What is the International Rule ie Guaranteed Contracts?

What is the current rule that pretains to international players in relation to guaranteed NBA contracts?  If teams draft a U.S. player in the first round the team is obligated to sign them to a guaranteed rookie contract.  If a team drafts an international player in the first round what is the procedure?  Do all international players need to be bought out of their current contract or do they only declare if their current contract is set to expire and if they need to be bought out does the NBA team know what that amount will be before they draft them?  If a NBA team drafts an international player they can let them develop overseas.  Right?  Then later do both the player and the NBA need to agree that the player is ready to come here or can the player just announce they are coming and the NBA team is obligated to offer them a guaranteed contract?  Is the salary then this years slot or do the NBA team and player work out a deal?  

I’m just trying to figure out why the last couple of 1st rd picks are not always international players.  Why would a NBA team draft an end of the bench U.S. player (or do NBA peeps think they will find a player late in rd 1) instead of a Bertans or Mirotic late?