A collision on a two-lane road, who is to blame? (Details inside. )

The two-lane road I talk about is one lane up and one lane down, if that makes sense.
I thought of this question while riding my bicycle, so it can be two bicycles colliding but cars are also okay.
One vehicle is driving towards the other, and on the wrong side of the road/wrong lane.
The other is driving on the right (as in correct) side/right lane but the person driving isn’t paying full attention for a second.
They collide.
Suppose there is damage on both bikes/cars, who will be considered at fault?
Who’s guilty morally, who legally?