/*
    * Copyright (C) 2017 Two Sigma Open Source
    * and other copyright owners as documented in the project's IP log.
    *
    * This program and the accompanying materials are made available
    * under the terms of the Eclipse Distribution License v1.0 which
    * accompanies this distribution, is reproduced below, and is
    * available at http://www.eclipse.org/org/documents/edl-v10.php
    *
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or
   * without modification, are permitted provided that the following
   * conditions are met:
   *
   * - Redistributions of source code must retain the above copyright
   *   notice, this list of conditions and the following disclaimer.
   *
   * - Redistributions in binary form must reproduce the above
   *   copyright notice, this list of conditions and the following
   *   disclaimer in the documentation and/or other materials provided
   *   with the distribution.
   *
   * - Neither the name of the Eclipse Foundation, Inc. nor the
   *   names of its contributors may be used to endorse or promote
   *   products derived from this software without specific prior
   *   written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND
   * CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES,
   * INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
   * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
   * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
   */
  
  package org.eclipse.jgit.internal.storage.file;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  import java.io.BufferedReader;
  import java.io.File;
  import java.io.IOException;
  import java.nio.file.Files;
  import java.nio.file.NoSuchFileException;
  import java.nio.file.attribute.FileTime;
  import java.text.MessageFormat;
  import java.text.ParseException;
  import java.time.Instant;
  
  import org.eclipse.jgit.api.errors.JGitInternalException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.lib.ConfigConstants;
  import org.eclipse.jgit.util.GitDateParser;
  import org.eclipse.jgit.util.SystemReader;
  
  /**
   * This class manages the gc.log file for a {@link FileRepository}.
   */
  class GcLog {
  	private final FileRepository repo;
  
  	private final File logFile;
  
  	private final LockFile lock;
  
  	private Instant gcLogExpire;
  
  	private static final String LOG_EXPIRY_DEFAULT = "1.day.ago"; //$NON-NLS-1$
  
  	private boolean nonEmpty = false;
  
  	/**
  	 * Construct a GcLog object for a {@link FileRepository}
  	 *
  	 * @param repo
  	 *            the repository
  	 */
  	GcLog(FileRepository repo) {
  		this.repo = repo;
  		logFile = new File(repo.getDirectory(), "gc.log"); //$NON-NLS-1$
  		lock = new LockFile(logFile);
  	}
  
  	private Instant getLogExpiry() throws ParseException {
  		if (gcLogExpire == null) {
  			String logExpiryStr = repo.getConfig().getString(
  					ConfigConstants.CONFIG_GC_SECTION, null,
  					ConfigConstants.CONFIG_KEY_LOGEXPIRY);
  			if (logExpiryStr == null) {
  				logExpiryStr = LOG_EXPIRY_DEFAULT;
  			}
 			gcLogExpire = GitDateParser.parse(logExpiryStr, null,
 					SystemReader.getInstance().getLocale()).toInstant();
 		}
 		return gcLogExpire;
 	}
 
 	private boolean autoGcBlockedByOldLockFile(boolean background) {
 		try {
 			FileTime lastModified = Files.getLastModifiedTime(logFile.toPath());
 			if (lastModified.toInstant().compareTo(getLogExpiry()) > 0) {
 				// There is an existing log file, which is too recent to ignore
 				if (!background) {
 					try (BufferedReader reader = Files
 							.newBufferedReader(logFile.toPath())) {
 						char[] buf = new char[1000];
 						int len = reader.read(buf, 0, 1000);
 						String oldError = new String(buf, 0, len);
 
 						throw new JGitInternalException(MessageFormat.format(
 								JGitText.get().gcLogExists, oldError, logFile));
 					}
 				}
 				return true;
 			}
 		} catch (NoSuchFileException e) {
 			// No existing log file, OK.
 		} catch (IOException | ParseException e) {
 			throw new JGitInternalException(e.getMessage(), e);
 		}
 		return false;
 	}
 
 	/**
 	 * Lock the GC log file for updates
 	 *
 	 * @param background
 	 *            If true, and if gc.log already exists, unlock and return false
 	 * @return {@code true} if we hold the lock
 	 */
 	boolean lock(boolean background) {
 		try {
 			if (!lock.lock()) {
 				return false;
 			}
 		} catch (IOException e) {
 			throw new JGitInternalException(e.getMessage(), e);
 		}
 		if (autoGcBlockedByOldLockFile(background)) {
 			lock.unlock();
 			return false;
 		}
 		return true;
 	}
 
 	/**
 	 * Unlock (roll back) the GC log lock
 	 */
 	void unlock() {
 		lock.unlock();
 	}
 
 	/**
 	 * Commit changes to the gc log, if there have been any writes. Otherwise,
 	 * just unlock and delete the existing file (if any)
 	 *
 	 * @return true if committing (or unlocking/deleting) succeeds.
 	 */
 	boolean commit() {
 		if (nonEmpty) {
 			return lock.commit();
 		} else {
 			logFile.delete();
 			lock.unlock();
 			return true;
 		}
 	}
 
 	/**
 	 * Write to the pending gc log. Content will be committed upon a call to
 	 * commit()
 	 *
 	 * @param content
 	 *            The content to write
 	 * @throws IOException
 	 */
 	void write(String content) throws IOException {
 		if (content.length() > 0) {
 			nonEmpty = true;
 		}
 		lock.write(content.getBytes(UTF_8));
 	}
 }