return the 24H geomagnetic index
      */
     public double get24HoursKp(final AbsoluteDate date) {
         // get the daily Ap
         final double ap = getDailyAp(date);
 
         // get the corresponding Kp index from
         // equation 4 in [1] for Ap to Kp conversion
         return 1.89 * FastMath.asinh(0.154 * ap);
     }
 
     /** {@inheritDoc} */
     public double getDailyFlux(final AbsoluteDate date) {
         return getMeanFlux(date.shiftedBy(-Constants.JULIAN_DAY));
     }
 
     public double getAverageFlux(final AbsoluteDate date) {
         // Extract closest neighbours average
         final List<TimeStampedDouble> neighbors = averageFluxCache.getNeighbors(date).collect(Collectors.toList());
 
         // Create linear interpolating function
         final double[] x = new double[] { 0, 1 };
         final double[] y = neighbors.stream().map(TimeStampedDouble::getValue).mapToDouble(Double::doubleValue).toArray();
 
         final LinearInterpolator interpolator          = new LinearInterpolator();
         final UnivariateFunction interpolatingFunction = interpolator.interpolate(x, y);
 
         // Interpolate
         final AbsoluteDate previousDate = neighbors.get(0).getDate();
         final AbsoluteDate nextDate     = neighbors.get(1).getDate();
         return interpolatingFunction.value(date.durationFrom(previousDate) / nextDate.durationFrom(previousDate));
     }
 
     /** {@inheritDoc} */
     public double[] getAp(final AbsoluteDate date) {
         // Gets the AP for the current date
         final double ap = getDailyAp(date);
 
         // Retuns an array of Ap filled in with the daily Ap only
         return new double[] { ap, ap, ap, ap, ap, ap, ap };
     }
 
     /**
      * Gets the daily Ap index.
      *
      * @param date the current date
      *
      * @return the daily Ap index
      */
     private double getDailyAp(final AbsoluteDate date) {
         return getLinearInterpolation(date, LineParameters::getAp);
     }
 
     /**
      * Get the strength level for activity.
      *
      * @return strength level to set
      */
     public StrengthLevel getStrengthLevel() {
         return strengthLevel;
     }
 
     /** Strength level of activity. */
     public enum StrengthLevel {
 
         /** Strong level of activity. */
         STRONG,
 
         /** Average level of activity. */
         AVERAGE,
 
         /** Weak level of activity. */
         WEAK
 
     }
 
     /** Generator generating average flux data between given dates. */
     private class AverageFluxGenerator implements TimeStampedGenerator<TimeStampedDouble> {
 
         /** {@inheritDoc} */
         @Override
         public List<TimeStampedDouble> generate(final AbsoluteDate existingDate, final AbsoluteDate date) {
             // No prior data in the cache
             if (existingDate == null) {
                 return generateDataFromEarliestToLatestDates(getCurrentDay(date), getNextDay(date));
             }
             // Prior data in the cache, fill with data between date and existing date
             if (date.isBefore(existingDate)) {
                 return generateDataFromEarliestToLatestDates(date, existingDate);
             }
             return generateDataFromEarliestToLatestDates(existingDate, date);
         }
 
         /**
          * Generate data from earliest to latest date.
          *
          * @param earliest earliest date
          * @param latest latest date
          *
          * @return data generated from earliest to latest date
          */
         private List<TimeStampedDouble> generateDataFromEarliestToLatestDates(final AbsoluteDate earliest,
                                                                               final AbsoluteDate latest) {
             final List<TimeStampedDouble> generated = new ArrayList<>();
 
             // Add next computed average until it brackets the latest date
             AbsoluteDate latestNeighbourDate = getCurrentDay(earliest);
             while (latestNeighbourDate.isBeforeOrEqualTo(latest)) {
                 generated.add(computeAverageFlux(latestNeighbourDate));
                 latestNeighbourDate = getNextDay(latestNeighbourDate);
             }
             return generated;
         }
 
         /**
          * Get the current day at midnight.
          *
          * @param date date
          *
          * @return current day at midnight.
          */
         private AbsoluteDate getCurrentDay(final AbsoluteDate date) {
             // Find previous day date time components
             final TimeScale      utc            = getUTC();
             final DateComponents dateComponents = date.getComponents(utc).getDate();
 
             // Create absolute date for previous day
             return new AbsoluteDate(new DateTimeComponents(dateComponents, TimeComponents.H00), utc);
         }
 
         /**
          * Get the next day at midnight.
          *
          * @param date date
          *
          * @return next day at midnight.
          */
         private AbsoluteDate getNextDay(final AbsoluteDate date) {
             // Find previous day date time components
             final TimeScale      utc               = getUTC();
             final DateComponents dateComponents    = date.getComponents(utc).getDate();
             final DateComponents shiftedComponents = new DateComponents(dateComponents, 1);
 
             // Create absolute date for previous day
             return new AbsoluteDate(new DateTimeComponents(shiftedComponents, TimeComponents.H00), utc);
         }
 
         /**
          * Compute the average flux for given absolute date.
          *
          * @param date date at which the average flux is desired
          *
          * @return average flux
          */
         private TimeStampedDouble computeAverageFlux(final AbsoluteDate date) {
             // Extract list of neighbors to compute average
             final TimeStampedGenerator<LineParameters> generator   = getCache().getGenerator();
             final AbsoluteDate                         initialDate = date.shiftedBy(-40 * Constants.JULIAN_DAY);
             final AbsoluteDate                         finalDate   = date.shiftedBy(40 * Constants.JULIAN_DAY);
             final List<LineParameters>                 monthlyData = generator.generate(initialDate, finalDate);
 
             // Create interpolator for given data
             final LinearInterpolator interpolator = new LinearInterpolator();
 
             final double[] x = monthlyData.stream().map(param -> param.getDate().durationFrom(initialDate))
                                           .mapToDouble(Double::doubleValue).toArray();
             final double[] y = monthlyData.stream().map(LineParameters::getF107).mapToDouble(Double::doubleValue).toArray();
 
             final UnivariateFunction interpolatingFunction = interpolator.interpolate(x, y);
 
             // Loops over the 81 days centered on the given date
             double average = 0;
             for (int i = -40; i < 41; i++) {
                 average += interpolatingFunction.value(date.shiftedBy(i * Constants.JULIAN_DAY).durationFrom(initialDate));
             }
 
             // Returns the 81 day average flux
             return new TimeStampedDouble(average / 81, date);
         }
     }
 
 }