Adding an item to existing order

gistfile1.php

<?php

class WhatEver
{
    
    /**
     * Adds a product to existing order
     *
     * @param string      $orderIncrementId Order increment id
     * @param string      $itemSku          Product SKU
     * @param float|false $price            Product price
     *
     * @return void
     */
    public function addOrderItem($orderIncrementId, $itemSku, $price)
    {
        $order = Mage::getModel('sales/order');
        if ($price === false) {
            $price = 0.0;
        }
    
        /* @var $order Mage_Sales_Model_Order */
    
        $order->loadByIncrementId($orderIncrementId);
    
        if (!$order->getId()) {
            echo 'Order ' . $orderIncrementId . ' not found' . PHP_EOL;
            return;
        }
    
        $product = Mage::getModel('catalog/product')->loadByAttribute('sku', $itemSku);
    
        if (!$product->getId()) {
            echo 'Product ' . $itemSku . ' not found' . PHP_EOL;
            return;
        }
    
        $configurableProduct = Mage::getModel('catalog/product_type_configurable');
        $configurableProductId = $configurableProduct
            ->getParentIdsByChild($product->getId());
    
        if (count($configurableProductId) == 1) {
            $configurableProductId = $configurableProductId[0];
        } else {
            $configurableProductId = false;
        }
    
        if ($configurableProductId == false) {
            echo 'Configurable product not found ' . PHP_EOL;
        }
    
        // Required to get proper store-view attribute's value labels
        $store = Mage::app()->getStore('store_code');
        Mage::app()->setCurrentStore($store);
    
        $invoice = $order->getInvoiceCollection()->getFirstItem();
    
        $productOptions = array(
            'info_buyRequest' => array(
                'product' => $configurableProductId,
                'qty' => '1.0000',
                'related_product' => '',
            ),
            'attributes_info' => array(),
            'simple_name' => $product->getName(),
            'simple_sku' => $itemSku,
            'product_calculations' => 1,
            'shipment_type' => 0,
            'giftcard_lifetime' => null,
            'giftcard_is_redeemable' => 0,
            'giftcard_email_template' => null,
            'giftcard_type' => null,
        );
    
        $configurableProduct = $this->_getProductAttributes($configurableProductId, $product, $productOptions);
    
        $itemData = array(
            'order_id' => $order->getId(),
            'store_id' => $store->getId(),
            'product_id' => $configurableProductId,
            'product_type' => Mage_Catalog_Model_Product_Type::TYPE_CONFIGURABLE,
            'product_options' => serialize($productOptions),
            'weight' => 1,
            'is_virtual' => 0,
            'sku' => $itemSku,
            'name' => $configurableProduct->getName(),
            'is_qty_decimal' => 0,
            'qty_invoiced' => 1,
            'qty_ordered' => 1,
            'price' => $price,
            'base_price' => $price,
            'original_price' => $configurableProduct->getPrice(),
            'base_original_price' => $configurableProduct->getPrice(),
            'row_total' => $price,
            'base_row_total' => $price,
            'row_invoiced' => $price,
            'base_row_invoiced' => $price,
            'row_weight' => 1,
            'price_incl_tax' => $price,
            'base_price_incl_tax' => $price,
            'row_total_incl_tax' => $price,
            'base_row_total_incl_tax' => $price,
    
        );
    
        $parentItem = Mage::getModel('sales/order_item')
                        ->setData($itemData)
                        ->save();
    
        $invoiceItemData = array(
            'parent_id' => $invoice->getId(),
            'base_price' => $price,
            'qty' => 1,
            'product_id' => $configurableProductId,
            'order_item_id' => $parentItem->getId(),
            'sku' => $itemSku,
            'name' => $configurableProduct->getName()
        );
    
        Mage::getModel('sales/order_invoice_item')
            ->setData($invoiceItemData)
            ->save();
    
        $itemData['parent_item_id'] = $parentItem->getId();
        $itemData['product_type'] = Mage_Catalog_Model_Product_Type::TYPE_SIMPLE;
        $itemData['product_id'] = $product->getId();
        $itemData['name'] = $product->getName();
        unset($itemData['price']);
        unset($itemData['base_price']);
        unset($itemData['original_price']);
        unset($itemData['base_original_price']);
        unset($itemData['row_total']);
        unset($itemData['base_row_total']);
        unset($itemData['row_invoiced']);
        unset($itemData['base_row_invoiced']);
        unset($itemData['row_weight']);
        unset($itemData['price_incl_tax']);
        unset($itemData['base_price_incl_tax']);
        unset($itemData['row_total_incl_tax']);
        unset($itemData['base_row_total_incl_tax']);
    
        unset($productOptions['attributes_info']);
        unset($productOptions['simple_name']);
        unset($productOptions['simple_sku']);
        unset($productOptions['product_calculations']);
        unset($productOptions['shipment_type']);
    
        $itemData['product_options'] = serialize($productOptions);
    
        $childItem = Mage::getModel('sales/order_item')
            ->setData($itemData)
            ->save();
    
        $invoiceItemData = array(
            'parent_id' => $invoice->getId(),
            'base_price' => $price,
            'qty' => 1,
            'product_id' => $product->getId(),
            'order_item_id' => $childItem->getId(),
            'sku' => $itemSku,
            'name' => $product->getName()
        );
    
        Mage::getModel('sales/order_invoice_item')
            ->setData($invoiceItemData)
            ->save();
    }
    
    
    /**
     * Fills product attributes values
     *
     * @param int                        $configurableProductId Configurable product id
     * @param Mage_Catalog_Model_Product $product               Simple product instance
     * @param array                      &$productOptions       Product options
     *
     * @return Mage_Catalog_Model_Product_Type_Configurable
     */
    protected function _getProductAttributes($configurableProductId, $product, &$productOptions)
    {
        $configurableProduct = Mage::getModel('catalog/product')->load($configurableProductId);
        $configurableAttributes = $configurableProduct->getTypeInstance()->getConfigurableAttributesAsArray();
        foreach ($configurableAttributes as $attribute) {
            $attributeValue = $product->getData($attribute['attribute_code']);
            $attributeValueReadable = '';
            $productOptions['info_buyRequest']['super_attribute'][$attribute['attribute_id']] = $attributeValue;
            foreach ($attribute['values'] as $attributeValueData) {
                if ($attributeValue == $attributeValueData['value_index']) {
                    $attributeValueReadable = $attributeValueData['label'];
                    break;
                }
            }
            $productOptions['attributes_info'][] = array(
                'label' => $attribute['label'],
                'value' => $attributeValueReadable,
            );
        }
    
        return $configurableProduct;
    }
    
}