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.Deque;
020import java.util.LinkedList;
021import java.util.List;
022import java.util.concurrent.locks.Lock;
023import java.util.concurrent.locks.ReentrantLock;
024import org.apiguardian.api.API;
025import org.apiguardian.api.API.Status;
026import org.slf4j.Logger;
027import org.slf4j.LoggerFactory;
028
029/**
030 * A collection representing a chain of configurers to apply to a file manager.
031 *
032 * <p>This is used to provide a set of ordered configuration operations to perform on newly
033 * created file managers to prepare them for consumption in test cases. Common operations
034 * may include: 
035 *
036 * <ul>
037 *   <li>Automatically configuring the annotation processor paths;</li>
038 *   <li>Creating empty locations to prevent compilers raising exceptions;</li>
039 *   <li>Installing logging interceptors.</li>
040 * </ul>
041 *
042 * <p>When configuring a file manager with this chain, each configurer is invoked in the
043 * provided order. Configurers themselves must return a file manager as a result of the
044 * configure operation. This operation may return the input file manager if the operation
045 * mutated the input, or it may return a different file manager instance. In the latter
046 * case, subsequent configuration operations internally will use the new file manager.
047 * The last returned file manager in the chain will be used as the final returned result.
048 * This enables configurers to wrap file managers in proxies or delegating implementations
049 * to intercept or override existing behaviours.
050 *
051 * <p>While not designed for concurrent use, all operations are shielded by a
052 * lock to guard against potentially confusing behaviour, should this component be shared across
053 * multiple physical or virtual threads.
054 *
055 * @author Ashley Scopes
056 * @since 0.0.1
057 */
058@API(since = "0.0.1", status = Status.STABLE)
059public final class JctFileManagerConfigurerChain {
060
061  private static final Logger LOGGER = LoggerFactory.getLogger(JctFileManagerConfigurerChain.class);
062
063  private final Lock lock;
064  private final Deque<JctFileManagerConfigurer> configurers;
065
066  /**
067   * Initialise this chain.
068   */
069  public JctFileManagerConfigurerChain() {
070    lock = new ReentrantLock();
071    configurers = new LinkedList<>();
072  }
073
074  /**
075   * Add a configurer to the start of the chain.
076   *
077   * @param configurer the configurer to add.
078   * @return this chain for further calls.
079   */
080  public JctFileManagerConfigurerChain addFirst(JctFileManagerConfigurer configurer) {
081    lock.lock();
082    try {
083      configurers.addFirst(configurer);
084    } finally {
085      lock.unlock();
086    }
087    return this;
088  }
089
090  /**
091   * Add a configurer to the end of the chain.
092   *
093   * @param configurer the configurer to add.
094   * @return this chain for further calls.
095   */
096  public JctFileManagerConfigurerChain addLast(JctFileManagerConfigurer configurer) {
097    lock.lock();
098    try {
099      configurers.addLast(configurer);
100    } finally {
101      lock.unlock();
102    }
103    return this;
104  }
105
106  /**
107   * Get an immutable copy of the list of configurers.
108   *
109   * @return the list of configurers.
110   */
111  public List<JctFileManagerConfigurer> list() {
112    lock.lock();
113    try {
114      return List.copyOf(configurers);
115    } finally {
116      lock.unlock();
117    }
118  }
119
120  /**
121   * Apply each configurer to the given file manager in order.
122   *
123   * @param fileManager the file manager to configure.
124   * @return the configured file manager to use. This may or may not be the same object as the input
125   *     parameter, depending on how the configurers manipulate the input object.
126   */
127  public JctFileManager configure(JctFileManager fileManager) {
128    lock.lock();
129    try {
130      for (var configurer : configurers) {
131        if (configurer.isEnabled()) {
132          LOGGER.debug("Applying {} to file manager {}", configurer, fileManager);
133          // Configurers can totally replace the existing file manager
134          // if they choose.
135          fileManager = configurer.configure(fileManager);
136        } else {
137          LOGGER.trace("Skipping {}", configurer);
138        }
139      }
140    } finally {
141      lock.unlock();
142    }
143
144    return fileManager;
145  }
146}