<?php
// Replace with your API Key
define("API_KEY", "dcf65ee699fe13eec2baaf06d1cfb6826e150a0d");

try {
    if (isset($_SERVER["HTTP_X_SG_SIGNATURE"])) {
        // Handling incoming SMS messages
        if (isset($_POST["messages"])) {
            $hash = base64_encode(hash_hmac('sha256', $_POST["messages"], API_KEY, true));
            if ($hash === $_SERVER["HTTP_X_SG_SIGNATURE"]) {
                $messages = json_decode($_POST["messages"], true);

                foreach ($messages as $message) {
                    // Check if message content is "hi" and respond
                    if (strtolower($message["message"]) === "hi") {
                        // You can respond using an API call here, for example:
                        // sendReply($message["number"], "Hello! How can I help you?");
                    }
                }
            } else {
                throw new Exception("Signature doesn't match!");
            }
        }
        // Handling USSD requests
        else if (isset($_POST["ussdRequest"])) {
            $hash = base64_encode(hash_hmac('sha256', $_POST["ussdRequest"], API_KEY, true));
            if ($hash === $_SERVER["HTTP_X_SG_SIGNATURE"]) {
                $ussdRequest = json_decode($_POST["ussdRequest"]);
                $deviceID = $ussdRequest->deviceID;
                $simSlot = $ussdRequest->simSlot;
                $request = $ussdRequest->request;
                $response = $ussdRequest->response;

                // Perform actions based on USSD data
            } else {
                throw new Exception("Signature doesn't match!");
            }
        }
    } else {
        http_response_code(400);
        error_log("Signature not found!");
    }
} catch (Exception $e) {
    http_response_code(401);
    error_log($e->getMessage());
}
?>