/*
 * 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.generator;

import org.apache.flink.api.java.ExecutionEnvironment;
import org.apache.flink.graph.Graph;
import org.apache.flink.types.LongValue;
import org.apache.flink.types.NullValue;
import org.apache.flink.util.Preconditions;

/**
 * @see <a href="http://mathworld.wolfram.com/PathGraph.html">Path Graph at Wolfram MathWorld</a>
 */
public class PathGraph
extends AbstractGraphGenerator<LongValue, NullValue, NullValue> {

	public static final int MINIMUM_VERTEX_COUNT = 2;

	// Required to create the DataSource
	private final ExecutionEnvironment env;

	// Required configuration
	private long vertexCount;

	/**
	 * An undirected {@link Graph} with {@code n} vertices where each vertex
	 * v<sub>i</sub> connects to adjacent vertices v<sub>i+1</sub> when
	 * {@code i < n-1} and v<sub>i-1</sub> when {@code i > 0}.
	 * <p>
	 * A {@code PathGraph} is distinguished from a {@code CycleGraph} in that
	 * the first and last vertex are not connected, breaking the cycle.
	 *
	 * @param env the Flink execution environment
	 * @param vertexCount number of vertices
	 */
	public PathGraph(ExecutionEnvironment env, long vertexCount) {
		Preconditions.checkArgument(vertexCount >= MINIMUM_VERTEX_COUNT,
			"Vertex count must be at least " + MINIMUM_VERTEX_COUNT);

		this.env = env;
		this.vertexCount = vertexCount;
	}

	@Override
	public Graph<LongValue, NullValue, NullValue> generate() {
		return new GridGraph(env)
			.addDimension(vertexCount, false)
			.setParallelism(parallelism)
			.generate();
	}
}