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SDK to develop generators part of the Sixpack solution

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package dev.sixpack.client;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

import static java.nio.charset.StandardCharsets.UTF_8;

public class HmacHelper {

    public static Mac macFactory(String apiKey) {
        if (apiKey == null) {
            throw new IllegalArgumentException("The API Key provided is null");
        }
        if (apiKey.isEmpty()) {
            throw new IllegalArgumentException("The API Key provided is empty");
        }
        try {
            Mac mac = Mac.getInstance("HmacSHA256");
            mac.init(new SecretKeySpec(apiKey.getBytes(UTF_8), "HmacSHA256"));
            return mac;
        } catch (NoSuchAlgorithmException | InvalidKeyException e) {
            throw new RuntimeException("Failed to initialize HMAC-SHA256", e);
        }
    }

    private static final char[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();

    public static String bytesToHex(byte[] bytes) {
        char[] hexChars = new char[bytes.length * 2];
        for (int j = 0; j < bytes.length; j++) {
            int v = bytes[j] & 0xFF;
            hexChars[j * 2] = HEX_ARRAY[v >>> 4];
            hexChars[j * 2 + 1] = HEX_ARRAY[v & 0x0F];
        }
        return new String(hexChars);
    }
}