/*
 * 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.support;

import java.text.MessageFormat;
import java.util.HashMap;
import java.util.Locale;
import java.util.Map;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.springframework.lang.Nullable;
import org.springframework.util.ObjectUtils;

Base class for message source implementations, providing support infrastructure such as MessageFormat handling but not implementing concrete methods defined in the MessageSource. 
AbstractMessageSource derives from this class, providing concrete getMessage implementations that delegate to a central template method for message code resolution. 
Author:
Juergen Hoeller
Since:
2.5.5/**
 * Base class for message source implementations, providing support infrastructure
 * such as {@link java.text.MessageFormat} handling but not implementing concrete
 * methods defined in the {@link org.springframework.context.MessageSource}.
 *
 * <p>{@link AbstractMessageSource} derives from this class, providing concrete
 * {@code getMessage} implementations that delegate to a central template
 * method for message code resolution.
 *
 * @author Juergen Hoeller
 * @since 2.5.5
 */
public abstract class MessageSourceSupport {

	private static final MessageFormat INVALID_MESSAGE_FORMAT = new MessageFormat("");

	
Logger available to subclasses. /** Logger available to subclasses. */
	protected final Log logger = LogFactory.getLog(getClass());

	private boolean alwaysUseMessageFormat = false;

	
Cache to hold already generated MessageFormats per message.
Used for passed-in default messages. MessageFormats for resolved
codes are cached on a specific basis in subclasses.
/**
	 * Cache to hold already generated MessageFormats per message.
	 * Used for passed-in default messages. MessageFormats for resolved
	 * codes are cached on a specific basis in subclasses.
	 */
	private final Map<String, Map<Locale, MessageFormat>> messageFormatsPerMessage = new HashMap<>();


	
Set whether to always apply the MessageFormat rules, parsing even messages without arguments. 
Default is "false": Messages without arguments are by default
returned as-is, without parsing them through MessageFormat.
Set this to "true" to enforce MessageFormat for all messages,
expecting all message texts to be written with MessageFormat escaping.
For example, MessageFormat expects a single quote to be escaped
as "''". If your message texts are all written with such escaping,
even when not defining argument placeholders, you need to set this
flag to "true". Else, only message texts with actual arguments
are supposed to be written with MessageFormat escaping.
See Also:
MessageFormat/**
	 * Set whether to always apply the {@code MessageFormat} rules,
	 * parsing even messages without arguments.
	 * <p>Default is "false": Messages without arguments are by default
	 * returned as-is, without parsing them through MessageFormat.
	 * Set this to "true" to enforce MessageFormat for all messages,
	 * expecting all message texts to be written with MessageFormat escaping.
	 * <p>For example, MessageFormat expects a single quote to be escaped
	 * as "''". If your message texts are all written with such escaping,
	 * even when not defining argument placeholders, you need to set this
	 * flag to "true". Else, only message texts with actual arguments
	 * are supposed to be written with MessageFormat escaping.
	 * @see java.text.MessageFormat
	 */
	public void setAlwaysUseMessageFormat(boolean alwaysUseMessageFormat) {
		this.alwaysUseMessageFormat = alwaysUseMessageFormat;
	}

	
Return whether to always apply the MessageFormat rules, parsing even
messages without arguments.
/**
	 * Return whether to always apply the MessageFormat rules, parsing even
	 * messages without arguments.
	 */
	protected boolean isAlwaysUseMessageFormat() {
		return this.alwaysUseMessageFormat;
	}


