/*
 * Copyright (C) 2010, Google Inc.
 * Copyright (C) 2010, Matthias Sohn <matthias.sohn@sap.com>
 * Copyright (C) 2010, Jens Baumgart <jens.baumgart@sap.com> 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.util;

import static java.nio.charset.StandardCharsets.UTF_8;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InterruptedIOException;
import java.nio.channels.FileChannel;
import java.nio.file.AtomicMoveNotSupportedException;
import java.nio.file.CopyOption;
import java.nio.file.DirectoryNotEmptyException;
import java.nio.file.Files;
import java.nio.file.InvalidPathException;
import java.nio.file.LinkOption;
import java.nio.file.NoSuchFileException;
import java.nio.file.Path;
import java.nio.file.StandardCopyOption;
import java.nio.file.StandardOpenOption;
import java.nio.file.attribute.BasicFileAttributeView;
import java.nio.file.attribute.BasicFileAttributes;
import java.nio.file.attribute.FileTime;
import java.nio.file.attribute.PosixFileAttributeView;
import java.nio.file.attribute.PosixFileAttributes;
import java.nio.file.attribute.PosixFilePermission;
import java.text.MessageFormat;
import java.text.Normalizer;
import java.text.Normalizer.Form;
import java.time.Instant;
import java.util.ArrayList;
import java.util.List;
import java.util.Locale;
import java.util.Random;
import java.util.regex.Pattern;
import java.util.stream.Stream;

import org.eclipse.jgit.internal.JGitText;
import org.eclipse.jgit.lib.Constants;
import org.eclipse.jgit.util.FS.Attributes;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * File Utilities
 */
public class FileUtils {
	private static final Logger LOG = LoggerFactory.getLogger(FileUtils.class);

	private static final Random RNG = new Random();

	/**
	 * Option to delete given {@code File}
	 */
	public static final int NONE = 0;

	/**
	 * Option to recursively delete given {@code File}
	 */
	public static final int RECURSIVE = 1;

	/**
	 * Option to retry deletion if not successful
	 */
	public static final int RETRY = 2;

	/**
	 * Option to skip deletion if file doesn't exist
	 */
	public static final int SKIP_MISSING = 4;

	/**
	 * Option not to throw exceptions when a deletion finally doesn't succeed.
	 * @since 2.0
	 */
	public static final int IGNORE_ERRORS = 8;

	/**
	 * Option to only delete empty directories. This option can be combined with
	 * {@link #RECURSIVE}
	 *
	 * @since 3.0
	 */
	public static final int EMPTY_DIRECTORIES_ONLY = 16;

	/**
	 * Safe conversion from {@link java.io.File} to {@link java.nio.file.Path}.
	 *
	 * @param f
	 *            {@code File} to be converted to {@code Path}
	 * @return the path represented by the file
	 * @throws java.io.IOException
	 *             in case the path represented by the file is not valid (
	 *             {@link java.nio.file.InvalidPathException})
	 * @since 4.10
	 */
	public static Path toPath(File f) throws IOException {
		try {
			return f.toPath();
		} catch (InvalidPathException ex) {
			throw new IOException(ex);
		}
	}

	/**
	 * Delete file or empty folder
	 *
	 * @param f
	 *            {@code File} to be deleted
	 * @throws java.io.IOException
	 *             if deletion of {@code f} fails. This may occur if {@code f}
	 *             didn't exist when the method was called. This can therefore
	 *             cause java.io.IOExceptions during race conditions when
	 *             multiple concurrent threads all try to delete the same file.
	 */
	public static void delete(File f) throws IOException {
		delete(f, NONE);
	}

	/**
	 * Delete file or folder
	 *
	 * @param f
	 *            {@code File} to be deleted
	 * @param options
	 *            deletion options, {@code RECURSIVE} for recursive deletion of
	 *            a subtree, {@code RETRY} to retry when deletion failed.
	 *            Retrying may help if the underlying file system doesn't allow
	 *            deletion of files being read by another thread.
	 * @throws java.io.IOException
	 *             if deletion of {@code f} fails. This may occur if {@code f}
	 *             didn't exist when the method was called. This can therefore
	 *             cause java.io.IOExceptions during race conditions when
	 *             multiple concurrent threads all try to delete the same file.
	 *             This exception is not thrown when IGNORE_ERRORS is set.
	 */
	public static void delete(File f, int options) throws IOException {
		FS fs = FS.DETECTED;
		if ((options & SKIP_MISSING) != 0 && !fs.exists(f))
			return;

