Unregistered users

My shop is almost ready to open; just a few adjustments.

How can I do to prevent unregistered users to click buy.
I'd like that the unregistered users could view all the articles with prices but when they click on buy the system go automatically to login.
Is it possible?

Now the system goes to login with ceckout.

That's already what I'm seeing on your website. When you click on buy, you get the popup telling you that the product has been added in the cart. Then, if you click to go to the checkout, you get the login/registration form if you're not already logged in and you can't finish your order without logging in or registering.

Maybe I expressed myself badly. English is not my native language.
I wanted to say, the system should send to login before ceckout, just when I click on add to cart.

That's not possible. But you would have a first step of your checkout with only the login/registration step displayed by changing the checkout workflow option of the configuration. Wouldn't that be the same for you ?

I'm sorry; it is not the same.
But never mind! It isn't very important.
Thanks