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# -*- 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()
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