minecraft launcher won't launch

I have a macbook air and i've downloaded minecraft on it before like maybe a year ago and it worked perfectly fine, but i deleted it for some time and recently i tried redownloading it but everytime I press play, it says an unexpected error occured and the game crashed and i cant figure out why   i tried switching versions of it and pressing play but it crashes for all versions  help. also for the version i put 1.6.93 legacy but it wouldnt let me put any other versions so ye