/*
 *  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.tomcat.util.buf;

import org.apache.tomcat.util.res.StringManager;

/**
 * Tables useful when converting byte arrays to and from strings of hexadecimal digits. Code from Ajp11, from Apache's
 * JServ.
 */
public final class HexUtils {

    /**
     * Private constructor to prevent instantiation.
     */
    private HexUtils() {
    }

    private static final StringManager sm = StringManager.getManager(HexUtils.class);

    // -------------------------------------------------------------- Constants

    /**
     * Table for HEX to DEC byte translation.
     */
    private static final int[] DEC = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, -1, -1, -1, -1, -1, -1, -1, 10, 11, 12, 13, 14, 15,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 10,
            11, 12, 13, 14, 15, };


    /**
     * Table for DEC to HEX byte translation.
     */
    private static final byte[] HEX =
            { (byte) '0', (byte) '1', (byte) '2', (byte) '3', (byte) '4', (byte) '5', (byte) '6', (byte) '7',
                    (byte) '8', (byte) '9', (byte) 'a', (byte) 'b', (byte) 'c', (byte) 'd', (byte) 'e', (byte) 'f' };


    /**
     * Table for byte to hex string translation.
     */
    private static final char[] hex = "0123456789abcdef".toCharArray();


    // --------------------------------------------------------- Static Methods

    /**
     * Get the decimal value of the character at the given index.
     *
     * @param index the character index
     *
     * @return the decimal value, or -1 if the character is not a valid hex digit
     */
    public static int getDec(int index) {
        // Fast for correct values, slower for incorrect ones
        try {
            return DEC[index - '0'];
        } catch (ArrayIndexOutOfBoundsException ex) {
            return -1;
        }
    }


    /**
     * Get the hexadecimal byte for the given index.
     *
     * @param index the index into the hex table
     *
     * @return the hexadecimal byte
     */
    public static byte getHex(int index) {
        return HEX[index];
    }


    /**
     * Convert a character to a hexadecimal string representation.
     *
     * @param c the character to convert
     *
     * @return the hexadecimal string representation of the character
     */
    public static String toHexString(char c) {
        // 2 bytes / 4 hex digits
        StringBuilder sb = new StringBuilder(4);

        sb.append(hex[(c & 0xf000) >> 12]);
        sb.append(hex[(c & 0x0f00) >> 8]);

        sb.append(hex[(c & 0xf0) >> 4]);
        sb.append(hex[(c & 0x0f)]);

        return sb.toString();
    }


    /**
     * Convert a byte array to a hexadecimal string representation.
     *
     * @param bytes the byte array to convert
     *
     * @return the hexadecimal string, or {@code null} if the input is {@code null}
     */
    public static String toHexString(byte[] bytes) {
        if (null == bytes) {
            return null;
        }

        StringBuilder sb = new StringBuilder(bytes.length << 1);

        for (byte aByte : bytes) {
            sb.append(hex[(aByte & 0xf0) >> 4]).append(hex[(aByte & 0x0f)]);
        }

        return sb.toString();
    }


    /**
     * Convert a hexadecimal string to a byte array.
     *
     * @param input the hexadecimal string to convert
     *
     * @return the byte array, or {@code null} if the input is {@code null}
     *
     * @throws IllegalArgumentException if the input has an odd number of characters
     *                                  or contains non-hexadecimal characters
     */
    public static byte[] fromHexString(String input) {
        if (input == null) {
            return null;
        }

        if ((input.length() & 1) == 1) {
            // Odd number of characters
            throw new IllegalArgumentException(sm.getString("hexUtils.fromHex.oddDigits"));
        }

        char[] inputChars = input.toCharArray();
        byte[] result = new byte[input.length() >> 1];
        for (int i = 0; i < result.length; i++) {
            int upperNibble = getDec(inputChars[2 * i]);
            int lowerNibble = getDec(inputChars[2 * i + 1]);
            if (upperNibble < 0 || lowerNibble < 0) {
                // Non-hex character
                throw new IllegalArgumentException(sm.getString("hexUtils.fromHex.nonHex"));
            }
            result[i] = (byte) ((upperNibble << 4) + lowerNibble);
        }
        return result;
    }
}
