/*
 * Copyright (C) 2010, Robin Rosenberg 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 org.eclipse.jgit.lib.ConfigConstants.CONFIG_CORE_SECTION;
import static org.eclipse.jgit.lib.ConfigConstants.CONFIG_KEY_SUPPORTSATOMICFILECREATION;

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.FileAlreadyExistsException;
import java.nio.file.FileStore;
import java.nio.file.FileSystemException;
import java.nio.file.Files;
import java.nio.file.InvalidPathException;
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.Map;
import java.util.Optional;
import java.util.Set;
import java.util.UUID;
import java.util.concurrent.ConcurrentHashMap;

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.Repository;
import org.eclipse.jgit.lib.StoredConfig;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

Base FS for POSIX based systems
Since:
3.0/**
 * Base FS for POSIX based systems
 *
 * @since 3.0
 */
public class FS_POSIX extends FS {
	private static final Logger LOG = LoggerFactory.getLogger(FS_POSIX.class);

	private static final String DEFAULT_GIT_LOCATION = "/usr/bin/git"; //$NON-NLS-1$

	private static final int DEFAULT_UMASK = 0022;
	private volatile int umask = -1;

	private static final Map<FileStore, Boolean> CAN_HARD_LINK = new ConcurrentHashMap<>();

	private volatile AtomicFileCreation supportsAtomicFileCreation = AtomicFileCreation.UNDEFINED;

	private enum AtomicFileCreation {
		SUPPORTED, NOT_SUPPORTED, UNDEFINED
	}

	
Default constructor.
/**
	 * Default constructor.
	 */
	protected FS_POSIX() {
	}

	
Constructor
Params:
src – 
           FS to copy some settings from/**
	 * 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;
		}
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public FS newInstance() {
		return new FS_POSIX(this);
	}

	
Set the umask, overriding any value observed from the shell.
Params:
umask – 
           mask to apply when creating files.
Since:
4.0/**
	 * 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;
	}

	
Returns:
mask returned from running umask command in shell./** @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;
		}
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	protected File discoverGitExe() {
		String path = SystemReader.getInstance().getenv("PATH"); //$NON-NLS-1$
		File gitExe = searchPath(path, "git"); //$NON-NLS-1$

		if (SystemReader.getInstance().isMacOS()) {
			if (gitExe == null
					|| DEFAULT_GIT_LOCATION.equals(gitExe.getPath())) {
				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.
					try {
						String 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());
						if (!StringUtils.isEmptyOrNull(w)) {
							gitExe = new File(w);
						}
					} catch (CommandFailedException e) {
						LOG.warn(e.getMessage());
					}
				}
			}
			if (gitExe != null
					&& DEFAULT_GIT_LOCATION.equals(gitExe.getPath())) {
				// If we still have the default git exe, it's an XCode wrapper
				// that may prompt the user to install the XCode command line
				// tools if not already present. Avoid the prompt by returning
				// null if no XCode git is there.
				try {
					String w = readPipe(userHome(),
							new String[] { "xcode-select", "-p" }, //$NON-NLS-1$ //$NON-NLS-2$
							Charset.defaultCharset().name());
					if (StringUtils.isEmptyOrNull(w)) {
						gitExe = null;
					} else {
						File realGitExe = new File(new File(w),
								DEFAULT_GIT_LOCATION.substring(1));
						if (!realGitExe.exists()) {
							gitExe = null;
						}
					}
				} catch (CommandFailedException e) {
					gitExe = null;
				}
			}
		}

		return gitExe;
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public boolean isCaseSensitive() {
		return !SystemReader.getInstance().isMacOS();
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public boolean supportsExecute() {
		return true;
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public boolean canExecute(File f) {
		return FileUtils.canExecute(f);
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public boolean setExecute(File f, boolean canExecute) {
		if (!isFile(f))
			return false;
		if (!canExecute)
			return f.setExecutable(false, false);

		try {
			Path path = FileUtils.toPath(f);
			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);
		}
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@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;
	}