		if ((options & RECURSIVE) != 0 && fs.isDirectory(f)) {
			final File[] items = f.listFiles();
			if (items != null) {
				List<File> files = new ArrayList<>();
				List<File> dirs = new ArrayList<>();
				for (File c : items)
					if (c.isFile())
						files.add(c);
					else
						dirs.add(c);
				// Try to delete files first, otherwise options
				// EMPTY_DIRECTORIES_ONLY|RECURSIVE will delete empty
				// directories before aborting, depending on order.
				for (File file : files)
					delete(file, options);
				for (File d : dirs)
					delete(d, options);
			}
		}

		boolean delete = false;
		if ((options & EMPTY_DIRECTORIES_ONLY) != 0) {
			if (f.isDirectory()) {
				delete = true;
			} else if ((options & IGNORE_ERRORS) == 0) {
				throw new IOException(MessageFormat.format(
						JGitText.get().deleteFileFailed, f.getAbsolutePath()));
			}
		} else {
			delete = true;
		}

		if (delete) {
			IOException t = null;
			Path p = f.toPath();
			boolean tryAgain;
			do {
				tryAgain = false;
				try {
					Files.delete(p);
					return;
				} catch (NoSuchFileException | FileNotFoundException e) {
					handleDeleteException(f, e, options,
							SKIP_MISSING | IGNORE_ERRORS);
					return;
				} catch (DirectoryNotEmptyException e) {
					handleDeleteException(f, e, options, IGNORE_ERRORS);
					return;
				} catch (IOException e) {
					if (!f.canWrite()) {
						tryAgain = f.setWritable(true);
					}
					if (!tryAgain) {
						t = e;
					}
				}
			} while (tryAgain);

			if ((options & RETRY) != 0) {
				for (int i = 1; i < 10; i++) {
					try {
						Thread.sleep(100);
					} catch (InterruptedException ex) {
						// ignore
					}
					try {
						Files.deleteIfExists(p);
						return;
					} catch (IOException e) {
						t = e;
					}
				}
			}
			handleDeleteException(f, t, options, IGNORE_ERRORS);
		}
	}

	private static void handleDeleteException(File f, IOException e,
			int allOptions, int checkOptions) throws IOException {
		if (e != null && (allOptions & checkOptions) == 0) {
			throw new IOException(MessageFormat.format(
					JGitText.get().deleteFileFailed, f.getAbsolutePath()), e);
		}
	}

	/**
	 * Rename a file or folder. If the rename fails and if we are running on a
	 * filesystem where it makes sense to repeat a failing rename then repeat
	 * the rename operation up to 9 times with 100ms sleep time between two
	 * calls. Furthermore if the destination exists and is directory hierarchy
	 * with only directories in it, the whole directory hierarchy will be
	 * deleted. If the target represents a non-empty directory structure, empty
	 * subdirectories within that structure may or may not be deleted even if
	 * the method fails. Furthermore if the destination exists and is a file
	 * then the file will be deleted and then the rename is retried.
	 * <p>
	 * This operation is <em>not</em> atomic.
	 *
	 * @see FS#retryFailedLockFileCommit()
	 * @param src
	 *            the old {@code File}
	 * @param dst
	 *            the new {@code File}
	 * @throws java.io.IOException
	 *             if the rename has failed
	 * @since 3.0
	 */
	public static void rename(File src, File dst)
			throws IOException {
		rename(src, dst, StandardCopyOption.REPLACE_EXISTING);
	}

