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/*
 * Copyright (C) 2007 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.collect;

import static com.google.common.base.Preconditions.checkNotNull;
import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtIncompatible;
import com.google.common.base.Equivalence;
import com.google.common.base.Function;
import com.google.common.collect.MapMakerInternalMap.ReferenceEntry;
import java.util.concurrent.ConcurrentMap;

/**
 *  Contains static methods pertaining to instances of {@link Interner}.
 *
 *  @author Kevin Bourrillion
 *  @since 3.0
 *
 * @deprecated The Google Guava Core Libraries are deprecated and will not be part of the AEM SDK after April 2023
 */
@Beta
@Deprecated(since = "2022-12-01")
public final class Interners {

    private Interners() {
    }

    /**
     * Returns a new thread-safe interner which retains a strong reference to each instance it has
     * interned, thus preventing these instances from being garbage-collected. If this retention is
     * acceptable, this implementation may perform better than {@link #newWeakInterner}. Note that
     * unlike {@link String#intern}, using this interner does not consume memory in the permanent
     * generation.
     */
    public static  Interner newStrongInterner() {
        final ConcurrentMap map = new MapMaker().makeMap();
        return new Interner() {

            @Override
            public E intern(E sample) {
                E canonical = map.putIfAbsent(checkNotNull(sample), sample);
                return (canonical == null) ? sample : canonical;
            }
        };
    }

    /**
     * Returns a new thread-safe interner which retains a weak reference to each instance it has
     * interned, and so does not prevent these instances from being garbage-collected. This most
     * likely does not perform as well as {@link #newStrongInterner}, but is the best alternative
     * when the memory usage of that implementation is unacceptable. Note that unlike {@link
     * String#intern}, using this interner does not consume memory in the permanent generation.
     */
    @GwtIncompatible("java.lang.ref.WeakReference")
    public static  Interner newWeakInterner() {
        return new WeakInterner();
    }

    // @deprecated The Google Guava Core Libraries are deprecated and will not be part of the AEM SDK after April 2023
    @Deprecated(since = "2022-12-01")
    private static class WeakInterner implements Interner {

        // MapMaker is our friend, we know about this type
        private final MapMakerInternalMap map = new MapMaker().weakKeys().keyEquivalence(Equivalence.equals()).makeCustomMap();

        @Override
        public E intern(E sample) {
            while (true) {
                // trying to read the canonical...
                ReferenceEntry entry = map.getEntry(sample);
                if (entry != null) {
                    E canonical = entry.getKey();
                    if (canonical != null) {
                        // only matters if weak/soft keys are used
                        return canonical;
                    }
                }
                // didn't see it, trying to put it instead...
                Dummy sneaky = map.putIfAbsent(sample, Dummy.VALUE);
                if (sneaky == null) {
                    return sample;
                } else {
                    /* Someone beat us to it! Trying again...
           *
           * Technically this loop not guaranteed to terminate, so theoretically (extremely
           * unlikely) this thread might starve, but even then, there is always going to be another
           * thread doing progress here.
           */
                }
            }
        }

        private enum Dummy {

            VALUE
        }
    }

    /**
     * Returns a function that delegates to the {@link Interner#intern} method of the given interner.
     *
     * @since 8.0
     */
    public static  Function asFunction(Interner interner) {
        return new InternerFunction(checkNotNull(interner));
    }

    // @deprecated The Google Guava Core Libraries are deprecated and will not be part of the AEM SDK after April 2023
    @Deprecated(since = "2022-12-01")
    private static class InternerFunction implements Function {

        private final Interner interner;

        public InternerFunction(Interner interner) {
            this.interner = interner;
        }

        @Override
        public E apply(E input) {
            return interner.intern(input);
        }

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

        @Override
        public boolean equals(Object other) {
            if (other instanceof InternerFunction) {
                InternerFunction that = (InternerFunction) other;
                return interner.equals(that.interner);
            }
            return false;
        }
    }
}