/*
 * Copyright 2024-2025 OmniOne.
 *
 * Licensed 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.omnione.did.sdk.utility.Encodings;

/**
 * Utilities for going to and from ASCII-HEX representation.
 */
public class Base16 {

	/**
	 * Encodes an array of bytes as hex symbols.
	 * @param bytes the array of bytes to encode
	 * @return the resulting hex string
	 */
	public static String toHex(byte[] bytes) {
		return toHex(bytes, null);
	}

	/**
	 * Encodes an array of bytes as hex symbols.
	 * @param bytes the array of bytes to encode
	 * @param separator the separator to use between two bytes, can be null
	 * @return the resulting hex string
	 */
	public static String toHex(byte[] bytes, String separator) {
		return toHex(bytes, 0, bytes.length, separator);
	}

	/**
	 * Encodes an array of bytes as hex symbols.
	 * @param bytes the array of bytes to encode
	 * @param offset the start offset in the array of bytes
	 * @param length the number of bytes to encode
	 * @return the resulting hex string
	 */
	public static String toHex(byte[] bytes, int offset, int length) {
		return toHex(bytes, offset, length, null);
	}

	/**
	 * Encodes a single byte to hex symbols.
	 * @param b the byte to encode
	 * @return the resulting hex string
	 */
	public static String toHex(byte b) {
		StringBuilder sb = new StringBuilder();
		appendByteAsHex(sb, b);
		return sb.toString();
	}

	/**
	 * Encodes an array of bytes as hex symbols.
	 * @param bytes the array of bytes to encode
	 * @param offset the start offset in the array of bytes
	 * @param length the number of bytes to encode
	 * @param separator the separator to use between two bytes, can be null
	 * @return the resulting hex string
	 */
	public static String toHex(byte[] bytes, int offset, int length, String separator) {
		StringBuilder result = new StringBuilder();
		for (int i = 0; i < length; i++) {
			int unsignedByte = bytes[i + offset] & 0xff;

			if (unsignedByte < 16) {
				result.append("0");
			}

			result.append(Integer.toHexString(unsignedByte));
			if (separator != null && i + 1 < length) {
				result.append(separator);
			}
		}
		return result.toString();
	}

	/**
	 * Get the byte representation of an ASCII-HEX string.
	 * @param hexString The string to convert to bytes
	 * @return The byte representation of the ASCII-HEX string.
	 */
	public static byte[] toBytes(String hexString) {
		if (hexString == null || hexString.length() % 2 != 0) {
			throw new RuntimeException(
					"Input string must contain an even number of characters");
		}
		char[] hex = hexString.toCharArray();
		int length = hex.length / 2;
		byte[] raw = new byte[length];
		for (int i = 0; i < length; i++) {
			int high = Character.digit(hex[i * 2], 16);
			int low = Character.digit(hex[i * 2 + 1], 16);
			if (high < 0 || low < 0) {
				throw new RuntimeException(
						"Invalid hex digit " + hex[i * 2] + hex[i * 2 + 1]);
			}
			int value = (high << 4) | low;
			if (value > 127)
				value -= 256;
			raw[i] = (byte) value;
		}
		return raw;
	}

	public static byte[] toBytesReversed(String hexString) {
		byte[] rawBytes = toBytes(hexString);

		for (int i = 0; i < rawBytes.length / 2; i++) {
			byte temp = rawBytes[rawBytes.length - i - 1];
			rawBytes[rawBytes.length - i - 1] = rawBytes[i];
			rawBytes[i] = temp;
		}

		return rawBytes;
	}

	public static void appendByteAsHex(StringBuilder sb, byte b) {
		int unsignedByte = b & 0xFF;
		if (unsignedByte < 16) {
			sb.append("0");
		}
		sb.append(Integer.toHexString(unsignedByte));
	}

}
