/*
    * Copyright (C) 2009, Google Inc.
    * Copyright (C) 2009, Robin Rosenberg <robin.rosenberg@dewire.com>
    * Copyright (C) 2009, Yann Simon <yann.simon.fr@gmail.com>
    * Copyright (C) 2012, Daniel Megert <daniel_megert@ch.ibm.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 java.io.File;
  import java.io.IOException;
  import java.net.InetAddress;
  import java.net.UnknownHostException;
  import java.nio.charset.Charset;
  import java.nio.charset.IllegalCharsetNameException;
  import java.nio.charset.UnsupportedCharsetException;
  import java.nio.file.InvalidPathException;
  import java.nio.file.Path;
  import java.nio.file.Paths;
  import java.security.AccessController;
  import java.security.PrivilegedAction;
  import java.text.DateFormat;
  import java.text.SimpleDateFormat;
  import java.util.Locale;
  import java.util.TimeZone;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.eclipse.jgit.errors.ConfigInvalidException;
  import org.eclipse.jgit.errors.CorruptObjectException;
  import org.eclipse.jgit.internal.JGitText;
  import org.eclipse.jgit.lib.Config;
  import org.eclipse.jgit.lib.Constants;
  import org.eclipse.jgit.lib.ObjectChecker;
  import org.eclipse.jgit.lib.StoredConfig;
  import org.eclipse.jgit.storage.file.FileBasedConfig;
  import org.eclipse.jgit.util.time.MonotonicClock;
  import org.eclipse.jgit.util.time.MonotonicSystemClock;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Interface to read values from the system.
   * <p>
   * When writing unit tests, extending this interface with a custom class
   * permits to simulate an access to a system variable or property and
   * permits to control the user's global configuration.
   * </p>
   */
  public abstract class SystemReader {
  
  	private static final Logger LOG = LoggerFactory
  			.getLogger(SystemReader.class);
  
  	private static final SystemReader DEFAULT;
  
  	private static volatile Boolean isMacOS;
  
  	private static volatile Boolean isWindows;
  
  	private static volatile Boolean isLinux;
  
  	static {
  		SystemReader r = new Default();
  		r.init();
  		DEFAULT = r;
  	}
  
  	private static class Default extends SystemReader {
  		private volatile String hostname;
  
  		@Override
  		public String getenv(String variable) {
  			return System.getenv(variable);
  		}
  
  		@Override
  		public String getProperty(String key) {
  			return System.getProperty(key);
  		}
  
  		@Override
  		public FileBasedConfig openSystemConfig(Config parent, FS fs) {
  			if (StringUtils
  					.isEmptyOrNull(getenv(Constants.GIT_CONFIG_NOSYSTEM_KEY))) {
  				File configFile = fs.getGitSystemConfig();
  				if (configFile != null) {
  					return new FileBasedConfig(parent, configFile, fs);
  				}
  			}
  			return new FileBasedConfig(parent, null, fs) {
  				@Override
  				public void load() {
  					// empty, do not load
 				}
 
 				@Override
 				public boolean isOutdated() {
 					// regular class would bomb here
 					return false;
 				}
 			};
 		}
 
 		@Override
 		public FileBasedConfig openUserConfig(Config parent, FS fs) {
 			return new FileBasedConfig(parent, new File(fs.userHome(), ".gitconfig"), //$NON-NLS-1$
 					fs);
 		}
 
 		private Path getXDGConfigHome(FS fs) {
 			String configHomePath = getenv(Constants.XDG_CONFIG_HOME);
 			if (StringUtils.isEmptyOrNull(configHomePath)) {
 				configHomePath = new File(fs.userHome(), ".config") //$NON-NLS-1$
 						.getAbsolutePath();
 			}
 			try {
 				return Paths.get(configHomePath);
 			} catch (InvalidPathException e) {
 				LOG.error(JGitText.get().logXDGConfigHomeInvalid,
 						configHomePath, e);
 			}
 			return null;
 		}
 
 		@Override
 		public FileBasedConfig openJGitConfig(Config parent, FS fs) {
 			Path xdgPath = getXDGConfigHome(fs);
 			if (xdgPath != null) {
 				Path configPath = xdgPath.resolve("jgit") //$NON-NLS-1$
 						.resolve(Constants.CONFIG);
 				return new FileBasedConfig(parent, configPath.toFile(), fs);
 			}
 			return new FileBasedConfig(parent,
 					new File(fs.userHome(), ".jgitconfig"), fs); //$NON-NLS-1$
 		}
 
 		@Override
 		public String getHostname() {
 			if (hostname == null) {
 				try {
 					InetAddress localMachine = InetAddress.getLocalHost();
 					hostname = localMachine.getCanonicalHostName();
 				} catch (UnknownHostException e) {
 					// we do nothing
 					hostname = "localhost"; //$NON-NLS-1$
 				}
 				assert hostname != null;
 			}
 			return hostname;
 		}
 
