001/*
002 * Copyright (C) 2022 - 2024, the original author or authors.
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * 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
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016package io.github.ascopes.jct.filemanagers.config;
017
018import io.github.ascopes.jct.filemanagers.JctFileManager;
019import java.util.LinkedList;
020import java.util.List;
021import org.apiguardian.api.API;
022import org.apiguardian.api.API.Status;
023import org.slf4j.Logger;
024import org.slf4j.LoggerFactory;
025
026/**
027 * A collection representing a chain of configurers to apply to a file manager.
028 *
029 * <p>This is used to provide a set of ordered configuration operations to perform on newly
030 * created file managers to prepare them for consumption in test cases. Common operations
031 * may include: 
032 *
033 * <ul>
034 *   <li>Automatically configuring the annotation processor paths;</li>
035 *   <li>Creating empty locations to prevent compilers raising exceptions;</li>
036 *   <li>Installing logging interceptors.</li>
037 * </ul>
038 *
039 * <p>When configuring a file manager with this chain, each configurer is invoked in the
040 * provided order. Configurers themselves must return a file manager as a result of the
041 * configure operation. This operation may return the input file manager if the operation
042 * mutated the input, or it may return a different file manager instance. In the latter
043 * case, subsequent configuration operations internally will use the new file manager.
044 * The last returned file manager in the chain will be used as the final returned result.
045 * This enables configurers to wrap file managers in proxies or delegating implementations
046 * to intercept or override existing behaviours.
047 *
048 * <p>This class is not thread-safe.
049 *
050 * @author Ashley Scopes
051 * @since 0.0.1
052 */
053@API(since = "0.0.1", status = Status.STABLE)
054public final class JctFileManagerConfigurerChain {
055
056  private static final Logger log = LoggerFactory.getLogger(JctFileManagerConfigurerChain.class);
057
058  private final LinkedList<JctFileManagerConfigurer> configurers;
059
060  /**
061   * Initialise this chain.
062   */
063  public JctFileManagerConfigurerChain() {
064    configurers = new LinkedList<>();
065  }
066
067  /**
068   * Add a configurer to the start of the chain.
069   *
070   * @param configurer the configurer to add.
071   * @return this chain for further calls.
072   */
073  public JctFileManagerConfigurerChain addFirst(JctFileManagerConfigurer configurer) {
074    configurers.addFirst(configurer);
075    return this;
076  }
077
078  /**
079   * Add a configurer to the end of the chain.
080   *
081   * @param configurer the configurer to add.
082   * @return this chain for further calls.
083   */
084  public JctFileManagerConfigurerChain addLast(JctFileManagerConfigurer configurer) {
085    configurers.addLast(configurer);
086    return this;
087  }
088
089  /**
090   * Get an immutable copy of the list of configurers.
091   *
092   * @return the list of configurers.
093   */
094  public List<JctFileManagerConfigurer> list() {
095    return List.copyOf(configurers);
096  }
097
098  /**
099   * Apply each configurer to the given file manager in order.
100   *
101   * @param fileManager the file manager to configure.
102   * @return the configured file manager to use. This may or may not be the same object as the input
103   *     parameter, depending on how the configurers manipulate the input object.
104   */
105  public JctFileManager configure(JctFileManager fileManager) {
106    for (var configurer : configurers) {
107      if (configurer.isEnabled()) {
108        log.debug("Applying {} to file manager {}", configurer, fileManager);
109        // Configurers can totally replace the existing file manager
110        // if they choose.
111        fileManager = configurer.configure(fileManager);
112      } else {
113        log.trace("Skipping {}", configurer);
114      }
115    }
116    return fileManager;
117  }
118}