	@Override
	String shellQuote(String cmd) {
		return QuotedString.BOURNE.quote(cmd);
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@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);
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public boolean retryFailedLockFileCommit() {
		return false;
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public void setHidden(File path, boolean hidden) throws IOException {
		// no action on POSIX
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public Attributes getAttributes(File path) {
		return FileUtils.getFileAttributesPosix(this, path);
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public File normalize(File file) {
		return FileUtils.normalize(file);
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public String normalize(String name) {
		return FileUtils.normalize(name);
	}

	
{@inheritDoc} /** {@inheritDoc} */
	@Override
	public boolean supportsAtomicCreateNewFile() {
		if (supportsAtomicFileCreation == AtomicFileCreation.UNDEFINED) {
			try {
				StoredConfig config = SystemReader.getInstance().getUserConfig();
				String value = config.getString(CONFIG_CORE_SECTION, null,
						CONFIG_KEY_SUPPORTSATOMICFILECREATION);
				if (value != null) {
					supportsAtomicFileCreation = StringUtils.toBoolean(value)
							? AtomicFileCreation.SUPPORTED
							: AtomicFileCreation.NOT_SUPPORTED;
				} else {
					supportsAtomicFileCreation = AtomicFileCreation.SUPPORTED;
				}
			} catch (IOException | ConfigInvalidException e) {
				LOG.warn(JGitText.get().assumeAtomicCreateNewFile, e);
				supportsAtomicFileCreation = AtomicFileCreation.SUPPORTED;
			}
		}
		return supportsAtomicFileCreation == AtomicFileCreation.SUPPORTED;
	}

	@Override
	@SuppressWarnings("boxing")
	/**
	 * {@inheritDoc}
	 * <p>
	 * 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 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.
	 *
	 * @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()) {
			return true;
		}
		Path lockPath = lock.toPath();
		Path link = null;
		FileStore store = null;
		try {
			store = Files.getFileStore(lockPath);
		} catch (SecurityException e) {
			return true;
		}
		try {
			Boolean canLink = CAN_HARD_LINK.computeIfAbsent(store,
					s -> Boolean.TRUE);
			if (Boolean.FALSE.equals(canLink)) {
				return true;
			}
			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(MessageFormat.format(
						JGitText.get().failedAtomicFileCreation, lockPath,
						nlink));
				return false;
			} else if (nlink < 2) {
				CAN_HARD_LINK.put(store, Boolean.FALSE);
			}
			return true;
		} catch (UnsupportedOperationException | IllegalArgumentException e) {
			CAN_HARD_LINK.put(store, Boolean.FALSE);
			return true;
		} finally {
			if (link != null) {
				Files.delete(link);
			}
		}
	}

	
{@inheritDoc}
 An implementation of the File#createNewFile() semantics which can create a unique file atomically also on NFS. If the config option core.supportsAtomicCreateNewFile = true (which is the default) then simply Files#createFile() is called. But if 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. 
Params:
file – 
           the unique file to be created atomically
Throws:
IOException – 
See Also:
https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html
Returns:
LockToken this lock token must be held until the file is no
        longer needed
Since:
5.0/**
	 * {@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 Files#createFile() 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 {
		Path path;
		try {
			path = file.toPath();
			Files.createFile(path);
		} catch (FileAlreadyExistsException | InvalidPathException e) {
			return token(false, null);
		}
		if (supportsAtomicCreateNewFile()) {
			return token(true, null);
		}
		Path link = null;
		FileStore store = null;
		try {
			store = Files.getFileStore(path);
		} catch (SecurityException e) {
			return token(true, null);
		}
		try {
			Boolean canLink = CAN_HARD_LINK.computeIfAbsent(store,
					s -> Boolean.TRUE);
			if (Boolean.FALSE.equals(canLink)) {
				return token(true, null);
			}
			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) {
				CAN_HARD_LINK.put(store, Boolean.FALSE);
			}
			return token(true, link);
		} catch (UnsupportedOperationException | IllegalArgumentException
				| FileSystemException | SecurityException e) {
			CAN_HARD_LINK.put(store, Boolean.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());
	}
}