	/**
	 * Rename a file or folder using the passed
	 * {@link java.nio.file.CopyOption}s. If the rename fails and if we are
	 * running on a filesystem where it makes sense to repeat a failing rename
	 * then repeat the rename operation up to 9 times with 100ms sleep time
	 * between two calls. Furthermore if the destination exists and is a
	 * directory hierarchy with only directories in it, the whole directory
	 * hierarchy will be deleted. If the target represents a non-empty directory
	 * structure, empty subdirectories within that structure may or may not be
	 * deleted even if the method fails. Furthermore if the destination exists
	 * and is a file then the file will be replaced if
	 * {@link java.nio.file.StandardCopyOption#REPLACE_EXISTING} has been set.
	 * If {@link java.nio.file.StandardCopyOption#ATOMIC_MOVE} has been set the
	 * rename will be done atomically or fail with an
	 * {@link java.nio.file.AtomicMoveNotSupportedException}
	 *
	 * @param src
	 *            the old file
	 * @param dst
	 *            the new file
	 * @param options
	 *            options to pass to
	 *            {@link java.nio.file.Files#move(java.nio.file.Path, java.nio.file.Path, CopyOption...)}
	 * @throws java.nio.file.AtomicMoveNotSupportedException
	 *             if file cannot be moved as an atomic file system operation
	 * @throws java.io.IOException
	 *             if an IO error occurred
	 * @since 4.1
	 */
	public static void rename(final File src, final File dst,
			CopyOption... options)
					throws AtomicMoveNotSupportedException, IOException {
		int attempts = FS.DETECTED.retryFailedLockFileCommit() ? 10 : 1;
		IOException finalError = null;
		while (--attempts >= 0) {
			try {
				Files.move(toPath(src), toPath(dst), options);
				return;
			} catch (AtomicMoveNotSupportedException e) {
				throw e;
			} catch (IOException e) {
				if (attempts == 0) {
					// Only delete on the last attempt.
					try {
						if (!dst.delete()) {
							delete(dst, EMPTY_DIRECTORIES_ONLY | RECURSIVE);
						}
						// On *nix there is no try, you do or do not
						Files.move(toPath(src), toPath(dst), options);
						return;
					} catch (IOException e2) {
						e2.addSuppressed(e);
						finalError = e2;
					}
				}
			}
			if (attempts > 0) {
				try {
					Thread.sleep(100);
				} catch (InterruptedException e) {
					throw new IOException(MessageFormat.format(
							JGitText.get().renameFileFailed,
							src.getAbsolutePath(), dst.getAbsolutePath()), e);
				}
			}
		}
		throw new IOException(
				MessageFormat.format(JGitText.get().renameFileFailed,
						src.getAbsolutePath(), dst.getAbsolutePath()),
				finalError);
	}

	/**
	 * Creates the directory named by this abstract pathname.
	 *
	 * @param d
	 *            directory to be created
	 * @throws java.io.IOException
	 *             if creation of {@code d} fails. This may occur if {@code d}
	 *             did exist when the method was called. This can therefore
	 *             cause java.io.IOExceptions during race conditions when
	 *             multiple concurrent threads all try to create the same
	 *             directory.
	 */
	public static void mkdir(File d)
			throws IOException {
		mkdir(d, false);
	}

	/**
	 * Creates the directory named by this abstract pathname.
	 *
	 * @param d
	 *            directory to be created
	 * @param skipExisting
	 *            if {@code true} skip creation of the given directory if it
	 *            already exists in the file system
	 * @throws java.io.IOException
	 *             if creation of {@code d} fails. This may occur if {@code d}
	 *             did exist when the method was called. This can therefore
	 *             cause java.io.IOExceptions during race conditions when
	 *             multiple concurrent threads all try to create the same
	 *             directory.
	 */
	public static void mkdir(File d, boolean skipExisting)
			throws IOException {
		if (!d.mkdir()) {
			if (skipExisting && d.isDirectory())
				return;
			throw new IOException(MessageFormat.format(
					JGitText.get().mkDirFailed, d.getAbsolutePath()));
		}
	}

	/**
	 * Creates the directory named by this abstract pathname, including any
	 * necessary but nonexistent parent directories. Note that if this operation
	 * fails it may have succeeded in creating some of the necessary parent
	 * directories.
	 *
	 * @param d
	 *            directory to be created
	 * @throws java.io.IOException
	 *             if creation of {@code d} fails. This may occur if {@code d}
	 *             did exist when the method was called. This can therefore
	 *             cause java.io.IOExceptions during race conditions when
	 *             multiple concurrent threads all try to create the same
	 *             directory.
	 */
	public static void mkdirs(File d) throws IOException {
		mkdirs(d, false);
	}

	/**
	 * Creates the directory named by this abstract pathname, including any
	 * necessary but nonexistent parent directories. Note that if this operation
	 * fails it may have succeeded in creating some of the necessary parent
	 * directories.
	 *
	 * @param d
	 *            directory to be created
	 * @param skipExisting
	 *            if {@code true} skip creation of the given directory if it
	 *            already exists in the file system
	 * @throws java.io.IOException
	 *             if creation of {@code d} fails. This may occur if {@code d}
	 *             did exist when the method was called. This can therefore
	 *             cause java.io.IOExceptions during race conditions when
	 *             multiple concurrent threads all try to create the same
	 *             directory.
	 */
	public static void mkdirs(File d, boolean skipExisting)
			throws IOException {
		if (!d.mkdirs()) {
			if (skipExisting && d.isDirectory())
				return;
			throw new IOException(MessageFormat.format(
					JGitText.get().mkDirsFailed, d.getAbsolutePath()));
		}
	}

