/*
    * Copyright (C) 2010, Robin Rosenberg
    * 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.util;
  
  import java.io.BufferedReader;
  import java.io.File;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.io.PrintStream;
  import java.nio.charset.Charset;
  import java.nio.file.Files;
  import java.nio.file.Path;
  import java.nio.file.Paths;
  import java.nio.file.attribute.PosixFilePermission;
  import java.text.MessageFormat;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.List;
  import java.util.Optional;
  import java.util.Set;
  import java.util.UUID;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.api.errors.JGitInternalException;
  import org.eclipse.jgit.errors.CommandFailedException;
  import org.eclipse.jgit.errors.ConfigInvalidException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.lib.ConfigConstants;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.storage.file.FileBasedConfig;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Base FS for POSIX based systems
   *
   * @since 3.0
   */
  public class FS_POSIX extends FS {
  	private final static Logger LOG = LoggerFactory.getLogger(FS_POSIX.class);
  
  	private static final int DEFAULT_UMASK = 0022;
  	private volatile int umask = -1;
  
  	private volatile boolean supportsUnixNLink = true;
  
  	private volatile Boolean supportsAtomicCreateNewFile;
  
  	/** Default constructor. */
  	protected FS_POSIX() {
  	}
  
  	/**
  	 * Constructor
  	 *
  	 * @param src
  	 *            FS to copy some settings from
  	 */
 	protected FS_POSIX(FS src) {
 		super(src);
 		if (src instanceof FS_POSIX) {
 			umask = ((FS_POSIX) src).umask;
 		}
 	}
 
 	@SuppressWarnings("boxing")
 	private void determineAtomicFileCreationSupport() {
 		// @TODO: enhance SystemReader to support this without copying code
 		Boolean ret = getAtomicFileCreationSupportOption(
 				SystemReader.getInstance().openUserConfig(null, this));
 		if (ret == null && StringUtils.isEmptyOrNull(SystemReader.getInstance()
 				.getenv(Constants.GIT_CONFIG_NOSYSTEM_KEY))) {
 			ret = getAtomicFileCreationSupportOption(
 					SystemReader.getInstance().openSystemConfig(null, this));
 		}
 		supportsAtomicCreateNewFile = (ret == null) || ret;
 	}
 
 	private Boolean getAtomicFileCreationSupportOption(FileBasedConfig config) {
 		try {
 			config.load();
 			String value = config.getString(ConfigConstants.CONFIG_CORE_SECTION,
 					null,
 					ConfigConstants.CONFIG_KEY_SUPPORTSATOMICFILECREATION);
 			if (value == null) {
 				return null;
 			}
 			return Boolean.valueOf(StringUtils.toBoolean(value));
 		} catch (IOException | ConfigInvalidException e) {
 			return Boolean.TRUE;
 		}
 	}
 
 	@Override
 	public FS newInstance() {
 		return new FS_POSIX(this);
 	}
 
 	/**
 	 * Set the umask, overriding any value observed from the shell.
 	 *
 	 * @param umask
 	 *            mask to apply when creating files.
 	 * @since 4.0
 	 */
 	public void setUmask(int umask) {
 		this.umask = umask;
 	}
 
 	private int umask() {
 		int u = umask;
 		if (u == -1) {
 			u = readUmask();
 			umask = u;
 		}
 		return u;
 	}
 
 	/** @return mask returned from running {@code umask} command in shell. */
 	private static int readUmask() {
 		try {
 			Process p = Runtime.getRuntime().exec(
 					new String[] { "sh", "-c", "umask" }, //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
 					null, null);
 			try (BufferedReader lineRead = new BufferedReader(
 					new InputStreamReader(p.getInputStream(), Charset
 							.defaultCharset().name()))) {
 				if (p.waitFor() == 0) {
 					String s = lineRead.readLine();
 					if (s != null && s.matches("0?\\d{3}")) { //$NON-NLS-1$
 						return Integer.parseInt(s, 8);
 					}
 				}
 				return DEFAULT_UMASK;
 			}
 		} catch (Exception e) {
 			return DEFAULT_UMASK;
 		}
 	}
 
