package home;

public class Checksum {
	/**Êä³öУÑéÂë*/
	public static String calculateChecksum(String input) {		
		if (input == null) {// ¼ì²éÊäÈëÊÇ·ñΪ¿Õ
			throw new IllegalArgumentException("ÊäÈë²»ÄÜΪnull");
		}
		String cleanInput = input.replaceAll("\\s", "");// ÒƳýËùÓпոñ

		// ÑéÖ¤´¦ÀíºóµÄ×Ö·û´®
		if (cleanInput.length() < 8 || !cleanInput.startsWith("55AA")) {
			throw new IllegalArgumentException("ÊäÈë×Ö·û´®±ØÐëÒÔ55AA¿ªÍ·ÇÒ³¤¶ÈÖÁÉÙΪ8£¨È¥³ý¿Õ¸ñºó£©");
		}
		// È¥µô°üÍ·(55AA)ºÍ×îºó4¸ö×Ö·û
		String dataPart = cleanInput.substring(4, cleanInput.length() - 4);

		// ¼ì²éÖм䲿·Ö³¤¶ÈÊÇ·ñΪżÊý
		if (dataPart.length() % 2 != 0) {
			throw new IllegalArgumentException("Öм䲿·Ö³¤¶È±ØÐëÊÇżÊý£¨È¥³ý¿Õ¸ñºó£©");
		}

		int sum = 0;
		// ÿÁ½¸ö×Ö·û½âÎöΪһ¸ö×Ö½Ú
		for (int i = 0; i < dataPart.length(); i += 2) {
			String byteStr = dataPart.substring(i, i + 2);
			int byteValue = Integer.parseInt(byteStr, 16);
			sum = (sum + byteValue) & 0xFFFF; // ±£³Ö16λ·¶Î§
		}

		// È¡·´²¢±£³Ö16λ
		int checksum = (~sum) & 0xFFFF;

		// ÏÔʽ´¦Àí¸ßλÔÚÇ°¸ñʽ
		int  lowByte= (checksum >>> 8) & 0xFF;  // ¸ß8λ
		int  highByte= checksum & 0xFF;           // µÍ8λ

		// ¸ñʽ»¯Îª4λʮÁù½øÖÆ×Ö·û´®£¨´óд£©£¬¸ßλÔÚÇ°
		
		return String.format("%02X%02X", highByte, lowByte);
	}
	
//	public static void main(String args[]) {
//		String input="55AA03070204020320FFFF";
//		calculateChecksum(input);
//	}
}