def concatenate_nfa(self, nfa: NFA, char_to_concatenate: str) -> NFA:
"""
concatenate_nfa
Concatenate a regex char to an existing NFA.
:param nfa: The existing NFA.
:param char_to_concatenate: Character from regex to concatenate.
:return: The resulting NFA.
"""
# As states are added, update the last state to connect from
# if this isn't the first char of the regex (only a start state), add an epsilon transition.
if len(nfa.states) > 1:
self.last_state = nfa.add_epsilon_connector(self.last_state)
# add the last state as an last close group
self.last_closed_group = self.last_state
# Connect to to new state on concat_char
if self.union_in_progress:
self.last_state = nfa.add_normal_char(
self.last_state, char_to_concatenate, True,
self.union_in_progress[-1][1])
elif self.last_star:
self.last_state = nfa.add_normal_char(self.last_state,
char_to_concatenate, True,
self.last_star[-1])
self.last_star = self.last_star[:-1]
else:
self.last_state = nfa.add_normal_char(self.last_state,
char_to_concatenate, True,
self.open_groups[-1])
return nfa
