/*
    * Copyright (C) 2007, Robin Rosenberg <robin.rosenberg@dewire.com>
    * Copyright (C) 2006-2021, Shawn O. Pearce <spearce@spearce.org> 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 org.eclipse.jgit.lib.Constants.LOCK_SUFFIX;
  
  import java.io.File;
  import java.io.FileInputStream;
  import java.io.FileNotFoundException;
  import java.io.FileOutputStream;
  import java.io.FilenameFilter;
  import java.io.IOException;
  import java.io.OutputStream;
  import java.nio.ByteBuffer;
  import java.nio.channels.Channels;
  import java.nio.channels.FileChannel;
  import java.nio.file.Files;
  import java.nio.file.StandardCopyOption;
  import java.nio.file.attribute.FileTime;
  import java.text.MessageFormat;
  import java.time.Instant;
  import java.util.concurrent.TimeUnit;
  
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.util.FS;
  import org.eclipse.jgit.util.FS.LockToken;
  import org.eclipse.jgit.util.FileUtils;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Git style file locking and replacement.
   * <p>
   * To modify a ref file Git tries to use an atomic update approach: we write the
   * new data into a brand new file, then rename it in place over the old name.
   * This way we can just delete the temporary file if anything goes wrong, and
   * nothing has been damaged. To coordinate access from multiple processes at
   * once Git tries to atomically create the new temporary file under a well-known
   * name.
   */
  public class LockFile {
  	private static final Logger LOG = LoggerFactory.getLogger(LockFile.class);
  
  	/**
  	 * Unlock the given file.
  	 * <p>
  	 * This method can be used for recovering from a thrown
  	 * {@link org.eclipse.jgit.errors.LockFailedException} . This method does
  	 * not validate that the lock is or is not currently held before attempting
  	 * to unlock it.
  	 *
  	 * @param file
  	 *            a {@link java.io.File} object.
  	 * @return true if unlocked, false if unlocking failed
  	 */
  	public static boolean unlock(File file) {
  		final File lockFile = getLockFile(file);
  		final int flags = FileUtils.RETRY | FileUtils.SKIP_MISSING;
  		try {
  			FileUtils.delete(lockFile, flags);
  		} catch (IOException ignored) {
  			// Ignore and return whether lock file still exists
  		}
  		return !lockFile.exists();
  	}
  
  	/**
  	 * Get the lock file corresponding to the given file.
  	 *
  	 * @param file
  	 * @return lock file
  	 */
  	static File getLockFile(File file) {
  		return new File(file.getParentFile(),
  				file.getName() + LOCK_SUFFIX);
  	}
  
  	/** Filter to skip over active lock files when listing a directory. */
  	static final FilenameFilter FILTER = (File dir,
  			String name) -> !name.endsWith(LOCK_SUFFIX);
  
  	private final File ref;
  
  	private final File lck;
  
  	private boolean haveLck;
  
  	private FileOutputStream os;
 
 	private boolean needSnapshot;
 
 	private boolean fsync;
 
 	private boolean isAppend;
 
 	private boolean written;
 
 	private FileSnapshot commitSnapshot;
 
 	private LockToken token;
 
 	/**
 	 * Create a new lock for any file.
 	 *
 	 * @param f
 	 *            the file that will be locked.
 	 */
 	public LockFile(File f) {
 		ref = f;
 		lck = getLockFile(ref);
 	}
 
 	/**
 	 * Try to establish the lock.
 	 *
 	 * @return true if the lock is now held by the caller; false if it is held
 	 *         by someone else.
 	 * @throws java.io.IOException
 	 *             the temporary output file could not be created. The caller
 	 *             does not hold the lock.
 	 */
 	public boolean lock() throws IOException {
 		if (haveLck) {
 			throw new IllegalStateException(
 					MessageFormat.format(JGitText.get().lockAlreadyHeld, ref));
 		}
 		FileUtils.mkdirs(lck.getParentFile(), true);
 		try {
 			token = FS.DETECTED.createNewFileAtomic(lck);
 		} catch (IOException e) {
 			LOG.error(JGitText.get().failedCreateLockFile, lck, e);
 			throw e;
 		}
 		boolean obtainedLock = token.isCreated();
 		if (obtainedLock) {
 			haveLck = true;
 			isAppend = false;
 			written = false;
 		} else {
 			closeToken();
 		}
 		return obtainedLock;
 	}
 
