ImmutableTimeStampedCache.java
/* Contributed in the public domain.
* 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.utils;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import org.hipparchus.exception.LocalizedCoreFormats;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitIllegalArgumentException;
import org.orekit.errors.OrekitIllegalStateException;
import org.orekit.errors.OrekitMessages;
import org.orekit.errors.TimeStampedCacheException;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.ChronologicalComparator;
import org.orekit.time.TimeStamped;
/**
* A cache of {@link TimeStamped} data that provides concurrency through
* immutability. This strategy is suitable when all of the cached data is stored
* in memory. (For example, {@link org.orekit.time.UTCScale UTCScale}) This
* class then provides convenient methods for accessing the data.
*
* @author Evan Ward
* @param <T> the type of data
*/
public class ImmutableTimeStampedCache<T extends TimeStamped>
implements TimeStampedCache<T> {
/**
* A single chronological comparator since instances are thread safe.
*/
private static final ChronologicalComparator CMP = new ChronologicalComparator();
/**
* An empty immutable cache that always throws an exception on attempted
* access.
*/
@SuppressWarnings("rawtypes")
private static final ImmutableTimeStampedCache EMPTY_CACHE =
new EmptyTimeStampedCache<TimeStamped>();
/**
* the cached data. Be careful not to modify it after the constructor, or
* return a reference that allows mutating this list.
*/
private final List<T> data;
/**
* the size list to return from {@link #getNeighbors(AbsoluteDate)}.
*/
private final int neighborsSize;
/**
* Create a new cache with the given neighbors size and data.
*
* @param neighborsSize the size of the list returned from
* {@link #getNeighbors(AbsoluteDate)}. Must be less than or equal to
* {@code data.size()}.
* @param data the backing data for this cache. The list will be copied to
* ensure immutability. To guarantee immutability the entries in
* {@code data} must be immutable themselves. There must be more data
* than {@code neighborsSize}.
* @throws IllegalArgumentException if {@code neightborsSize > data.size()}
* or if {@code neighborsSize} is negative
*/
public ImmutableTimeStampedCache(final int neighborsSize,
final Collection<? extends T> data) {
// parameter check
if (neighborsSize > data.size()) {
throw new OrekitIllegalArgumentException(OrekitMessages.NOT_ENOUGH_CACHED_NEIGHBORS,
data.size(), neighborsSize);
}
if (neighborsSize < 1) {
throw new OrekitIllegalArgumentException(LocalizedCoreFormats.NUMBER_TOO_SMALL,
neighborsSize, 0);
}
// assign instance variables
this.neighborsSize = neighborsSize;
// sort and copy data first
this.data = new ArrayList<T>(data);
Collections.sort(this.data, CMP);
}
/**
* private constructor for {@link #EMPTY_CACHE}.
*/
private ImmutableTimeStampedCache() {
this.data = null;
this.neighborsSize = 0;
}
/** {@inheritDoc} */
public List<T> getNeighbors(final AbsoluteDate central)
throws TimeStampedCacheException {
// find central index
final int i = findIndex(central);
// check index in in the range of the data
if (i < 0) {
throw new TimeStampedCacheException(OrekitMessages.UNABLE_TO_GENERATE_NEW_DATA_BEFORE,
this.getEarliest().getDate());
} else if (i >= this.data.size()) {
throw new TimeStampedCacheException(OrekitMessages.UNABLE_TO_GENERATE_NEW_DATA_AFTER,
this.getLatest().getDate());
}
// force unbalanced range if necessary
int start = FastMath.max(0, i - (this.neighborsSize - 1) / 2);
final int end = FastMath.min(this.data.size(), start +
this.neighborsSize);
start = end - this.neighborsSize;
// return list without copying
return Collections.unmodifiableList(this.data.subList(start, end));
}
/**
* Find the index, i, to {@link #data} such that {@code data[i] <= t} and
* {@code data[i+1] > t} if {@code data[i+1]} exists.
*
* @param t the time
* @return the index of the data at or just before {@code t}, {@code -1} if
* {@code t} is before the first entry, or {@code data.size()} if
* {@code t} is after the last entry.
*/
private int findIndex(final AbsoluteDate t) {
// Guaranteed log(n) time
int i = Collections.binarySearch(this.data, t, CMP);
if (i == -this.data.size() - 1) {
// beyond last entry
i = this.data.size();
} else if (i < 0) {
// did not find exact match, but contained in data interval
i = -i - 2;
}
return i;
}
public int getNeighborsSize() {
return this.neighborsSize;
}
public T getEarliest() {
return this.data.get(0);
}
public T getLatest() {
return this.data.get(this.data.size() - 1);
}
/**
* Get all of the data in this cache.
*
* @return a sorted collection of all data passed in the
* {@link #ImmutableTimeStampedCache(int, Collection) constructor}.
*/
public List<T> getAll() {
return Collections.unmodifiableList(this.data);
}
/** {@inheritDoc} */
@Override
public String toString() {
return "Immutable cache with " + this.data.size() + " entries";
}
/**
* An empty immutable cache that always throws an exception on attempted
* access.
*/
private static class EmptyTimeStampedCache<T extends TimeStamped> extends ImmutableTimeStampedCache<T> {
/** {@inheritDoc} */
@Override
public List<T> getNeighbors(final AbsoluteDate central)
throws TimeStampedCacheException {
throw new TimeStampedCacheException(
OrekitMessages.NO_CACHED_ENTRIES);
};
/** {@inheritDoc} */
@Override
public int getNeighborsSize() {
return 0;
}
/** {@inheritDoc} */
@Override
public T getEarliest() {
throw new OrekitIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
};
/** {@inheritDoc} */
@Override
public T getLatest() {
throw new OrekitIllegalStateException(OrekitMessages.NO_CACHED_ENTRIES);
}
/** {@inheritDoc} */
@Override
public List<T> getAll() {
return Collections.emptyList();
}
/** {@inheritDoc} */
@Override
public String toString() {
return "Empty immutable cache";
}
};
/**
* Get an empty immutable cache, cast to the correct type.
* @param <TS> the type of data
* @return an empty {@link ImmutableTimeStampedCache}.
*/
@SuppressWarnings("unchecked")
public static final <TS extends TimeStamped> ImmutableTimeStampedCache<TS> emptyCache() {
return (ImmutableTimeStampedCache<TS>) EMPTY_CACHE;
}
}