2 Week Portugal Itinerary help - no car - Lisbon/Porto/Madeira

Hi all! We've interested in 2 weeks Portugal trip in August and are struggling with putting together an itinerary. We are interested in Lisbon, Porto and Madeira mainly, unsure if this is feasible in 2 weeks. We will not be renting a car and relying on public transport for the entire trip. Any suggestions would be great! Open to seeing other cities/areas as well :)