//...
use yii\filters\AccessControl;
use yii\filters\VerbFilter;
use yii\helpers\Html;
 
class CustomerController extends Controller
{
    public function behaviors()
    {
        return [
            'access' => [
                'class' => AccessControl::className(),
                'rules' => [
                    [
                        'actions' => [/* ... */ 'export'],
                        'allow' => true,
                        'roles' => ['@'],  // @ = Authenticated users
                    ],
                ],
            ],
            //...
        ];
    }
 
    //...
 
    /**
     * Generated export files containing of all existing Customers.
     * @param none
     * @return mixed
     */
    public function actionExport($type='csv')
    {
        $models = Customer::find()->All();
 
        switch($type) {
            case 'excel':
                //--------------------
                // Excel Export
                //--------------------
                $filename = 'Customer-Data-'.Date('YmdGis').".xls";
                header("Content-type: application/vnd-ms-excel"); 
                header("Content-Disposition: attachment; filename=".$filename);
 
                echo '<table border="1" width="100%">
                    <thead>
                        <tr>
                            <th>account_number</th>
                            <th>contact</th>
                            <th>company_name</th>
                            <th>address1</th>
                            <th>address2</th>
                            <th>city</th>
                            <th>state_prov</th>
                            <th>postal_code</th>
                            <th>country</th>
                            <th>phone</th>
                            <th>phone_ext</th>
                            <th>email</th>
                            <th>website</th>
                            <th>ship_address_id</th>
                            <th>notes</th>
                            <th>status</th>
                        </tr>
                    </thead>';
 
                foreach($models as $row){
                    echo '
                        <tr>
                            <td>'.$row['account_number']  .'</td>
                            <td>'.$row['contact']         .'</td>
                            <td>'.$row['company_name']    .'</td>
                            <td>'.$row['address1']        .'</td>
                            <td>'.$row['address2']        .'</td>
                            <td>'.$row['city']            .'</td>
                            <td>'.$row['state_prov']      .'</td>
                            <td>'.$row['postal_code']     .'</td>
                            <td>'.$row['country']         .'</td>
                            <td>'.$row['phone']           .'</td>
                            <td>'.$row['phone_ext']       .'</td>
                            <td>'.$row['email']           .'</td>
                            <td>'.$row['website']         .'</td>
                            <td>'.$row['ship_address_id'] .'</td>
                            <td>'.$row['notes']           .'</td>
                            <td>'.$row['status']          .'</td>
                        </tr>
                    ';
                }
                echo '</table>';
                break;
 
            case 'csv':
            default:
                //--------------------
                // CSV Export
                //--------------------
                $filename = 'Customer-Data-'.Date('YmdGis').".csv";
                header("Content-type: text/csv"); $extension = 'csv'; 
                header("Content-Disposition: attachment; filename=".$filename);
 
                // header row
                $data = implode("\t", [
                    'account_number', 'contact', 'company_name', 
                    'address1', 'address2', 'city', 'state_prov', 'postal_code', 'country', 
                    'phone', 'phone_ext', 'email', 'website', 'ship_address_id', 'notes', 'status'
                ]) . "\n";
 
                // data row
                foreach($models as $row) {
                    $data .= implode("\t", [
                        $row['account_number']  ,
                        $row['contact']         ,
                        $row['company_name']    ,
                        $row['address1']        ,
                        $row['address2']        ,
                        $row['city']            ,
                        $row['state_prov']      ,
                        $row['postal_code']     ,
                        $row['country']         ,
                        $row['phone']           ,
                        $row['phone_ext']       ,
                        $row['email']           ,
                        $row['website']         ,
                        $row['ship_address_id'] ,
                        str_replace("\r\n", "|", Html::encode($row['notes'])),
                        $row['status']          ,
                    ]) . "\n";
                }
 
                // return data results
                echo $data;
                break;
        }
    }
}