How to integration CCAvenue in codeigniter 3

public function initiate_payment() {
    $data = array(
        'merchant_id' => 'your_merchant_id',
        'order_id' => 'your_unique_order_id',
        'amount' => 'the_order_amount',
        'redirect_url' => 'your_callback_url',
        'cancel_url' => 'your_cancel_url',
        'language' => 'EN',
    );
    
    // Encrypt the form data using the CCAvenue API
    // ...
    
    // Redirect the customer to the CCAvenue payment page
    // ...
}

// Step 5: Encrypt the form data using the CCAvenue API
$encrypted_data = $this->ccavenue->encrypt($data);

// Step 6: Redirect the customer to the CCAvenue payment page
$this->load->view('ccavenue_payment', array('encrypted_data' => $encrypted_data));

// Step 7: Implement a callback function to receive and process the response from CCAvenue
public function callback() {
    // Decrypt the response from CCAvenue
    $response = $this->ccavenue->decrypt($_POST['encResp']);
    
    // Verify the authenticity of the response
    if ($this->ccavenue->verify($response)) {
        // Update the order status
        $status = $response['order_status'];
        $order_id = $response['order_id'];
        // ...
    } else {
        // Handle the error
        // ...
    }
}

class Ccavenue {
    private $working_key;
    private $access_code;
    
    public function __construct($params = array()) {
        $this->working_key = $params['working_key'];
        $this->access_code = $params['access_code'];
    }
    
    public function encrypt($plaintext) {
        $key = $this->working_key;
        $plaintext .= "&Checksum=" . $this->generateChecksum($plaintext, $key);
        $encrypted = base64_encode($this->aesEncrypt($plaintext));
        return $encrypted;
    }
    
    public function decrypt($encrypted) {
        $decrypted = $this->aesDecrypt(base64_decode($encrypted));
        $data = $this->getArray($decrypted);
        return $data;
    }
    
    public function verify($response) {
        $checksum = $this->generateChecksum($this->getSignatureString($response), $this->working_key);
        return $checksum == $response['checksum'];
    }
    
    private function aesEncrypt($plainText) {
        $secretKey = $this->getSecretKey();
        $initVector = $this->access_code;
        $openSSLString = "AES-128-CBC";
        $encryptedText = openssl_encrypt($plainText, $openSSLString, $secretKey, 0, $initVector);
        return $encryptedText;
    }
    
    private function aesDecrypt($encryptedText) {
        $secretKey = $this->getSecretKey();
        $initVector = $this->access_code;
        $openSSLString = "AES-128-CBC";
        $decryptedText = openssl_decrypt($encryptedText, $openSSLString, $secretKey, 0, $initVector);
        return $decryptedText;
    }
    
    private function generateChecksum($data, $key) {
        return hash_hmac
    }

    private function getArray($data) {
        $data = explode("&", $data);
        $arr = array();
        foreach ($data as $dat) {
            $d = explode("=", $dat);
            $arr[$d[0]] = $d[1];
        }
        return $arr;
    }

    private function getSignatureString($data) {
        $str = "";
        foreach ($data as $key => $value) {
            if ($key != 'checksum') {
                $str .= "$value|";
            }
        }
        return $str;
    }

    private function getSecretKey() {
        $hex = $this->working_key;
        $key = pack('H*', $hex);
        return $key;
    }
}