import java.util.Map;

public class QRCodeGenerator {

    public static void main(String[] args) {
        String bankCode = "vietinbank";
        String bankAccount = "1013772070";
        String amount = "100000";
        String message = "Hello";
        Map<String, String> bankIdByCode = new HashMap<>();
        bankIdByCode.put("vcb", "970436");
        bankIdByCode.put("vietinbank", "970415");
        String bankId = bankIdByCode.get(bankCode);
        StringBuilder part12Builder = new StringBuilder()
            .append("00")
            .append(String.format("%02d", bankId.length()))
            .append(bankId)
            .append("01")
            .append(String.format("%02d", bankAccount.length()))
            .append(bankAccount);
        StringBuilder part11Builder = new StringBuilder()
            .append("0010A000000727")
            .append("01")
            .append(String.format("%02d", part12Builder.length()))
            .append(part12Builder)
            .append("0208QRIBFTTA");
        StringBuilder part1Builder = new StringBuilder()
            .append("38")
            .append(String.format("%02d", part11Builder.length()))
            .append(part11Builder);
        StringBuilder part21Builder = new StringBuilder()
            .append("08")
            .append(String.format("%02d", message.length()))
            .append(message);
        String part2 = new StringBuilder()
            .append("5303704")
            .append("54")
            .append(String.format("%02d", amount.length()))
            .append(amount)
            .append("5802VN")
            .append("62")
            .append(String.format("%02d", part21Builder.length()))
            .append(part21Builder)
            .toString();
        StringBuilder builder = new StringBuilder()
            .append("000201")
            .append("010212")
            .append(part1Builder)
            .append(part2)
            .append("6304");
        String qrcodeContent = builder
            .append(generateCheckSum(builder.toString()).toUpperCase())
            .toString();
        System.out.println(qrcodeContent);
    }

    private static String generateCheckSum(String text) {
        int crc = 0xFFFF;          // initial value
        int polynomial = 0x1021;   // 0001 0000 0010 0001  (0, 5, 12)
        byte[] bytes = text.getBytes();
        for (byte b : bytes) {
            for (int i = 0; i < 8; i++) {
                boolean bit = ((b   >> (7-i) & 1) == 1);
                boolean c15 = ((crc >> 15    & 1) == 1);
                crc <<= 1;
                if (c15 ^ bit) crc ^= polynomial;
            }
        }
        return Integer.toHexString(crc & 0xFFFF);
    }
}