package com.jn.langx.codec;


import com.jn.langx.util.io.Charsets;

import java.nio.charset.Charset;

/**
 * Converts hexadecimal Strings. The charset used for certain operation can be set, the default is set in
 * {@link #DEFAULT_CHARSET_NAME}
 * <p>
 * This class is thread-safe.
 */
public class Hex implements BinaryEncoder, BinaryDecoder {

    public static final Charset DEFAULT_CHARSET = Charsets.UTF_8;
    public static final String DEFAULT_CHARSET_NAME = "UTF-8";

    /**
     * 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'};

    /**
     * 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.
     * @throws DecoderException Thrown if an odd number or illegal of characters is supplied
     */
    public static byte[] decodeHex(final char[] data) throws DecoderException {

        final int len = data.length;

        if ((len & 0x01) != 0) {
            throw new DecoderException("Odd number of characters.");
        }

        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;
    }

    /**
     * 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 char[] encodeHex(final byte[] data) {
        return encodeHex(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
     */
    public static char[] encodeHex(final byte[] data, final boolean toLowerCase) {
        return encodeHex(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
     */
    protected static char[] encodeHex(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 an array of bytes into a String representing the hexadecimal values of each byte in order. The returned
     * String 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 String containing hexadecimal characters
     * @since 1.4
     */
    public static String encodeHexString(final byte[] data) {
        return new String(encodeHex(data));
    }

    /**
     * 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
     * @throws DecoderException Thrown if ch is an illegal hex character
     */
    protected static int toDigit(final char ch, final int index) throws DecoderException {
        final int digit = Character.digit(ch, 16);
        if (digit == -1) {
            throw new DecoderException("Illegal hexadecimal character " + ch + " at index " + index);
        }
        return digit;
    }

    private final Charset charset;

    /**
     * Creates a new codec with the default charset name {@link #DEFAULT_CHARSET}
     */
    public Hex() {
        // use default encoding
        this.charset = DEFAULT_CHARSET;
    }

    /**
     * Creates a new codec with the given Charset.
     *
     * @param charset the charset.
     * @since 1.7
     */
    public Hex(final Charset charset) {
        this.charset = charset;
    }

    /**
     * Creates a new codec with the given charset name.
     *
     * @param charsetName the charset name.
     * @throws java.nio.charset.UnsupportedCharsetException If the named charset is unavailable
     * @since 1.4
     * @since 1.7 throws UnsupportedCharsetException if the named charset is unavailable
     */
    public Hex(final String charsetName) {
        this(Charset.forName(charsetName));
    }

    /**
     * Converts an array of character bytes 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 array An array of character bytes containing hexadecimal digits
     * @return A byte array containing binary data decoded from the supplied byte array (representing characters).
     * @throws DecoderException Thrown if an odd number of characters is supplied to this function
     * @see #decodeHex(char[])
     */
    @Override
    public byte[] decode(final byte[] array) throws DecoderException {
        return decodeHex(new String(array, getCharset()).toCharArray());
    }

    /**
     * Converts a String or an array of character bytes representing hexadecimal values into an array of bytes of those
     * same values. The returned array will be half the length of the passed String or 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 object A String or, an array of character bytes containing hexadecimal digits
     * @return A byte array containing binary data decoded from the supplied byte array (representing characters).
     * @throws DecoderException Thrown if an odd number of characters is supplied to this function or the object is not a String or
     *                          char[]
     * @see #decodeHex(char[])
     */
    @Override
    public Object decode(final Object object) throws DecoderException {
        try {
            final char[] charArray = object instanceof String ? ((String) object).toCharArray() : (char[]) object;
            return decodeHex(charArray);
        } catch (final ClassCastException e) {
            throw new DecoderException(e.getMessage(), e);
        }
    }

    /**
     * Converts an array of bytes into an array of bytes for the 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.
     * <p>
     * The conversion from hexadecimal characters to the returned bytes is performed with the charset named by
     * {@link #getCharset()}.
     * </p>
     *
     * @param array a byte[] to convert to Hex characters
     * @return A byte[] containing the bytes of the hexadecimal characters
     * @see #encodeHex(byte[])
     * @since 1.7 No longer throws IllegalStateException if the charsetName is invalid.
     */
    @Override
    public byte[] encode(final byte[] array) {
        return encodeHexString(array).getBytes(this.getCharset());
    }

    /**
     * Converts a String or 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 String or array, as it takes two
     * characters to represent any given byte.
     * <p>
     * The conversion from hexadecimal characters to bytes to be encoded to performed with the charset named by
     * {@link #getCharset()}.
     * </p>
     *
     * @param object a String, or byte[] to convert to Hex characters
     * @return A char[] containing hexadecimal characters
     * @throws EncoderException Thrown if the given object is not a String or byte[]
     * @see #encodeHex(byte[])
     */
    @Override
    public Object encode(final Object object) throws EncoderException {
        try {
            final byte[] byteArray = object instanceof String ?
                    ((String) object).getBytes(this.getCharset()) : (byte[]) object;
            return encodeHex(byteArray);
        } catch (final ClassCastException e) {
            throw new EncoderException(e.getMessage(), e);
        }
    }

    /**
     * Gets the charset.
     *
     * @return the charset.
     * @since 1.7
     */
    public Charset getCharset() {
        return this.charset;
    }

    /**
     * Gets the charset name.
     *
     * @return the charset name.
     * @since 1.4
     */
    public String getCharsetName() {
        return this.charset.name();
    }

    /**
     * Returns a string representation of the object, which includes the charset name.
     *
     * @return a string representation of the object.
     */
    @Override
    public String toString() {
        return super.toString() + "[charsetName=" + this.charset + "]";
    }
}
