/* Copyright 2002-2013 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.analytical;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.Iterator;
  import java.util.List;
  
  import org.apache.commons.math3.exception.NoBracketingException;
  import org.apache.commons.math3.exception.TooManyEvaluationsException;
  import org.apache.commons.math3.util.FastMath;
  import org.orekit.attitudes.Attitude;
  import org.orekit.attitudes.AttitudeProvider;
  import org.orekit.errors.OrekitException;
  import org.orekit.errors.PropagationException;
  import org.orekit.frames.Frame;
  import org.orekit.orbits.Orbit;
  import org.orekit.propagation.AbstractPropagator;
  import org.orekit.propagation.BoundedPropagator;
  import org.orekit.propagation.SpacecraftState;
  import org.orekit.propagation.events.EventDetector;
  import org.orekit.propagation.events.EventState;
  import org.orekit.propagation.sampling.OrekitStepInterpolator;
  import org.orekit.time.AbsoluteDate;
  import org.orekit.utils.PVCoordinates;
  import org.orekit.utils.PVCoordinatesProvider;
  
  /** Common handling of {@link org.orekit.propagation.Propagator} methods for analytical propagators.
   * <p>
   * This abstract class allows to provide easily the full set of {@link
   * org.orekit.propagation.Propagator Propagator} methods, including all propagation
   * modes support and discrete events support for any simple propagation method. Only
   * two methods must be implemented by derived classes: {@link #propagateOrbit(AbsoluteDate)}
   * and {@link #getMass(AbsoluteDate)}. The first method should perform straightforward
   * propagation starting from some internally stored initial state up to the specified target date.
   * </p>
   * @author Luc Maisonobe
   */
  public abstract class AbstractAnalyticalPropagator extends AbstractPropagator {
  
      /** Internal steps interpolator. */
      private final BasicStepInterpolator interpolator;
  
      /** Provider for attitude computation. */
      private PVCoordinatesProvider pvProvider;
  
      /** Start date of last propagation. */
      private AbsoluteDate lastPropagationStart;
  
      /** End date of last propagation. */
      private AbsoluteDate lastPropagationEnd;
  
      /** Initialization indicator of events states. */
      private boolean statesInitialized;
  
      /** Indicator for last step. */
      private boolean isLastStep;
  
      /** Event steps. */
      private final Collection<EventState<?>> eventsStates;
  
      /** Build a new instance.
       * @param attitudeProvider provider for attitude computation
       */
      protected AbstractAnalyticalPropagator(final AttitudeProvider attitudeProvider) {
          setAttitudeProvider(attitudeProvider);
          interpolator             = new BasicStepInterpolator();
          pvProvider               = new LocalPVProvider();
          lastPropagationStart     = AbsoluteDate.PAST_INFINITY;
          lastPropagationEnd       = AbsoluteDate.FUTURE_INFINITY;
          statesInitialized        = false;
          eventsStates             = new ArrayList<EventState<?>>();
      }
  
      /** {@inheritDoc} */
      public BoundedPropagator getGeneratedEphemeris() {
          return new BoundedPropagatorView(lastPropagationStart, lastPropagationEnd);
      }
  
      /** {@inheritDoc} */
      public <T extends EventDetector> void addEventDetector(final T detector) {
          eventsStates.add(new EventState<T>(detector));
     }
 
     /** {@inheritDoc} */
     public Collection<EventDetector> getEventsDetectors() {
         final List<EventDetector> list = new ArrayList<EventDetector>();
         for (final EventState<?> state : eventsStates) {
             list.add(state.getEventDetector());
         }
         return Collections.unmodifiableCollection(list);
     }
 
     /** {@inheritDoc} */
     public void clearEventsDetectors() {
         eventsStates.clear();
     }
 
     /** {@inheritDoc} */
     public SpacecraftState propagate(final AbsoluteDate start, final AbsoluteDate target)
         throws PropagationException {
         try {
 
             lastPropagationStart = start;
 
             final double dt      = target.durationFrom(start);
             final double epsilon = FastMath.ulp(dt);
             interpolator.storeDate(start);
             SpacecraftState state = interpolator.getInterpolatedState();
 
             // evaluate step size
             final double stepSize;
             if (getMode() == MASTER_MODE) {
                 if (Double.isNaN(getFixedStepSize())) {
                     stepSize = FastMath.copySign(state.getKeplerianPeriod() / 100, dt);
                 } else {
                     stepSize = FastMath.copySign(getFixedStepSize(), dt);
                 }
             } else {
                 stepSize = dt;
             }
 
