/*
 * 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.struts2.util;

import java.util.regex.Pattern;

/**
 * Helper class to convert wildcard expression to regular expression
 */
public class WildcardUtil {

    /**
     * Convert wildcard pattern to Pattern
     * @param pattern String containing wildcard pattern
     * @return compiled regular expression as a Pattern
     */
    public static Pattern compileWildcardPattern(String pattern) {
        StringBuilder buf = new StringBuilder(pattern);

        for (int i=buf.length()-1; i>=0; i--)
        {
            char c = buf.charAt(i);
            if (c == '*' && (i == 0 || buf.charAt(i-1) != '\\'))
            {
                buf.insert(i+1, '?');
                buf.insert(i, '.');
            }
            else if (c == '*')
            {
                i--;	// skip backslash, too
            }
            else if (needsBackslashToBeLiteralInRegex(c))
            {
                buf.insert(i, '\\');
            }
        }

        return Pattern.compile(buf.toString());
    }

    /**
     * @param c character to test
     * @return true if the given character must be escaped to be a literal
     * inside a regular expression.
     */

    private static final String theSpecialRegexCharList = ".[]\\?*+{}|()^$";

    public static boolean needsBackslashToBeLiteralInRegex(
        char c)
    {
        return (theSpecialRegexCharList.indexOf(c) >= 0);
    }

}
