/*
 * 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.streaming.api.scala.function

import org.apache.flink.annotation.Public
import org.apache.flink.api.common.functions.Function
import org.apache.flink.streaming.api.windowing.windows.Window
import org.apache.flink.util.Collector

import java.io.Serializable

/**
 * Base interface for functions that are evaluated over keyed (grouped) windows.
 *
 * @tparam IN
 *   The type of the input value.
 * @tparam OUT
 *   The type of the output value.
 * @tparam KEY
 *   The type of the key.
 * @deprecated
 *   All Flink Scala APIs are deprecated and will be removed in a future Flink major version. You
 *   can still build your application in Scala, but you should move to the Java version of either
 *   the DataStream and/or Table API.
 * @see
 *   <a href="https://s.apache.org/flip-265">FLIP-265 Deprecate and remove Scala API support</a>
 */
@deprecated(org.apache.flink.api.scala.FLIP_265_WARNING, since = "1.18.0")
@Public
trait WindowFunction[IN, OUT, KEY, W <: Window] extends Function with Serializable {

  /**
   * Evaluates the window and outputs none or several elements.
   *
   * @param key
   *   The key for which this window is evaluated.
   * @param window
   *   The window that is being evaluated.
   * @param input
   *   The elements in the window being evaluated.
   * @param out
   *   A collector for emitting elements.
   * @throws Exception
   *   The function may throw exceptions to fail the program and trigger recovery.
   */
  def apply(key: KEY, window: W, input: Iterable[IN], out: Collector[OUT])
}
