Add product discount calculation and update handling for dynamic usage logs

- Introduced `getProductDiscountPercentage` method to calculate accurate discounts for users across products, categories, and global settings.
- Adjusted `importUsageLogs` to refine date modifier parameter and enhance `usage log` checks.
- Enhanced `orders_o` to include product discount logic with stricter type casting for consistency.
- Added `updateFieldsWhere` method for selective database updates based on specific conditions.
- Updated `customers_o` to handle updates for existing customers while adding new ones.

services/nginx/app/objects/users_o.php

@@ -699,6 +699,34 @@ class users_o extends db
         return $discount;
     }
 
+    /**
+     * Get the final price of the product for the user
+     * This includes:
+     * - Global discount (If the product allows category inheritance of discounts)
+     * - Category discount (If the product allows category inheritance of discounts)
+     * - Product discount (If the product has a custom price)
+     */
+    public function getProductDiscountPercentage(int $product_id): int|null
+    {
+        self::requireSelected();
+        // Get the product by ID
+        $product = (new products_o())->select((int)$product_id);
+        $doesProductAllowCategoryDiscount = (bool)$product->apply_category_discount->value();
+        $economic_discount_percentage = $this->getEconomicCustomerDiscountPercentage();
+        $discount_percentage = $this->getCustomPrice($product_id);
+        // If the product allows category inheritance of discounts, get the category discounts
+        if ($doesProductAllowCategoryDiscount) {
+            // If the category discount is higher than the product discount, use the category discount
+            if ($economic_discount_percentage > $discount_percentage) {
+                $discount_percentage = $economic_discount_percentage;
+            }
+        }
+        // If the discount percentage is null, return 0
+        return $discount_percentage === null ? 0 : (int)$discount_percentage;
+    }
+
+
+
     /**
      * Get all custom prices (DISCOUNT) for the user
      * @return array The custom prices