Creating a woocommerce shipping method based on total number of cart items.

woo-shipping-methods.php

<?php

function your_shipping_method_init() {
    if ( ! class_exists( 'WC_Your_Shipping_Method' ) ) {
        class WC_Your_Shipping_Method extends WC_Shipping_Method {
            
            /*----------------------------------------------------------------
                    Constructor for your shipping class 
            ----------------------------------------------------------------*/
            public function __construct() {
                $this->id                 = 'your_shipping_method'; // Id for your shipping method. Should be uunique.
                $this->method_title       = __( 'Your Shipping Method' );  // Title shown in admin
                $this->method_description = __( 'Description of your shipping method' ); // Description shown in admin

                $this->enabled            = "yes"; // This can be added as an setting but for this example its forced enabled
                $this->title              = "My Shipping Method"; // This can be added as an setting but for this example its forced.

                $this->init();
            }

            /*----------------------------------------------------------------
                Init your settings
            ----------------------------------------------------------------*/
            function init() {
                // Load the settings API
                $this->init_form_fields(); // This is part of the settings API. Override the method to add your own settings
                $this->init_settings(); // This is part of the settings API. Loads settings you previously init.

                // Save settings in admin if you have any defined
                add_action( 'woocommerce_update_options_shipping_' . $this->id, array( $this, 'process_admin_options' ) );
            }

            /*----------------------------------------------------------------
                calculate_shipping function.
            ----------------------------------------------------------------*/

            public function calculate_shipping( $package ) {
                global $woocommerce;

                $carttotal = $woocommerce->cart->cart_contents_count;

                /*
                    1-5 packs 5,000
                    6-10 packs 10,000
                    11-15 packs 15,000
                    16-20 packs 20,000

                */
                if($carttotal > 20){
                    $cost = 0;//Free delivery for above 20 packs
                }else if($carttotal >= 16 && $carttotal <= 20){
                    $cost = 20000;
                }else if($carttotal >= 11 && $carttotal <= 15){
                    $cost = 15000;
                }else if($carttotal >= 6 && $carttotal <= 10){
                    $cost = 10000;
                }else if($carttotal <= 5 && $carttotal >= 1){
                    $cost = 5000;
                }

                $rate = array(
                    'id' => $this->id,
                    'label' => 'Shipping',
                    'cost' => $cost,
                );

                // Register the rate
                $this->add_rate( $rate );

            }
        }
    }
}

add_action( 'woocommerce_shipping_init', 'your_shipping_method_init' );

function add_your_shipping_method( $methods ) {
    $methods['your_shipping_method'] = 'WC_Your_Shipping_Method';
    return $methods;
}

add_filter( 'woocommerce_shipping_methods', 'add_your_shipping_method' );