 	/**
 	 * Try to establish the lock for appending.
 	 *
 	 * @return true if the lock is now held by the caller; false if it is held
 	 *         by someone else.
 	 * @throws java.io.IOException
 	 *             the temporary output file could not be created. The caller
 	 *             does not hold the lock.
 	 */
 	public boolean lockForAppend() throws IOException {
 		if (!lock()) {
 			return false;
 		}
 		copyCurrentContent();
 		isAppend = true;
 		written = false;
 		return true;
 	}
 
 	// For tests only
 	boolean isLocked() {
 		return haveLck;
 	}
 
 	private FileOutputStream getStream() throws IOException {
 		return new FileOutputStream(lck, isAppend);
 	}
 
 	/**
 	 * Copy the current file content into the temporary file.
 	 * <p>
 	 * This method saves the current file content by inserting it into the
 	 * temporary file, so that the caller can safely append rather than replace
 	 * the primary file.
 	 * <p>
 	 * This method does nothing if the current file does not exist, or exists
 	 * but is empty.
 	 *
 	 * @throws java.io.IOException
 	 *             the temporary file could not be written, or a read error
 	 *             occurred while reading from the current file. The lock is
 	 *             released before throwing the underlying IO exception to the
 	 *             caller.
 	 * @throws java.lang.RuntimeException
 	 *             the temporary file could not be written. The lock is released
 	 *             before throwing the underlying exception to the caller.
 	 */
 	public void copyCurrentContent() throws IOException {
 		requireLock();
 		try (FileOutputStream out = getStream()) {
 			try (FileInputStream fis = new FileInputStream(ref)) {
 				if (fsync) {
 					FileChannel in = fis.getChannel();
 					long pos = 0;
 					long cnt = in.size();
 					while (0 < cnt) {
 						long r = out.getChannel().transferFrom(in, pos, cnt);
 						pos += r;
 						cnt -= r;
 					}
 				} else {
 					final byte[] buf = new byte[2048];
 					int r;
 					while ((r = fis.read(buf)) >= 0) {
 						out.write(buf, 0, r);
 					}
 				}
 			} catch (FileNotFoundException fnfe) {
 				if (ref.exists()) {
 					throw fnfe;
 				}
 				// Don't worry about a file that doesn't exist yet, it
 				// conceptually has no current content to copy.
 			}
 		} catch (IOException | RuntimeException | Error ioe) {
 			unlock();
 			throw ioe;
 		}
 	}
 
 	/**
 	 * Write an ObjectId and LF to the temporary file.
 	 *
 	 * @param id
 	 *            the id to store in the file. The id will be written in hex,
 	 *            followed by a sole LF.
 	 * @throws java.io.IOException
 	 *             the temporary file could not be written. The lock is released
 	 *             before throwing the underlying IO exception to the caller.
 	 * @throws java.lang.RuntimeException
 	 *             the temporary file could not be written. The lock is released
 	 *             before throwing the underlying exception to the caller.
 	 */
 	public void write(ObjectId id) throws IOException {
 		byte[] buf = new byte[Constants.OBJECT_ID_STRING_LENGTH + 1];
 		id.copyTo(buf, 0);
 		buf[Constants.OBJECT_ID_STRING_LENGTH] = '\n';
 		write(buf);
 	}
 
