Vignette portal API for creating migration tool for SharePoint 2013 using C#

Hi 

Since we did not find any specific tool for migrating Vignette portal to SharePoint 2013 we are planning to create a custom windows application (Tool) for migrating Vignette portal objects to SharePoint 2013 directly. Do we have any API's exposed by open text Vignette CMS to access objects and create a migration tool to migrate the data to SharePoint 2013 directly?

Any help/pointer in this regard is highly appreciated.

Thanks