/*
 * 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.functions.windowing;

import java.util.Collections;
import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.common.functions.RuntimeContext;
import org.apache.flink.api.common.functions.util.FunctionUtils;
import org.apache.flink.configuration.Configuration;
import org.apache.flink.streaming.api.windowing.windows.Window;
import org.apache.flink.util.Collector;

/**
 * Internal {@link ProcessWindowFunction} that is used for implementing a fold on a window
 * configuration that only allows {@link AllWindowFunction} and cannot directly execute a
 * {@link ReduceFunction}.
 */
@Internal
public class ReduceApplyProcessWindowFunction<K, W extends Window, T, R>
	extends ProcessWindowFunction<T, R, K, W> {

	private static final long serialVersionUID = 1L;

	private final ReduceFunction<T> reduceFunction;
	private final ProcessWindowFunction<T, R, K, W> windowFunction;
	private transient InternalProcessApplyWindowContext<T, R, K, W> ctx;

	public ReduceApplyProcessWindowFunction(ReduceFunction<T> reduceFunction, ProcessWindowFunction<T, R, K, W> windowFunction) {
		this.windowFunction = windowFunction;
		this.reduceFunction = reduceFunction;
	}

	@Override
	public void process(K k, final Context context, Iterable<T> input, Collector<R> out) throws Exception {

		T curr = null;
		for (T val: input) {
			if (curr == null) {
				curr = val;
			} else {
				curr = reduceFunction.reduce(curr, val);
			}
		}

		this.ctx.window = context.window();
		this.ctx.context = context;
		windowFunction.process(k, ctx, Collections.singletonList(curr), out);
	}

	@Override
	public void clear(final Context context) throws Exception {
		this.ctx.window = context.window();
		this.ctx.context = context;
		windowFunction.clear(ctx);
	}

	@Override
	public void open(Configuration configuration) throws Exception {
		FunctionUtils.openFunction(this.windowFunction, configuration);
		ctx = new InternalProcessApplyWindowContext<>(windowFunction);
	}

	@Override
	public void close() throws Exception {
		FunctionUtils.closeFunction(this.windowFunction);
	}

	@Override
	public void setRuntimeContext(RuntimeContext t) {
		super.setRuntimeContext(t);

		FunctionUtils.setFunctionRuntimeContext(this.windowFunction, t);
	}

}