             // initialize event detectors
             for (final EventState<?> es : eventsStates) {
                 es.init(state, target);
             }
 
             // initialize step handler
             if (getStepHandler() != null) {
                 getStepHandler().init(state, target);
             }
 
             // iterate over the propagation range
             statesInitialized = false;
             isLastStep = false;
             do {
 
                 // go ahead one step size
                 interpolator.shift();
                 final AbsoluteDate t = interpolator.getCurrentDate().shiftedBy(stepSize);
                 if ((dt == 0) || ((dt > 0) ^ (t.compareTo(target) <= 0))) {
                     // current step exceeds target
                     interpolator.storeDate(target);
                 } else {
                     // current step is within range
                     interpolator.storeDate(t);
                 }
 
                 // accept the step, trigger events and step handlers
                 state = acceptStep(target, epsilon);
 
             } while (!isLastStep);
 
             // return the last computed state
             lastPropagationEnd = state.getDate();
             setStartDate(state.getDate());
             return state;
 
         } catch (PropagationException pe) {
             throw pe;
         } catch (OrekitException oe) {
             throw PropagationException.unwrap(oe);
         } catch (TooManyEvaluationsException tmee) {
             throw PropagationException.unwrap(tmee);
         } catch (NoBracketingException nbe) {
             throw PropagationException.unwrap(nbe);
         }
     }
 
     /** Accept a step, triggering events and step handlers.
      * @param target final propagation time
      * @param epsilon threshold for end date detection
      * @return state at the end of the step
      * @exception OrekitException if the switching function cannot be evaluated
      * @exception TooManyEvaluationsException if an event cannot be located
      * @exception NoBracketingException if bracketing cannot be performed
      */
     protected SpacecraftState acceptStep(final AbsoluteDate target, final double epsilon)
         throws OrekitException, TooManyEvaluationsException, NoBracketingException {
 
         AbsoluteDate previousT = interpolator.getGlobalPreviousDate();
         AbsoluteDate currentT  = interpolator.getGlobalCurrentDate();
 
         // initialize the events states if needed
         if (!statesInitialized) {
 
             if (!eventsStates.isEmpty()) {
                 // initialize the events states
                 final AbsoluteDate t0 = interpolator.getPreviousDate();
                 interpolator.setInterpolatedDate(t0);
                 final SpacecraftState y = interpolator.getInterpolatedState();
                 for (final EventState<?> state : eventsStates) {
                     state.reinitializeBegin(y, interpolator.isForward());
                 }
             }
 
             statesInitialized = true;
 
         }
 
         // search for next events that may occur during the step
         final List<EventState<?>> occurringEvents = new ArrayList<EventState<?>>();
         for (final EventState<?> state : eventsStates) {
             if (state.evaluateStep(interpolator)) {
                 // the event occurs during the current step
                 occurringEvents.add(state);
             }
         }
 
         // chronological or reverse chronological sorter, according to propagation direction
         final int orderingSign = interpolator.isForward() ? +1 : -1;
         final Comparator<EventState<?>> sorter = new Comparator<EventState<?>>() {
 
             /** {@inheritDoc} */
             public int compare(final EventState<?> es0, final EventState<?> es1) {
                 return orderingSign * es0.getEventTime().compareTo(es1.getEventTime());
             }
 
         };
 
         while (!occurringEvents.isEmpty()) {
 
             // handle the chronologically first event
             Collections.sort(occurringEvents, sorter);
             final Iterator<EventState<?>> iterator = occurringEvents.iterator();
             final EventState<?> currentEvent = iterator.next();
             iterator.remove();
 
             // restrict the interpolator to the first part of the step, up to the event
             final AbsoluteDate eventT = currentEvent.getEventTime();
             interpolator.setSoftPreviousDate(previousT);
             interpolator.setSoftCurrentDate(eventT);
 
             // trigger the event
             interpolator.setInterpolatedDate(eventT);
             final SpacecraftState eventY = interpolator.getInterpolatedState();
             currentEvent.stepAccepted(eventY);
             isLastStep = currentEvent.stop();
 
             // handle the first part of the step, up to the event
             if (getStepHandler() != null) {
                 getStepHandler().handleStep(interpolator, isLastStep);
             }
 
             if (isLastStep) {
                 // the event asked to stop integration
                 return eventY;
             }
 
             final SpacecraftState resetState = currentEvent.reset(eventY);
             if (resetState != null) {
                 resetInitialState(resetState);
                 return resetState;
             }
 
