org.chronos.chronodb.internal.util.NavigableMapUtils Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of org.chronos.chronodb.api Show documentation
Versioned data storage, embeddable and easy to use.
The newest version!
package org.chronos.chronodb.internal.util;

import static com.google.common.base.Preconditions.*;

import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NavigableMap;
import java.util.function.Predicate;

import com.google.common.collect.Lists;
import com.google.common.collect.Maps;

public class NavigableMapUtils {

	public static , V> List> entriesAround(final NavigableMap map, final K key, final int count) {
		checkNotNull(map, "Precondition violation - argument 'map' must not be NULL!");
		checkNotNull(key, "Precondition violation - argument 'key' must not be NULL!");
		checkArgument(count >= 0, "Precondition violation - argument 'count' must not be negative!");
		NavigableMap smallerMap = map.headMap(key, false).descendingMap();
		NavigableMap largerMap = map.tailMap(key, true);
		List> resultList = Lists.newArrayList();
		int sizeLower = count / 2;
		int sizeLarger = count - sizeLower;

		if (smallerMap.size() < sizeLower) {
			if (largerMap.size() < sizeLarger) {
				// we don't have enough entries anyways; throw everything into the list
				resultList.addAll(smallerMap.entrySet());
				resultList.addAll(largerMap.entrySet());
			} else {
				// we don't have enough entries on the "smaller" side, but enough entries
				// on the other side.
				// take everything from the smaller side
				resultList.addAll(smallerMap.entrySet());
				// take the remaining entries from the larger side (if we have enough)
				int limit = count - smallerMap.size();
				int added = 0;
				for (Entry binaryEntry : largerMap.entrySet()) {
					if (added >= limit) {
						break;
					}
					resultList.add(binaryEntry);
					added++;
				}
			}
		} else {
			if (largerMap.size() < sizeLarger) {
				// we don't have enough entries on the "larger" side, but enough entries on
				// the other side.
				// take everything from the larger side
				resultList.addAll(largerMap.entrySet());
				// take the remaining entries from the smaller side (if we have enough)
				int limit = count - largerMap.size();
				int added = 0;
				for (Entry binaryEntry : smallerMap.entrySet()) {
					if (added >= limit) {
						break;
					}
					resultList.add(binaryEntry);
					added++;
				}
			} else {
				// enough entries on both sides
				int added = 0;
				for (Entry binaryEntry : smallerMap.entrySet()) {
					if (added >= sizeLower) {
						break;
					}
					resultList.add(binaryEntry);
					added++;
				}
				added = 0;
				for (Entry binaryEntry : largerMap.entrySet()) {
					if (added >= sizeLarger) {
						break;
					}
					resultList.add(binaryEntry);
					added++;
				}
			}
		}
		return resultList;
	}

}