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/*
 * Original Guava code is copyright (C) 2015 The Guava Authors.
 * Modifications from Guava are copyright (C) 2015 DiffPlug.
 *
 * 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 java.io.Serializable;
import java.lang.ref.WeakReference;
import java.lang.reflect.Field;
import java.util.EnumSet;
import java.util.HashMap;
import java.util.Map;
import java.util.WeakHashMap;

import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;

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

/**
 * Utility methods for working with {@link Enum} instances.
 *
 * @author Steve McKay
 *
 * @since 9.0
 */
@CheckReturnValue
@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 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);
		return Platform.getEnumIfPresent(enumClass, value);
	}

	@GwtIncompatible("java.lang.ref.WeakReference")
	private static final Map>, Map>>> enumConstantCache = new WeakHashMap>, Map>>>();

	@GwtIncompatible("java.lang.ref.WeakReference")
	private static > Map>> populateCache(
			Class enumClass) {
		Map>> result = new HashMap>>();
		for (T enumInstance : EnumSet.allOf(enumClass)) {
			result.put(enumInstance.name(), new WeakReference>(enumInstance));
		}
		enumConstantCache.put(enumClass, result);
		return result;
	}

	@GwtIncompatible("java.lang.ref.WeakReference")
	static > Map>> getEnumConstants(
			Class enumClass) {
		synchronized (enumConstantCache) {
			Map>> constants = enumConstantCache.get(enumClass);
			if (constants == null) {
				constants = populateCache(enumClass);
			}
			return constants;
		}
	}

	/**
	 * Returns a converter that converts between strings and {@code enum} values of type
	 * {@code enumClass} using {@link Enum#valueOf(Class, String)} and {@link Enum#name()}. The
	 * converter will throw an {@code IllegalArgumentException} if the argument is not the name of
	 * any enum constant in the specified enum.
	 *
	 * @since 16.0
	 */
	public static > Converter stringConverter(final Class enumClass) {
		return new StringConverter(enumClass);
	}

	private static final class StringConverter> extends Converter
			implements Serializable {

		private final Class enumClass;

		StringConverter(Class enumClass) {
			this.enumClass = checkNotNull(enumClass);
		}

		@Override
		protected T doForward(String value) {
			return Enum.valueOf(enumClass, value);
		}

		@Override
		protected String doBackward(T enumValue) {
			return enumValue.name();
		}

		@Override
		public boolean equals(@Nullable Object object) {
			if (object instanceof StringConverter) {
				StringConverter that = (StringConverter) object;
				return this.enumClass.equals(that.enumClass);
			}
			return false;
		}

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

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

		private static final long serialVersionUID = 0L;
	}
}