/*
 * Copyright 2013-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file 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 com.amazonaws.util;

/**
 * A Base 16 codec implementation.
 *
 * @author Hanson Char
 */
class Base16Codec implements Codec {
    private static final int OFFSET_OF_a = 'a' - 10;
    private static final int OFFSET_OF_A = 'A' - 10;
    private static final int MASK_4BITS = (1 << 4) - 1;

    private static class LazyHolder {
        private static final byte[] DECODED = decodeTable();

        private static byte[] decodeTable() {
            final byte[] dest = new byte['f' + 1];

            for (int i = 0; i <= 'f'; i++)
            {
                if (i >= '0' && i <= '9')
                    dest[i] = (byte) (i - '0');
                else if (i >= 'A' && i <= 'F')
                    dest[i] = (byte) (i - OFFSET_OF_A);
                else if (i >= 'a' && i <= 'f')
                    dest[i] = (byte) (i - OFFSET_OF_a);
                else
                    dest[i] = -1;
            }
            return dest;
        }
    }

    private final byte[] ALPAHBETS = CodecUtils.toBytesDirect("0123456789ABCDEF");

    @Override
    public byte[] encode(byte[] src) {
        byte[] dest = new byte[src.length * 2];
        byte p;

        for (int i = 0, j = 0; i < src.length; i++) {
            dest[j++] = ALPAHBETS[(p = src[i]) >>> 4 & MASK_4BITS];
            dest[j++] = ALPAHBETS[p & MASK_4BITS];
        }
        return dest;
    }

    @Override
    public byte[] decode(byte[] src, final int length)
    {
        if (length % 2 != 0) {
            throw new IllegalArgumentException(
                    "Input is expected to be encoded in multiple of 2 bytes but found: "
                            + length);
        }
        final byte[] dest = new byte[length / 2];

        for (int i = 0, j = 0; j < dest.length; j++)
        {
            dest[j] = (byte)
                    (
                    pos(src[i++]) << 4 | pos(src[i++])
                    );

        }
        return dest;
    }

    protected int pos(byte in) {
        int pos = LazyHolder.DECODED[in];

        if (pos > -1)
            return pos;
        throw new IllegalArgumentException("Invalid base 16 character: \'" + (char) in + "\'");
    }
}