001/*
002 * Copyright (C) 2022 - 2023, 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.ArrayDeque;
020import java.util.Deque;
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 chain of configurers to apply to a file manager.
031 *
032 * <p>While not designed for concurrent use, all operations are shielded by a
033 * lock to guard against potentially confusing behaviour, should this component be shared across
034 * multiple physical and virtual threads.
035 *
036 * @author Ashley Scopes
037 * @since 0.0.1
038 */
039@API(since = "0.0.1", status = Status.STABLE)
040public final class JctFileManagerConfigurerChain {
041
042  private static final Logger LOGGER = LoggerFactory.getLogger(JctFileManagerConfigurerChain.class);
043
044  private final Lock lock;
045  private final Deque<JctFileManagerConfigurer> configurers;
046
047  /**
048   * Initialise this chain.
049   */
050  public JctFileManagerConfigurerChain() {
051    lock = new ReentrantLock();
052    configurers = new ArrayDeque<>(16);
053  }
054
055  /**
056   * Add a configurer to the start of the chain.
057   *
058   * @param configurer the configurer to add.
059   * @return this chain for further calls.
060   */
061  public JctFileManagerConfigurerChain addFirst(JctFileManagerConfigurer configurer) {
062    lock.lock();
063    try {
064      configurers.addFirst(configurer);
065    } finally {
066      lock.unlock();
067    }
068    return this;
069  }
070
071  /**
072   * Add a configurer to the end of the chain.
073   *
074   * @param configurer the configurer to add.
075   * @return this chain for further calls.
076   */
077  public JctFileManagerConfigurerChain addLast(JctFileManagerConfigurer configurer) {
078    lock.lock();
079    try {
080      configurers.addLast(configurer);
081    } finally {
082      lock.unlock();
083    }
084    return this;
085  }
086
087  /**
088   * Get an immutable copy of the list of configurers.
089   *
090   * @return the list of configurers.
091   */
092  public List<JctFileManagerConfigurer> list() {
093    lock.lock();
094    try {
095      return List.copyOf(configurers);
096    } finally {
097      lock.unlock();
098    }
099  }
100
101  /**
102   * Apply each configurer to the given file manager in order.
103   *
104   * @param fileManager the file manager to configure.
105   * @return the configured file manager to use. This may or may not be the same object as the input
106   *     parameter, depending on how the configurers manipulate the input object.
107   */
108  public JctFileManager configure(JctFileManager fileManager) {
109    lock.lock();
110    try {
111      for (var configurer : configurers) {
112        if (configurer.isEnabled()) {
113          LOGGER.debug("Applying {} to file manager", configurer);
114          fileManager = configurer.configure(fileManager);
115        } else {
116          LOGGER.trace("Skipping {}", configurer);
117        }
118      }
119    } finally {
120      lock.unlock();
121    }
122
123    return fileManager;
124  }
125}