	
Render the given default message String. The default message is
passed in as specified by the caller and can be rendered into
a fully formatted default message shown to the user.
The default implementation passes the String to formatMessage, resolving any argument placeholders found in them. Subclasses may override this method to plug in custom processing of default messages. 
Params:
defaultMessage – the passed-in default message String
args – array of arguments that will be filled in for params within the message, or null if none.
locale – the Locale used for formatting
See Also:
formatMessage(String, Object[], Locale)
Returns:
the rendered default message (with resolved arguments)/**
	 * Render the given default message String. The default message is
	 * passed in as specified by the caller and can be rendered into
	 * a fully formatted default message shown to the user.
	 * <p>The default implementation passes the String to {@code formatMessage},
	 * resolving any argument placeholders found in them. Subclasses may override
	 * this method to plug in custom processing of default messages.
	 * @param defaultMessage the passed-in default message String
	 * @param args array of arguments that will be filled in for params within
	 * the message, or {@code null} if none.
	 * @param locale the Locale used for formatting
	 * @return the rendered default message (with resolved arguments)
	 * @see #formatMessage(String, Object[], java.util.Locale)
	 */
	protected String renderDefaultMessage(String defaultMessage, @Nullable Object[] args, Locale locale) {
		return formatMessage(defaultMessage, args, locale);
	}

	
Format the given message String, using cached MessageFormats.
By default invoked for passed-in default messages, to resolve
any argument placeholders found in them.
Params:
msg – the message to format
args – array of arguments that will be filled in for params within the message, or null if none
locale – the Locale used for formatting
Returns:
the formatted message (with resolved arguments)/**
	 * Format the given message String, using cached MessageFormats.
	 * By default invoked for passed-in default messages, to resolve
	 * any argument placeholders found in them.
	 * @param msg the message to format
	 * @param args array of arguments that will be filled in for params within
	 * the message, or {@code null} if none
	 * @param locale the Locale used for formatting
	 * @return the formatted message (with resolved arguments)
	 */
	protected String formatMessage(String msg, @Nullable Object[] args, Locale locale) {
		if (!isAlwaysUseMessageFormat() && ObjectUtils.isEmpty(args)) {
			return msg;
		}
		MessageFormat messageFormat = null;
		synchronized (this.messageFormatsPerMessage) {
			Map<Locale, MessageFormat> messageFormatsPerLocale = this.messageFormatsPerMessage.get(msg);
			if (messageFormatsPerLocale != null) {
				messageFormat = messageFormatsPerLocale.get(locale);
			}
			else {
				messageFormatsPerLocale = new HashMap<>();
				this.messageFormatsPerMessage.put(msg, messageFormatsPerLocale);
			}
			if (messageFormat == null) {
				try {
					messageFormat = createMessageFormat(msg, locale);
				}
				catch (IllegalArgumentException ex) {
					// Invalid message format - probably not intended for formatting,
					// rather using a message structure with no arguments involved...
					if (isAlwaysUseMessageFormat()) {
						throw ex;
					}
					// Silently proceed with raw message if format not enforced...
					messageFormat = INVALID_MESSAGE_FORMAT;
				}
				messageFormatsPerLocale.put(locale, messageFormat);
			}
		}
		if (messageFormat == INVALID_MESSAGE_FORMAT) {
			return msg;
		}
		synchronized (messageFormat) {
			return messageFormat.format(resolveArguments(args, locale));
		}
	}

	
Create a MessageFormat for the given message and Locale.
Params:
msg – the message to create a MessageFormat for
locale – the Locale to create a MessageFormat for
Returns:
the MessageFormat instance/**
	 * Create a MessageFormat for the given message and Locale.
	 * @param msg the message to create a MessageFormat for
	 * @param locale the Locale to create a MessageFormat for
	 * @return the MessageFormat instance
	 */
	protected MessageFormat createMessageFormat(String msg, Locale locale) {
		return new MessageFormat(msg, locale);
	}

	
Template method for resolving argument objects.
The default implementation simply returns the given argument array as-is.
Can be overridden in subclasses in order to resolve special argument types.
Params:
args – the original argument array
locale – the Locale to resolve against
Returns:
the resolved argument array/**
	 * Template method for resolving argument objects.
	 * <p>The default implementation simply returns the given argument array as-is.
	 * Can be overridden in subclasses in order to resolve special argument types.
	 * @param args the original argument array
	 * @param locale the Locale to resolve against
	 * @return the resolved argument array
	 */
	protected Object[] resolveArguments(@Nullable Object[] args, Locale locale) {
		return (args != null ? args : new Object[0]);
	}

}