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<?php
// Filters
add_filter( 'woocommerce_get_catalog_ordering_args', 'custom_woocommerce_get_catalog_ordering_args' );
add_filter( 'woocommerce_default_catalog_orderby_options', 'custom_woocommerce_catalog_orderby' );
add_filter( 'woocommerce_catalog_orderby', 'custom_woocommerce_catalog_orderby' );
 
 // Apply custom args to main query
function custom_woocommerce_get_catalog_ordering_args( $args ) {

	$orderby_value = isset( $_GET['orderby'] ) ? woocommerce_clean( $_GET['orderby'] ) : apply_filters( 'woocommerce_default_catalog_orderby', get_option( 'woocommerce_default_catalog_orderby' ) );
 
	if ( 'oldest_to_recent' == $orderby_value ) {
		$args['orderby'] = 'date';
		$args['order'] = 'ASC';
	}
 
	return $args;
}
 
// Create new sorting method
function custom_woocommerce_catalog_orderby( $sortby ) {
	
	$sortby['oldest_to_recent'] = __( 'Oldest to most recent', 'woocommerce' );
	
	return $sortby;
}