Hide shipping rates based on the quantities of items

functions.php

    add_filter( 'woocommerce_package_rates', 'wf_adjust_shipping_rate', 10, 2 );
    function wf_adjust_shipping_rate( $available_shipping_methods, $packages ){
        // Total quantity is total unit
        $unit = 0;
        $apply_final_filter = TRUE;
        foreach ( $packages['contents'] as $item ) {
            $unit+=$item['quantity'];
        }
        
        // if unit less than 3  , show D_FIRST_CLASS only
        if( $unit < 3 ){
           	$shipping_methods = array();
            if( !empty( $available_shipping_methods['wf_shipping_usps:D_FIRST_CLASS'] ) ){
                $apply_final_filter = FALSE;
                $shipping_methods['wf_shipping_usps:D_FIRST_CLASS'] = $available_shipping_methods['wf_shipping_usps:D_FIRST_CLASS'];
                $available_shipping_methods = $shipping_methods;
            }
        }// if unit between 3 and 30 , show D_STANDARD_POST only
        elseif( $unit > 2 && $unit < 31 ){
           	$shipping_methods = array();
            if(!empty($available_shipping_methods['wf_shipping_usps:D_STANDARD_POST'])){
                $apply_final_filter = FALSE;
                $shipping_methods['wf_shipping_usps:D_STANDARD_POST'] = $available_shipping_methods['wf_shipping_usps:D_STANDARD_POST'];
                $available_shipping_methods = $shipping_methods;
            }
        }
        
        // if no above conditions met , remove all USPS service
        if( $apply_final_filter ){
            foreach ($available_shipping_methods as $index => $data) {
                if (strpos($index, 'wf_shipping_usps') !== false) {
                   unset($available_shipping_methods[$index]);
                }
            }
        }
        
        return $available_shipping_methods;
    }