/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.i18n;

import java.util.Locale;
import java.util.TimeZone;

import org.springframework.core.NamedInheritableThreadLocal;
import org.springframework.core.NamedThreadLocal;
import org.springframework.lang.Nullable;

Simple holder class that associates a LocaleContext instance with the current thread. The LocaleContext will be inherited by any child threads spawned by the current thread if the inheritable flag is set to true. 
Used as a central holder for the current Locale in Spring,
wherever necessary: for example, in MessageSourceAccessor.
DispatcherServlet automatically exposes its current Locale here.
Other applications can expose theirs too, to make classes like
MessageSourceAccessor automatically use that Locale.
Author:
Juergen Hoeller, Nicholas Williams
See Also:
LocaleContext
MessageSourceAccessor
DispatcherServlet
Since:
1.2/**
 * Simple holder class that associates a LocaleContext instance
 * with the current thread. The LocaleContext will be inherited
 * by any child threads spawned by the current thread if the
 * {@code inheritable} flag is set to {@code true}.
 *
 * <p>Used as a central holder for the current Locale in Spring,
 * wherever necessary: for example, in MessageSourceAccessor.
 * DispatcherServlet automatically exposes its current Locale here.
 * Other applications can expose theirs too, to make classes like
 * MessageSourceAccessor automatically use that Locale.
 *
 * @author Juergen Hoeller
 * @author Nicholas Williams
 * @since 1.2
 * @see LocaleContext
 * @see org.springframework.context.support.MessageSourceAccessor
 * @see org.springframework.web.servlet.DispatcherServlet
 */
public final class LocaleContextHolder {

	private static final ThreadLocal<LocaleContext> localeContextHolder =
			new NamedThreadLocal<>("LocaleContext");

	private static final ThreadLocal<LocaleContext> inheritableLocaleContextHolder =
			new NamedInheritableThreadLocal<>("LocaleContext");

	// Shared default locale at the framework level
	@Nullable
	private static Locale defaultLocale;

	// Shared default time zone at the framework level
	@Nullable
	private static TimeZone defaultTimeZone;


	private LocaleContextHolder() {
	}


	
Reset the LocaleContext for the current thread.
/**
	 * Reset the LocaleContext for the current thread.
	 */
	public static void resetLocaleContext() {
		localeContextHolder.remove();
		inheritableLocaleContextHolder.remove();
	}

	
Associate the given LocaleContext with the current thread,
not exposing it as inheritable for child threads.
The given LocaleContext may be a TimeZoneAwareLocaleContext, containing a locale with associated time zone information. 
Params:
localeContext – the current LocaleContext, or null to reset the thread-bound context
See Also:
SimpleLocaleContext
SimpleTimeZoneAwareLocaleContext/**
	 * Associate the given LocaleContext with the current thread,
	 * <i>not</i> exposing it as inheritable for child threads.
	 * <p>The given LocaleContext may be a {@link TimeZoneAwareLocaleContext},
	 * containing a locale with associated time zone information.
	 * @param localeContext the current LocaleContext,
	 * or {@code null} to reset the thread-bound context
	 * @see SimpleLocaleContext
	 * @see SimpleTimeZoneAwareLocaleContext
	 */
	public static void setLocaleContext(@Nullable LocaleContext localeContext) {
		setLocaleContext(localeContext, false);
	}

	
Associate the given LocaleContext with the current thread.
The given LocaleContext may be a TimeZoneAwareLocaleContext, containing a locale with associated time zone information. 
Params:
localeContext – the current LocaleContext, or null to reset the thread-bound context
inheritable – whether to expose the LocaleContext as inheritable for child threads (using an InheritableThreadLocal)
See Also:
SimpleLocaleContext
SimpleTimeZoneAwareLocaleContext/**
	 * Associate the given LocaleContext with the current thread.
	 * <p>The given LocaleContext may be a {@link TimeZoneAwareLocaleContext},
	 * containing a locale with associated time zone information.
	 * @param localeContext the current LocaleContext,
	 * or {@code null} to reset the thread-bound context
	 * @param inheritable whether to expose the LocaleContext as inheritable
	 * for child threads (using an {@link InheritableThreadLocal})
	 * @see SimpleLocaleContext
	 * @see SimpleTimeZoneAwareLocaleContext
	 */
	public static void setLocaleContext(@Nullable LocaleContext localeContext, boolean inheritable) {
		if (localeContext == null) {
			resetLocaleContext();
		}
		else {
			if (inheritable) {
				inheritableLocaleContextHolder.set(localeContext);
				localeContextHolder.remove();
			}
			else {
				localeContextHolder.set(localeContext);
				inheritableLocaleContextHolder.remove();
			}
		}
	}

