🧠 Mastering The Singleton Pattern In Laravel For Payment Gateways (Stripe, SSLCommerz, Bkash)

Integrating payment gateways like Stripe, SSLCommerz, or Bkash is a common need in web development. But if not done right, it can lead to messy, repeated code and poor resource management.

In this blog, we’ll explore how to implement a clean, scalable, and reusable payment system using the Singleton Pattern, Strategy Pattern, and Dependency Injection in Laravel.

📌 What You’ll Learn

✅ What is the Singleton Pattern
✅ Why and when to use it in Laravel
✅ How to integrate multiple payment gateways (Stripe, SSLCommerz, Bkash)
✅ How to make your architecture SOLID, testable, and extensible
✅ Full code example with folder structure

🔍 What is the Singleton Pattern?

The Singleton Pattern ensures a class has only one instance throughout the application and provides a global access point to it.

Instead of creating a new object every time, we use one shared instance.

✅ Why Use Singleton for Payment Gateways?

• Avoids repeated SDK initialization

• Saves memory and ensures consistent behavior

• Centralizes and simplifies gateway logic

• Works perfectly with Laravel’s Service Container

🧱 Recommended Folder Structure

To keep things modular and clean:

app/
├── Gateways/
│   ├── Contracts/
│   │   └── PaymentGatewayInterface.php
│   ├── StripeGateway.php
│   ├── SSLCommerzGateway.php
│   └── BkashGateway.php
├── Services/
│   └── PaymentGatewayService.php

🧩 Step 1: Define the Payment Gateway Interface

app/Gateways/Contracts/PaymentGatewayInterface.php

namespace App\Gateways\Contracts;

interface PaymentGatewayInterface
{
    public function charge(float $amount, string $currency): array;
    public function refund(string $transactionId): array;
}

This defines a contract that all gateways (Stripe, SSLCommerz, Bkash) must follow.

💳 Step 2: Create Gateway Implementations

Each gateway implements the PaymentGatewayInterface.

🔹 Stripe Gateway

app/Gateways/StripeGateway.php

namespace App\Gateways;

use App\Gateways\Contracts\PaymentGatewayInterface;

class StripeGateway implements PaymentGatewayInterface
{
    protected $config;

    public function __construct()
    {
        $this->config = config('services.stripe');
    }

    public function charge(float $amount, string $currency): array
    {
        return [
            'gateway' => 'stripe',
            'status' => 'success',
            'transaction_id' => uniqid('stripe_txn_'),
            'amount' => $amount,
            'currency' => $currency,
        ];
    }

    public function refund(string $transactionId): array
    {
        return [
            'gateway' => 'stripe',
            'status' => 'refunded',
            'transaction_id' => $transactionId,
        ];
    }
}

🔹 SSLCommerz Gateway

app/Gateways/SSLCommerzGateway.php

namespace App\Gateways;

use App\Gateways\Contracts\PaymentGatewayInterface;

class SSLCommerzGateway implements PaymentGatewayInterface
{
    protected $config;

    public function __construct()
    {
        $this->config = config('services.sslcommerz');
    }

    public function charge(float $amount, string $currency): array
    {
        return [
            'gateway' => 'sslcommerz',
            'status' => 'success',
            'transaction_id' => uniqid('ssl_txn_'),
            'amount' => $amount,
            'currency' => $currency,
        ];
    }

    public function refund(string $transactionId): array
    {
        return [
            'gateway' => 'sslcommerz',
            'status' => 'refunded',
            'transaction_id' => $transactionId,
        ];
    }
}

🔹 Bkash Gateway

app/Gateways/BkashGateway.php

namespace App\Gateways;

use App\Gateways\Contracts\PaymentGatewayInterface;

class BkashGateway implements PaymentGatewayInterface
{
    protected $config;

    public function __construct()
    {
        $this->config = config('services.bkash');
    }

    public function charge(float $amount, string $currency): array
    {
        return [
            'gateway' => 'bkash',
            'status' => 'success',
            'transaction_id' => uniqid('bkash_txn_'),
            'amount' => $amount,
            'currency' => $currency,
        ];
    }

    public function refund(string $transactionId): array
    {
        return [
            'gateway' => 'bkash',
            'status' => 'refunded',
            'transaction_id' => $transactionId,
        ];
    }
}

🛠️ Step 3: Create the PaymentGatewayService (Singleton-Friendly)

app/Services/PaymentGatewayService.php

namespace App\Services;

use App\Gateways\Contracts\PaymentGatewayInterface;

class PaymentGatewayService
{
    protected PaymentGatewayInterface $gateway;

    public function __construct(PaymentGatewayInterface $gateway)
    {
        $this->gateway = $gateway;
    }

    public function charge(float $amount, string $currency = 'BDT'): array
    {
        return $this->gateway->charge($amount, $currency);
    }

    public function refund(string $transactionId): array
    {
        return $this->gateway->refund($transactionId);
    }
}

Now, Laravel will inject the gateway using Dependency Injection, making it testable and extensible.

🧩 Step 4: Register Bindings in Service Container

app/Providers/AppServiceProvider.php

use App\Gateways\Contracts\PaymentGatewayInterface;
use App\Gateways\StripeGateway;

public function register()
{
    // Bind the default gateway
    $this->app->bind(PaymentGatewayInterface::class, function () {
        return new StripeGateway(); // You can switch to SSLCommerzGateway or BkashGateway
    });

    $this->app->singleton(\App\Services\PaymentGatewayService::class);
}

You can make this dynamic using a config or based on request data if needed.

📟 Step 5: Use in Controller (With DI)

use App\Services\PaymentGatewayService;

class PaymentController extends Controller
{
    public function pay(PaymentGatewayService $paymentService)
    {
        $response = $paymentService->charge(1500, 'BDT');
        return response()->json($response);
    }

    public function refund(PaymentGatewayService $paymentService, string $transactionId)
    {
        $response = $paymentService->refund($transactionId);
        return response()->json($response);
    }

    // Optional: Dynamically switch gateway
    public function payWithBkash()
    {
        $bkash = new \App\Gateways\BkashGateway();
        $payment = new PaymentGatewayService($bkash);
        return response()->json($payment->charge(2000));
    }
}

🧠 Benefits of This Architecture

🧾 Summary