/*
 * 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.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.

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.

/**
 * 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 Boolean isMacOS;

	private static Boolean isWindows;

	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
Returns:
the current SystemReader instance./**
	 * 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.
Params:
newReader – 
           the new instance to use when accessing properties, or null for
           the default 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;
		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 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/**
	 * 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".
Returns:
the canonical hostname/**
	 * 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
Params:
variable – 
           system variable to read
Returns:
value of the system variable/**
	 * 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
Params:
key – 
           of the system property to read
Returns:
value of the system property/**
	 * 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 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. 
Params:
parent – 
           a config with values not found directly in the returned config
fs – 
           the file system abstraction which will be necessary to perform
           certain file system operations.
Returns:
the git configuration found in the user home/**
	 * 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 getSystemConfig() to get the current system-wide git configuration since it manages automatic reloading when the gitconfig file was modified and avoids unnecessary reloads. 
Params:
parent – 
           a config with values not found directly in the returned
           config. Null is a reasonable value here.
fs – 
           the file system abstraction which will be necessary to perform
           certain file system operations.
Returns:
the gitconfig configuration found in the system-wide "etc"
        directory/**
	 * 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 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. 
Params:
parent – 
           a config with values not found directly in the returned config
fs – 
           the file system abstraction which will be necessary to perform
           certain file system operations.
Returns:
the jgit configuration located at $XDG_CONFIG_HOME/jgit/config
Since:
5.5.2/**
	 * 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.
Throws:
ConfigInvalidException – 
            if configuration is invalid
IOException – 
            if something went wrong when reading files
Returns:
the git configuration found in the user home
Since:
5.1.9/**
	 * 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.
Throws:
ConfigInvalidException – 
            if configuration is invalid
IOException – 
            if something went wrong when reading files
Returns:
the jgit configuration located at $XDG_CONFIG_HOME/jgit/config
Since:
5.5.2/**
	 * 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.
Throws:
ConfigInvalidException – 
            if configuration is invalid
IOException – 
            if something went wrong when reading files
Returns:
the gitconfig configuration found in the system-wide "etc"
        directory
Since:
5.1.9/**
	 * 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
Params:
config – 
           configuration to reload if outdated
Throws:
ConfigInvalidException – 
            if configuration is invalid
IOException – 
            if something went wrong when reading files/**
	 * 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
Returns:
the current system time/**
	 * Get the current system time
	 *
	 * @return the current system time
	 */
	public abstract long getCurrentTime();

	
Get clock instance preferred by this system.
Returns:
clock instance preferred by this system.
Since:
4.6/**
	 * 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
Params:
when – 
           a system timestamp
Returns:
the local time zone/**
	 * 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
Returns:
system time zone, possibly mocked for testing
Since:
1.2/**
	 * 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
Returns:
the locale to use
Since:
1.2/**
	 * Get the locale to use
	 *
	 * @return the locale to use
	 * @since 1.2
	 */
	public Locale getLocale() {
		return Locale.getDefault();
	}

	
Returns a simple date format instance as specified by the given pattern.
Params:
pattern –  the pattern as defined in SimpleDateFormat(String)
Returns:
the simple date format
Since:
2.0/**
	 * 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.
Params:
pattern –  the pattern as defined in SimpleDateFormat(String)
locale –  locale to be used for the SimpleDateFormat
Returns:
the simple date format
Since:
3.2/**
	 * 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.
Params:
dateStyle –  the date style as specified in DateFormat.getDateTimeInstance(int, int)
timeStyle –  the time style as specified in DateFormat.getDateTimeInstance(int, int)
Returns:
the date format
Since:
2.0/**
	 * 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.
Returns:
true if we are running on Windows./**
	 * 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
Returns:
true if we are running on Mac OS X/**
	 * 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();
	}

	private String getOsName() {
		return AccessController.doPrivileged(
				(PrivilegedAction<String>) () -> getProperty("os.name") //$NON-NLS-1$
		);
	}

	
Check tree path entry for validity.
 Scans a multi-directory path string such as "src/main.c". 
Params:
path – path string to scan.
Throws:
CorruptObjectException – path is invalid.
Since:
3.6/**
	 * 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.
 Scans a multi-directory path string such as "src/main.c". 
Params:
path – 
           path string to scan.
Throws:
CorruptObjectException – 
            path is invalid.
Since:
4.2/**
	 * 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);
	}
}