 		@Override
 		public long getCurrentTime() {
 			return System.currentTimeMillis();
 		}
 
 		@Override
 		public int getTimezone(long when) {
 			return getTimeZone().getOffset(when) / (60 * 1000);
 		}
 	}
 
 	private static volatile SystemReader INSTANCE = DEFAULT;
 
 	/**
 	 * Get the current SystemReader instance
 	 *
 	 * @return the current SystemReader instance.
 	 */
 	public static SystemReader getInstance() {
 		return INSTANCE;
 	}
 
 	/**
 	 * Set a new SystemReader instance to use when accessing properties.
 	 *
 	 * @param newReader
 	 *            the new instance to use when accessing properties, or null for
 	 *            the default instance.
 	 */
 	public static void setInstance(SystemReader newReader) {
 		isMacOS = null;
 		isWindows = null;
 		isLinux = null;
 		if (newReader == null)
 			INSTANCE = DEFAULT;
 		else {
 			newReader.init();
 			INSTANCE = newReader;
 		}
 	}
 
 	private ObjectChecker platformChecker;
 
 	private AtomicReference<FileBasedConfig> systemConfig = new AtomicReference<>();
 
 	private AtomicReference<FileBasedConfig> userConfig = new AtomicReference<>();
 
 	private AtomicReference<FileBasedConfig> jgitConfig = new AtomicReference<>();
 
 	private volatile Charset defaultCharset;
 
 	private void init() {
 		// Creating ObjectChecker must be deferred. Unit tests change
 		// behavior of is{Windows,MacOS} in constructor of subclass.
 		if (platformChecker == null)
 			setPlatformChecker();
 	}
 
 	/**
 	 * Should be used in tests when the platform is explicitly changed.
 	 *
 	 * @since 3.6
 	 */
 	protected final void setPlatformChecker() {
 		platformChecker = new ObjectChecker()
 			.setSafeForWindows(isWindows())
 			.setSafeForMacOS(isMacOS());
 	}
 
 	/**
 	 * Gets the hostname of the local host. If no hostname can be found, the
 	 * hostname is set to the default value "localhost".
 	 *
 	 * @return the canonical hostname
 	 */
 	public abstract String getHostname();
 
 	/**
 	 * Get value of the system variable
 	 *
 	 * @param variable
 	 *            system variable to read
 	 * @return value of the system variable
 	 */
 	public abstract String getenv(String variable);
 
 	/**
 	 * Get value of the system property
 	 *
 	 * @param key
 	 *            of the system property to read
 	 * @return value of the system property
 	 */
 	public abstract String getProperty(String key);
 
 	/**
 	 * Open the git configuration found in the user home. Use
 	 * {@link #getUserConfig()} to get the current git configuration in the user
 	 * home since it manages automatic reloading when the gitconfig file was
 	 * modified and avoids unnecessary reloads.
 	 *
 	 * @param parent
 	 *            a config with values not found directly in the returned config
 	 * @param fs
 	 *            the file system abstraction which will be necessary to perform
 	 *            certain file system operations.
 	 * @return the git configuration found in the user home
 	 */
 	public abstract FileBasedConfig openUserConfig(Config parent, FS fs);
 
 	/**
 	 * Open the gitconfig configuration found in the system-wide "etc"
 	 * directory. Use {@link #getSystemConfig()} to get the current system-wide
 	 * git configuration since it manages automatic reloading when the gitconfig
 	 * file was modified and avoids unnecessary reloads.
 	 *
 	 * @param parent
 	 *            a config with values not found directly in the returned
 	 *            config. Null is a reasonable value here.
 	 * @param fs
 	 *            the file system abstraction which will be necessary to perform
 	 *            certain file system operations.
 	 * @return the gitconfig configuration found in the system-wide "etc"
 	 *         directory
 	 */
 	public abstract FileBasedConfig openSystemConfig(Config parent, FS fs);
 
 	/**
 	 * Open the jgit configuration located at $XDG_CONFIG_HOME/jgit/config. Use
 	 * {@link #getJGitConfig()} to get the current jgit configuration in the
 	 * user home since it manages automatic reloading when the jgit config file
 	 * was modified and avoids unnecessary reloads.
 	 *
 	 * @param parent
 	 *            a config with values not found directly in the returned config
 	 * @param fs
 	 *            the file system abstraction which will be necessary to perform
 	 *            certain file system operations.
 	 * @return the jgit configuration located at $XDG_CONFIG_HOME/jgit/config
 	 * @since 5.5.2
 	 */
 	public abstract FileBasedConfig openJGitConfig(Config parent, FS fs);
 
