Complemento directo e indirecto

[nil]

hey I have problems related to CD and CI.
1-can CI have other prepositions other than "a" or "para",or maybe no prepositions at all?
for example:
-Puse azúcar en tu café ( en )(tu cafe is CI but "en" is the preposition?)

what about CD when its a human like,it should always have "a"?

2-why sometimes there are 2 CI in the sentence,like:
Le compré un regalo a mi amiga.


3-when sometimes there's no CD but there is CI?

thanks!