/**
 * Handles "checkOrder" and "paymentAviso" requests.
 * @param array $request payment parameters
 */
public function processRequest($request) {
    $this->log("Start " . $this->action);
    $this->log("Security type " . $this->settings->SECURITY_TYPE);
    if ($this->settings->SECURITY_TYPE == "MD5") {
        $this->log("Request: " . print_r($request, true));
        // If the MD5 checking fails, respond with "1" error code
        if (!$this->checkMD5($request)) {
            $response = $this->buildResponse($this->action, $request['invoiceId'], 1);
            $this->sendResponse($response);
        }
    } else if ($this->settings->SECURITY_TYPE == "PKCS7") {
        // Checking for a certificate sign. If the checking fails, respond with "200" error code.
        if (($request = $this->verifySign()) == null) {
            $response = $this->buildResponse($this->action, null, 200);
            $this->sendResponse($response);
        }
        $this->log("Request: " . print_r($request, true));
    }
    $response = null;
    if ($this->action == 'checkOrder') {
        $response = $this->checkOrder($request);
    } else {
        $response = $this->paymentAviso($request);
    }
    $this->sendResponse($response);
}

/**
 * Checking the MD5 sign.
 * @param  array $request payment parameters
 * @return bool true if MD5 hash is correct
 */
private function checkMD5($request) {
    $str = $request['action'] . ";" .
        $request['orderSumAmount'] . ";" . $request['orderSumCurrencyPaycash'] . ";" .
        $request['orderSumBankPaycash'] . ";" . $request['shopId'] . ";" .
        $request['invoiceId'] . ";" . $request['customerNumber'] . ";" . $this->settings->SHOP_PASSWORD;
    $this->log("String to md5: " . $str);
    $md5 = strtoupper(md5($str));
    if ($md5 != strtoupper($request['md5'])) {
        $this->log("Wait for md5:" . $md5 . ", recieved md5: " . $request['md5']);
        return false;
    }
    return true;
}

/**
 * Checking for sign when XML/PKCS#7 scheme is used.
 * @return array if request is successful, returns key-value array of request params, null otherwise.
 */
private function verifySign() {
    $descriptorspec = array(0 => array("pipe", "r"), 1 => array("pipe", "w"), 2 => array("pipe", "w"));
    $certificate = 'yookassa.pem';
    $process = proc_open('openssl smime -verify -inform PEM -nointern -certfile ' . $certificate . ' -CAfile ' . $certificate,
        $descriptorspec, $pipes);
    if (is_resource($process)) {
        // Getting data from request body.
        $data = file_get_contents($this->settings->request_source); // "php://input"
        fwrite($pipes[0], $data);
        fclose($pipes[0]);
        $content = stream_get_contents($pipes[1]);
        fclose($pipes[1]);
        $resCode = proc_close($process);
        if ($resCode != 0) {
            return null;
        } else {
            $this->log("Row xml: " . $content);
            $xml = simplexml_load_string($content);
            $array = json_decode(json_encode($xml), TRUE);
            return $array["@attributes"];
        }
    }
    return null;
}

/**
 * CheckOrder request processing. We suppose there are no item with price less
 * than 100 rubles in the shop.
 * @param  array $request payment parameters
 * @return string         prepared XML response
 */
private function checkOrder($request) {
    $response = null;
    if ($request['orderSumAmount'] < 100) {
        $response = $this->buildResponse($this->action, $request['invoiceId'], 100, "The amount should be more than 100 rubles.");
    } else {
        $response = $this->buildResponse($this->action, $request['invoiceId'], 0);
    }
    return $response;
}

/**
 * PaymentAviso request processing.
 * @param  array $request payment parameters
 * @return string prepared response in XML format
 */
private function paymentAviso($request) {
    return $this->buildResponse($this->action, $request['invoiceId'], 0);
}

/**
 * Building XML response.
 * @param  string $functionName  "checkOrder" or "paymentAviso" string
 * @param  string $invoiceId     transaction number
 * @param  string $result_code   result code
 * @param  string $message       error message. May be null.
 * @return string                prepared XML response
 */
private function buildResponse($functionName, $invoiceId, $result_code, $message = null) {
    try {
        $performedDatetime = Utils::formatDate(new DateTime());
        $response = '<?xml version="1.0" encoding="UTF-8"?><' . $functionName . 'Response performedDatetime="' . $performedDatetime .
            '" code="' . $result_code . '" ' . ($message != null ? 'message="' . $message . '"' : "") . ' invoiceId="' . $invoiceId . '" shopId="' . $this->settings->SHOP_ID . '"/>';
        return $response;
    } catch (\Exception $e) {
        $this->log($e);
    }
    return null;
}