	
Return the LocaleContext associated with the current thread, if any.
Returns:
the current LocaleContext, or null if none/**
	 * Return the LocaleContext associated with the current thread, if any.
	 * @return the current LocaleContext, or {@code null} if none
	 */
	@Nullable
	public static LocaleContext getLocaleContext() {
		LocaleContext localeContext = localeContextHolder.get();
		if (localeContext == null) {
			localeContext = inheritableLocaleContextHolder.get();
		}
		return localeContext;
	}

	
Associate the given Locale with the current thread,
preserving any TimeZone that may have been set already.
Will implicitly create a LocaleContext for the given Locale,
not exposing it as inheritable for child threads.
Params:
locale – the current Locale, or null to reset the locale part of thread-bound context
See Also:
setTimeZone(TimeZone)
SimpleLocaleContext(Locale)/**
	 * Associate the given Locale with the current thread,
	 * preserving any TimeZone that may have been set already.
	 * <p>Will implicitly create a LocaleContext for the given Locale,
	 * <i>not</i> exposing it as inheritable for child threads.
	 * @param locale the current Locale, or {@code null} to reset
	 * the locale part of thread-bound context
	 * @see #setTimeZone(TimeZone)
	 * @see SimpleLocaleContext#SimpleLocaleContext(Locale)
	 */
	public static void setLocale(@Nullable Locale locale) {
		setLocale(locale, false);
	}

	
Associate the given Locale with the current thread,
preserving any TimeZone that may have been set already.
Will implicitly create a LocaleContext for the given Locale.
Params:
locale – the current Locale, or null to reset the locale part of thread-bound context
inheritable – whether to expose the LocaleContext as inheritable for child threads (using an InheritableThreadLocal)
See Also:
setTimeZone(TimeZone, boolean)
SimpleLocaleContext(Locale)/**
	 * Associate the given Locale with the current thread,
	 * preserving any TimeZone that may have been set already.
	 * <p>Will implicitly create a LocaleContext for the given Locale.
	 * @param locale the current Locale, or {@code null} to reset
	 * the locale part of thread-bound context
	 * @param inheritable whether to expose the LocaleContext as inheritable
	 * for child threads (using an {@link InheritableThreadLocal})
	 * @see #setTimeZone(TimeZone, boolean)
	 * @see SimpleLocaleContext#SimpleLocaleContext(Locale)
	 */
	public static void setLocale(@Nullable Locale locale, boolean inheritable) {
		LocaleContext localeContext = getLocaleContext();
		TimeZone timeZone = (localeContext instanceof TimeZoneAwareLocaleContext ?
				((TimeZoneAwareLocaleContext) localeContext).getTimeZone() : null);
		if (timeZone != null) {
			localeContext = new SimpleTimeZoneAwareLocaleContext(locale, timeZone);
		}
		else if (locale != null) {
			localeContext = new SimpleLocaleContext(locale);
		}
		else {
			localeContext = null;
		}
		setLocaleContext(localeContext, inheritable);
	}

	
Set a shared default locale at the framework level,
as an alternative to the JVM-wide default locale.
NOTE: This can be useful to set an application-level
default locale which differs from the JVM-wide default locale.
However, this requires each such application to operate against
locally deployed Spring Framework jars. Do not deploy Spring
as a shared library at the server level in such a scenario!
Params:
locale – the default locale (or null for none, letting lookups fall back to Locale.getDefault())
See Also:
getLocale()
Locale.getDefault()
Since:
4.3.5/**
	 * Set a shared default locale at the framework level,
	 * as an alternative to the JVM-wide default locale.
	 * <p><b>NOTE:</b> This can be useful to set an application-level
	 * default locale which differs from the JVM-wide default locale.
	 * However, this requires each such application to operate against
	 * locally deployed Spring Framework jars. Do not deploy Spring
	 * as a shared library at the server level in such a scenario!
	 * @param locale the default locale (or {@code null} for none,
	 * letting lookups fall back to {@link Locale#getDefault()})
	 * @since 4.3.5
	 * @see #getLocale()
	 * @see Locale#getDefault()
	 */
	public static void setDefaultLocale(@Nullable Locale locale) {
		LocaleContextHolder.defaultLocale = locale;
	}

