/*
    * Copyright (C) 2017 Two Sigma Open Source and others
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  
  package org.eclipse.jgit.internal.storage.file;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  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.ParseException;
  import java.time.Instant;
  
  import org.eclipse.jgit.api.errors.JGitInternalException;
  import org.eclipse.jgit.lib.ConfigConstants;
  import org.eclipse.jgit.util.FileUtils;
  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() {
  		try {
  			FileTime lastModified = Files.getLastModifiedTime(FileUtils.toPath(logFile));
  			if (lastModified.toInstant().compareTo(getLogExpiry()) > 0) {
  				// There is an existing log file, which is too recent to ignore
  				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
  	 *
  	 * @return {@code true} if we hold the lock
  	 */
  	boolean lock() {
  		try {
  			if (!lock.lock()) {
  				return false;
  			}
  		} catch (IOException e) {
  			throw new JGitInternalException(e.getMessage(), e);
  		}
  		if (autoGcBlockedByOldLockFile()) {
 			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();
 		}
 		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));
 	}
 }