 	/**
 	 * Write arbitrary data to the temporary file.
 	 *
 	 * @param content
 	 *            the bytes to store in the temporary file. No additional bytes
 	 *            are added, so if the file must end with an LF it must appear
 	 *            at the end of the byte array.
 	 * @throws java.io.IOException
 	 *             the temporary file could not be written. The lock is released
 	 *             before throwing the underlying IO exception to the caller.
 	 * @throws java.lang.RuntimeException
 	 *             the temporary file could not be written. The lock is released
 	 *             before throwing the underlying exception to the caller.
 	 */
 	public void write(byte[] content) throws IOException {
 		requireLock();
 		try (FileOutputStream out = getStream()) {
 			if (written) {
 				throw new IOException(MessageFormat
 						.format(JGitText.get().lockStreamClosed, ref));
 			}
 			if (fsync) {
 				FileChannel fc = out.getChannel();
 				ByteBuffer buf = ByteBuffer.wrap(content);
 				while (0 < buf.remaining()) {
 					fc.write(buf);
 				}
 				fc.force(true);
 			} else {
 				out.write(content);
 			}
 			written = true;
 		} catch (IOException | RuntimeException | Error ioe) {
 			unlock();
 			throw ioe;
 		}
 	}
 
 	/**
 	 * Obtain the direct output stream for this lock.
 	 * <p>
 	 * The stream may only be accessed once, and only after {@link #lock()} has
 	 * been successfully invoked and returned true. Callers must close the
 	 * stream prior to calling {@link #commit()} to commit the change.
 	 *
 	 * @return a stream to write to the new file. The stream is unbuffered.
 	 */
 	public OutputStream getOutputStream() {
 		requireLock();
 
 		if (written || os != null) {
 			throw new IllegalStateException(MessageFormat
 					.format(JGitText.get().lockStreamMultiple, ref));
 		}
 
 		return new OutputStream() {
 
 			private OutputStream out;
 
 			private boolean closed;
 
 			private OutputStream get() throws IOException {
 				if (written) {
 					throw new IOException(MessageFormat
 							.format(JGitText.get().lockStreamMultiple, ref));
 				}
 				if (out == null) {
 					os = getStream();
 					if (fsync) {
 						out = Channels.newOutputStream(os.getChannel());
 					} else {
 						out = os;
 					}
 				}
 				return out;
 			}
 
 			@Override
 			public void write(byte[] b, int o, int n) throws IOException {
 				get().write(b, o, n);
 			}
 
 			@Override
 			public void write(byte[] b) throws IOException {
 				get().write(b);
 			}
 
 			@Override
 			public void write(int b) throws IOException {
 				get().write(b);
 			}
 
 			@Override
 			public void close() throws IOException {
 				if (closed) {
 					return;
 				}
 				closed = true;
 				try {
 					if (written) {
 						throw new IOException(MessageFormat
 								.format(JGitText.get().lockStreamClosed, ref));
 					}
 					if (out != null) {
 						if (fsync) {
 							os.getChannel().force(true);
 						}
 						out.close();
 						os = null;
 					}
 					written = true;
 				} catch (IOException | RuntimeException | Error ioe) {
 					unlock();
 					throw ioe;
 				}
 			}
 		};
 	}
 
 	void requireLock() {
 		if (!haveLck) {
 			unlock();
 			throw new IllegalStateException(MessageFormat.format(JGitText.get().lockOnNotHeld, ref));
 		}
 	}
 
 	/**
 	 * Request that {@link #commit()} remember modification time.
 	 * <p>
 	 * This is an alias for {@code setNeedSnapshot(true)}.
 	 *
 	 * @param on
 	 *            true if the commit method must remember the modification time.
 	 */
 	public void setNeedStatInformation(boolean on) {
 		setNeedSnapshot(on);
 	}
 
 	/**
 	 * Request that {@link #commit()} remember the
 	 * {@link org.eclipse.jgit.internal.storage.file.FileSnapshot}.
 	 *
 	 * @param on
 	 *            true if the commit method must remember the FileSnapshot.
 	 */
 	public void setNeedSnapshot(boolean on) {
 		needSnapshot = on;
 	}
 
 	/**
 	 * Request that {@link #commit()} force dirty data to the drive.
 	 *
 	 * @param on
 	 *            true if dirty data should be forced to the drive.
 	 */
 	public void setFSync(boolean on) {
 		fsync = on;
 	}
 
