[Woocommerce] Change customer's download expiry date based on quantity purchased by customer, where quantity equals year. Fires after successful checkout but right before showing the thank you page.

thp_wc_change_download_expiry_based_on_quantity.php

<?php

function thp_wc_change_download_expiry_based_on_quantity( $order_id ) {
	
	$order = wc_get_order( $order_id );
	
	foreach ($order->get_items() as $item_id => $item ) {
		
		$product = $item->get_product();
		$product_id = $product->get_id();
		
		if ($product_id == 119) { //product ID
			$item_quantity = $item->get_quantity();
			
			$data_store = WC_Data_Store::load( 'customer-download' );
			$download_permissions = $data_store->get_downloads(
				[
				'order_id' => $order->get_id()
				]
			);
			if ( $download_permissions && count( $download_permissions ) > 0 ) {
				foreach ( $download_permissions as $download ) {
					//$new_expiry = date( 'Y-m-d H:i:s', strtotime( '+ '. ( $item_quantity * 365 ) .' days' ) );
					$new_expiry = date( 'Y-m-d H:i:s', strtotime( '+ '.$item_quantity.' years' ) );
					$download->set_access_expires( $new_expiry );
					$download->save();
				}
			}
		}
	}
}
add_action( 'woocommerce_before_thankyou', 'thp_wc_change_download_expiry_based_on_quantity' );