/* Copyright 2002-2024 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;
  
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.HashMap;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Map;
  import java.util.Queue;
  
  import org.hipparchus.linear.RealMatrix;
  import org.orekit.attitudes.AttitudeProvider;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.OrekitMessages;
  import org.orekit.frames.Frame;
  import org.orekit.propagation.sampling.StepHandlerMultiplexer;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.DoubleArrayDictionary;
  import org.orekit.utils.TimeSpanMap;
  
  /** Common handling of {@link Propagator} methods for analytical propagators.
   * <p>
   * This abstract class allows to provide easily the full set of {@link Propagator}
   * methods, including all propagation modes support and discrete events support for
   * any simple propagation method.
   * </p>
   * @author Luc Maisonobe
   */
  public abstract class AbstractPropagator implements Propagator {
  
      /** Multiplexer for step handlers. */
      private final StepHandlerMultiplexer multiplexer;
  
      /** Start date. */
      private AbsoluteDate startDate;
  
      /** Attitude provider. */
      private AttitudeProvider attitudeProvider;
  
      /** Providers for additional states. */
      private final List<AdditionalStateProvider> additionalStateProviders;
  
      /** States managed by no generators. */
      private final Map<String, TimeSpanMap<double[]>> unmanagedStates;
  
      /** Initial state. */
      private SpacecraftState initialState;
  
      /** Harvester for State Transition Matrix and Jacobian matrix. */
      private AbstractMatricesHarvester harvester;
  
      /** Build a new instance.
       */
      protected AbstractPropagator() {
          multiplexer              = new StepHandlerMultiplexer();
          additionalStateProviders = new ArrayList<>();
          unmanagedStates          = new HashMap<>();
          harvester                = null;
      }
  
      /** Set a start date.
       * @param startDate start date
       */
      protected void setStartDate(final AbsoluteDate startDate) {
          this.startDate = startDate;
      }
  
      /** Get the start date.
       * @return start date
       */
      protected AbsoluteDate getStartDate() {
          return startDate;
      }
  
      /**  {@inheritDoc} */
      public AttitudeProvider getAttitudeProvider() {
          return attitudeProvider;
      }
  
      /**  {@inheritDoc} */
      public void setAttitudeProvider(final AttitudeProvider attitudeProvider) {
          this.attitudeProvider = attitudeProvider;
      }
 
     /** {@inheritDoc} */
     public SpacecraftState getInitialState() {
         return initialState;
     }
 
     /** {@inheritDoc} */
     public Frame getFrame() {
         return initialState.getFrame();
     }
 
     /** {@inheritDoc} */
     public void resetInitialState(final SpacecraftState state) {
         initialState = state;
         setStartDate(state.getDate());
     }
 
     /** {@inheritDoc} */
     public StepHandlerMultiplexer getMultiplexer() {
         return multiplexer;
     }
 
     /** {@inheritDoc} */
     @Override
     public void addAdditionalStateProvider(final AdditionalStateProvider provider) {
 
         // check if the name is already used
         if (isAdditionalStateManaged(provider.getName())) {
             // this additional state is already registered, complain
             throw new OrekitException(OrekitMessages.ADDITIONAL_STATE_NAME_ALREADY_IN_USE,
                                       provider.getName());
         }
 
         // this is really a new name, add it
         additionalStateProviders.add(provider);
 
     }
 
     /** {@inheritDoc} */
     @Override
     public List<AdditionalStateProvider> getAdditionalStateProviders() {
         return Collections.unmodifiableList(additionalStateProviders);
     }
 
     /** {@inheritDoc} */
     @Override
     public MatricesHarvester setupMatricesComputation(final String stmName, final RealMatrix initialStm,
                                                       final DoubleArrayDictionary initialJacobianColumns) {
         if (stmName == null) {
             throw new OrekitException(OrekitMessages.NULL_ARGUMENT, "stmName");
         }
         harvester = createHarvester(stmName, initialStm, initialJacobianColumns);
         return harvester;
     }
 
     /** Create the harvester suitable for propagator.
      * @param stmName State Transition Matrix state name
      * @param initialStm initial State Transition Matrix ∂Y/∂Y₀,
      * if null (which is the most frequent case), assumed to be 6x6 identity
      * @param initialJacobianColumns initial columns of the Jacobians matrix with respect to parameters,
      * if null or if some selected parameters are missing from the dictionary, the corresponding
      * initial column is assumed to be 0
      * @return harvester to retrieve computed matrices during and after propagation
      * @since 11.1
      */
     protected AbstractMatricesHarvester createHarvester(final String stmName, final RealMatrix initialStm,
                                                         final DoubleArrayDictionary initialJacobianColumns) {
         // FIXME: not implemented as of 11.1
         throw new UnsupportedOperationException();
     }
 