             // prepare handling of the remaining part of the step
             previousT = eventT;
             interpolator.setSoftPreviousDate(eventT);
             interpolator.setSoftCurrentDate(currentT);
 
             // check if the same event occurs again in the remaining part of the step
             if (currentEvent.evaluateStep(interpolator)) {
                 // the event occurs during the current step
                 occurringEvents.add(currentEvent);
             }
 
         }
 
         final double remaining = target.durationFrom(currentT);
         if (interpolator.isForward()) {
             isLastStep = remaining <  epsilon;
         } else {
             isLastStep = remaining > -epsilon;
         }
         if (isLastStep) {
             currentT = target;
         }
 
         interpolator.setInterpolatedDate(currentT);
         final SpacecraftState currentY = interpolator.getInterpolatedState();
         for (final EventState<?> state : eventsStates) {
             state.stepAccepted(currentY);
             isLastStep = isLastStep || state.stop();
         }
 
         // handle the remaining part of the step, after all events if any
         if (getStepHandler() != null) {
             getStepHandler().handleStep(interpolator, isLastStep);
         }
 
         return currentY;
 
     }
 
     /** Get the mass.
      * @param date target date for the orbit
      * @return mass mass
      * @exception PropagationException if some parameters are out of bounds
      */
     protected abstract double getMass(final AbsoluteDate date)
         throws PropagationException;
 
     /** Get PV coordinates provider.
      * @return PV coordinates provider
      */
     public PVCoordinatesProvider getPvProvider() {
         return pvProvider;
     }
 
     /** Extrapolate an orbit up to a specific target date.
      * @param date target date for the orbit
      * @return extrapolated parameters
      * @exception PropagationException if some parameters are out of bounds
      */
     protected abstract Orbit propagateOrbit(final AbsoluteDate date)
         throws PropagationException;
 
     /** Propagate an orbit without any fancy features.
      * <p>This method is similar in spirit to the {@link #propagate} method,
      * except that it does <strong>not</strong> call any handler during
      * propagation, nor any discrete events, not additional states. It always
      * stop exactly at the specified date.</p>
      * @param date target date for propagation
      * @return state at specified date
      * @exception PropagationException if propagation cannot reach specified date
      */
     protected SpacecraftState basicPropagate(final AbsoluteDate date) throws PropagationException {
         try {
 
             // evaluate orbit
             final Orbit orbit = propagateOrbit(date);
 
             // evaluate attitude
             final Attitude attitude =
                 getAttitudeProvider().getAttitude(pvProvider, date, orbit.getFrame());
 
             // build raw state
             return new SpacecraftState(orbit, attitude, getMass(date));
 
         } catch (OrekitException oe) {
             throw new PropagationException(oe);
         }
     }
 
     /** Internal PVCoordinatesProvider for attitude computation. */
     private class LocalPVProvider implements PVCoordinatesProvider {
 
         /** {@inheritDoc} */
         public PVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame frame)
             throws OrekitException {
             return propagateOrbit(date).getPVCoordinates(frame);
         }
 
     }
 
     /** {@link BoundedPropagator} view of the instance. */
     private class BoundedPropagatorView extends AbstractAnalyticalPropagator implements BoundedPropagator {
 
         /** Min date. */
         private final AbsoluteDate minDate;
 
         /** Max date. */
         private final AbsoluteDate maxDate;
 
         /** Simple constructor.
          * @param startDate start date of the propagation
          * @param endDate end date of the propagation
          */
         public BoundedPropagatorView(final AbsoluteDate startDate, final AbsoluteDate endDate) {
             super(AbstractAnalyticalPropagator.this.getAttitudeProvider());
             if (startDate.compareTo(endDate) <= 0) {
                 minDate = startDate;
                 maxDate = endDate;
             } else {
                 minDate = endDate;
                 maxDate = startDate;
             }
         }
 
         /** {@inheritDoc} */
         public AbsoluteDate getMinDate() {
             return minDate;
         }
 
         /** {@inheritDoc} */
         public AbsoluteDate getMaxDate() {
             return maxDate;
         }
 
         /** {@inheritDoc} */
         protected Orbit propagateOrbit(final AbsoluteDate target)
             throws PropagationException {
             return AbstractAnalyticalPropagator.this.propagateOrbit(target);
         }
 
         /** {@inheritDoc} */
         public double getMass(final AbsoluteDate date) throws PropagationException {
             return AbstractAnalyticalPropagator.this.getMass(date);
         }
 
