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/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.apache.flink.runtime.state;

import org.apache.flink.util.Preconditions;

import java.io.Serializable;
import java.util.Iterator;

/**
 * This class defines a range of key-group indexes. Key-groups are the granularity into which the keyspace of a job
 * is partitioned for keyed state-handling in state backends. The boundaries of the range are inclusive.
 */
public class KeyGroupRange implements KeyGroupsList, Serializable {

	private static final long serialVersionUID = 4869121477592070607L;

	/** The empty key-group */
	public static final KeyGroupRange EMPTY_KEY_GROUP_RANGE = new KeyGroupRange();

	private final int startKeyGroup;
	private final int endKeyGroup;

	/**
	 * Empty KeyGroup Constructor
	 */
	private KeyGroupRange() {
		this.startKeyGroup = 0;
		this.endKeyGroup = -1;
	}

	/**
	 * Defines the range [startKeyGroup, endKeyGroup]
	 *
	 * @param startKeyGroup start of the range (inclusive)
	 * @param endKeyGroup end of the range (inclusive)
	 */
	public KeyGroupRange(int startKeyGroup, int endKeyGroup) {
		Preconditions.checkArgument(startKeyGroup >= 0);
		Preconditions.checkArgument(startKeyGroup <= endKeyGroup);
		this.startKeyGroup = startKeyGroup;
		this.endKeyGroup = endKeyGroup;
		Preconditions.checkArgument(getNumberOfKeyGroups() >= 0, "Potential overflow detected.");
	}


	/**
	 * Checks whether or not a single key-group is contained in the range.
	 *
	 * @param keyGroup Key-group to check for inclusion.
	 * @return True, only if the key-group is in the range.
	 */
	@Override
	public boolean contains(int keyGroup) {
		return keyGroup >= startKeyGroup && keyGroup <= endKeyGroup;
	}

	/**
	 * Create a range that represent the intersection between this range and the given range.
	 *
	 * @param other A KeyGroupRange to intersect.
	 * @return Key-group range that is the intersection between this and the given key-group range.
	 */
	public KeyGroupRange getIntersection(KeyGroupRange other) {
		int start = Math.max(startKeyGroup, other.startKeyGroup);
		int end = Math.min(endKeyGroup, other.endKeyGroup);
		return start <= end ? new KeyGroupRange(start, end) : EMPTY_KEY_GROUP_RANGE;
	}

	/**
	 *
	 * @return The number of key-groups in the range
	 */
	@Override
	public int getNumberOfKeyGroups() {
		return 1 + endKeyGroup - startKeyGroup;
	}

	/**
	 *
	 * @return The first key-group in the range.
	 */
	public int getStartKeyGroup() {
		return startKeyGroup;
	}

	/**
	 *
	 * @return The last key-group in the range.
	 */
	public int getEndKeyGroup() {
		return endKeyGroup;
	}

	@Override
	public int getKeyGroupId(int idx) {
		if (idx < 0 || idx > getNumberOfKeyGroups()) {
			throw new IndexOutOfBoundsException("Key group index out of bounds: " + idx);
		}
		return startKeyGroup + idx;
	}

	@Override
	public boolean equals(Object o) {
		if (this == o) {
			return true;
		}
		if (!(o instanceof KeyGroupRange)) {
			return false;
		}

		KeyGroupRange that = (KeyGroupRange) o;
		return startKeyGroup == that.startKeyGroup && endKeyGroup == that.endKeyGroup;
	}


	@Override
	public int hashCode() {
		int result = startKeyGroup;
		result = 31 * result + endKeyGroup;
		return result;
	}

	@Override
	public String toString() {
		return "KeyGroupRange{" +
				"startKeyGroup=" + startKeyGroup +
				", endKeyGroup=" + endKeyGroup +
				'}';
	}

	@Override
	public Iterator iterator() {
		return new KeyGroupIterator();
	}

	private final class KeyGroupIterator implements Iterator {

		public KeyGroupIterator() {
			this.iteratorPos = 0;
		}

		private int iteratorPos;

		@Override
		public boolean hasNext() {
			return iteratorPos < getNumberOfKeyGroups();
		}

		@Override
		public Integer next() {
			int rv = startKeyGroup + iteratorPos;
			++iteratorPos;
			return rv;
		}

		@Override
		public void remove() {
			throw new UnsupportedOperationException("Unsupported by this iterator!");
		}
	}

	/**
	 * Factory method that also handles creation of empty key-groups.
	 *
	 * @param startKeyGroup start of the range (inclusive)
	 * @param endKeyGroup end of the range (inclusive)
	 * @return the key-group from start to end or an empty key-group range.
	 */
	public static KeyGroupRange of(int startKeyGroup, int endKeyGroup) {
		return startKeyGroup <= endKeyGroup ? new KeyGroupRange(startKeyGroup, endKeyGroup) : EMPTY_KEY_GROUP_RANGE;
	}
}