 	@Override
 	protected File discoverGitExe() {
 		String path = SystemReader.getInstance().getenv("PATH"); //$NON-NLS-1$
 		File gitExe = searchPath(path, "git"); //$NON-NLS-1$
 
 		if (gitExe == null) {
 			if (SystemReader.getInstance().isMacOS()) {
 				if (searchPath(path, "bash") != null) { //$NON-NLS-1$
 					// On MacOSX, PATH is shorter when Eclipse is launched from the
 					// Finder than from a terminal. Therefore try to launch bash as a
 					// login shell and search using that.
 					String w;
 					try {
 						w = readPipe(userHome(),
 							new String[]{"bash", "--login", "-c", "which git"}, // //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$ //$NON-NLS-4$
 							Charset.defaultCharset().name());
 					} catch (CommandFailedException e) {
 						LOG.warn(e.getMessage());
 						return null;
 					}
 					if (!StringUtils.isEmptyOrNull(w)) {
 						gitExe = new File(w);
 					}
 				}
 			}
 		}
 
 		return gitExe;
 	}
 
 	@Override
 	public boolean isCaseSensitive() {
 		return !SystemReader.getInstance().isMacOS();
 	}
 
 	@Override
 	public boolean supportsExecute() {
 		return true;
 	}
 
 	@Override
 	public boolean canExecute(File f) {
 		return FileUtils.canExecute(f);
 	}
 
 	@Override
 	public boolean setExecute(File f, boolean canExecute) {
 		if (!isFile(f))
 			return false;
 		if (!canExecute)
 			return f.setExecutable(false);
 
 		try {
 			Path path = f.toPath();
 			Set<PosixFilePermission> pset = Files.getPosixFilePermissions(path);
 
 			// owner (user) is always allowed to execute.
 			pset.add(PosixFilePermission.OWNER_EXECUTE);
 
 			int mask = umask();
 			apply(pset, mask, PosixFilePermission.GROUP_EXECUTE, 1 << 3);
 			apply(pset, mask, PosixFilePermission.OTHERS_EXECUTE, 1);
 			Files.setPosixFilePermissions(path, pset);
 			return true;
 		} catch (IOException e) {
 			// The interface doesn't allow to throw IOException
 			final boolean debug = Boolean.parseBoolean(SystemReader
 					.getInstance().getProperty("jgit.fs.debug")); //$NON-NLS-1$
 			if (debug)
 				System.err.println(e);
 			return false;
 		}
 	}
 
 	private static void apply(Set<PosixFilePermission> set,
 			int umask, PosixFilePermission perm, int test) {
 		if ((umask & test) == 0) {
 			// If bit is clear in umask, permission is allowed.
 			set.add(perm);
 		} else {
 			// If bit is set in umask, permission is denied.
 			set.remove(perm);
 		}
 	}
 
 	@Override
 	public ProcessBuilder runInShell(String cmd, String[] args) {
 		List<String> argv = new ArrayList<>(4 + args.length);
 		argv.add("sh"); //$NON-NLS-1$
 		argv.add("-c"); //$NON-NLS-1$
 		argv.add(cmd + " \"$@\""); //$NON-NLS-1$
 		argv.add(cmd);
 		argv.addAll(Arrays.asList(args));
 		ProcessBuilder proc = new ProcessBuilder();
 		proc.command(argv);
 		return proc;
 	}
 
 	/**
 	 * @since 4.0
 	 */
 	@Override
 	public ProcessResult runHookIfPresent(Repository repository, String hookName,
 			String[] args, PrintStream outRedirect, PrintStream errRedirect,
 			String stdinArgs) throws JGitInternalException {
 		return internalRunHookIfPresent(repository, hookName, args, outRedirect,
 				errRedirect, stdinArgs);
 	}
 
 	@Override
 	public boolean retryFailedLockFileCommit() {
 		return false;
 	}
 
 	@Override
 	public boolean supportsSymlinks() {
 		return true;
 	}
 
 	@Override
 	public void setHidden(File path, boolean hidden) throws IOException {
 		// no action on POSIX
 	}
 
 	/**
 	 * @since 3.3
 	 */
 	@Override
 	public Attributes getAttributes(File path) {
 		return FileUtils.getFileAttributesPosix(this, path);
 	}
 
 	/**
 	 * @since 3.3
 	 */
 	@Override
 	public File normalize(File file) {
 		return FileUtils.normalize(file);
 	}
 
 	/**
 	 * @since 3.3
 	 */
 	@Override
 	public String normalize(String name) {
 		return FileUtils.normalize(name);
 	}
 
 	/**
 	 * @since 3.7
 	 */
 	@Override
 	public File findHook(Repository repository, String hookName) {
 		final File gitdir = repository.getDirectory();
 		if (gitdir == null) {
 			return null;
 		}
 		final Path hookPath = gitdir.toPath().resolve(Constants.HOOKS)
 				.resolve(hookName);
 		if (Files.isExecutable(hookPath))
 			return hookPath.toFile();
 		return null;
 	}
 
 	@Override
 	public boolean supportsAtomicCreateNewFile() {
 		if (supportsAtomicCreateNewFile == null) {
 			determineAtomicFileCreationSupport();
 		}
 		return supportsAtomicCreateNewFile.booleanValue();
 	}
 
