Cannot start game

Yesterday the game worked great. Today when I started the game, it performed some sort of update, and now the game won't start, giving the error:
Error: Could not find or load main class net.minecraft.client.main.Main

Entire launcher log attached, but not much information to be gained from it.

Next I re-downloaded the installer, ran it, and selected 'Repair'. No change to the outcome. Then I uninstalled Minecraft and re-installed from scratch. No change.

I only bought my account a few weeks ago. Life is too short for this kind of headache, so if this the quality of the Minecraft product, I can do without it. How can I get my money back? Just ridiculous.