/*
 * 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.
 * <p>
 * The key is internally represented as {@link Windowed Windowed&lt;K&gt;} that comprises the plain key
 * and the {@link Window} that represents window start- and end-timestamp.
 * <p>
 * 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 <K>   type of the record keys
 * @param <AGG> type of the aggregated values
 */
public interface SessionStore<K, AGG> extends StateStore, ReadOnlySessionStore<K, AGG> {

    /**
     * Fetch any sessions with the matching key and the sessions end is &ge; earliestSessionEndTime and the sessions
     * start is &le; latestSessionStartTime
     *
     * This iterator must be closed after use.
     *
     * @param key the key to return sessions for
     * @param earliestSessionEndTime the end timestamp of the earliest session to search for
     * @param latestSessionStartTime the end timestamp of the latest session to search for
     * @return iterator of sessions with the matching key and aggregated values
     * @throws NullPointerException If null is used for key.
     */
    KeyValueIterator<Windowed<K>, AGG> findSessions(final K key, final long earliestSessionEndTime, final long latestSessionStartTime);

    /**
     * Fetch any sessions in the given range of keys and the sessions end is &ge; earliestSessionEndTime and the sessions
     * start is &le; latestSessionStartTime
     *
     * This iterator must be closed after use.
     *
     * @param keyFrom The first key that could be in the range
     * @param keyTo The last key that could be in the range
     * @param earliestSessionEndTime the end timestamp of the earliest session to search for
     * @param latestSessionStartTime the end timestamp of the latest session to search for
     * @return iterator of sessions with the matching keys and aggregated values
     * @throws NullPointerException If null is used for any key.
     */
    KeyValueIterator<Windowed<K>, AGG> findSessions(final K keyFrom, final K keyTo, final long earliestSessionEndTime, final long latestSessionStartTime);

    /**
     * Get the value of key from a single session.
     *
     * @param key            the key to fetch
     * @param startTime      start timestamp of the session
     * @param endTime        end timestamp of the session
     * @return The value or {@code null} if no session associated with the key can be found
     * @throws NullPointerException If {@code null} is used for any key.
     */
    AGG fetchSession(final K key, final long startTime, final long endTime);

    /**
     * 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<K> 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<K> sessionKey, final AGG aggregate);
}
