/*
 * 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.delta;

import org.apache.flink.annotation.PublicEvolving;
import org.apache.flink.streaming.api.functions.windowing.delta.extractor.Extractor;

/**
 * Extend this abstract class to implement a delta function which is aware of
 * extracting the data on which the delta is calculated from a more complex data
 * structure. For example in case you want to be able to run a delta only on one
 * field of a Tuple type or only on some fields from an array.
 *
 * @param <DATA>
 *            The input data type. The input of this type will be passed to the
 *            extractor which will transform into a TO-object. The delta
 *            function then runs on this TO-object.
 * @param <TO>
 *            The type on which the delta function runs. (The type of the delta
 *            function)
 */
@PublicEvolving
public abstract class ExtractionAwareDeltaFunction<DATA, TO> implements DeltaFunction<DATA> {

	private static final long serialVersionUID = 6927486219702689554L;

	private Extractor<DATA, TO> converter;

	public ExtractionAwareDeltaFunction(Extractor<DATA, TO> converter) {
		this.converter = converter;
	}

	/**
	 * This method takes the two data point and runs the set extractor on it.
	 * The delta function implemented at {@link #getNestedDelta} is then called
	 * with the extracted data. In case no extractor is set the input data gets
	 * passes to {@link #getNestedDelta} as-is. The return value is just
	 * forwarded from {@link #getNestedDelta}.
	 *
	 * @param oldDataPoint
	 *            the older data point as raw data (before extraction).
	 * @param newDataPoint
	 *            the new data point as raw data (before extraction).
	 * @return the delta between the two points.
	 */
	@SuppressWarnings("unchecked")
	@Override
	public double getDelta(DATA oldDataPoint, DATA newDataPoint) {
		if (converter == null) {
			// In case no conversion/extraction is required, we can cast DATA to
			// TO
			// => Therefore, "unchecked" warning is suppressed for this method.
			return getNestedDelta((TO) oldDataPoint, (TO) newDataPoint);
		} else {
			return getNestedDelta(converter.extract(oldDataPoint), converter.extract(newDataPoint));
		}

	}

	/**
	 * This method is exactly the same as
	 * {@link DeltaFunction#getDelta(Object, Object)} except that it gets the
	 * result of the previously done extractions as input. Therefore, this
	 * method only does the actual calculation of the delta but no data
	 * extraction or conversion.
	 *
	 * @param oldDataPoint
	 *            the older data point.
	 * @param newDataPoint
	 *            the new data point.
	 * @return the delta between the two points.
	 */
	public abstract double getNestedDelta(TO oldDataPoint, TO newDataPoint);

}