/* Copyright 2002-2019 CS Systèmes d'Information
    * Licensed to CS Systèmes d'Information (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.Collection;
  import java.util.List;
  
  import org.orekit.attitudes.AttitudeProvider;
  import org.orekit.attitudes.InertialProvider;
  import org.orekit.frames.Frame;
  import org.orekit.propagation.events.EventDetector;
  import org.orekit.propagation.sampling.OrekitFixedStepHandler;
  import org.orekit.propagation.sampling.OrekitStepHandler;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.PVCoordinatesProvider;
  
  /** This interface provides a way to propagate an orbit at any time.
   *
   * <p>This interface is the top-level abstraction for orbit propagation.
   * It only allows propagation to a predefined date.
   * It is implemented by analytical models which have no time limit,
   * by orbit readers based on external data files, by numerical integrators
   * using rich force models and by continuous models built after numerical
   * integration has been completed and dense output data as been
   * gathered.</p>
   * <p>Note that one single propagator cannot be called from multiple threads.
   * Its configuration can be changed as there is at least a {@link
   * #resetInitialState(SpacecraftState)} method, and even propagators that do
   * not support resetting state (like the {@link
   * org.orekit.propagation.analytical.tle.TLEPropagator TLEPropagator} do
   * cache some internal data during computation. However, as long as they
   * are configured with independent building blocks (mainly event handlers
   * and step handlers that may preserve some internal state), and as long
   * as they are called from one thread only, they <em>can</em> be used in
   * multi-threaded applications. Synchronizing several propagators to run in
   * parallel is also possible using {@link PropagatorsParallelizer}.</p>
   * @author Luc Maisonobe
   * @author V&eacute;ronique Pommier-Maurussane
   *
   */
  
  public interface Propagator extends PVCoordinatesProvider {
  
      /** Default mass. */
      double DEFAULT_MASS = 1000.0;
  
      /** Default attitude provider. */
      AttitudeProvider DEFAULT_LAW = InertialProvider.EME2000_ALIGNED;
  
      /** Indicator for slave mode. */
      int SLAVE_MODE = 0;
  
      /** Indicator for master mode. */
      int MASTER_MODE = 1;
  
      /** Indicator for ephemeris generation mode. */
      int EPHEMERIS_GENERATION_MODE = 2;
  
      /** Get the current operating mode of the propagator.
       * @return one of {@link #SLAVE_MODE}, {@link #MASTER_MODE},
       * {@link #EPHEMERIS_GENERATION_MODE}
       * @see #setSlaveMode()
       * @see #setMasterMode(double, OrekitFixedStepHandler)
       * @see #setMasterMode(OrekitStepHandler)
       * @see #setEphemerisMode()
       */
      int getMode();
  
      /** Set the propagator to slave mode.
       * <p>This mode is used when the user needs only the final orbit at the target time.
       *  The (slave) propagator computes this result and return it to the calling
       *  (master) application, without any intermediate feedback.
       * <p>This is the default mode.</p>
       * @see #setMasterMode(double, OrekitFixedStepHandler)
       * @see #setMasterMode(OrekitStepHandler)
       * @see #setEphemerisMode()
       * @see #getMode()
       * @see #SLAVE_MODE
       */
      void setSlaveMode();
  
      /** Set the propagator to master mode with fixed steps.
       * <p>This mode is used when the user needs to have some custom function called at the
       * end of each finalized step during integration. The (master) propagator integration
       * loop calls the (slave) application callback methods at each finalized step.</p>
      * @param h fixed stepsize (s)
      * @param handler handler called at the end of each finalized step
      * @see #setSlaveMode()
      * @see #setMasterMode(OrekitStepHandler)
      * @see #setEphemerisMode()
      * @see #getMode()
      * @see #MASTER_MODE
      */
     void setMasterMode(double h, OrekitFixedStepHandler handler);
 
     /** Set the propagator to master mode with variable steps.
      * <p>This mode is used when the user needs to have some custom function called at the
      * end of each finalized step during integration. The (master) propagator integration
      * loop calls the (slave) application callback methods at each finalized step.</p>
      * @param handler handler called at the end of each finalized step
      * @see #setSlaveMode()
      * @see #setMasterMode(double, OrekitFixedStepHandler)
      * @see #setEphemerisMode()
      * @see #getMode()
      * @see #MASTER_MODE
      */
     void setMasterMode(OrekitStepHandler handler);
 
     /** Set the propagator to ephemeris generation mode.
      *  <p>This mode is used when the user needs random access to the orbit state at any time
      *  between the initial and target times, and in no sequential order. A typical example is
      *  the implementation of search and iterative algorithms that may navigate forward and
      *  backward inside the propagation range before finding their result.</p>
      *  <p>Beware that since this mode stores <strong>all</strong> intermediate results,
      *  it may be memory intensive for long integration ranges and high precision/short
      *  time steps.</p>
      * @see #getGeneratedEphemeris()
      * @see #setSlaveMode()
      * @see #setMasterMode(double, OrekitFixedStepHandler)
      * @see #setMasterMode(OrekitStepHandler)
      * @see #getMode()
      * @see #EPHEMERIS_GENERATION_MODE
      */
     void setEphemerisMode();
 
