How Do You Counter Ganks Top Lane?

So here I am, Jayce in top lane. 3 minutes in, I have river warded and see a Vi come up to the brush. I go back and she leaves, I come back to the middle of the river to farm cs again. I get my enemy laner down to half health, and decide to go in on him to kill him. Vi went all the ways around the jungle, to come top through the back side (which I couldnt ward due to ward times), and boom I die.

Later, I get a vision ward and place it in the jungle brush, and a normal ward in river brush. She then comes top, destroys my ward, runs off. I place a ward there again after a minute, then she hits the plants, reveals my ward, destroys it, and she camps my lane because I have no ward.

How on earth am I suppose to do anything against this? If I sit under tower, Kennen would just farm passively while I wait for creeps to come to the tower. If I go in to farm, I just get killed by Vi and Kennen. Do I seriously need to buy a sightstone..