/*
 * 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.graph.asm.degree.annotate.undirected;

import org.apache.flink.api.common.operators.base.JoinOperatorBase.JoinHint;
import org.apache.flink.api.java.DataSet;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.graph.Edge;
import org.apache.flink.graph.Graph;
import org.apache.flink.graph.Vertex;
import org.apache.flink.graph.asm.degree.annotate.DegreeAnnotationFunctions.JoinEdgeWithVertexDegree;
import org.apache.flink.graph.utils.proxy.GraphAlgorithmWrappingDataSet;
import org.apache.flink.graph.utils.proxy.OptionalBoolean;
import org.apache.flink.types.LongValue;
import org.apache.flink.util.Preconditions;

import static org.apache.flink.api.common.ExecutionConfig.PARALLELISM_DEFAULT;

/**
 * Annotates edges of an undirected graph with degree of the target vertex.
 *
 * @param <K> ID type
 * @param <VV> vertex value type
 * @param <EV> edge value type
 */
public class EdgeTargetDegree<K, VV, EV>
extends GraphAlgorithmWrappingDataSet<K, VV, EV, Edge<K, Tuple2<EV, LongValue>>> {

	// Optional configuration
	private OptionalBoolean reduceOnSourceId = new OptionalBoolean(false, false);

	private int parallelism = PARALLELISM_DEFAULT;

	/**
	 * The degree can be counted from either the edge source or target IDs.
	 * By default the target IDs are counted. Reducing on source IDs may
	 * optimize the algorithm if the input edge list is sorted by source ID.
	 *
	 * @param reduceOnSourceId set to {@code true} if the input edge list
	 *                         is sorted by target ID
	 * @return this
	 */
	public EdgeTargetDegree<K, VV, EV> setReduceOnSourceId(boolean reduceOnSourceId) {
		this.reduceOnSourceId.set(reduceOnSourceId);

		return this;
	}

	/**
	 * Override the operator parallelism.
	 *
	 * @param parallelism operator parallelism
	 * @return this
	 */
	public EdgeTargetDegree<K, VV, EV> setParallelism(int parallelism) {
		Preconditions.checkArgument(parallelism > 0 || parallelism == PARALLELISM_DEFAULT,
			"The parallelism must be greater than zero.");

		this.parallelism = parallelism;

		return this;
	}

	@Override
	protected String getAlgorithmName() {
		return EdgeTargetDegree.class.getName();
	}

	@Override
	protected boolean mergeConfiguration(GraphAlgorithmWrappingDataSet other) {
		Preconditions.checkNotNull(other);

		if (! EdgeSourceDegree.class.isAssignableFrom(other.getClass())) {
			return false;
		}

		EdgeTargetDegree rhs = (EdgeTargetDegree) other;

		reduceOnSourceId.mergeWith(rhs.reduceOnSourceId);
		parallelism = (parallelism == PARALLELISM_DEFAULT) ? rhs.parallelism :
			((rhs.parallelism == PARALLELISM_DEFAULT) ? parallelism : Math.min(parallelism, rhs.parallelism));

		return true;
	}

	@Override
	public DataSet<Edge<K, Tuple2<EV, LongValue>>> runInternal(Graph<K, VV, EV> input)
			throws Exception {
		// t, d(t)
		DataSet<Vertex<K, LongValue>> vertexDegrees = input
			.run(new VertexDegree<K, VV, EV>()
				.setReduceOnTargetId(!reduceOnSourceId.get())
				.setParallelism(parallelism));

		// s, t, d(t)
		return input.getEdges()
			.join(vertexDegrees, JoinHint.REPARTITION_HASH_SECOND)
			.where(1)
			.equalTo(0)
			.with(new JoinEdgeWithVertexDegree<K, EV, LongValue>())
				.setParallelism(parallelism)
				.name("Edge target degree");
	}
}