WooCommerce conditional subtotal cart discounts

EVD Cart Discount Rules

<?php 
/**
 * Plugin Name: EVD - Card Discount Rules
 * Plugin URI: https://rwky.ro
 * Description: Discount rules for cart
 * Version: 1.0
 * Author: Eduard Vasile Doloc
 * Author URI: http://rwky.ro
 * Developer: Eduard Vasile Doloc
 * Developer URI: http://rwky.ro
 * Text Domain: evd_discounts
 * Domain Path: /languages
 *
 * WC requires at least: 2.2
 * WC tested up to: 3.3.5
 *
 * License: GNU General Public License v3.0
 * License URI: http://www.gnu.org/licenses/gpl-3.0.html
 */
 
 /**
 * Check if WooCommerce is active - we don't want that, do we?
 **/
 
 function evd_woo_is_absent() {
     if (!defined('WC_VERSION')) {
    ?>
    <div class="error notice">
        <p>
            <?php _e( 'EVD Cart Discount Rules - <strong>WooCommerce is not active!</strong>', 'evd_discounts' ); ?>
        </p>
    </div>
    <?php
         
     }
}
add_action( 'admin_notices', 'woo_is_absent' );


// Magic & logic
add_action('woocommerce_cart_calculate_fees', 'evd_woo_discounts');
function evd_woo_discounts() {
  global $woocommerce;
  $excluded_amount = $discount_percent = 0;
  $working_total   = $woocommerce->cart->cart_contents_total;
 
  # Only apply manual discount if no coupons are applied
  if (!$woocommerce->cart->applied_coupons) {
 
    # Find any items in cart that belong to the restricted categories
    foreach ($woocommerce->cart->cart_contents as $item) {
      $product_categories = get_the_terms($item['product_id'], 'product_cat');
      if (empty($product_categories) || is_wp_error($product_categories) || !$product_categories) {
        if (is_wp_error($product_categories)) {
          wp_die($product_categories->get_error_message());
        }
        else {
          $product_categories = new WP_Error('no_product_categories', "The product \"".$item->post_title."\" doesn't have any categories attached, thus no discounts can be calculated.", "Fatal Error");
          wp_die($product_categories);
        }
      }
      foreach ($excluded_categories as $excluded_category) {
        foreach ($product_categories as $category) {
          if ($excluded_category == $category->term_id) {
            $excluded_amount += $item['line_subtotal']; # Increase our discounted amount
            $working_total -= $item['line_subtotal'];   # Decrease our discounted amount
          }
        }
      }
    }
 
    # Logic to determine WHICH discount to apply based on subtotal
    if ($working_total >= 100 && $working_total < 149) {
      $discount_percent = 10;
    }
    elseif ($working_total >= 150 && $working_total < 249) {
      $discount_percent = 15;
    }
    elseif ($working_total >= 250 && $working_total < 349) {
      $discount_percent = 20;
    }
    elseif ($working_total >= 350 && $working_total < 499) {
      $discount_percent = 25;
    }
    elseif ($working_total >= 500) {
      $discount_percent = 30;
    }
    else {
      $discount_percent = 0;
    }
 
    # Make sure cart total is eligible for discount
    if ($discount_percent > 0) {
      $discount_amount  = ( ( ($discount_percent/100) * $working_total ) * -1 );
      $woocommerce->cart->add_fee('Discount', $discount_amount);
    }
  }
}