refactor switching and sensing methods into separate classes

[xaver-k]

RE: https://github.com/kantlivelong/OctoPrint-PSUControl/issues/223#issuecomment-913915951_

Move the different switching and sensing methods into their own self-contained classes (see example below). This improves clarity in the code and simplifies testing, error-handing and makes it easy to add or modify switching and sensing implementations.

Note: Implementing this will change the codebase quite a bit and will likely conflict with any other PRs written at the same time.

Possible implementation (click to expand):

```python # # for python 2.7 backwards compatibility, see https://stackoverflow.com/a/41622155 # ---------------------------------------------------------------- # import sys import abc if sys.version_info >= (3, 4): ABC = abc.ABC else: ABC = abc.ABCMeta('ABC', (), {}) # # define general interfaces and shared fuctionality # ---------------------------------------------------------------- # class SwitcherBase(ABC): """ base class for switching the PSU on and off """ def __init__(self, logger): self._logger = logger @abc.abstractmethod def set_psu_state(self, state): # type: (bool) -> None """ switch the PSU on or off """ def cleanup(self): """ clean up any used resources """ class SenserBase(ABC): """ base class for sensing the PSU's current state """ def __init__(self, logger): self._logger = logger @abc.abstractmethod def get_psu_state(self): # type: () -> Optional[bool] """ read the current on / off state of the PSU and return it as a boolean, return None if the state is unknown """ def cleanup(self): """ clean up any used resources """ pass # # implementation of the specific methods # ---------------------------------------------------------------- # class GPIOSwitcher(SwitcherBase): """ switches PSU state via GPIO """ def __init__(self, path, pin_number, inverted, logger): super(GPIOSwitcher, self).__init__(logger) self._logger.info("Configuring GPIO for pin {}".format(pin_number)) try: self._pin = periphery.CdevGPIO( path=path, line=pin_number, direction="out", inverted=inverted, ) except Exception as e: self._logger.exception( "Exception while setting up GPIO pin {}".format(pin_number) ) self._pin = None raise e def set_psu_state(self, state): if self._pin is not None: self._pin.write() def cleanup(self): self._logger.debug("Cleaning up sensing pin {}".format(self._pin.name())) if self._pin is not None: # should work, even if we try to clean up the same GPIO twice self._pin.close() class SystemSenser(SenserBase): """ reads PSU state via user-supplied system command """ def __init__(self, sense_command, logger): super(SystemSenser, self).__init__(logger) self._sense_command = sense_command def get_psu_state(self): p = subprocess.Popen(self._sense_command, shell=True) self._logger.debug( "Sensing system command executed. PID={}, Command={}".format(p.pid, self._sense_command)) p.wait() # TODO: set a timeout? r = p.returncode self._logger.debug("Sensing system command returned: {}".format(r)) return not bool(r) # # use a factory function to produce the right switcher and senser objects based on the config # ---------------------------------------------------------------- # class PSUControl(...): ... @classmethod def _switcher_senser_factory(self, config, logger): # type: (...) -> Tuple[SenserBase, SwitcherBase] if config['switchingMethod'] == 'GCODE': ... elif config['switchingMethod'] == 'SYSTEM': ... ... ```

[xaver-k]

I should probably have mentioned that I would be happy to provide a draft-PR if there is an interest in the proposed changes.