001/* -*- mode: Java; c-basic-offset: 2; indent-tabs-mode: nil; coding: utf-8-unix -*-
002 *
003 * Copyright © 2026 microBean™.
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
006 * the License. You may obtain a copy of the License at
007 *
008 *     http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
011 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
012 * specific language governing permissions and limitations under the License.
013 */
014package org.microbean.attributes;
015
016import java.util.List;
017import java.util.Map;
018
019import java.util.concurrent.ConcurrentHashMap;
020
021/**
022 * A simple, mutable, concurrent, {@link Attributed}-aware cache of objects.
023 *
024 * @param <T> the type of object to be normalized
025 *
026 * @author <a href="https://about.me/lairdnelson" target="_top">Laird Nelson</a>
027 *
028 * @see #normalize(Object)
029 */
030public final class Normalizer<T> {
031
032  private final Map<Key<? extends T>, T> cache;
033
034  /**
035   * Creates a new {@link Normalizer}.
036   */
037  public Normalizer() {
038    super();
039    this.cache = new ConcurrentHashMap<>();
040  }
041
042  /**
043   * <dfn>Normalizes</dfn> the supplied {@code element} such that if this {@link Normalizer} already has an {@linkplain
044   * Object#equals(Object) equivalent} cached element, the cached element is returned, and, if it does not, the supplied
045   * {@code element} is cached indefinitely and returned.
046   *
047   * <p><strong>Note:</strong> if the supplied {@code element} is an {@link Attributed} implementation, then, in
048   * accordance with the {@link Attributed} contract, it must not include its {@linkplain Attributed#attributes()
049   * attributes} in its equality or {@linkplain Attributed#hashCode() hashcode} computations, or undefined behavior may
050   * result.</p>
051   *
052   * @param element the element to normalize; may be {@code null} in which case {@code null} is returned
053   *
054   * @return the supplied {@code element} or a previously cached {@linkplain Object#equals(Object) equivalent} element
055   */
056  public final T normalize(final T element) {
057    return element instanceof Attributed a ? this.cache.computeIfAbsent(new Key<>(a.attributes(), element), k -> k.element()) : element;
058  }
059
060  private static final record Key<T>(List<Attributes> attributes, T element) implements Attributed {}
061  
062}