/*
 * 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.jackrabbit.util;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Implements the encode and decode routines as specified for XML name to SQL
 * identifier conversion in ISO 9075-14:2003.<br>
 * If a character <code>c</code> is not valid at a certain position in an XML 1.0
 * NCName it is encoded in the form: '_x' + hexValueOf(c) + '_'.
 */
public class ISO9075 {

    /** Hidden constructor. */
    private ISO9075() { }

    /** Pattern on an encoded character */
    private static final Pattern ENCODE_PATTERN = Pattern.compile("_x\\p{XDigit}{4}_");

    /** Padding characters */
    private static final char[] PADDING = new char[] {'0', '0', '0'};

    /** All the possible hex digits */
    private static final String HEX_DIGITS = "0123456789abcdefABCDEF";

    /**
     * Encodes <code>name</code> as specified in ISO 9075.
     * @param name the <code>String</code> to encode.
     * @return the encoded <code>String</code> or <code>name</code> if it does
     *   not need encoding.
     */
    public static String encode(String name) {
        // quick check for root node name
        if (name.length() == 0) {
            return name;
        }
        if (XMLChar.isValidName(name) && name.indexOf("_x") < 0) {
            // already valid
            return name;
        } else {
            // encode
            StringBuffer encoded = new StringBuffer();
            for (int i = 0; i < name.length(); i++) {
                if (i == 0) {
                    // first character of name
                    if (XMLChar.isNameStart(name.charAt(i))) {
                        if (needsEscaping(name, i)) {
                            // '_x' must be encoded
                            encode('_', encoded);
                        } else {
                            encoded.append(name.charAt(i));
                        }
                    } else {
                        // not valid as first character -> encode
                        encode(name.charAt(i), encoded);
                    }
                } else if (!XMLChar.isName(name.charAt(i))) {
                    encode(name.charAt(i), encoded);
                } else {
                    if (needsEscaping(name, i)) {
                        // '_x' must be encoded
                        encode('_', encoded);
                    } else {
                        encoded.append(name.charAt(i));
                    }
                }
            }
            return encoded.toString();
        }
    }

    /**
     * Encodes <code>path</code> as specified in ISO 9075. Please note that
     * the character '<code>[</code>' is not encoded but rather interpreted as
     * the start of an index in a path segment.
     *
     * @param path the <code>String</code> to encode.
     * @return the encoded <code>String</code>.
     */
    public static String encodePath(String path) {
        String[] names = Text.explode(path, '/', true);
        StringBuffer encoded = new StringBuffer(path.length());
        for (int i = 0; i < names.length; i++) {
            // detect index
            String index = null;
            int idx = names[i].indexOf('[');
            if (idx != -1) {
                index = names[i].substring(idx);
                names[i] = names[i].substring(0, idx);
            }
            encoded.append(encode(names[i]));
            if (index != null) {
                encoded.append(index);
            }
            if (i < names.length - 1) {
                encoded.append('/');
            }
        }
        return encoded.toString();
    }

    /**
     * Decodes the <code>name</code>.
     * @param name the <code>String</code> to decode.
     * @return the decoded <code>String</code>.
     */
    public static String decode(String name) {
        // quick check
        if (name.indexOf("_x") < 0) {
            // not encoded
            return name;
        }
        StringBuffer decoded = new StringBuffer();
        Matcher m = ENCODE_PATTERN.matcher(name);
        while (m.find()) {
            char ch = (char) Integer.parseInt(m.group().substring(2, 6), 16);
            if (ch == '$' || ch == '\\') {
                m.appendReplacement(decoded, "\\" + ch);
            } else {
                m.appendReplacement(decoded, Character.toString(ch));
            }
        }
        m.appendTail(decoded);
        return decoded.toString();
    }

    //-------------------------< internal >-------------------------------------

    /**
     * Encodes the character <code>c</code> as a String in the following form:
     * <code>"_x" + hex value of c + "_"</code>. Where the hex value has
     * four digits if the character with possibly leading zeros.
     * <p>
     * Example: ' ' (the space character) is encoded to: _x0020_
     * @param c the character to encode
     * @param b the encoded character is appended to <code>StringBuffer</code>
     *  <code>b</code>.
     */
    private static void encode(char c, StringBuffer b) {
        b.append("_x");
        String hex = Integer.toHexString(c);
        b.append(PADDING, 0, 4 - hex.length());
        b.append(hex);
        b.append("_");
    }

    /**
     * Returns true if <code>name.charAt(location)</code> is the underscore
     * character and the following character sequence is 'xHHHH_' where H
     * is a hex digit.
     * @param name the name to check.
     * @param location the location to look at.
     * @throws ArrayIndexOutOfBoundsException if location > name.length()
     */
    private static boolean needsEscaping(String name, int location)
            throws ArrayIndexOutOfBoundsException {
        if (name.charAt(location) == '_' && name.length() >= location + 6) {
            return name.charAt(location + 1) == 'x'
                && HEX_DIGITS.indexOf(name.charAt(location + 2)) != -1
                && HEX_DIGITS.indexOf(name.charAt(location + 3)) != -1
                && HEX_DIGITS.indexOf(name.charAt(location + 4)) != -1
                && HEX_DIGITS.indexOf(name.charAt(location + 5)) != -1;
        } else {
            return false;
        }
    }
}
