WooCommerce custom shipping method plugin

mytheme_shipping_plugin.php

<?php 
//I found a few tutorials for making custom WooCommerce shipping methods but most were confusing or didn't work any more.
//This is a simple custom shipping method. 
//It originally calculated a fee per 'delivery day' based on some date meta on the cart items, but for this example it's a hard-coded flat fee. 
//See calculate_shipping()

//Step 1:
//Save this code (minus these instructions) in a file in your plugins directory, preferably in its own subdirectory eg myplugin_shipping/myplugin_shipping.php

//Step 2:
//Find and replace the following strings (case sensitive, use the same patterns) with variations of your plugin name
/*    
    myplugin_name - used for various hook and method names
    WC_Myplugin_Delivery_Method - shipping class name
    My Plugin - text shown to end user in labels
*/

//Step 3:
//Enable the plugin, then enable the shipping method in WC settings (it should have its own settings tab)

//Step 4:
//Cross fingers and test
?>

<?php

/**
* Plugin Name: My Plugin Delivery Shipping method
* Description: Custom shipping method plugin for WooCommerce
*/

if ( ! defined( 'WPINC' ) ){
    die('security by preventing any direct access to your plugin file');
}

if ( in_array( 'woocommerce/woocommerce.php', apply_filters( 'active_plugins', get_option( 'active_plugins' ) ) ) ) {

    function myplugin_name_delivery_init() {
        if ( ! class_exists( 'WC_Myplugin_Delivery_Method' ) ) {
            class WC_Myplugin_Delivery_Method extends WC_Shipping_Method {
                /**
                 * Constructor for your shipping class
                 *
                 * @access public
                 * @return void
                 */
                public function __construct($instance_id = 0) {
                    $this->id                 = 'myplugin_name_delivery'; // Id for your shipping method. Should be uunique.
                    $this->instance_id  = absint( $instance_id );
                    $this->method_title       = __( 'My Plugin Delivery' );  // Title shown in admin
                    $this->method_description = __( 'Flat delivery fee per day' ); // Description shown in admin

                    $this->init();

                    $this->title = !empty($this->settings['title']) ? $this->settings['title'] : 'My Plugin Delivery'; // This can be added as an setting but for this example its forced.
                    //$this->enabled = isset($this->settings['enabled']) ? $this->settings['enabled'] : 'yes';
                    $this->flat_fee = isset($this->settings['flat_fee']) ? $this->settings['flat_fee'] : '4.00';


                }

                /**
                 * Init your settings
                 *
                 * @access public
                 * @return void
                 */
                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' ) );
                }

                function init_form_fields() {

                    $this->form_fields = array(

                        'enabled' => array(
                            'title'       => __( 'Enable', 'dc_raq' ),
                            'type'        => 'checkbox',
                            'description' => __( 'Enable this shipping method.', 'dc_raq' ),
                            'default'     => 'yes'
                        ),

                        'title' => array(
                            'title'       => __( 'Title', 'dc_raq' ),
                            'type'        => 'text',
                            'description' => __( 'Title to be displayed on site', 'dc_raq' ),
                            'default'     => __( 'Request a Quote', 'dc_raq' )
                        ),

                        'flat_fee' => array(
                            'title'       => __( 'Flat fee per day', 'dc_raq' ),
                            'type'        => 'text',
                            'description' => __( 'Delivery fee per day', 'dc_raq' ),
                            'default'     => '4'
                        ),

                    );

                }

                /**
                 * calculate_shipping function.
                 *
                 * @access public
                 *
                 * @param mixed $package
                 *
                 * @return void
                 */

                public function calculate_shipping( $package = array() ) {

                    //Most carts will contain only one $package but sometimes there are more eg WooCommerce Subscriptions has a separate package for its recurring cart
                    //That's why we will look at $package only, not WC()->cart, to calculate shipping
                    
                    //Calculate your shipping fee here. $package['contents'] is the same structure as a WC cart                    
                    /*
                        foreach($package['contents'] as $item_id => $item){
                            //$_product = $item['data'];
                            //etc                            
                        }                    
                     */

                    $fee = 1.99; //for the demo, just use a flat $1.99

                    //Add the fee you calculated
                    $rate = array(
                        'id'       => $this->id,
                        'label'    => $this->title,
                        'cost'     => $fee,
                        'calc_tax' => 'per_item',
                        'package' => $package
                    );

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

                }//calculate_shipping()
            }
        }
    }

    add_action( 'woocommerce_shipping_init', 'myplugin_name_delivery_init' );

    function myplugin_name_delivery_shipping_method( $methods ) {
        $methods['myplugin_name_delivery'] = 'WC_Myplugin_Delivery_Method';

        return $methods;
    }

    add_filter( 'woocommerce_shipping_methods', 'myplugin_name_delivery_shipping_method' );
}