content: /*
   * 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.beam.sdk.state;
  
  import java.util.Map;
  import java.util.function.Function;
  import javax.annotation.Nullable;
  
  /**
   * A {@link ReadableState} cell mapping keys to values.
   *
   * <p>Implementations of this form of state are expected to implement map operations efficiently as
   * supported by some associated backing key-value store.
   *
   * @param <K> the type of keys maintained by this map
   * @param <V> the type of mapped values
   */
  public interface MapState<K, V> extends State {
  
    /**
     * Associates the specified value with the specified key in this state.
     *
     * <p>Changes will not be reflected in the results returned by previous calls to {@link
     * ReadableState#read} on the results any of the reading methods ({@link #get}, {@link #keys},
     * {@link #values}, and {@link #entries}).
     */
    void put(K key, V value);
  
    /**
     * A deferred read-followed-by-write.
     *
     * <p>When {@code read()} is called on the result or state is committed, it forces a read of the
     * map and reconciliation with any pending modifications.
     *
     * <p>If the specified key is not already associated with a value (or is mapped to {@code null})
     * associates it with the given value and returns {@code null}, else returns the current value.
     *
     * <p>Changes will not be reflected in the results returned by previous calls to {@link
     * ReadableState#read} on the results any of the reading methods ({@link #get}, {@link #keys},
     * {@link #values}, and {@link #entries}).
     */
    default ReadableState<V> putIfAbsent(K key, V value) {
      return computeIfAbsent(key, k -> value);
    }
  
    /**
     * A deferred read-followed-by-write.
     *
     * <p>When {@code read()} is called on the result or state is committed, it forces a read of the
     * map and reconciliation with any pending modifications.
     *
     * <p>If the specified key is not already associated with a value (or is mapped to {@code null})
     * associates it with the computed and returns {@code null}, else returns the current value.
     *
     * <p>Changes will not be reflected in the results returned by previous calls to {@link
     * ReadableState#read} on the results any of the reading methods ({@link #get}, {@link #keys},
     * {@link #values}, and {@link #entries}).
     */
    ReadableState<V> computeIfAbsent(K key, Function<? super K, ? extends V> mappingFunction);
  
    /**
     * Remove the mapping for a key from this map if it is present.
     *
     * <p>Changes will not be reflected in the results returned by previous calls to {@link
     * ReadableState#read} on the results any of the reading methods ({@link #get}, {@link #keys},
     * {@link #values}, and {@link #entries}).
     */
    void remove(K key);
  
    /**
     * A deferred lookup, using null values if the item is not found.
     *
     * <p>A user is encouraged to call {@code get} for all relevant keys and call {@code readLater()}
     * on the results.
     *
     * <p>When {@code read()} is called, a particular state implementation is encouraged to perform
     * all pending reads in a single batch.
     */
    ReadableState<V> get(K key);
  
    /**
     * A deferred lookup.
     *
     * <p>A user is encouraged to call {@code get} for all relevant keys and call {@code readLater()}
     * on the results.
     *
     * <p>When {@code read()} is called, a particular state implementation is encouraged to perform
     * all pending reads in a single batch.
     */
    ReadableState<V> getOrDefault(K key, @Nullable V defaultValue);
  
    /** Returns an {@link Iterable} over the keys contained in this map. */
    ReadableState<Iterable<K>> keys();
  
    /** Returns an {@link Iterable} over the values contained in this map. */
    ReadableState<Iterable<V>> values();
  
    /** Returns an {@link Iterable} over the key-value pairs contained in this map. */
    ReadableState<Iterable<Map.Entry<K, V>>> entries();
  
    /**
     * Returns a {@link ReadableState} whose {@link ReadableState#read} method will return true if
     * this state is empty at the point when that {@link ReadableState#read} call returns.
     */
    ReadableState<Boolean> isEmpty();
  }
  