 	/**
 	 * Wait until the lock file information differs from the old file.
 	 * <p>
 	 * This method tests the last modification date. If both are the same, this
 	 * method sleeps until it can force the new lock file's modification date to
 	 * be later than the target file.
 	 *
 	 * @throws java.lang.InterruptedException
 	 *             the thread was interrupted before the last modified date of
 	 *             the lock file was different from the last modified date of
 	 *             the target file.
 	 */
 	public void waitForStatChange() throws InterruptedException {
 		FileSnapshot o = FileSnapshot.save(ref);
 		FileSnapshot n = FileSnapshot.save(lck);
 		long fsTimeResolution = FS.getFileStoreAttributes(lck.toPath())
 				.getFsTimestampResolution().toNanos();
 		while (o.equals(n)) {
 			TimeUnit.NANOSECONDS.sleep(fsTimeResolution);
 			try {
 				Files.setLastModifiedTime(lck.toPath(),
 						FileTime.from(Instant.now()));
 			} catch (IOException e) {
 				n.waitUntilNotRacy();
 			}
 			n = FileSnapshot.save(lck);
 		}
 	}
 
 	/**
 	 * Commit this change and release the lock.
 	 * <p>
 	 * If this method fails (returns false) the lock is still released.
 	 *
 	 * @return true if the commit was successful and the file contains the new
 	 *         data; false if the commit failed and the file remains with the
 	 *         old data.
 	 * @throws java.lang.IllegalStateException
 	 *             the lock is not held.
 	 */
 	public boolean commit() {
 		if (os != null) {
 			unlock();
 			throw new IllegalStateException(MessageFormat.format(JGitText.get().lockOnNotClosed, ref));
 		}
 
 		saveStatInformation();
 		try {
 			FileUtils.rename(lck, ref, StandardCopyOption.ATOMIC_MOVE);
 			haveLck = false;
 			isAppend = false;
 			written = false;
 			closeToken();
 			return true;
 		} catch (IOException e) {
 			unlock();
 			return false;
 		}
 	}
 
 	private void closeToken() {
 		if (token != null) {
 			token.close();
 			token = null;
 		}
 	}
 
 	private void saveStatInformation() {
 		if (needSnapshot)
 			commitSnapshot = FileSnapshot.save(lck);
 	}
 
 	/**
 	 * Get the modification time of the output file when it was committed.
 	 *
 	 * @return modification time of the lock file right before we committed it.
 	 * @deprecated use {@link #getCommitLastModifiedInstant()} instead
 	 */
 	@Deprecated
 	public long getCommitLastModified() {
 		return commitSnapshot.lastModified();
 	}
 
 	/**
 	 * Get the modification time of the output file when it was committed.
 	 *
 	 * @return modification time of the lock file right before we committed it.
 	 */
 	public Instant getCommitLastModifiedInstant() {
 		return commitSnapshot.lastModifiedInstant();
 	}
 
 	/**
 	 * Get the {@link FileSnapshot} just before commit.
 	 *
 	 * @return get the {@link FileSnapshot} just before commit.
 	 */
 	public FileSnapshot getCommitSnapshot() {
 		return commitSnapshot;
 	}
 
 	/**
 	 * Update the commit snapshot {@link #getCommitSnapshot()} before commit.
 	 * <p>
 	 * This may be necessary if you need time stamp before commit occurs, e.g
 	 * while writing the index.
 	 */
 	public void createCommitSnapshot() {
 		saveStatInformation();
 	}
 
 	/**
 	 * Unlock this file and abort this change.
 	 * <p>
 	 * The temporary file (if created) is deleted before returning.
 	 */
 	public void unlock() {
 		if (os != null) {
 			try {
 				os.close();
 			} catch (IOException e) {
 				LOG.error(MessageFormat
 						.format(JGitText.get().unlockLockFileFailed, lck), e);
 			}
 			os = null;
 		}
 
 		if (haveLck) {
 			haveLck = false;
 			try {
 				FileUtils.delete(lck, FileUtils.RETRY);
 			} catch (IOException e) {
 				LOG.error(MessageFormat
 						.format(JGitText.get().unlockLockFileFailed, lck), e);
 			} finally {
 				closeToken();
 			}
 		}
 		isAppend = false;
 		written = false;
 	}
 
 	/** {@inheritDoc} */
 	@SuppressWarnings("nls")
 	@Override
 	public String toString() {
 		return "LockFile[" + lck + ", haveLck=" + haveLck + "]";
 	}
 }