Developing Payment Gateways

extension/myvendor/
├── admin/
│   ├── controller/payment/mypayment.php
│   ├── language/en-gb/payment/mypayment.php
│   └── view/template/payment/mypayment.twig
└── catalog/
    ├── controller/payment/mypayment.php
    └── language/en-gb/payment/mypayment.php

<?php
namespace Opencart\Admin\Controller\Extension\Opencart\Payment;

class BankTransfer extends \Opencart\System\Engine\Controller {
    public function index(): void {
        $this->load->language('extension/opencart/payment/bank_transfer');
        
        $this->document->setTitle($this->language->get('heading_title'));
        
        $data['breadcrumbs'] = [];
        
        $data['breadcrumbs'][] = [
            'text' => $this->language->get('text_home'),
            'href' => $this->url->link('common/dashboard', 'user_token=' . $this->session->data['user_token'])
        ];
        
        $data['save'] = $this->url->link('extension/opencart/payment/bank_transfer.save', 'user_token=' . $this->session->data['user_token']);
        $data['back'] = $this->url->link('marketplace/extension', 'user_token=' . $this->session->data['user_token'] . '&type=payment');
        
        // Load configuration
        $data['payment_bank_transfer_status'] = $this->config->get('payment_bank_transfer_status');
        $data['payment_bank_transfer_sort_order'] = $this->config->get('payment_bank_transfer_sort_order');
        
        // Load order statuses
        $this->load->model('localisation/order_status');
        $data['order_statuses'] = $this->model_localisation_order_status->getOrderStatuses();
        
        // Load geo zones
        $this->load->model('localisation/geo_zone');
        $data['geo_zones'] = $this->model_localisation_geo_zone->getGeoZones();
        
        $this->response->setOutput($this->load->view('extension/opencart/payment/bank_transfer', $data));
    }
    
    public function save(): void {
        $this->load->language('extension/opencart/payment/bank_transfer');
        
        $json = [];
        
        if (!$this->user->hasPermission('modify', 'extension/opencart/payment/bank_transfer')) {
            $json['error']['warning'] = $this->language->get('error_permission');
        }
        
        if (!$json) {
            $this->load->model('setting/setting');
            $this->model_setting_setting->editSetting('payment_bank_transfer', $this->request->post);
            
            $json['success'] = $this->language->get('text_success');
        }
        
        $this->response->addHeader('Content-Type: application/json');
        $this->response->setOutput(json_encode($json));
    }
}

<?php
namespace Opencart\Catalog\Controller\Extension\Opencart\Payment;

class BankTransfer extends \Opencart\System\Engine\Controller {
    /**
     * Index - Display payment method
     *
     * @return string
     */
    public function index(): string {
        $this->load->language('extension/opencart/payment/bank_transfer');
        
        $data['bank'] = nl2br($this->config->get('payment_bank_transfer_bank_' . $this->config->get('config_language_id')));
        $data['language'] = $this->config->get('config_language');
        
        return $this->load->view('extension/opencart/payment/bank_transfer', $data);
    }
    
    /**
     * Confirm - Process payment
     *
     * @return void
     */
    public function confirm(): void {
        $this->load->language('extension/opencart/payment/bank_transfer');
        
        $json = [];
        
        if (!isset($this->session->data['order_id'])) {
            $json['error'] = $this->language->get('error_order');
        }
        
        // Validate order
        if (isset($this->session->data['order_id'])) {
            $this->load->model('checkout/order');
            
            $order_info = $this->model_checkout_order->getOrder($this->session->data['order_id']);
            
            if (!$order_info) {
                $json['redirect'] = $this->url->link('checkout/failure', 'language=' . $this->config->get('config_language'), true);
                unset($this->session->data['order_id']);
            }
        }
        
        // Validate payment method
        if (!isset($this->session->data['payment_method']) || 
            $this->session->data['payment_method']['code'] != 'bank_transfer.bank_transfer') {
            $json['error'] = $this->language->get('error_payment_method');
        }
        
        if (!$json) {
            // Add order history
            $comment  = $this->language->get('text_instruction') . "\n\n";
            $comment .= $this->config->get('payment_bank_transfer_bank_' . $this->config->get('config_language_id')) . "\n\n";
            $comment .= $this->language->get('text_payment');
            
            $this->load->model('checkout/order');
            
