There was a movie with two boys and two girls. Its plot took place in summer. One of the boys mother was present. I remember two things very well: the boys were smoking pot (they found cannabis growing wild next to a house); and (more to the end of the movie) a boy and a girl were playing strip poker / blackjack, the other two were kissing in a cave(?) – I think someone attacked them there. The movie ends when one of the boys was returning home (on a train?) and read a message from the other boy that there was only 300-something days left till summer. (I watched it about 20 years ago; language of movie: English).