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/*
 * 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.util;

import org.apache.flink.util.function.CheckedSupplier;

import javax.annotation.Nullable;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.util.Objects;

import static org.apache.flink.util.Preconditions.checkNotNull;

/**
 * Wrapper around an object representing either a success (with a given value) or a failure cause.
 */
public class OptionalFailure implements Serializable {
	private static final long serialVersionUID = 1L;

	@Nullable
	private transient T value;

	@Nullable
	private Throwable failureCause;

	private OptionalFailure(@Nullable T value, @Nullable Throwable failureCause) {
		this.value = value;
		this.failureCause = failureCause;
	}

	public static  OptionalFailure of(T value) {
		return new OptionalFailure<>(value, null);
	}

	public static  OptionalFailure ofFailure(Throwable failureCause) {
		return new OptionalFailure<>(null, failureCause);
	}

	/**
	 * @return wrapped {@link OptionalFailure} returned by {@code valueSupplier} or wrapped failure if
	 * {@code valueSupplier} has thrown an {@link Exception}.
	 */
	public static  OptionalFailure createFrom(CheckedSupplier valueSupplier) {
		try {
			return of(valueSupplier.get());
		} catch (Exception ex) {
			return ofFailure(ex);
		}
	}

	/**
	 * @return stored value or throw a {@link FlinkException} with {@code failureCause}.
	 */
	public T get() throws FlinkException {
		if (value != null) {
			return value;
		}
		checkNotNull(failureCause);
		throw new FlinkException(failureCause);
	}

	/**
	 * @return same as {@link #get()} but throws a {@link FlinkRuntimeException}.
	 */
	public T getUnchecked() throws FlinkRuntimeException {
		if (value != null) {
			return value;
		}
		checkNotNull(failureCause);
		throw new FlinkRuntimeException(failureCause);
	}

	public Throwable getFailureCause() {
		return checkNotNull(failureCause);
	}

	public boolean isFailure() {
		return failureCause != null;
	}

	@Override
	public int hashCode() {
		return Objects.hash(value, failureCause);
	}

	@Override
	public boolean equals(Object obj) {
		if (obj == null) {
			return false;
		}
		if (obj == this) {
			return true;
		}
		if (!(obj instanceof OptionalFailure)) {
			return false;
		}
		OptionalFailure other = (OptionalFailure) obj;
		return Objects.equals(value, other.value) &&
			Objects.equals(failureCause, other.failureCause);
	}

	private void writeObject(ObjectOutputStream stream) throws IOException {
		stream.defaultWriteObject();
		stream.writeObject(value);
	}

	private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
		stream.defaultReadObject();
		value = (T) stream.readObject();
	}

	@Override
	public String toString() {
		return getClass().getSimpleName() + "{value=" + value + ", failureCause=" + failureCause + "}";
	}
}