     /**
      * Set the propagator to ephemeris generation mode with the specified handler for each
      * integration step.
      *
      * <p>This mode is used when the user needs random access to the orbit state at any
      * time between the initial and target times, as well as access to the steps computed
      * by the integrator as in Master Mode. A typical example is the implementation of
      * search and iterative algorithms that may navigate forward and backward inside the
      * propagation range before finding their result.</p>
      *
      * <p>Beware that since this mode stores <strong>all</strong> intermediate results, it
      * may be memory intensive for long integration ranges and high precision/short time
      * steps.</p>
      *
      * @param handler handler called at the end of each finalized step
      * @see #setEphemerisMode()
      * @see #getGeneratedEphemeris()
      * @see #setSlaveMode()
      * @see #setMasterMode(double, OrekitFixedStepHandler)
      * @see #setMasterMode(OrekitStepHandler)
      * @see #getMode()
      * @see #EPHEMERIS_GENERATION_MODE
      */
     void setEphemerisMode(OrekitStepHandler handler);
 
     /** Get the ephemeris generated during propagation.
      * @return generated ephemeris
      * @exception IllegalStateException if the propagator was not set in ephemeris
      * generation mode before propagation
      * @see #setEphemerisMode()
      */
     BoundedPropagator getGeneratedEphemeris() throws IllegalStateException;
 
     /** Get the propagator initial state.
      * @return initial state
      */
     SpacecraftState getInitialState();
 
     /** Reset the propagator initial state.
      * @param state new initial state to consider
      */
     void resetInitialState(SpacecraftState state);
 
     /** Add a set of user-specified state parameters to be computed along with the orbit propagation.
      * @param additionalStateProvider provider for additional state
      */
     void addAdditionalStateProvider(AdditionalStateProvider additionalStateProvider);
 
     /** Get an unmodifiable list of providers for additional state.
      * @return providers for the additional states
      */
     List<AdditionalStateProvider> getAdditionalStateProviders();
 
     /** Check if an additional state is managed.
      * <p>
      * Managed states are states for which the propagators know how to compute
      * its evolution. They correspond to additional states for which an
      * {@link AdditionalStateProvider additional state provider} has been registered
      * by calling the {@link #addAdditionalStateProvider(AdditionalStateProvider)
      * addAdditionalStateProvider} method. If the propagator is an {@link
      * org.orekit.propagation.integration.AbstractIntegratedPropagator integrator-based
      * propagator}, the states for which a set of {@link
      * org.orekit.propagation.integration.AdditionalEquations additional equations} has
      * been registered by calling the {@link
      * org.orekit.propagation.integration.AbstractIntegratedPropagator#addAdditionalEquations(
      * org.orekit.propagation.integration.AdditionalEquations) addAdditionalEquations}
      * method are also counted as managed additional states.
      * </p>
      * <p>
      * Additional states that are present in the {@link #getInitialState() initial state}
      * but have no evolution method registered are <em>not</em> considered as managed states.
      * These unmanaged additional states are not lost during propagation, though. Their
      * value will simply be copied unchanged throughout propagation.
      * </p>
      * @param name name of the additional state
      * @return true if the additional state is managed
      */
     boolean isAdditionalStateManaged(String name);
 
     /** Get all the names of all managed states.
      * @return names of all managed states
      */
     String[] getManagedAdditionalStates();
 
     /** Add an event detector.
      * @param detector event detector to add
      * @see #clearEventsDetectors()
      * @see #getEventsDetectors()
      * @param <T> class type for the generic version
      */
     <T extends EventDetector> void addEventDetector(T detector);
 
     /** Get all the events detectors that have been added.
      * @return an unmodifiable collection of the added detectors
      * @see #addEventDetector(EventDetector)
      * @see #clearEventsDetectors()
      */
     Collection<EventDetector> getEventsDetectors();
 
     /** Remove all events detectors.
      * @see #addEventDetector(EventDetector)
      * @see #getEventsDetectors()
      */
     void clearEventsDetectors();
 
     /** Get attitude provider.
      * @return attitude provider
      */
     AttitudeProvider getAttitudeProvider();
 
     /** Set attitude provider.
      * @param attitudeProvider attitude provider
      */
     void setAttitudeProvider(AttitudeProvider attitudeProvider);
 
     /** Get the frame in which the orbit is propagated.
      * <p>
      * The propagation frame is the definition frame of the initial
      * state, so this method should be called after this state has
      * been set, otherwise it may return null.
      * </p>
      * @return frame in which the orbit is propagated
      * @see #resetInitialState(SpacecraftState)
      */
     Frame getFrame();
 
     /** Propagate towards a target date.
      * <p>Simple propagators use only the target date as the specification for
      * computing the propagated state. More feature rich propagators can consider
      * other information and provide different operating modes or G-stop
      * facilities to stop at pinpointed events occurrences. In these cases, the
      * target date is only a hint, not a mandatory objective.</p>
      * @param target target date towards which orbit state should be propagated
      * @return propagated state
      */
     SpacecraftState propagate(AbsoluteDate target);
 
     /** Propagate from a start date towards a target date.
      * <p>Those propagators use a start date and a target date to
      * compute the propagated state. For propagators using event detection mechanism,
      * if the provided start date is different from the initial state date, a first,
      * simple propagation is performed, without processing any event computation.
      * Then complete propagation is performed from start date to target date.</p>
      * @param start start date from which orbit state should be propagated
      * @param target target date to which orbit state should be propagated
      * @return propagated state
      */
     SpacecraftState propagate(AbsoluteDate../../org/orekit/time/AbsoluteDate.html#AbsoluteDate">AbsoluteDate start, AbsoluteDate target);
 
 }