/*
 * 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.utils.proxy;

import org.apache.flink.graph.GraphAlgorithm;

/**
 * A multi-state boolean.
 * <p>
 * This class is used by {@link GraphAlgorithm} configuration options to set a
 * default value which can be overwritten. The default value is also used when
 * algorithm configurations are merged and conflict.
 */
public class OptionalBoolean {

	protected enum State {
		UNSET,
		FALSE,
		TRUE,
		CONFLICTING
	}

	private State state = State.UNSET;

	private final boolean valueIfUnset;

	private final boolean valueIfConflicting;

	/**
	 * An {@code OptionalBoolean} has three possible states: true, false, and
	 * "unset". The value is set when merged with a value of true or false. The
	 * state returns to unset either explicitly or when true is merged with false.
	 *
	 * @param valueIfUnset the value to return when the object's state is unset
	 * @param valueIfConflicting the value to return when the object's state is conflicting
	 */
	public OptionalBoolean(boolean valueIfUnset, boolean valueIfConflicting) {
		this.valueIfUnset = valueIfUnset;
		this.valueIfConflicting = valueIfConflicting;
	}

	/**
	 * Get the boolean state.
	 *
	 * @return boolean state
	 */
	public boolean get() {
		switch (state) {
			case UNSET:
				return valueIfUnset;
			case FALSE:
				return false;
			case TRUE:
				return true;
			case CONFLICTING:
				return valueIfConflicting;
			default:
				throw new RuntimeException("Unknown state");
		}
	}

	/**
	 * Set the boolean state.
	 *
	 * @param value boolean state
	 */
	public void set(boolean value) {
		this.state = (value ? State.TRUE : State.FALSE);
	}

	/**
	 * Reset to the unset state.
	 */
	public void unset() {
		this.state = State.UNSET;
	}

	/**
	 * Get the actual state.
	 *
	 * @return actual state
	 */
	protected State getState() {
		return state;
	}

	/**
	 * The conflicting states are true with false and false with true.
	 *
	 * @param other object to test with
	 * @return whether the objects conflict
	 */
	public boolean conflictsWith(OptionalBoolean other) {
		return state == State.CONFLICTING
			|| other.state == State.CONFLICTING
			|| (state == State.TRUE && other.state == State.FALSE)
			|| (state == State.FALSE && other.state == State.TRUE);
	}

	/**
	 * State transitions:
	 *  if the states are the same then no change
	 *  if either state is unset then change to the other state
	 *  if the states are conflicting then set to the conflicting state
	 *
	 * @param other object from which to merge state
	 */
	public void mergeWith(OptionalBoolean other) {
		if (state == other.state) {
			// no change in state
		} else if (state == State.UNSET) {
			state = other.state;
		} else if (other.state == State.UNSET) {
			// no change in state
		} else {
			state = State.CONFLICTING;
		}
	}
}