 	@Override
 	@SuppressWarnings("boxing")
 	/**
 	 * An implementation of the File#createNewFile() semantics which works also
 	 * on NFS. If the config option
 	 * {@code core.supportsAtomicCreateNewFile = true} (which is the default)
 	 * then simply File#createNewFile() is called.
 	 *
 	 * But if {@code core.supportsAtomicCreateNewFile = false} then after
 	 * successful creation of the lock file a hardlink to that lock file is
 	 * created and the attribute nlink of the lock file is checked to be 2. If
 	 * multiple clients manage to create the same lock file nlink would be
 	 * greater than 2 showing the error.
 	 *
 	 * @see "https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html"
 	 *
 	 * @deprecated use {@link FS_POSIX#createNewFileAtomic(File)} instead
 	 * @since 4.5
 	 */
 	@Deprecated
 	public boolean createNewFile(File lock) throws IOException {
 		if (!lock.createNewFile()) {
 			return false;
 		}
 		if (supportsAtomicCreateNewFile() || !supportsUnixNLink) {
 			return true;
 		}
 		Path lockPath = lock.toPath();
 		Path link = null;
 		try {
 			link = Files.createLink(
 					Paths.get(lock.getAbsolutePath() + ".lnk"), //$NON-NLS-1$
 					lockPath);
 			Integer nlink = (Integer) (Files.getAttribute(lockPath,
 					"unix:nlink")); //$NON-NLS-1$
 			if (nlink > 2) {
 				LOG.warn("nlink of link to lock file {0} was not 2 but {1}", //$NON-NLS-1$
 						lock.getPath(), nlink);
 				return false;
 			} else if (nlink < 2) {
 				supportsUnixNLink = false;
 			}
 			return true;
 		} catch (UnsupportedOperationException | IllegalArgumentException e) {
 			supportsUnixNLink = false;
 			return true;
 		} finally {
 			if (link != null) {
 				Files.delete(link);
 			}
 		}
 	}
 
 	/**
 	 * {@inheritDoc}
 	 * <p>
 	 * An implementation of the File#createNewFile() semantics which can create
 	 * a unique file atomically also on NFS. If the config option
 	 * {@code core.supportsAtomicCreateNewFile = true} (which is the default)
 	 * then simply File#createNewFile() is called.
 	 *
 	 * But if {@code core.supportsAtomicCreateNewFile = false} then after
 	 * successful creation of the lock file a hard link to that lock file is
 	 * created and the attribute nlink of the lock file is checked to be 2. If
 	 * multiple clients manage to create the same lock file nlink would be
 	 * greater than 2 showing the error. The hard link needs to be retained
 	 * until the corresponding file is no longer needed in order to prevent that
 	 * another process can create the same file concurrently using another NFS
 	 * client which might not yet see the file due to caching.
 	 *
 	 * @see "https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html"
 	 * @param file
 	 *            the unique file to be created atomically
 	 * @return LockToken this lock token must be held until the file is no
 	 *         longer needed
 	 * @throws IOException
 	 * @since 5.0
 	 */
 	@Override
 	public LockToken createNewFileAtomic(File file) throws IOException {
 		if (!file.createNewFile()) {
 			return token(false, null);
 		}
 		if (supportsAtomicCreateNewFile() || !supportsUnixNLink) {
 			return token(true, null);
 		}
 		Path link = null;
 		Path path = file.toPath();
 		try {
 			link = Files.createLink(Paths.get(uniqueLinkPath(file)), path);
 			Integer nlink = (Integer) (Files.getAttribute(path,
 					"unix:nlink")); //$NON-NLS-1$
 			if (nlink.intValue() > 2) {
 				LOG.warn(MessageFormat.format(
 						JGitText.get().failedAtomicFileCreation, path, nlink));
 				return token(false, link);
 			} else if (nlink.intValue() < 2) {
 				supportsUnixNLink = false;
 			}
 			return token(true, link);
 		} catch (UnsupportedOperationException | IllegalArgumentException e) {
 			supportsUnixNLink = false;
 			return token(true, link);
 		}
 	}
 
 	private static LockToken token(boolean created, @Nullable Path p) {
 		return ((p != null) && Files.exists(p))
 				? new LockToken(created, Optional.of(p))
 				: new LockToken(created, Optional.empty());
 	}
 
 	private static String uniqueLinkPath(File file) {
 		UUID id = UUID.randomUUID();
 		return file.getAbsolutePath() + "." //$NON-NLS-1$
 				+ Long.toHexString(id.getMostSignificantBits())
 				+ Long.toHexString(id.getLeastSignificantBits());
 	}
 }