How HCP Cloud Portal reuse the contents from the on-premise NW portal??

What should be the starting point when we need to plan a Migration from the on premise Enterprise Portal solution to SAP HANA Cloud Portal.

Assuming that the existing on premise Enterprise Portal is hosting Custom WDJ solutions, WDA iViews, ESS/MSS , BI/BOBJ Reports etc, SAPUI5 solution, Java Application etc and they need to be migrated to SAP HANA Cloud Portal.