            $this->model_checkout_order->addHistory(
                $this->session->data['order_id'],
                $this->config->get('payment_bank_transfer_order_status_id'),
                $comment,
                true
            );
            
            $json['redirect'] = $this->url->link('checkout/success', 'language=' . $this->config->get('config_language'), true);
        }
        
        $this->response->addHeader('Content-Type: application/json');
        $this->response->setOutput(json_encode($json));
    }
}

public function index(): string {
    $this->load->language('extension/myvendor/payment/mypayment');
    
    $data['api_key'] = $this->config->get('payment_mypayment_api_key');
    $data['button_confirm'] = $this->language->get('button_confirm');
    
    return $this->load->view('extension/myvendor/payment/mypayment', $data);
}

public function confirm(): void {
    $json = [];
    
    if (!isset($this->session->data['order_id'])) {
        $json['error'] = 'Order not found';
    }
    
    if (!$json) {
        // Process payment with API
        $result = $this->processPayment($this->session->data['order_id']);
        
        if ($result['success']) {
            $this->load->model('checkout/order');
            $this->model_checkout_order->addHistory(
                $this->session->data['order_id'],
                $this->config->get('payment_mypayment_order_status_id'),
                'Payment processed',
                true
            );
            
            $json['redirect'] = $this->url->link('checkout/success');
        } else {
            $json['error'] = $result['error'];
        }
    }
    
    $this->response->addHeader('Content-Type: application/json');
    $this->response->setOutput(json_encode($json));
}

private function processPayment(int $order_id): array {
    $this->load->model('checkout/order');
    $order_info = $this->model_checkout_order->getOrder($order_id);
    
    // Prepare API request
    $data = [
        'amount'      => $order_info['total'],
        'currency'    => $order_info['currency_code'],
        'order_id'    => $order_id,
        'return_url'  => $this->url->link('extension/myvendor/payment/mypayment.callback'),
        'cancel_url'  => $this->url->link('checkout/checkout')
    ];
    
    $curl = curl_init();
    
    curl_setopt($curl, CURLOPT_URL, 'https://api.paymentgateway.com/process');
    curl_setopt($curl, CURLOPT_POST, true);
    curl_setopt($curl, CURLOPT_POSTFIELDS, http_build_query($data));
    curl_setopt($curl, CURLOPT_RETURNTRANSFER, true);
    curl_setopt($curl, CURLOPT_HTTPHEADER, [
        'Authorization: Bearer ' . $this->config->get('payment_mypayment_api_key')
    ]);
    
    $response = curl_exec($curl);
    $http_code = curl_getinfo($curl, CURLINFO_HTTP_CODE);
    
    curl_close($curl);
    
    $result = json_decode($response, true);
    
    if ($http_code == 200 && isset($result['transaction_id'])) {
        return [
            'success' => true,
            'transaction_id' => $result['transaction_id']
        ];
    } else {
        return [
            'success' => false,
            'error' => $result['error'] ?? 'Payment failed'
        ];
    }
}

public function callback(): void {
    // Validate callback
    $transaction_id = $this->request->get['transaction_id'] ?? '';
    $order_id = $this->request->get['order_id'] ?? 0;
    
    if (!$transaction_id || !$order_id) {
        $this->response->redirect($this->url->link('checkout/failure'));
        return;
    }
    
    // Verify with payment gateway
    $verified = $this->verifyTransaction($transaction_id);
    
    if ($verified) {
        $this->load->model('checkout/order');
        $this->model_checkout_order->addHistory(
            $order_id,
            $this->config->get('payment_mypayment_completed_status_id'),
            'Payment verified: ' . $transaction_id,
            true
        );
        
        $this->response->redirect($this->url->link('checkout/success'));
    } else {
        $this->response->redirect($this->url->link('checkout/failure'));
    }
}

// Settings to save
$settings = [
    'payment_mypayment_api_key'              => 'YOUR_API_KEY',
    'payment_mypayment_api_secret'           => 'YOUR_SECRET',
    'payment_mypayment_test_mode'            => 1,
    'payment_mypayment_order_status_id'      => 1,
    'payment_mypayment_completed_status_id'  => 5,
    'payment_mypayment_geo_zone_id'          => 0,
    'payment_mypayment_status'               => 1,
    'payment_mypayment_sort_order'           => 1
];

$this->model_setting_setting->editSetting('payment_mypayment', $settings);