/*
 * 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.drivers.parameter;

import org.apache.flink.api.java.utils.ParameterTool;
import org.apache.flink.client.program.ProgramParametrizationException;
import org.apache.flink.graph.Graph;
import org.apache.flink.graph.drivers.parameter.Simplify.Ordering;
import org.apache.flink.types.NullValue;

/**
 * A simple graph has no self-loops (edges where the source and target vertices
 * are the same) and no duplicate edges. Flink stores an undirected graph as
 * a directed graph where each undirected edge is represented by a directed
 * edge in each direction.
 *
 * This {@link Parameter} indicates whether to simplify the graph and if the
 * graph should be directed or undirected.
 */
public class Simplify
implements Parameter<Ordering> {

	public enum Ordering {
		// leave the graph unchanged
		NONE,

		// create a simple, directed graph
		DIRECTED,

		// create a simple, undirected graph
		UNDIRECTED,

		// create a simple, undirected graph
		// remove input edges where source < target before symmetrizing the graph
		UNDIRECTED_CLIP_AND_FLIP,
	}

	private Ordering value;

	/**
	 * Add this parameter to the list of parameters stored by owner.
	 *
	 * @param owner the {@link Parameterized} using this {@link Parameter}
	 */
	public Simplify(ParameterizedBase owner) {
		owner.addParameter(this);
	}

	@Override
	public String getUsage() {
		return "[--simplify <directed | undirected [--clip_and_flip]>]";
	}

	@Override
	public void configure(ParameterTool parameterTool) {
		String ordering = parameterTool.get("simplify");

		if (ordering == null) {
			value = Ordering.NONE;
		} else {
			switch (ordering.toLowerCase()) {
				case "directed":
					value = Ordering.DIRECTED;
					break;
				case "undirected":
					value = parameterTool.has("clip_and_flip") ? Ordering.UNDIRECTED_CLIP_AND_FLIP : Ordering.UNDIRECTED;
					break;
				default:
					throw new ProgramParametrizationException(
						"Expected 'directed' or 'undirected' ordering but received '" + ordering + "'");
			}
		}
	}

	@Override
	public Ordering getValue() {
		return value;
	}

	/**
	 * Simplify the given graph based on the configured value.
	 *
	 * @param graph input graph
	 * @param <T> graph key type
	 * @return output graph
	 * @throws Exception on error
	 */
	public <T extends Comparable<T>> Graph<T, NullValue, NullValue> simplify(Graph<T, NullValue, NullValue> graph)
			throws Exception {

		switch (value) {
			case DIRECTED:
				graph = graph
					.run(new org.apache.flink.graph.asm.simple.directed.Simplify<T, NullValue, NullValue>());
				break;
			case UNDIRECTED:
				graph = graph
					.run(new org.apache.flink.graph.asm.simple.undirected.Simplify<T, NullValue, NullValue>(false));
				break;
			case UNDIRECTED_CLIP_AND_FLIP:
				graph = graph
					.run(new org.apache.flink.graph.asm.simple.undirected.Simplify<T, NullValue, NullValue>(true));
				break;
		}

		return graph;
	}

	public String getShortString() {
		switch (value) {
			case DIRECTED:
				return "d";
			case UNDIRECTED:
				return "u";
			case UNDIRECTED_CLIP_AND_FLIP:
				return "ɔ";
			default:
				return "";
		}
	}
}