handler.php

<?php

if (!defined('ABSPATH')) {
    define('SUPER_SIMPLE_STRIPE_BUTTON', true);

    require_once 'common.php';

    require_once 'functions.php';

    header('Content-Type: application/json');

    if (!defined('S3B_PUBLISHABLE_KEY') || !defined('S3B_SECRET_KEY')) {
        http_response_code(500);
        echo json_encode([
            'result' => 'ERROR',
            'message' => 'Internal server error.',
        ]);
        exit();
    }

    \Stripe\Stripe::setApiKey(S3B_SECRET_KEY);

    if ($_SERVER['REQUEST_METHOD'] == 'POST') {
        $input = file_get_contents('php://input');
        $body = json_decode($input);

        if (json_last_error() !== JSON_ERROR_NONE) {
            http_response_code(400);
            echo json_encode([
                'result' => 'ERROR',
                'message' => 'Invalid request.',
            ]);
            exit();
        }
    }

    $cmd = $_GET['cmd'];

    $result = [
        'result' => 'ERROR',
        'message' => 'Unknown error',
    ];

    switch ($cmd) {
        case 'create-checkout-session':
            $result['data'] = s3bCreateCheckoutSession($body);
            $result['result'] = 'OK';
            $result['message'] = 'Success';
            break;
        case 'get-checkout-session':
            $result['data'] = s3bGetCheckoutSession();
            $result['result'] = 'OK';
            $result['message'] = 'Success';
            break;
        case 'get-stripe-key':
            $result['data'] = s3bGetStripeKey();
            $result['result'] = 'OK';
            $result['message'] = 'Success';
            break;
        default:
            $result['message'] = 'Unknown cmd';
            $result['data'] = $cmd;
            break;
    }

    echo json_encode($result);
}