AggregateBoundedAttitudeProvider

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package org.orekit.attitudes;

import java.util.Collection;
import java.util.Map.Entry;
import java.util.ArrayList;
import java.util.NavigableMap;
import java.util.List;
import java.util.TreeMap;
import java.util.stream.Stream;

import org.hipparchus.CalculusFieldElement;
import org.hipparchus.Field;
import org.hipparchus.geometry.euclidean.threed.FieldRotation;
import org.hipparchus.geometry.euclidean.threed.Rotation;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.frames.Frame;
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.utils.FieldPVCoordinatesProvider;
import org.orekit.utils.PVCoordinatesProvider;
import org.orekit.utils.ParameterDriver;

/**
 * A {@link BoundedAttitudeProvider} that covers a larger time span from several constituent
 * attitude providers that cover shorter time spans.
 *
 * @author Bryan Cazabonne
 * @since 10.3
 */
public class AggregateBoundedAttitudeProvider implements BoundedAttitudeProvider {

    /** Constituent attitude provider. */
    private final NavigableMap<AbsoluteDate, BoundedAttitudeProvider> providers;

    /**
     * Constructor.
     * @param providers attitude providers that provide the backing data for this instance.
     *                  There must be at least one attitude provider in the collection.
     *                  If there are gaps between the {@link BoundedAttitudeProvider#getMaxDate()}
     *                  of one attitude provider and the {@link BoundedAttitudeProvider#getMinDate()}
     *                  of the next attitude provider an exception may be thrown by any method of
     *                  this class at any time. If there are overlaps between the the {@link
     *                  BoundedAttitudeProvider#getMaxDate()} of one attitude provider and the {@link
     *                  BoundedAttitudeProvider#getMinDate()} of the next attitude provider then the
     *                  attitude provider with the latest {@link BoundedAttitudeProvider#getMinDate()}
     *                  is used.
     */
    public AggregateBoundedAttitudeProvider(final Collection<? extends BoundedAttitudeProvider> providers) {

        // Check if the collection is empty
        if (providers.isEmpty()) {
            throw new OrekitException(OrekitMessages.NOT_ENOUGH_ATTITUDE_PROVIDERS);
        }

        // Initialize map
        this.providers = new TreeMap<>();

        // Loop on providers
        for (final BoundedAttitudeProvider provider : providers) {
            // Fill collection
            this.providers.put(provider.getMinDate(), provider);
        }

    }

    /** {@inheritDoc} */
    @Override
    public Attitude getAttitude(final PVCoordinatesProvider pvProv, final AbsoluteDate date,
                                final Frame frame) {

        // Get the attitude provider for the given date
        final BoundedAttitudeProvider provider = getAttitudeProvider(date);

        // Build attitude
        return provider.getAttitude(pvProv, date, frame);

    }

    /** {@inheritDoc} */
    @Override
    public <T extends CalculusFieldElement<T>> FieldAttitude<T> getAttitude(final FieldPVCoordinatesProvider<T> pvProv,
                                                                            final FieldAbsoluteDate<T> date,
                                                                            final Frame frame) {

        // Get the attitude provider for the given date
        final BoundedAttitudeProvider provider = getAttitudeProvider(date.toAbsoluteDate());

        // Build attitude
        return provider.getAttitude(pvProv, date, frame);

    }

    /** {@inheritDoc} */
    @Override
    public Rotation getAttitudeRotation(final PVCoordinatesProvider pvProv, final AbsoluteDate date, final Frame frame) {
        return getAttitudeProvider(date).getAttitudeRotation(pvProv, date, frame);
    }

    /** {@inheritDoc} */
    @Override
    public <T extends CalculusFieldElement<T>> FieldRotation<T> getAttitudeRotation(final FieldPVCoordinatesProvider<T> pvProv,
                                                                                    final FieldAbsoluteDate<T> date,
                                                                                    final Frame frame) {
        return getAttitudeProvider(date.toAbsoluteDate()).getAttitudeRotation(pvProv, date, frame);
    }

    @Override
    public AbsoluteDate getMinDate() {
        return providers.firstEntry().getValue().getMinDate();
    }

    /** {@inheritDoc} */
    @Override
    public AbsoluteDate getMaxDate() {
        return providers.lastEntry().getValue().getMaxDate();
    }

    /**
     * Get the attitude provider to use for the given date.
     * @param date of query
     * @return attitude provider to use on date.
     */
    private BoundedAttitudeProvider getAttitudeProvider(final AbsoluteDate date) {
        final Entry<AbsoluteDate, BoundedAttitudeProvider> attitudeEntry = providers.floorEntry(date);
        if (attitudeEntry != null) {
            return attitudeEntry.getValue();
        } else {
            // Let the first attitude provider throw the exception
            return providers.firstEntry().getValue();
        }
    }

    /** {@inheritDoc} */
    @Override
    public Stream<EventDetector> getEventDetectors() {
        final List<AbsoluteDate> dates = new ArrayList<>(providers.navigableKeySet());
        final DateDetector detector = getDateDetector(dates.toArray(new AbsoluteDate[0]));
        return Stream.concat(Stream.of(detector), getEventDetectors(getParametersDrivers()));
    }

    /** {@inheritDoc} */
    @Override
    public <T extends CalculusFieldElement<T>> Stream<FieldEventDetector<T>> getFieldEventDetectors(final Field<T> field) {
        final List<AbsoluteDate> dates = new ArrayList<>(providers.navigableKeySet());
        final FieldDateDetector<T> detector = getFieldDateDetector(field, dates.toArray(new AbsoluteDate[0]));
        return Stream.concat(Stream.of(detector), getFieldEventDetectors(field, getParametersDrivers()));
    }

    /** {@inheritDoc} */
    @Override
    public List<ParameterDriver> getParametersDrivers() {
        final List<ParameterDriver> drivers = new ArrayList<>();
        providers.values().forEach(provider -> drivers.addAll(provider.getParametersDrivers()));
        return drivers;
    }
}