/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements. See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.logging.log4j.core.pattern;

import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.message.MultiformatMessage;

/**
 * Returns the event's rendered message in a StringBuilder.
 */
@Plugin(name = "MessagePatternConverter", category = PatternConverter.CATEGORY)
@ConverterKeys({ "m", "msg", "message" })
public final class MessagePatternConverter extends LogEventPatternConverter {

    private final String[] formats;

    private final Configuration config;

    /**
     * Private constructor.
     * @param options options, may be null.
     */
    private MessagePatternConverter(final Configuration config, final String[] options) {
        super("Message", "message");
        formats = options;
        this.config = config;
    }

    /**
     * Obtains an instance of pattern converter.
     *
     * @param config The Configuration.
     * @param options options, may be null.
     * @return instance of pattern converter.
     */
    public static MessagePatternConverter newInstance(final Configuration config, final String[] options) {
        return new MessagePatternConverter(config, options);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void format(final LogEvent event, final StringBuilder toAppendTo) {
        final Message msg = event.getMessage();
        if (msg != null) {
            String result;
            if (msg instanceof MultiformatMessage) {
                result = ((MultiformatMessage) msg).getFormattedMessage(formats);
            } else {
                result = msg.getFormattedMessage();
            }
            if (result != null) {
                toAppendTo.append(config != null && result.contains("${") ?
                    config.getStrSubstitutor().replace(event, result) : result);
            } else {
                toAppendTo.append("null");
            }
        }
    }
}

@@ -1387,16 +1387,63 @@
 rter %7B%0A%0A
+    private static final String NULL = %22null%22;%0A
     priv
@@ -1470,17 +1470,16 @@
 ormats;%0A
-%0A
     priv
@@ -2316,106 +2316,54 @@
 nal 
-Message msg = event.getMessage();%0A        if (msg != null) %7B%0A            String result;%0A  
+String result = messageString(event);%0A
         
   if
@@ -2362,203 +2362,142 @@
     
-  
 if (
-msg instanceof MultiformatMessage) %7B%0A                result = ((MultiformatMessage) msg).getFormattedMessage(formats);%0A            %7D else %7B%0A                result = msg.getFormattedMessage(
+result == NULL) %7B%0A            toAppendTo.append(NULL);%0A        %7D else %7B%0A            toAppendTo.append(replaceParams(event, result)
 );%0A 
@@ -2507,82 +2507,110 @@
     
+%7D%0A
     %7D%0A
+%0A
     
-        if (result != null) %7B%0A                toAppendTo.append(
+private String replaceParams(final LogEvent event, final String result) %7B%0A        return 
 conf
@@ -2647,24 +2647,16 @@
 %22$%7B%22) ?%0A
-        
         
@@ -2721,79 +2721,421 @@
 sult
-)
 ;%0A    
+%7D%0A%0A
     
-    %7D else %7B%0A                toAppendTo.append(%22null%22);%0A    
+private String messageString(final LogEvent event) %7B%0A        return messageString(event.getMessage());%0A    %7D%0A%0A    private String messageString(final Message msg) %7B%0A        String result;%0A        if (msg instanceof MultiformatMessage) %7B%0A            result = ((MultiformatMessage) msg).getFormattedMessage(formats);%0A        %7D else %7B%0A            result = msg == null ? NULL : msg.getFormattedMessage();%0A
     
@@ -3144,22 +3144,35 @@
   %7D%0A        
-%7D
+return result;
 %0A    %7D%0A%7D%0A

refactor #format into small methods with single responsibility