/*
 * 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
 *
 *      https://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.team_hermes.wireshare.util;

/**
 * Converts hexadecimal Strings.
 */
public final class Hex {
    /**
     * Used to build output as Hex
     */
    private static final char[] DIGITS_LOWER =
            {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f'};
    /**
     * Used to build output as Hex
     */
    private static final char[] DIGITS_UPPER =
            {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
    private Hex() {
    }

    /**
     * Converts an array of characters representing hexadecimal values into an array of bytes of those same values. The
     * returned array will be half the length of the passed array, as it takes two characters to represent any given
     * byte. An exception is thrown if the passed char array has an odd number of elements.
     *
     * @param data An array of characters containing hexadecimal digits
     * @return A byte array containing binary data decoded from the supplied char array.
     */
    public static byte[] decode(final char[] data) {
        final int len = data.length;
        final byte[] out = new byte[len >> 1];
        // two characters form the hex value.
        for (int i = 0, j = 0; j < len; i++) {
            int f = toDigit(data[j], j) << 4;
            j++;
            f = f | toDigit(data[j], j);
            j++;
            out[i] = (byte) (f & 0xFF);
        }
        return out;
    }

    public static byte[] decode(String data) {
        return decode(data.toCharArray());
    }

    /**
     * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
     * The returned array will be double the length of the passed array, as it takes two characters to represent any
     * given byte.
     *
     * @param data a byte[] to convert to Hex characters
     * @return A char[] containing hexadecimal characters
     */
    public static String encode(final byte[] data) {
        return new String(encode(data, true));
    }

    /**
     * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
     * The returned array will be double the length of the passed array, as it takes two characters to represent any
     * given byte.
     *
     * @param data        a byte[] to convert to Hex characters
     * @param toLowerCase <code>true</code> converts to lowercase, <code>false</code> to uppercase
     * @return A char[] containing hexadecimal characters
     * @since 1.4
     */
    public static char[] encode(final byte[] data, final boolean toLowerCase) {
        return encode(data, toLowerCase ? DIGITS_LOWER : DIGITS_UPPER);
    }

    /**
     * Converts an array of bytes into an array of characters representing the hexadecimal values of each byte in order.
     * The returned array will be double the length of the passed array, as it takes two characters to represent any
     * given byte.
     *
     * @param data     a byte[] to convert to Hex characters
     * @param toDigits the output alphabet
     * @return A char[] containing hexadecimal characters
     * @since 1.4
     */
    private static char[] encode(final byte[] data, final char[] toDigits) {
        final int l = data.length;
        final char[] out = new char[l << 1];
        // two characters form the hex value.
        for (int i = 0, j = 0; i < l; i++) {
            out[j++] = toDigits[(0xF0 & data[i]) >>> 4];
            out[j++] = toDigits[0x0F & data[i]];
        }
        return out;
    }

    /**
     * Converts a hexadecimal character to an integer.
     *
     * @param ch    A character to convert to an integer digit
     * @param index The index of the character in the source
     * @return An integer
     */
    private static int toDigit(final char ch, final int index) {
        final int digit = Character.digit(ch, 16);
        if (digit == -1) {
            throw new IllegalArgumentException("Illegal hexadecimal character " + ch + " at index " + index);
        }
        return digit;
    }
}