         /** {@inheritDoc} */
         public PVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame frame)
             throws OrekitException {
             return propagate(date).getPVCoordinates(frame);
         }
 
         /** {@inheritDoc} */
         public void resetInitialState(final SpacecraftState state) throws PropagationException {
             AbstractAnalyticalPropagator.this.resetInitialState(state);
         }
 
         /** {@inheritDoc} */
         public SpacecraftState getInitialState() throws PropagationException {
             return AbstractAnalyticalPropagator.this.getInitialState();
         }
 
     }
 
     /** Internal class for local propagation. */
     private class BasicStepInterpolator implements OrekitStepInterpolator {
 
         /** Global previous date. */
         private AbsoluteDate globalPreviousDate;
 
         /** Global current date. */
         private AbsoluteDate globalCurrentDate;
 
         /** Soft previous date. */
         private AbsoluteDate softPreviousDate;
 
         /** Soft current date. */
         private AbsoluteDate softCurrentDate;
 
         /** Interpolated state. */
         private SpacecraftState interpolatedState;
 
         /** Forward propagation indicator. */
         private boolean forward;
 
         /** Build a new instance from a basic propagator.
          */
         public BasicStepInterpolator() {
             globalPreviousDate = AbsoluteDate.PAST_INFINITY;
             globalCurrentDate  = AbsoluteDate.PAST_INFINITY;
             softPreviousDate   = AbsoluteDate.PAST_INFINITY;
             softCurrentDate    = AbsoluteDate.PAST_INFINITY;
         }
 
         /** Restrict step range to a limited part of the global step.
          * <p>
          * This method can be used to restrict a step and make it appear
          * as if the original step was smaller. Calling this method
          * <em>only</em> changes the value returned by {@link #getPreviousDate()},
          * it does not change any other property
          * </p>
          * @param softPreviousDate start of the restricted step
          */
         public void setSoftPreviousDate(final AbsoluteDate softPreviousDate) {
             this.softPreviousDate = softPreviousDate;
         }
 
         /** Restrict step range to a limited part of the global step.
          * <p>
          * This method can be used to restrict a step and make it appear
          * as if the original step was smaller. Calling this method
          * <em>only</em> changes the value returned by {@link #getCurrentDate()},
          * it does not change any other property
          * </p>
          * @param softCurrentDate end of the restricted step
          */
         public void setSoftCurrentDate(final AbsoluteDate softCurrentDate) {
             this.softCurrentDate  = softCurrentDate;
         }
 
         /**
          * Get the previous global grid point time.
          * @return previous global grid point time
          */
         public AbsoluteDate getGlobalPreviousDate() {
             return globalPreviousDate;
         }
 
         /**
          * Get the current global grid point time.
          * @return current global grid point time
          */
         public AbsoluteDate getGlobalCurrentDate() {
             return globalCurrentDate;
         }
 
         /** {@inheritDoc} */
         public AbsoluteDate getCurrentDate() {
             return softCurrentDate;
         }
 
         /** {@inheritDoc} */
         public AbsoluteDate getInterpolatedDate() {
             return interpolatedState.getDate();
         }
 
         /** {@inheritDoc} */
         public SpacecraftState getInterpolatedState() throws OrekitException {
             return interpolatedState;
         }
 
         /** {@inheritDoc} */
         public AbsoluteDate getPreviousDate() {
             return softPreviousDate;
         }
 
         /** {@inheritDoc} */
         public boolean isForward() {
             return forward;
         }
 
         /** {@inheritDoc} */
         public void setInterpolatedDate(final AbsoluteDate date) throws PropagationException {
 
             // compute the basic spacecraft state
             final SpacecraftState basicState = basicPropagate(date);
 
             // add the additional states
             interpolatedState = updateAdditionalStates(basicState);
 
         }
 
         /** Shift one step forward.
          * Copy the current date into the previous date, hence preparing the
          * interpolator for future calls to {@link #storeDate storeDate}
          */
         public void shift() {
             globalPreviousDate = globalCurrentDate;
             softPreviousDate   = globalPreviousDate;
             softCurrentDate    = globalCurrentDate;
         }
 
         /** Store the current step date.
          * @param date current date
          * @exception PropagationException if the state cannot be propagated at specified date
          */
         public void storeDate(final AbsoluteDate date)
             throws PropagationException {
             globalCurrentDate = date;
             softCurrentDate   = globalCurrentDate;
             forward           = globalCurrentDate.compareTo(globalPreviousDate) >= 0;
             setInterpolatedDate(globalCurrentDate);
         }
 
     }
 
 }