	/**
	 * Atomically creates a new, empty file named by this abstract pathname if
	 * and only if a file with this name does not yet exist. The check for the
	 * existence of the file and the creation of the file if it does not exist
	 * are a single operation that is atomic with respect to all other
	 * filesystem activities that might affect the file.
	 * <p>
	 * Note: this method should not be used for file-locking, as the resulting
	 * protocol cannot be made to work reliably. The
	 * {@link java.nio.channels.FileLock} facility should be used instead.
	 *
	 * @param f
	 *            the file to be created
	 * @throws java.io.IOException
	 *             if the named file already exists or if an I/O error occurred
	 */
	public static void createNewFile(File f) throws IOException {
		if (!f.createNewFile())
			throw new IOException(MessageFormat.format(
					JGitText.get().createNewFileFailed, f));
	}

	/**
	 * Create a symbolic link
	 *
	 * @param path
	 *            the path of the symbolic link to create
	 * @param target
	 *            the target of the symbolic link
	 * @return the path to the symbolic link
	 * @throws java.io.IOException
	 *             if an IO error occurred
	 * @since 4.2
	 */
	public static Path createSymLink(File path, String target)
			throws IOException {
		Path nioPath = toPath(path);
		if (Files.exists(nioPath, LinkOption.NOFOLLOW_LINKS)) {
			BasicFileAttributes attrs = Files.readAttributes(nioPath,
					BasicFileAttributes.class, LinkOption.NOFOLLOW_LINKS);
			if (attrs.isRegularFile() || attrs.isSymbolicLink()) {
				delete(path);
			} else {
				delete(path, EMPTY_DIRECTORIES_ONLY | RECURSIVE);
			}
		}
		if (SystemReader.getInstance().isWindows()) {
			target = target.replace('/', '\\');
		}
		Path nioTarget = toPath(new File(target));
		return Files.createSymbolicLink(nioPath, nioTarget);
	}

	/**
	 * Read target path of the symlink.
	 *
	 * @param path
	 *            a {@link java.io.File} object.
	 * @return target path of the symlink, or null if it is not a symbolic link
	 * @throws java.io.IOException
	 *             if an IO error occurred
	 * @since 3.0
	 */
	public static String readSymLink(File path) throws IOException {
		Path nioPath = toPath(path);
		Path target = Files.readSymbolicLink(nioPath);
		String targetString = target.toString();
		if (SystemReader.getInstance().isWindows()) {
			targetString = targetString.replace('\\', '/');
		} else if (SystemReader.getInstance().isMacOS()) {
			targetString = Normalizer.normalize(targetString, Form.NFC);
		}
		return targetString;
	}

	/**
	 * Create a temporary directory.
	 *
	 * @param prefix
	 *            prefix string
	 * @param suffix
	 *            suffix string
	 * @param dir
	 *            The parent dir, can be null to use system default temp dir.
	 * @return the temp dir created.
	 * @throws java.io.IOException
	 *             if an IO error occurred
	 * @since 3.4
	 */
	public static File createTempDir(String prefix, String suffix, File dir)
			throws IOException {
		final int RETRIES = 1; // When something bad happens, retry once.
		for (int i = 0; i < RETRIES; i++) {
			File tmp = File.createTempFile(prefix, suffix, dir);
			if (!tmp.delete())
				continue;
			if (!tmp.mkdir())
				continue;
			return tmp;
		}
		throw new IOException(JGitText.get().cannotCreateTempDir);
	}

	/**
	 * Expresses <code>other</code> as a relative file path from
	 * <code>base</code>. File-separator and case sensitivity are based on the
	 * current file system.
	 *
	 * See also
	 * {@link org.eclipse.jgit.util.FileUtils#relativizePath(String, String, String, boolean)}.
	 *
	 * @param base
	 *            Base path
	 * @param other
	 *            Destination path
	 * @return Relative path from <code>base</code> to <code>other</code>
	 * @since 4.8
	 */
	public static String relativizeNativePath(String base, String other) {
		return FS.DETECTED.relativize(base, other);
	}

	/**
	 * Expresses <code>other</code> as a relative file path from
	 * <code>base</code>. File-separator and case sensitivity are based on Git's
	 * internal representation of files (which matches Unix).
	 *
	 * See also
	 * {@link org.eclipse.jgit.util.FileUtils#relativizePath(String, String, String, boolean)}.
	 *
	 * @param base
	 *            Base path
	 * @param other
	 *            Destination path
	 * @return Relative path from <code>base</code> to <code>other</code>
	 * @since 4.8
	 */
	public static String relativizeGitPath(String base, String other) {
		return relativizePath(base, other, "/", false); //$NON-NLS-1$
	}


