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.kafka.streams.kstream;
  
  import org.apache.kafka.streams.kstream.internals.UnlimitedWindow;
  import org.apache.kafka.streams.kstream.internals.emitstrategy.WindowCloseStrategy;
  import org.apache.kafka.streams.kstream.internals.emitstrategy.WindowUpdateStrategy;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import java.util.HashMap;
  import java.util.Map;
  
  /**
   * This interface controls the strategy that can be used to control how we emit results in a processor.
   */
  public interface EmitStrategy {
  
      Logger log = LoggerFactory.getLogger(EmitStrategy.class);
  
      enum StrategyType {
          ON_WINDOW_UPDATE(0, new WindowUpdateStrategy()),
          ON_WINDOW_CLOSE(1, new WindowCloseStrategy());
  
          private final short code;
          private final EmitStrategy strategy;
  
          private short code() {
              return this.code;
          }
  
          private EmitStrategy strategy() {
              return this.strategy;
          }
  
          StrategyType(final int code, final EmitStrategy strategy) {
              this.code = (short) code;
              this.strategy = strategy;
          }
  
          private static final Map<Short, EmitStrategy> TYPE_TO_STRATEGY = new HashMap<>();
  
          static {
              for (final StrategyType type : StrategyType.values()) {
                  if (TYPE_TO_STRATEGY.put(type.code(), type.strategy()) != null)
                      throw new IllegalStateException("Code " + type.code() + " for type " +
                              type + " has already been used");
              }
          }
  
          public static EmitStrategy forType(final StrategyType type) {
              return TYPE_TO_STRATEGY.get(type.code());
          }
      }
  
      /**
       * Returns the strategy type.
       *
       * @return Emit strategy type
       */
      StrategyType type();
  
      /**
       * This strategy indicates that the aggregated result for a window will only be emitted when the
       * window closes instead of when there's an update to the window. Window close means that current
       * event time is larger than (window end time + grace period).
       *
       * <p>This strategy should only be used for windows which can close. An exception will be thrown
       * if it's used with {@link UnlimitedWindow}.
       *
       * @see TimeWindows
       * @see SlidingWindows
       * @see SessionWindows
       * @see UnlimitedWindows
       * @see WindowUpdateStrategy
       *
       * @return "window close" {@code EmitStrategy} instance
       */
      static EmitStrategy onWindowClose() {
          return new WindowCloseStrategy();
      }
  
      /**
       * This strategy indicates that the aggregated result for a window will be emitted every time
       * when there's an update to the window instead of when the window closes.
       *
       * @see TimeWindows
       * @see SlidingWindows
       * @see SessionWindows
       * @see UnlimitedWindows
       * @see WindowCloseStrategy
       *
       * @return "window update" {@code EmitStrategy} instance
       */
      static EmitStrategy onWindowUpdate() {
          return new WindowUpdateStrategy();
      }
  }
  