EE4 custom reg code example

//This code is not supported by Event Espresso
//This code is merely an example of how to use the filter FHEE__EE_Registration___generate_new_reg_code__new_reg_code

	function change_the_reg_id($new_reg_code, $this) {

		//EE doesn't store sequential ID's so let's make an option to hold the last one.
		$the_last_reg_id = get_option( 'my_current_reg_id' );

		//if the option is not set, then let's make it 1
		if( !isset($the_last_reg_id) ) {
			$the_last_reg_id = '1';
		}
		//otherwise lets increment it and then update the option.
		else {
			$the_last_reg_id = (int)$the_last_reg_id + 1;
			update_option( 'my_current_reg_id', $the_last_reg_id );
		}

		//modify the reg code with the new one and return it.
		$new_reg_code = $the_last_reg_id;
		return $new_reg_code;
	}
	add_filter('FHEE__EE_Registration_Processor___generate_reg_code__new_reg_code', 'change_the_reg_id', 10,2);