	/**
	 * Expresses <code>other</code> as a relative file path from <code>base</code>
	 * <p>
	 * For example, if called with the two following paths :
	 *
	 * <pre>
	 * <code>base = "c:\\Users\\jdoe\\eclipse\\git\\project"</code>
	 * <code>other = "c:\\Users\\jdoe\\eclipse\\git\\another_project\\pom.xml"</code>
	 * </pre>
	 *
	 * This will return "..\\another_project\\pom.xml".
	 *
	 * <p>
	 * <b>Note</b> that this will return the empty String if <code>base</code>
	 * and <code>other</code> are equal.
	 * </p>
	 *
	 * @param base
	 *            The path against which <code>other</code> should be
	 *            relativized. This will be assumed to denote the path to a
	 *            folder and not a file.
	 * @param other
	 *            The path that will be made relative to <code>base</code>.
	 * @param dirSeparator
	 *            A string that separates components of the path. In practice, this is "/" or "\\".
	 * @param caseSensitive
	 *            Whether to consider differently-cased directory names as distinct
	 * @return A relative path that, when resolved against <code>base</code>,
	 *         will yield the original <code>other</code>.
	 * @since 4.8
	 */
	public static String relativizePath(String base, String other, String dirSeparator, boolean caseSensitive) {
		if (base.equals(other))
			return ""; //$NON-NLS-1$

		final String[] baseSegments = base.split(Pattern.quote(dirSeparator));
		final String[] otherSegments = other.split(Pattern
				.quote(dirSeparator));

		int commonPrefix = 0;
		while (commonPrefix < baseSegments.length
				&& commonPrefix < otherSegments.length) {
			if (caseSensitive
					&& baseSegments[commonPrefix]
					.equals(otherSegments[commonPrefix]))
				commonPrefix++;
			else if (!caseSensitive
					&& baseSegments[commonPrefix]
							.equalsIgnoreCase(otherSegments[commonPrefix]))
				commonPrefix++;
			else
				break;
		}

		final StringBuilder builder = new StringBuilder();
		for (int i = commonPrefix; i < baseSegments.length; i++)
			builder.append("..").append(dirSeparator); //$NON-NLS-1$
		for (int i = commonPrefix; i < otherSegments.length; i++) {
			builder.append(otherSegments[i]);
			if (i < otherSegments.length - 1)
				builder.append(dirSeparator);
		}
		return builder.toString();
	}

	/**
	 * Determine if an IOException is a stale NFS file handle
	 *
	 * @param ioe
	 *            an {@link java.io.IOException} object.
	 * @return a boolean true if the IOException is a stale NFS file handle
	 * @since 4.1
	 */
	public static boolean isStaleFileHandle(IOException ioe) {
		String msg = ioe.getMessage();
		return msg != null
				&& msg.toLowerCase(Locale.ROOT)
						.matches("stale .*file .*handle"); //$NON-NLS-1$
	}

	/**
	 * Determine if a throwable or a cause in its causal chain is a stale NFS
	 * file handle
	 *
	 * @param throwable
	 *            a {@link java.lang.Throwable} object.
	 * @return a boolean true if the throwable or a cause in its causal chain is
	 *         a stale NFS file handle
	 * @since 4.7
	 */
	public static boolean isStaleFileHandleInCausalChain(Throwable throwable) {
		while (throwable != null) {
			if (throwable instanceof IOException
					&& isStaleFileHandle((IOException) throwable)) {
				return true;
			}
			throwable = throwable.getCause();
		}
		return false;
	}

	/**
	 * Like a {@link java.util.function.Function} but throwing an
	 * {@link Exception}.
	 *
	 * @param <A>
	 *            input type
	 * @param <B>
	 *            output type
	 * @since 6.2
	 */
	@FunctionalInterface
	public interface IOFunction<A, B> {

		/**
		 * Performs the function.
		 *
		 * @param t
		 *            input to operate on
		 * @return the output
		 * @throws Exception
		 *             if a problem occurs
		 */
		B apply(A t) throws Exception;
	}

	private static void backOff(long delay, IOException cause)
			throws IOException {
		try {
			Thread.sleep(delay);
		} catch (InterruptedException e) {
			IOException interruption = new InterruptedIOException();
			interruption.initCause(e);
			interruption.addSuppressed(cause);
			Thread.currentThread().interrupt(); // Re-set flag
			throw interruption;
		}
	}

