How to modify choices on Django Admin

I have a model that has a field named "state":

class Foo(models.Model):
    ...
    state = models.IntegerField(choices = STATES)
    ...

For every state, possible choices are a certain subset of all STATES. For example:

if foo.state == STATES.OPEN:     #if foo is open, possible states are CLOSED, CANCELED
    ...
if foo.state == STATES.PENDING:  #if foo is pending, possible states are OPEN,CANCELED
    ...

As a result, when foo.state changes to a new state, its set of possible choices changes also.

How can I implement this functionality on Admin add/change pages?