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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.kafka.streams.state;

import org.apache.kafka.streams.kstream.Window;
import org.apache.kafka.streams.kstream.Windowed;
import org.apache.kafka.streams.processor.StateStore;

/**
 * Interface for storing the aggregated values of sessions.
 * 
 * The key is internally represented as {@link Windowed Windowed<K>} that comprises the plain key
 * and the {@link Window} that represents window start- and end-timestamp.
 * 
 * If two sessions are merged, a new session with new start- and end-timestamp must be inserted into the store
 * while the two old sessions must be deleted.
 *
 * @param    type of the record keys
 * @param  type of the aggregated values
 */
public interface SessionStore extends StateStore, ReadOnlySessionStore {

    /**
     * Remove the session aggregated with provided {@link Windowed} key from the store
     * @param sessionKey key of the session to remove
     * @throws NullPointerException If null is used for sessionKey.
     */
    void remove(final Windowed sessionKey);

    /**
     * Write the aggregated value for the provided key to the store
     * @param sessionKey key of the session to write
     * @param aggregate  the aggregated value for the session, it can be null;
     *                   if the serialized bytes are also null it is interpreted as deletes
     * @throws NullPointerException If null is used for sessionKey.
     */
    void put(final Windowed sessionKey, final AGG aggregate);
}