import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.util.Base64;

public class SignatureGenerator {
    private static String bytesToHex(byte[] bytes) {
        StringBuilder sb = new StringBuilder();
        for (byte b : bytes) sb.append(String.format("%02x", b));
        return sb.toString();
    }

    public static String generateSignature(String date, String tokenSecret) throws Exception {
        MessageDigest sha256 = MessageDigest.getInstance("SHA-256");
        String fullHash = bytesToHex(sha256.digest(tokenSecret.getBytes(StandardCharsets.UTF_8)));
        String key = fullHash.substring(0, 32);
        sha256.reset();
        String iv = bytesToHex(sha256.digest(fullHash.getBytes(StandardCharsets.UTF_8))).substring(0, 16);

        Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE,
                new SecretKeySpec(key.getBytes(StandardCharsets.UTF_8), "AES"),
                new IvParameterSpec(iv.getBytes(StandardCharsets.UTF_8)));
        byte[] encrypted = cipher.doFinal(date.getBytes(StandardCharsets.UTF_8));

        return Base64.getEncoder().encodeToString(encrypted);
    }
}