/*
 * 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.log4j.helpers;

/**
 * Utility class for transforming strings.
 * 
 * @author Ceki G&uuml;lc&uuml;
 * @author Michael A. McAngus
 */
public class Transform {

    private static final String CDATA_START = "<![CDATA[";
    private static final String CDATA_END = "]]>";
    private static final String CDATA_PSEUDO_END = "]]&gt;";
    private static final String CDATA_EMBEDED_END = CDATA_END + CDATA_PSEUDO_END + CDATA_START;
    private static final int CDATA_END_LEN = CDATA_END.length();

    /**
     * This method takes a string which may contain HTML tags (ie, &lt;b&gt;,
     * &lt;table&gt;, etc) and replaces any '&lt;', '&gt;' , '&amp;' or '"'
     * characters with respective predefined entity references.
     *
     * @param input The text to be converted.
     * @return The input string with the special characters replaced.
     */
    static public String escapeTags(final String input) {
	// Check if the string is null, zero length or devoid of special characters
	// if so, return what was sent in.

	if (input == null || input.length() == 0 || (input.indexOf('"') == -1 && input.indexOf('&') == -1
		&& input.indexOf('<') == -1 && input.indexOf('>') == -1)) {
	    return input;
	}

	// Use a StringBuilder in lieu of String concatenation -- it is
	// much more efficient this way.

	StringBuilder buf = new StringBuilder(input.length() + 6);
	char ch = ' ';

	int len = input.length();
	for (int i = 0; i < len; i++) {
	    ch = input.charAt(i);
	    if (ch > '>') {
		buf.append(ch);
	    } else if (ch == '<') {
		buf.append("&lt;");
	    } else if (ch == '>') {
		buf.append("&gt;");
	    } else if (ch == '&') {
		buf.append("&amp;");
	    } else if (ch == '"') {
		buf.append("&quot;");
	    } else {
		buf.append(ch);
	    }
	}
	return buf.toString();
    }

    /**
     * Ensures that embeded CDEnd strings (]]&gt;) are handled properly within
     * message, NDC and throwable tag text.
     *
     * @param buf StringBuffer holding the XML data to this point. The initial
     *            CDStart (&lt;![CDATA[) and final CDEnd (]]&gt;) of the CDATA
     *            section are the responsibility of the calling method.
     * @param str The String that is inserted into an existing CDATA Section within
     *            buf.
     */
    static public void appendEscapingCDATA(final StringBuffer buf, final String str) {
	if (str != null) {
	    int end = str.indexOf(CDATA_END);
	    if (end < 0) {
		buf.append(str);
	    } else {
		int start = 0;
		while (end > -1) {
		    buf.append(str.substring(start, end));
		    buf.append(CDATA_EMBEDED_END);
		    start = end + CDATA_END_LEN;
		    if (start < str.length()) {
			end = str.indexOf(CDATA_END, start);
		    } else {
			return;
		    }
		}
		buf.append(str.substring(start));
	    }
	}
    }
}
