class ControllerExtensionModuleM2Pricing extends Controller {
    public function index() {
        $data['heading_title'] = $this->language->get('heading_title');

        if (($this->request->server['REQUEST_METHOD'] == 'POST') && $this->validate()) {
            $m2 = $this->request->post['m2'];
            $price_per_m2 = 10; // Örnek olarak 1 metrekare başına 10 birimlik fiyat
            $total_price = $m2 * $price_per_m2;
            
            $data['total_price'] = $total_price;
        }

        $data['entry_m2'] = $this->language->get('entry_m2');
        $data['button_calculate'] = $this->language->get('button_calculate');

        $data['action'] = $this->url->link('extension/module/m2_pricing', '', true);

        return $this->load->view('extension/module/m2_pricing', $data);
    }

    protected function validate() {
        if (!isset($this->request->post['m2']) || !is_numeric($this->request->post['m2']) || $this->request->post['m2'] <= 0) {
            $this->error['warning'] = $this->language->get('error_m2');
        }

        return !$this->error;
    }
}

// 2. View dosyası: catalog/view/theme/default/template/extension/module/m2_pricing.tpl

<div class="m2-pricing">
    <h2><?php echo $heading_title; ?></h2>
    <form action="<?php echo $action; ?>" method="post">
        <div class="form-group">
            <label for="m2"><?php echo $entry_m2; ?>:</label>
            <input type="text" name="m2" id="m2" class="form-control" />
        </div>
        <button type="submit" class="btn btn-primary"><?php echo $button_calculate; ?></button>
    </form>
    <?php if (isset($total_price)) { ?>
        <p>Total Price: <?php echo $total_price; ?></p>
    <?php } ?>
</div>

// 3. Dil dosyası: catalog/language/en-gb/extension/module/m2_pricing.php

$_['heading_title'] = 'M2 Pricing';
$_['entry_m2'] = 'Square Meters:';
$_['button_calculate'] = 'Calculate';
$_['error_m2'] = 'Please enter a valid number for square meters.';

?>