 	/**
 	 * Get the git configuration found in the user home. The configuration will
 	 * be reloaded automatically if the configuration file was modified. Also
 	 * reloads the system config if the system config file was modified. If the
 	 * configuration file wasn't modified returns the cached configuration.
 	 *
 	 * @return the git configuration found in the user home
 	 * @throws ConfigInvalidException
 	 *             if configuration is invalid
 	 * @throws IOException
 	 *             if something went wrong when reading files
 	 * @since 5.1.9
 	 */
 	public StoredConfig getUserConfig()
 			throws ConfigInvalidException, IOException {
 		FileBasedConfig c = userConfig.get();
 		if (c == null) {
 			userConfig.compareAndSet(null,
 					openUserConfig(getSystemConfig(), FS.DETECTED));
 			c = userConfig.get();
 		}
 		// on the very first call this will check a second time if the system
 		// config is outdated
 		updateAll(c);
 		return c;
 	}
 
 	/**
 	 * Get the jgit configuration located at $XDG_CONFIG_HOME/jgit/config. The
 	 * configuration will be reloaded automatically if the configuration file
 	 * was modified. If the configuration file wasn't modified returns the
 	 * cached configuration.
 	 *
 	 * @return the jgit configuration located at $XDG_CONFIG_HOME/jgit/config
 	 * @throws ConfigInvalidException
 	 *             if configuration is invalid
 	 * @throws IOException
 	 *             if something went wrong when reading files
 	 * @since 5.5.2
 	 */
 	public StoredConfig getJGitConfig()
 			throws ConfigInvalidException, IOException {
 		FileBasedConfig c = jgitConfig.get();
 		if (c == null) {
 			jgitConfig.compareAndSet(null,
 					openJGitConfig(null, FS.DETECTED));
 			c = jgitConfig.get();
 		}
 		updateAll(c);
 		return c;
 	}
 
 	/**
 	 * Get the gitconfig configuration found in the system-wide "etc" directory.
 	 * The configuration will be reloaded automatically if the configuration
 	 * file was modified otherwise returns the cached system level config.
 	 *
 	 * @return the gitconfig configuration found in the system-wide "etc"
 	 *         directory
 	 * @throws ConfigInvalidException
 	 *             if configuration is invalid
 	 * @throws IOException
 	 *             if something went wrong when reading files
 	 * @since 5.1.9
 	 */
 	public StoredConfig getSystemConfig()
 			throws ConfigInvalidException, IOException {
 		FileBasedConfig c = systemConfig.get();
 		if (c == null) {
 			systemConfig.compareAndSet(null,
 					openSystemConfig(getJGitConfig(), FS.DETECTED));
 			c = systemConfig.get();
 		}
 		updateAll(c);
 		return c;
 	}
 
 	/**
 	 * Update config and its parents if they seem modified
 	 *
 	 * @param config
 	 *            configuration to reload if outdated
 	 * @throws ConfigInvalidException
 	 *             if configuration is invalid
 	 * @throws IOException
 	 *             if something went wrong when reading files
 	 */
 	private void updateAll(Config config)
 			throws ConfigInvalidException, IOException {
 		if (config == null) {
 			return;
 		}
 		updateAll(config.getBaseConfig());
 		if (config instanceof FileBasedConfig) {
 			FileBasedConfig cfg = (FileBasedConfig) config;
 			if (cfg.isOutdated()) {
 				LOG.debug("loading config {}", cfg); //$NON-NLS-1$
 				cfg.load();
 			}
 		}
 	}
 
 	/**
 	 * Get the current system time
 	 *
 	 * @return the current system time
 	 */
 	public abstract long getCurrentTime();
 
 	/**
 	 * Get clock instance preferred by this system.
 	 *
 	 * @return clock instance preferred by this system.
 	 * @since 4.6
 	 */
 	public MonotonicClock getClock() {
 		return new MonotonicSystemClock();
 	}
 
 	/**
 	 * Get the local time zone
 	 *
 	 * @param when
 	 *            a system timestamp
 	 * @return the local time zone
 	 */
 	public abstract int getTimezone(long when);
 
 	/**
 	 * Get system time zone, possibly mocked for testing
 	 *
 	 * @return system time zone, possibly mocked for testing
 	 * @since 1.2
 	 */
 	public TimeZone getTimeZone() {
 		return TimeZone.getDefault();
 	}
 
 	/**
 	 * Get the locale to use
 	 *
 	 * @return the locale to use
 	 * @since 1.2
 	 */
 	public Locale getLocale() {
 		return Locale.getDefault();
 	}
 