	/**
	 * Invokes the given {@link IOFunction}, performing a limited number of
	 * re-tries if exceptions occur that indicate either a stale NFS file handle
	 * or that indicate that the file may be written concurrently.
	 *
	 * @param <T>
	 *            result type
	 * @param file
	 *            to read
	 * @param reader
	 *            for reading the file and creating an instance of {@code T}
	 * @return the result of the {@code reader}, or {@code null} if the file
	 *         does not exist
	 * @throws Exception
	 *             if a problem occurs
	 * @since 6.2
	 */
	public static <T> T readWithRetries(File file,
			IOFunction<File, ? extends T> reader)
			throws Exception {
		int maxStaleRetries = 5;
		int retries = 0;
		long backoff = 50;
		while (true) {
			try {
				try {
					return reader.apply(file);
				} catch (IOException e) {
					if (FileUtils.isStaleFileHandleInCausalChain(e)
							&& retries < maxStaleRetries) {
						if (LOG.isDebugEnabled()) {
							LOG.debug(MessageFormat.format(
									JGitText.get().packedRefsHandleIsStale,
									Integer.valueOf(retries)), e);
						}
						retries++;
						continue;
					}
					throw e;
				}
			} catch (FileNotFoundException noFile) {
				if (!file.isFile()) {
					return null;
				}
				// Probably Windows and some other thread is writing the file
				// concurrently.
				if (backoff > 1000) {
					throw noFile;
				}
				backOff(backoff, noFile);
				backoff *= 2; // 50, 100, 200, 400, 800 ms
			}
		}
	}

	/**
	 * Check if file is a symlink
	 *
	 * @param file
	 *            the file to be checked if it is a symbolic link
	 * @return {@code true} if the passed file is a symbolic link
	 */
	static boolean isSymlink(File file) {
		return Files.isSymbolicLink(file.toPath());
	}

	/**
	 * Get the lastModified attribute for a given file
	 *
	 * @param file
	 *            the file
	 * @return lastModified attribute for given file, not following symbolic
	 *         links
	 * @throws IOException
	 *             if an IO error occurred
	 * @deprecated use {@link #lastModifiedInstant(Path)} instead which returns
	 *             FileTime
	 */
	@Deprecated
	static long lastModified(File file) throws IOException {
		return Files.getLastModifiedTime(toPath(file), LinkOption.NOFOLLOW_LINKS)
				.toMillis();
	}

	/**
	 * Get last modified timestamp of a file
	 *
	 * @param path
	 *            file path
	 * @return lastModified attribute for given file, not following symbolic
	 *         links
	 */
	static Instant lastModifiedInstant(Path path) {
		try {
			return Files.getLastModifiedTime(path, LinkOption.NOFOLLOW_LINKS)
					.toInstant();
		} catch (NoSuchFileException e) {
			LOG.debug(
					"Cannot read lastModifiedInstant since path {} does not exist", //$NON-NLS-1$
					path);
			return Instant.EPOCH;
		} catch (IOException e) {
			LOG.error(MessageFormat
					.format(JGitText.get().readLastModifiedFailed, path), e);
			return Instant.ofEpochMilli(path.toFile().lastModified());
		}
	}

	/**
	 * Return all the attributes of a file, without following symbolic links.
	 *
	 * @param file
	 *            the file
	 * @return {@link BasicFileAttributes} of the file
	 * @throws IOException
	 *             in case of any I/O errors accessing the file
	 *
	 * @since 4.5.6
	 */
	static BasicFileAttributes fileAttributes(File file) throws IOException {
		return Files.readAttributes(file.toPath(), BasicFileAttributes.class, LinkOption.NOFOLLOW_LINKS);
	}

	/**
	 * Set the last modified time of a file system object.
	 *
	 * @param file
	 *            the file
	 * @param time
	 *            last modified timestamp
	 * @throws IOException
	 *             if an IO error occurred
	 */
	@Deprecated
	static void setLastModified(File file, long time) throws IOException {
		Files.setLastModifiedTime(toPath(file), FileTime.fromMillis(time));
	}

	/**
	 * Set the last modified time of a file system object.
	 *
	 * @param path
	 *            file path
	 * @param time
	 *            last modified timestamp of the file
	 * @throws IOException
	 *             if an IO error occurred
	 */
	static void setLastModified(Path path, Instant time)
			throws IOException {
		Files.setLastModifiedTime(path, FileTime.from(time));
	}

