Dynamic url parameters in a datasource

data.ds1.php

<!--
Usecase example: You want to unset the price filter if the $url-price is 0
-->
<?php
class datasourceds1 extends SectionDatasource
{
    public $dsParamROOTELEMENT = 'ds1';
    public $dsParamORDER = '{$url-order:desc}';
    public $dsParamPAGINATERESULTS = 'yes';
    public $dsParamLIMIT = '20';
    public $dsParamSTARTPAGE = '{$url-page}';
    public $dsParamREDIRECTONEMPTY = 'no';
    public $dsParamREDIRECTONFORBIDDEN = 'no';
    public $dsParamREDIRECTONREQUIRED = 'no';
    public $dsParamSORT = '{$url-sort}';
    public $dsParamHTMLENCODE = 'no';
    public $dsParamASSOCIATEDENTRYCOUNTS = 'no';
    public $dsParamFILTERS = array(
        '323' => '{$url-price}', //323 = id of the price field -> Entity Diagram Extension
    );
    public $dsParamINCLUDEDELEMENTS = array(
        'system:pagination',
        'system:date',
        'field1',
        'field2',
        'price'
        
    );
    public function __construct($env = null, $process_params = true)
    {
	    
	  if (strpos($_SERVER["REQUEST_URI"], "symphony")== false) //Hack not to have an error in symphony
	    {

      
      //var_dump(Symphony::Engine()->Page()->_param);die;
if ( Symphony::Engine()->Page()->_param['url-price']== '0')
{
  unset($this->dsParamFILTERS['323']);
} 	   	    

	   	    }
	   	    
	   	    
	   	    
        parent::__construct($env, $process_params);
        $this->_dependencies = array();
    }
    public function about()
    {
        return array(
            'name' => 'ds1',
            'author' => array(
                'name' => 'Wannes Debusschere',
                'website' => 'http://localhost:8080/xxx',
                'email' => 'info@e-xperience.be'),
            'version' => 'Symphony 2.7.7',
            'release-date' => '2018-06-27T13:29:35+00:00'
        );
    }
    public function getSource()
    {
        return '36';
    }
    public function allowEditorToParse()
    {
        return false;
    }
    public function execute(array &$param_pool = null)
    {
        $result = new XMLElement($this->dsParamROOTELEMENT);
        try{
            $result = parent::execute($param_pool);
        } catch (FrontendPageNotFoundException $e) {
            // Work around. This ensures the 404 page is displayed and
            // is not picked up by the default catch() statement below
            FrontendPageNotFoundExceptionHandler::render($e);
        } catch (Exception $e) {
            $result->appendChild(new XMLElement('error', $e->getMessage() . ' on ' . $e->getLine() . ' of file ' . $e->getFile()));
            return $result;
        }
        if ($this->_force_empty_result) {
            $result = $this->emptyXMLSet();
        }
        if ($this->_negate_result) {
            $result = $this->negateXMLSet();
        }
        return $result;
    }
}