| # -*- coding: utf-8 -*- |
| # |
| # Copyright 2011 Google Inc. All Rights Reserved. |
| # |
| |
| __author__ = 'kbaclawski@google.com (Krystian Baclawski)' |
| |
| from automation.common import events |
| |
| |
| class BasicStateMachine(object): |
| """Generic class for constructing state machines. |
| |
| Keeps all states and possible transition of a state machine. Ensures that |
| transition between two states is always valid. Also stores transition events |
| in a timeline object. |
| """ |
| state_machine = {} |
| final_states = [] |
| |
| def __init__(self, initial_state): |
| assert initial_state in self.state_machine,\ |
| 'Initial state does not belong to this state machine' |
| |
| self._state = initial_state |
| |
| self.timeline = events.EventHistory() |
| self.timeline.AddEvent(self._state) |
| |
| def __str__(self): |
| return self._state |
| |
| def __eq__(self, value): |
| if isinstance(value, BasicStateMachine): |
| value = str(value) |
| |
| return self._state == value |
| |
| def __ne__(self, value): |
| return not self == value |
| |
| def _TransitionAllowed(self, to_state): |
| return to_state in self.state_machine.get(self._state, []) |
| |
| def Change(self, new_state): |
| assert self._TransitionAllowed(new_state),\ |
| 'Transition from %s to %s not possible' % (self._state, new_state) |
| |
| self._state = new_state |
| |
| self.timeline.AddEvent(self._state) |
| |
| if self._state in self.final_states: |
| self.timeline.last.Finish() |
