/*
 * 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.annotation.Experimental;
import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.state.InternalCheckpointListener;
import org.apache.flink.api.common.state.v2.State;
import org.apache.flink.api.common.state.v2.StateDescriptor;
import org.apache.flink.api.common.typeutils.TypeSerializer;
import org.apache.flink.runtime.asyncprocessing.AsyncExecutionController;
import org.apache.flink.runtime.asyncprocessing.RecordContext;
import org.apache.flink.runtime.asyncprocessing.StateExecutor;
import org.apache.flink.runtime.asyncprocessing.StateRequestHandler;
import org.apache.flink.runtime.checkpoint.SnapshotType;
import org.apache.flink.runtime.state.v2.internal.InternalKeyedState;
import org.apache.flink.util.Disposable;

import javax.annotation.Nonnull;
import javax.annotation.Nullable;

import java.io.Closeable;

/**
 * An async keyed state backend provides methods supporting to access keyed state asynchronously and
 * in batch.
 */
@Internal
public interface AsyncKeyedStateBackend<K>
        extends Snapshotable<SnapshotResult<KeyedStateHandle>>,
                InternalCheckpointListener,
                PriorityQueueSetFactory,
                Disposable,
                Closeable,
                AsyncExecutionController.SwitchContextListener<K> {

    /**
     * Initializes with some contexts.
     *
     * @param stateRequestHandler which handles state request.
     */
    void setup(@Nonnull StateRequestHandler stateRequestHandler);

    /**
     * Creates or retrieves a keyed state backed by this state backend.
     *
     * @param <N> the type of namespace for partitioning.
     * @param <S> The type of the public API state.
     * @param <SV> The type of the stored state value.
     * @param defaultNamespace the default namespace for this state.
     * @param namespaceSerializer the serializer for namespace.
     * @param stateDesc The {@code StateDescriptor} that contains the name of the state.
     * @return A new key/value state backed by this backend.
     * @throws Exception Exceptions may occur during initialization of the state and should be
     *     forwarded.
     */
    <N, S extends State, SV> S getOrCreateKeyedState(
            N defaultNamespace,
            TypeSerializer<N> namespaceSerializer,
            StateDescriptor<SV> stateDesc)
            throws Exception;

    /**
     * Creates and returns a new state for internal usage.
     *
     * @param <N> the type of namespace for partitioning.
     * @param <S> The type of the public API state.
     * @param <SV> The type of the stored state value.
     * @param defaultNamespace the default namespace for this state.
     * @param namespaceSerializer the serializer for namespace.
     * @param stateDesc The {@code StateDescriptor} that contains the name of the state.
     * @throws Exception Exceptions may occur during initialization of the state.
     */
    @Nonnull
    <N, S extends InternalKeyedState, SV> S createStateInternal(
            @Nonnull N defaultNamespace,
            @Nonnull TypeSerializer<N> namespaceSerializer,
            @Nonnull StateDescriptor<SV> stateDesc)
            throws Exception;

    /**
     * Creates a {@code StateExecutor} which supports to execute a batch of state requests
     * asynchronously.
     *
     * <p>Notice that the {@code AsyncKeyedStateBackend} is responsible for shutting down the
     * StateExecutors created by itself when they are no longer in use.
     *
     * @return a {@code StateExecutor} which supports to execute a batch of state requests
     *     asynchronously.
     */
    @Nonnull
    StateExecutor createStateExecutor();

    /** Returns the key groups which this state backend is responsible for. */
    KeyGroupRange getKeyGroupRange();

    /** By default, a state backend does nothing when a key is switched in async processing. */
    @Override
    default void switchContext(@Nullable RecordContext<K> context) {}

    // TODO remove this once heap-based timers are working with ForSt incremental snapshots!
    /**
     * Whether the keyed state backend requires legacy synchronous timer snapshots.
     *
     * @param checkpointType
     * @return true as default in case of AsyncKeyedStateBackend
     */
    default boolean requiresLegacySynchronousTimerSnapshots(SnapshotType checkpointType) {
        return true;
    }

    /**
     * Whether it's safe to reuse key-values from the state-backend, e.g for the purpose of
     * optimization.
     *
     * <p>NOTE: this method should not be used to check for {@link InternalPriorityQueue}, as the
     * priority queue could be stored on different locations, e.g ForSt state-backend could store
     * that on JVM heap if configuring HEAP as the time-service factory.
     *
     * @return returns ture if safe to reuse the key-values from the state-backend.
     */
    default boolean isSafeToReuseKVState() {
        return false;
    }

    @Override
    void dispose();

    /**
     * @return fixed lower-case string identifying the type of the underlying state backend, e.g.
     *     rocksdb, hashmap, or unknown.
     */
    @Experimental
    String getBackendTypeIdentifier();
}
