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/*
 * Copyright (C) 2011 The Guava Authors
 *
 * 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.google.common.base;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.GwtIncompatible;

import java.io.Serializable;
import java.lang.reflect.Field;

import javax.annotation.Nullable;

/**
 * Utility methods for working with {@link Enum} instances.
 *
 * @author Steve McKay
 *
 * @since 9.0
 */
@GwtCompatible(emulated = true)
@Beta
public final class Enums {

  private Enums() {}

  /**
   * Returns the {@link Field} in which {@code enumValue} is defined.
   * For example, to get the {@code Description} annotation on the {@code GOLF}
   * constant of enum {@code Sport}, use
   * {@code Enums.getField(Sport.GOLF).getAnnotation(Description.class)}.
   *
   * @since 12.0
   */
  @GwtIncompatible("reflection")
  public static Field getField(Enum enumValue) {
    Class clazz = enumValue.getDeclaringClass();
    try {
      return clazz.getDeclaredField(enumValue.name());
    } catch (NoSuchFieldException impossible) {
      throw new AssertionError(impossible);
    }
  }

  /**
   * Returns a {@link Function} that maps an {@link Enum} name to the associated
   * {@code Enum} constant. The {@code Function} will return {@code null} if the
   * {@code Enum} constant does not exist.
   *
   * @param enumClass the {@link Class} of the {@code Enum} declaring the
   *     constant values.
   */
  public static > Function valueOfFunction(Class enumClass) {
    return new ValueOfFunction(enumClass);
  }

  /**
   * A {@link Function} that maps an {@link Enum} name to the associated
   * constant, or {@code null} if the constant does not exist.
   */
  private static final class ValueOfFunction>
      implements Function, Serializable {

    private final Class enumClass;

    private ValueOfFunction(Class enumClass) {
      this.enumClass = checkNotNull(enumClass);
    }

    @Override
    public T apply(String value) {
      try {
        return Enum.valueOf(enumClass, value);
      } catch (IllegalArgumentException e) {
        return null;
      }
    }

    @Override public boolean equals(@Nullable Object obj) {
      return obj instanceof ValueOfFunction &&
          enumClass.equals(((ValueOfFunction) obj).enumClass);
    }

    @Override public int hashCode() {
      return enumClass.hashCode();
    }

    @Override public String toString() {
      return "Enums.valueOf(" + enumClass + ")";
    }

    private static final long serialVersionUID = 0;
  }

  /**
   * Returns an optional enum constant for the given type, using {@link Enum#valueOf}. If the
   * constant does not exist, {@link Optional#absent} is returned. A common use case is for parsing
   * user input or falling back to a default enum constant. For example,
   * {@code Enums.getIfPresent(Country.class, countryInput).or(Country.DEFAULT);}
   *
   * @since 12.0
   */
  public static > Optional getIfPresent(Class enumClass, String value) {
    checkNotNull(enumClass);
    checkNotNull(value);
    try {
      return Optional.of(Enum.valueOf(enumClass, value));
    } catch (IllegalArgumentException iae) {
      return Optional.absent();
    }
  }
}