 	/**
 	 * Retrieves the default {@link Charset} depending on the system locale.
 	 *
 	 * @return the {@link Charset}
 	 * @since 6.0
 	 * @see <a href="https://openjdk.java.net/jeps/400">JEP 400</a>
 	 */
 	public Charset getDefaultCharset() {
 		Charset result = defaultCharset;
 		if (result == null) {
 			// JEP 400: Java 18 populates this system property.
 			String encoding = getProperty("native.encoding"); //$NON-NLS-1$
 			try {
 				if (!StringUtils.isEmptyOrNull(encoding)) {
 					result = Charset.forName(encoding);
 				}
 			} catch (IllegalCharsetNameException
 					| UnsupportedCharsetException e) {
 				LOG.error(JGitText.get().logInvalidDefaultCharset, encoding);
 			}
 			if (result == null) {
 				// This is always UTF-8 on Java >= 18.
 				result = Charset.defaultCharset();
 			}
 			defaultCharset = result;
 		}
 		return result;
 	}
 
 	/**
 	 * Returns a simple date format instance as specified by the given pattern.
 	 *
 	 * @param pattern
 	 *            the pattern as defined in
 	 *            {@link java.text.SimpleDateFormat#SimpleDateFormat(String)}
 	 * @return the simple date format
 	 * @since 2.0
 	 */
 	public SimpleDateFormat getSimpleDateFormat(String pattern) {
 		return new SimpleDateFormat(pattern);
 	}
 
 	/**
 	 * Returns a simple date format instance as specified by the given pattern.
 	 *
 	 * @param pattern
 	 *            the pattern as defined in
 	 *            {@link java.text.SimpleDateFormat#SimpleDateFormat(String)}
 	 * @param locale
 	 *            locale to be used for the {@code SimpleDateFormat}
 	 * @return the simple date format
 	 * @since 3.2
 	 */
 	public SimpleDateFormat getSimpleDateFormat(String pattern, Locale locale) {
 		return new SimpleDateFormat(pattern, locale);
 	}
 
 	/**
 	 * Returns a date/time format instance for the given styles.
 	 *
 	 * @param dateStyle
 	 *            the date style as specified in
 	 *            {@link java.text.DateFormat#getDateTimeInstance(int, int)}
 	 * @param timeStyle
 	 *            the time style as specified in
 	 *            {@link java.text.DateFormat#getDateTimeInstance(int, int)}
 	 * @return the date format
 	 * @since 2.0
 	 */
 	public DateFormat getDateTimeInstance(int dateStyle, int timeStyle) {
 		return DateFormat.getDateTimeInstance(dateStyle, timeStyle);
 	}
 
 	/**
 	 * Whether we are running on Windows.
 	 *
 	 * @return true if we are running on Windows.
 	 */
 	public boolean isWindows() {
 		if (isWindows == null) {
 			String osDotName = getOsName();
 			isWindows = Boolean.valueOf(osDotName.startsWith("Windows")); //$NON-NLS-1$
 		}
 		return isWindows.booleanValue();
 	}
 
 	/**
 	 * Whether we are running on Mac OS X
 	 *
 	 * @return true if we are running on Mac OS X
 	 */
 	public boolean isMacOS() {
 		if (isMacOS == null) {
 			String osDotName = getOsName();
 			isMacOS = Boolean.valueOf(
 					"Mac OS X".equals(osDotName) || "Darwin".equals(osDotName)); //$NON-NLS-1$ //$NON-NLS-2$
 		}
 		return isMacOS.booleanValue();
 	}
 
 	/**
 	 * Whether we are running on Linux.
 	 *
 	 * @return true if we are running on Linux.
 	 * @since 6.3
 	 */
 	public boolean isLinux() {
 		if (isLinux == null) {
 			String osname = getOsName();
 			isLinux = Boolean.valueOf(osname.toLowerCase().startsWith("linux")); //$NON-NLS-1$
 		}
 		return isLinux.booleanValue();
 	}
 
 	private String getOsName() {
 		return AccessController.doPrivileged(
 				(PrivilegedAction<String>) () -> getProperty("os.name") //$NON-NLS-1$
 		);
 	}
 
 	/**
 	 * Check tree path entry for validity.
 	 * <p>
 	 * Scans a multi-directory path string such as {@code "src/main.c"}.
 	 *
 	 * @param path path string to scan.
 	 * @throws org.eclipse.jgit.errors.CorruptObjectException path is invalid.
 	 * @since 3.6
 	 */
 	public void checkPath(String path) throws CorruptObjectException {
 		platformChecker.checkPath(path);
 	}
 
 	/**
 	 * Check tree path entry for validity.
 	 * <p>
 	 * Scans a multi-directory path string such as {@code "src/main.c"}.
 	 *
 	 * @param path
 	 *            path string to scan.
 	 * @throws org.eclipse.jgit.errors.CorruptObjectException
 	 *             path is invalid.
 	 * @since 4.2
 	 */
 	public void checkPath(byte[] path) throws CorruptObjectException {
 		platformChecker.checkPath(path, 0, path.length);
 	}
 }