     /** Get the harvester.
      * @return harvester, or null if it was not created
      * @since 11.1
      */
     protected AbstractMatricesHarvester getHarvester() {
         return harvester;
     }
 
     /** Update state by adding unmanaged states.
      * @param original original state
      * @return updated state, with unmanaged states included
      * @see #updateAdditionalStates(SpacecraftState)
      */
     protected SpacecraftState updateUnmanagedStates(final SpacecraftState original) {
 
         // start with original state,
         // which may already contain additional states, for example in interpolated ephemerides
         SpacecraftState updated = original;
 
         // update the states not managed by providers
         for (final Map.Entry<String, TimeSpanMap<double[]>> entry : unmanagedStates.entrySet()) {
             updated = updated.addAdditionalState(entry.getKey(),
                                                  entry.getValue().get(original.getDate()));
         }
 
         return updated;
 
     }
 
     /** Update state by adding all additional states.
      * @param original original state
      * @return updated state, with all additional states included
      * (including {@link #updateUnmanagedStates(SpacecraftState) unmanaged} states)
      * @see #addAdditionalStateProvider(AdditionalStateProvider)
      * @see #updateUnmanagedStates(SpacecraftState)
      */
     protected SpacecraftState updateAdditionalStates(final SpacecraftState original) {
 
         // start with original state and unmanaged states
         SpacecraftState updated = updateUnmanagedStates(original);
 
         // set up queue for providers
         final Queue<AdditionalStateProvider> pending = new LinkedList<>(getAdditionalStateProviders());
 
         // update the additional states managed by providers, taking care of dependencies
         int yieldCount = 0;
         while (!pending.isEmpty()) {
             final AdditionalStateProvider provider = pending.remove();
             if (provider.yields(updated)) {
                 // this generator has to wait for another one,
                 // we put it again in the pending queue
                 pending.add(provider);
                 if (++yieldCount >= pending.size()) {
                     // all pending providers yielded!, they probably need data not yet initialized
                     // we let the propagation proceed, if these data are really needed right now
                     // an appropriate exception will be triggered when caller tries to access them
                     break;
                 }
             } else {
                 // we can use this provider right now
                 updated    = provider.update(updated);
                 yieldCount = 0;
             }
         }
 
         return updated;
 
     }
 
     /**
      * Initialize the additional state providers at the start of propagation.
      * @param target date of propagation. Not equal to {@code initialState.getDate()}.
      * @since 11.2
      */
     protected void initializeAdditionalStates(final AbsoluteDate target) {
         for (final AdditionalStateProvider provider : additionalStateProviders) {
             provider.init(initialState, target);
         }
     }
 
     /** {@inheritDoc} */
     public boolean isAdditionalStateManaged(final String name) {
         for (final AdditionalStateProvider provider : additionalStateProviders) {
             if (provider.getName().equals(name)) {
                 return true;
             }
         }
         return false;
     }
 
     /** {@inheritDoc} */
     public String[] getManagedAdditionalStates() {
         final String[] managed = new String[additionalStateProviders.size()];
         for (int i = 0; i < managed.length; ++i) {
             managed[i] = additionalStateProviders.get(i).getName();
         }
         return managed;
     }
 
     /** {@inheritDoc} */
     public SpacecraftState propagate(final AbsoluteDate target) {
         if (startDate == null) {
             startDate = getInitialState().getDate();
         }
         return propagate(startDate, target);
     }
 
     /** Initialize propagation.
      * @since 10.1
      */
     protected void initializePropagation() {
 
         unmanagedStates.clear();
 
         if (initialState != null) {
             // there is an initial state
             // (null initial states occur for example in interpolated ephemerides)
             // copy the additional states present in initialState but otherwise not managed
             for (final DoubleArrayDictionary.Entry initial : initialState.getAdditionalStatesValues().getData()) {
                 if (!isAdditionalStateManaged(initial.getKey())) {
                     // this additional state is in the initial state, but is unknown to the propagator
                     // we store it in a way event handlers may change it
                     unmanagedStates.put(initial.getKey(), new TimeSpanMap<>(initial.getValue()));
                 }
             }
         }
     }
 
     /** Notify about a state change.
      * @param state new state
      */
     protected void stateChanged(final SpacecraftState state) {
         final AbsoluteDate date    = state.getDate();
         final boolean      forward = date.durationFrom(getStartDate()) >= 0.0;
         for (final DoubleArrayDictionary.Entry changed : state.getAdditionalStatesValues().getData()) {
             final TimeSpanMap<double[]> tsm = unmanagedStates.get(changed.getKey());
             if (tsm != null) {
                 // this is an unmanaged state
                 if (forward) {
                     tsm.addValidAfter(changed.getValue(), date, false);
                 } else {
                     tsm.addValidBefore(changed.getValue(), date, false);
                 }
             }
         }
     }
 
 }