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/*
 * (c) Copyright 2018 Palantir Technologies Inc. All rights reserved.
 *
 * Licensed 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 com.palantir.util;

import com.palantir.logsafe.UnsafeArg;
import com.palantir.logsafe.exceptions.SafeIllegalArgumentException;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public final class OptionalResolver {
    private OptionalResolver() {
        // Utility class
    }

    /**
     * Returns a single value corresponding to the value that is present in one or more of the Optionals provided.
     * This method throws if no Optionals provided contain values, or if the Optionals provided contain multiple
     * values that are not equal.
     * Null Optionals are considered not-present.
     */
    @SuppressWarnings("OptionalUsedAsFieldOrParameterType") // Used to process existing configuration files.
    public static  T resolve(Optional optional1, Optional optional2) {
        Set values = Stream.of(optional1, optional2)
                .filter(Objects::nonNull)
                .flatMap(Optional::stream)
                .collect(Collectors.toSet());

        if (values.size() == 1) {
            return values.iterator().next();
        } else if (values.size() > 1) {
            throw new SafeIllegalArgumentException(
                    "Contradictory values found, expected a single common value", UnsafeArg.of("values", values));
        } else {
            throw new SafeIllegalArgumentException("All Optionals provided were empty, couldn't determine a value.");
        }
    }
}