"""Clean Code in Python - Chapter 9: Common Design Patterns

> State
"""
import abc

from log import logger


class InvalidTransitionError(Exception):
 """Raised when trying to move to a target state from an unreachable source
 state.
 """


class MergeRequestState(abc.ABC):
 def __init__(self, merge_request):
 self._merge_request = merge_request

 @abc.abstractmethod
 def open(self):
 ...

 @abc.abstractmethod
 def close(self):
 ...

 @abc.abstractmethod
 def merge(self):
 ...

 def __str__(self):
 return self.__class__.__name__


class Open(MergeRequestState):
 def open(self):
 self._merge_request.approvals = 0

 def close(self):
 self._merge_request.approvals = 0
 self._merge_request.state = Closed

 def merge(self):
 logger.info("merging %s", self._merge_request)
 logger.info("deleting branch %s", self._merge_request.source_branch)
 self._merge_request.state = Merged


class Closed(MergeRequestState):
 def open(self):
 logger.info("reopening closed merge request %s", self._merge_request)
 self._merge_request.state = Open

 def close(self):
 """Current state."""

 def merge(self):
 raise InvalidTransitionError("can't merge a closed request")


class Merged(MergeRequestState):
 def open(self):
 raise InvalidTransitionError("already merged request")

 def close(self):
 raise InvalidTransitionError("already merged request")

 def merge(self):
 """Current state."""


class MergeRequest:
 def __init__(self, source_branch: str, target_branch: str) -> None:
 self.source_branch = source_branch
 self.target_branch = target_branch
 self._state = None
 self.approvals = 0
 self.state = Open

 @property
 def state(self):
 return self._state

 @state.setter
 def state(self, new_state_cls):
 self._state = new_state_cls(self)

 def open(self):
 return self.state.open()

 def close(self):
 return self.state.close()

 def merge(self):
 return self.state.merge()

 def __str__(self):
 return f"{self.target_branch}:{self.source_branch}"