	/**
	 * Whether the file exists
	 *
	 * @param file
	 *            the file
	 * @return {@code true} if the given file exists, not following symbolic
	 *         links
	 */
	static boolean exists(File file) {
		return Files.exists(file.toPath(), LinkOption.NOFOLLOW_LINKS);
	}

	/**
	 * Check if file is hidden (on Windows)
	 *
	 * @param file
	 *            the file
	 * @return {@code true} if the given file is hidden
	 * @throws IOException
	 *             if an IO error occurred
	 */
	static boolean isHidden(File file) throws IOException {
		return Files.isHidden(toPath(file));
	}

	/**
	 * Set a file hidden (on Windows)
	 *
	 * @param file
	 *            a {@link java.io.File} object.
	 * @param hidden
	 *            a boolean.
	 * @throws java.io.IOException
	 *             if an IO error occurred
	 * @since 4.1
	 */
	public static void setHidden(File file, boolean hidden) throws IOException {
		Files.setAttribute(toPath(file), "dos:hidden", Boolean.valueOf(hidden), //$NON-NLS-1$
				LinkOption.NOFOLLOW_LINKS);
	}

	/**
	 * Get file length
	 *
	 * @param file
	 *            a {@link java.io.File}.
	 * @return length of the given file
	 * @throws java.io.IOException
	 *             if an IO error occurred
	 * @since 4.1
	 */
	public static long getLength(File file) throws IOException {
		Path nioPath = toPath(file);
		if (Files.isSymbolicLink(nioPath))
			return Files.readSymbolicLink(nioPath).toString()
					.getBytes(UTF_8).length;
		return Files.size(nioPath);
	}

	/**
	 * Check if file is directory
	 *
	 * @param file
	 *            the file
	 * @return {@code true} if the given file is a directory, not following
	 *         symbolic links
	 */
	static boolean isDirectory(File file) {
		return Files.isDirectory(file.toPath(), LinkOption.NOFOLLOW_LINKS);
	}

	/**
	 * Check if File is a file
	 *
	 * @param file
	 *            the file
	 * @return {@code true} if the given file is a file, not following symbolic
	 *         links
	 */
	static boolean isFile(File file) {
		return Files.isRegularFile(file.toPath(), LinkOption.NOFOLLOW_LINKS);
	}

	/**
	 * Whether the path is a directory with files in it.
	 *
	 * @param dir
	 *            directory path
	 * @return {@code true} if the given directory path contains files
	 * @throws IOException
	 *             on any I/O errors accessing the path
	 *
	 * @since 5.11
	 */
	public static boolean hasFiles(Path dir) throws IOException {
		try (Stream<Path> stream = Files.list(dir)) {
			return stream.findAny().isPresent();
		}
	}

	/**
	 * Whether the given file can be executed.
	 *
	 * @param file
	 *            a {@link java.io.File} object.
	 * @return {@code true} if the given file can be executed.
	 * @since 4.1
	 */
	public static boolean canExecute(File file) {
		if (!isFile(file)) {
			return false;
		}
		return Files.isExecutable(file.toPath());
	}

	/**
	 * Get basic file attributes
	 *
	 * @param fs
	 *            a {@link org.eclipse.jgit.util.FS} object.
	 * @param file
	 *            the file
	 * @return non null attributes object
	 */
	static Attributes getFileAttributesBasic(FS fs, File file) {
		try {
			Path nioPath = toPath(file);
			BasicFileAttributes readAttributes = nioPath
					.getFileSystem()
					.provider()
					.getFileAttributeView(nioPath,
							BasicFileAttributeView.class,
							LinkOption.NOFOLLOW_LINKS).readAttributes();
			Attributes attributes = new Attributes(fs, file,
					true,
					readAttributes.isDirectory(),
					fs.supportsExecute() ? file.canExecute() : false,
					readAttributes.isSymbolicLink(),
					readAttributes.isRegularFile(), //
					readAttributes.creationTime().toMillis(), //
					readAttributes.lastModifiedTime().toInstant(),
					readAttributes.isSymbolicLink() ? Constants
							.encode(readSymLink(file)).length
							: readAttributes.size());
			return attributes;
		} catch (IOException e) {
			return new Attributes(file, fs);
		}
	}