	
Return the Locale associated with the current thread, if any, or the system default Locale otherwise. This is effectively a replacement for Locale.getDefault(), able to optionally respect a user-level Locale setting. 
Note: This method has a fallback to the shared default Locale, either at the framework level or at the JVM-wide system level. If you'd like to check for the raw LocaleContext content (which may indicate no specific locale through null, use getLocaleContext() and call LocaleContext.getLocale() 
See Also:
getLocaleContext()
LocaleContext.getLocale()
setDefaultLocale(Locale)
Locale.getDefault()
Returns:
the current Locale, or the system default Locale if no
specific Locale has been associated with the current thread/**
	 * Return the Locale associated with the current thread, if any,
	 * or the system default Locale otherwise. This is effectively a
	 * replacement for {@link java.util.Locale#getDefault()},
	 * able to optionally respect a user-level Locale setting.
	 * <p>Note: This method has a fallback to the shared default Locale,
	 * either at the framework level or at the JVM-wide system level.
	 * If you'd like to check for the raw LocaleContext content
	 * (which may indicate no specific locale through {@code null}, use
	 * {@link #getLocaleContext()} and call {@link LocaleContext#getLocale()}
	 * @return the current Locale, or the system default Locale if no
	 * specific Locale has been associated with the current thread
	 * @see #getLocaleContext()
	 * @see LocaleContext#getLocale()
	 * @see #setDefaultLocale(Locale)
	 * @see java.util.Locale#getDefault()
	 */
	public static Locale getLocale() {
		return getLocale(getLocaleContext());
	}

	
Return the Locale associated with the given user context, if any, or the system default Locale otherwise. This is effectively a replacement for Locale.getDefault(), able to optionally respect a user-level Locale setting. 
Params:
localeContext – the user-level locale context to check
See Also:
getLocale()
LocaleContext.getLocale()
setDefaultLocale(Locale)
Locale.getDefault()
Returns:
the current Locale, or the system default Locale if no
specific Locale has been associated with the current thread
Since:
5.0/**
	 * Return the Locale associated with the given user context, if any,
	 * or the system default Locale otherwise. This is effectively a
	 * replacement for {@link java.util.Locale#getDefault()},
	 * able to optionally respect a user-level Locale setting.
	 * @param localeContext the user-level locale context to check
	 * @return the current Locale, or the system default Locale if no
	 * specific Locale has been associated with the current thread
	 * @since 5.0
	 * @see #getLocale()
	 * @see LocaleContext#getLocale()
	 * @see #setDefaultLocale(Locale)
	 * @see java.util.Locale#getDefault()
	 */
	public static Locale getLocale(@Nullable LocaleContext localeContext) {
		if (localeContext != null) {
			Locale locale = localeContext.getLocale();
			if (locale != null) {
				return locale;
			}
		}
		return (defaultLocale != null ? defaultLocale : Locale.getDefault());
	}

	
Associate the given TimeZone with the current thread,
preserving any Locale that may have been set already.
Will implicitly create a LocaleContext for the given Locale,
not exposing it as inheritable for child threads.
Params:
timeZone – the current TimeZone, or null to reset the time zone part of the thread-bound context
See Also:
setLocale(Locale)
SimpleTimeZoneAwareLocaleContext(Locale, TimeZone)/**
	 * Associate the given TimeZone with the current thread,
	 * preserving any Locale that may have been set already.
	 * <p>Will implicitly create a LocaleContext for the given Locale,
	 * <i>not</i> exposing it as inheritable for child threads.
	 * @param timeZone the current TimeZone, or {@code null} to reset
	 * the time zone part of the thread-bound context
	 * @see #setLocale(Locale)
	 * @see SimpleTimeZoneAwareLocaleContext#SimpleTimeZoneAwareLocaleContext(Locale, TimeZone)
	 */
	public static void setTimeZone(@Nullable TimeZone timeZone) {
		setTimeZone(timeZone, false);
	}

	
Associate the given TimeZone with the current thread,
preserving any Locale that may have been set already.
Will implicitly create a LocaleContext for the given Locale.
Params:
timeZone – the current TimeZone, or null to reset the time zone part of the thread-bound context
inheritable – whether to expose the LocaleContext as inheritable for child threads (using an InheritableThreadLocal)
See Also:
setLocale(Locale, boolean)
SimpleTimeZoneAwareLocaleContext(Locale, TimeZone)/**
	 * Associate the given TimeZone with the current thread,
	 * preserving any Locale that may have been set already.
	 * <p>Will implicitly create a LocaleContext for the given Locale.
	 * @param timeZone the current TimeZone, or {@code null} to reset
	 * the time zone part of the thread-bound context
	 * @param inheritable whether to expose the LocaleContext as inheritable
	 * for child threads (using an {@link InheritableThreadLocal})
	 * @see #setLocale(Locale, boolean)
	 * @see SimpleTimeZoneAwareLocaleContext#SimpleTimeZoneAwareLocaleContext(Locale, TimeZone)
	 */
	public static void setTimeZone(@Nullable TimeZone timeZone, boolean inheritable) {
		LocaleContext localeContext = getLocaleContext();
		Locale locale = (localeContext != null ? localeContext.getLocale() : null);
		if (timeZone != null) {
			localeContext = new SimpleTimeZoneAwareLocaleContext(locale, timeZone);
		}
		else if (locale != null) {
			localeContext = new SimpleLocaleContext(locale);
		}
		else {
			localeContext = null;
		}
		setLocaleContext(localeContext, inheritable);
	}

