//Java validation code
import jakarta.servlet.http.HttpServletRequest;
import lombok.RequiredArgsConstructor;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.crypto.Mac;
import javax.crypto.spec.SecretKeySpec;
import java.io.BufferedReader;
import java.io.IOtException;
import java.io.InputStreamReader;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.util.Base64;
import java.util.stream.Collectors;

@RestController("/webhook/v1")
@RequiredArgsConstructor
public class WebhookController {
  @PostMapping("")
  public Object postWebhook(HttpServletRequest request) throws NoSuchAlgorithmException, InvalidKeyException {

    // Step 1: Signature extraction in HTTPservletRequest
    String signature = request.getHeader("eximbay-webhook-signature");

    // Issued secretkey
    String secretKey = "secretkey";

    // Step 2: requestData extraction
    String requestData = "";
    try (BufferedReader
    reader = new BufferedReader(new InputStreamReader(request.getInputStream()))) {
      requestData = reader.lines().collect(Collectors.joining(System.lineSeparator()));
    } catch (IOException e) {
      e.printStackTrace();
    }

    // Step 3: The provided HMAC signature validation code.
    Mac sha512_HMAC = Mac.getInstance("HmacSHA256");
    SecretKeySpec secret_key = new
    SecretKeySpec(secretKey.getBytes(), "HmacSHA256");
    sha512_HMAC.init(secret_key);
    byte[] hash = sha512_HMAC.doFinal(requestData.getBytes());
    String calculatedSignature = Base64.getEncoder().encodeToString(hash);

    //Step 4: After signature validation return a response
    if (signature.equals(calculatedSignature)) {

      // Signature has been verified.
      System.out.println("The signature has been verified. Proceed with sending the response.");

      // Processing code
      // ...
      return "{\"rescode\":\"0000\", \"resmsg\":\"Success\"}";
    } else {
      // Signature mismatch
      System.out.println("Signature mismatch.");

      // Processing code applied in the event of a signature mismatch.
      // ...
      return "{\"rescode\":\"XXXX\", \"resmsg\":\"signature_fail\"}";
    }
  }
}