	/**
	 * Get file system attributes for the given file.
	 *
	 * @param fs
	 *            a {@link org.eclipse.jgit.util.FS} object.
	 * @param file
	 *            a {@link java.io.File}.
	 * @return file system attributes for the given file.
	 * @since 4.1
	 */
	public static Attributes getFileAttributesPosix(FS fs, File file) {
		try {
			Path nioPath = toPath(file);
			PosixFileAttributes readAttributes = nioPath
					.getFileSystem()
					.provider()
					.getFileAttributeView(nioPath,
							PosixFileAttributeView.class,
							LinkOption.NOFOLLOW_LINKS).readAttributes();
			Attributes attributes = new Attributes(
					fs,
					file,
					true, //
					readAttributes.isDirectory(), //
					readAttributes.permissions().contains(
							PosixFilePermission.OWNER_EXECUTE),
					readAttributes.isSymbolicLink(),
					readAttributes.isRegularFile(), //
					readAttributes.creationTime().toMillis(), //
					readAttributes.lastModifiedTime().toInstant(),
					readAttributes.size());
			return attributes;
		} catch (IOException e) {
			return new Attributes(file, fs);
		}
	}

	/**
	 * NFC normalize a file (on Mac), otherwise do nothing
	 *
	 * @param file
	 *            a {@link java.io.File}.
	 * @return on Mac: NFC normalized {@link java.io.File}, otherwise the passed
	 *         file
	 * @since 4.1
	 */
	public static File normalize(File file) {
		if (SystemReader.getInstance().isMacOS()) {
			// TODO: Would it be faster to check with isNormalized first
			// assuming normalized paths are much more common
			String normalized = Normalizer.normalize(file.getPath(),
					Normalizer.Form.NFC);
			return new File(normalized);
		}
		return file;
	}

	/**
	 * On Mac: get NFC normalized form of given name, otherwise the given name.
	 *
	 * @param name
	 *            a {@link java.lang.String} object.
	 * @return on Mac: NFC normalized form of given name
	 * @since 4.1
	 */
	public static String normalize(String name) {
		if (SystemReader.getInstance().isMacOS()) {
			if (name == null)
				return null;
			return Normalizer.normalize(name, Normalizer.Form.NFC);
		}
		return name;
	}

	/**
	 * Best-effort variation of {@link java.io.File#getCanonicalFile()}
	 * returning the input file if the file cannot be canonicalized instead of
	 * throwing {@link java.io.IOException}.
	 *
	 * @param file
	 *            to be canonicalized; may be {@code null}
	 * @return canonicalized file, or the unchanged input file if
	 *         canonicalization failed or if {@code file == null}
	 * @throws java.lang.SecurityException
	 *             if {@link java.io.File#getCanonicalFile()} throws one
	 * @since 4.2
	 */
	public static File canonicalize(File file) {
		if (file == null) {
			return null;
		}
		try {
			return file.getCanonicalFile();
		} catch (IOException e) {
			return file;
		}
	}

	/**
	 * Convert a path to String, replacing separators as necessary.
	 *
	 * @param file
	 *            a {@link java.io.File}.
	 * @return file's path as a String
	 * @since 4.10
	 */
	public static String pathToString(File file) {
		final String path = file.getPath();
		if (SystemReader.getInstance().isWindows()) {
			return path.replace('\\', '/');
		}
		return path;
	}

	/**
	 * Touch the given file
	 *
	 * @param f
	 *            the file to touch
	 * @throws IOException
	 *             if an IO error occurred
	 * @since 5.1.8
	 */
	public static void touch(Path f) throws IOException {
		try (FileChannel fc = FileChannel.open(f, StandardOpenOption.CREATE,
				StandardOpenOption.APPEND, StandardOpenOption.SYNC)) {
			// touch
		}
		Files.setLastModifiedTime(f, FileTime.from(Instant.now()));
	}

	/**
	 * Compute a delay in a {@code min..max} interval with random jitter.
	 *
	 * @param last
	 *            amount of delay waited before the last attempt. This is used
	 *            to seed the next delay interval. Should be 0 if there was no
	 *            prior delay.
	 * @param min
	 *            shortest amount of allowable delay between attempts.
	 * @param max
	 *            longest amount of allowable delay between attempts.
	 * @return new amount of delay to wait before the next attempt.
	 *
	 * @since 5.6
	 */
	public static long delay(long last, long min, long max) {
		long r = Math.max(0, last * 3 - min);
		if (r > 0) {
			int c = (int) Math.min(r + 1, Integer.MAX_VALUE);
			r = RNG.nextInt(c);
		}
		return Math.max(Math.min(min + r, max), min);
	}
}