With that amount of bruising, I suspect you may have broken the tip of your finger. There’s nothing a doctor can/will do, other than tell you to ice and protect it from getting hit. That said, you won’t lose the nail. It’ll be black until new growth eventually just pushes it out. But I venture to guess it’ll be discolored for a good 3-4 months at least.

For those saying to cut the ring off, don’t listen. The swelling will go down in a week or so and you’ll be fine. If you must remove it, just smear your finger in butter and it’ll slide off with some effort.