	
Set a shared default time zone at the framework level,
as an alternative to the JVM-wide default time zone.
NOTE: This can be useful to set an application-level
default time zone which differs from the JVM-wide default time zone.
However, this requires each such application to operate against
locally deployed Spring Framework jars. Do not deploy Spring
as a shared library at the server level in such a scenario!
Params:
timeZone – the default time zone (or null for none, letting lookups fall back to TimeZone.getDefault())
See Also:
getTimeZone()
TimeZone.getDefault()
Since:
4.3.5/**
	 * Set a shared default time zone at the framework level,
	 * as an alternative to the JVM-wide default time zone.
	 * <p><b>NOTE:</b> This can be useful to set an application-level
	 * default time zone which differs from the JVM-wide default time zone.
	 * However, this requires each such application to operate against
	 * locally deployed Spring Framework jars. Do not deploy Spring
	 * as a shared library at the server level in such a scenario!
	 * @param timeZone the default time zone (or {@code null} for none,
	 * letting lookups fall back to {@link TimeZone#getDefault()})
	 * @since 4.3.5
	 * @see #getTimeZone()
	 * @see TimeZone#getDefault()
	 */
	public static void setDefaultTimeZone(@Nullable TimeZone timeZone) {
		defaultTimeZone = timeZone;
	}

	
Return the TimeZone associated with the current thread, if any, or the system default TimeZone otherwise. This is effectively a replacement for TimeZone.getDefault(), able to optionally respect a user-level TimeZone setting. 
Note: This method has a fallback to the shared default TimeZone, either at the framework level or at the JVM-wide system level. If you'd like to check for the raw LocaleContext content (which may indicate no specific time zone through null, use getLocaleContext() and call TimeZoneAwareLocaleContext.getTimeZone() after downcasting to TimeZoneAwareLocaleContext. 
See Also:
getLocaleContext()
TimeZoneAwareLocaleContext.getTimeZone()
setDefaultTimeZone(TimeZone)
TimeZone.getDefault()
Returns:
the current TimeZone, or the system default TimeZone if no
specific TimeZone has been associated with the current thread/**
	 * Return the TimeZone associated with the current thread, if any,
	 * or the system default TimeZone otherwise. This is effectively a
	 * replacement for {@link java.util.TimeZone#getDefault()},
	 * able to optionally respect a user-level TimeZone setting.
	 * <p>Note: This method has a fallback to the shared default TimeZone,
	 * either at the framework level or at the JVM-wide system level.
	 * If you'd like to check for the raw LocaleContext content
	 * (which may indicate no specific time zone through {@code null}, use
	 * {@link #getLocaleContext()} and call {@link TimeZoneAwareLocaleContext#getTimeZone()}
	 * after downcasting to {@link TimeZoneAwareLocaleContext}.
	 * @return the current TimeZone, or the system default TimeZone if no
	 * specific TimeZone has been associated with the current thread
	 * @see #getLocaleContext()
	 * @see TimeZoneAwareLocaleContext#getTimeZone()
	 * @see #setDefaultTimeZone(TimeZone)
	 * @see java.util.TimeZone#getDefault()
	 */
	public static TimeZone getTimeZone() {
		return getTimeZone(getLocaleContext());
	}

	
Return the TimeZone associated with the given user context, if any, or the system default TimeZone otherwise. This is effectively a replacement for TimeZone.getDefault(), able to optionally respect a user-level TimeZone setting. 
Params:
localeContext – the user-level locale context to check
See Also:
getTimeZone()
TimeZoneAwareLocaleContext.getTimeZone()
setDefaultTimeZone(TimeZone)
TimeZone.getDefault()
Returns:
the current TimeZone, or the system default TimeZone if no
specific TimeZone has been associated with the current thread
Since:
5.0/**
	 * Return the TimeZone associated with the given user context, if any,
	 * or the system default TimeZone otherwise. This is effectively a
	 * replacement for {@link java.util.TimeZone#getDefault()},
	 * able to optionally respect a user-level TimeZone setting.
	 * @param localeContext the user-level locale context to check
	 * @return the current TimeZone, or the system default TimeZone if no
	 * specific TimeZone has been associated with the current thread
	 * @since 5.0
	 * @see #getTimeZone()
	 * @see TimeZoneAwareLocaleContext#getTimeZone()
	 * @see #setDefaultTimeZone(TimeZone)
	 * @see java.util.TimeZone#getDefault()
	 */
	public static TimeZone getTimeZone(@Nullable LocaleContext localeContext) {
		if (localeContext instanceof TimeZoneAwareLocaleContext) {
			TimeZone timeZone = ((TimeZoneAwareLocaleContext) localeContext).getTimeZone();
			if (timeZone != null) {
				return timeZone;
			}
		}
		return (defaultTimeZone != null ? defaultTimeZone : TimeZone.getDefault());
	}

}