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# vim: set fileencoding=utf-8 : 

# 

# (C) 2011 Guido Guenther <agx@sigxcpu.org> 

#    This program is free software; you can redistribute it and/or modify 

#    it under the terms of the GNU General Public License as published by 

#    the Free Software Foundation; either version 2 of the License, or 

#    (at your option) any later version. 

# 

#    This program is distributed in the hope that it will be useful, 

#    but WITHOUT ANY WARRANTY; without even the implied warranty of 

#    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the 

#    GNU General Public License for more details. 

# 

#    You should have received a copy of the GNU General Public License 

#    along with this program; if not, write to the Free Software 

#    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA 

 

class Tristate(object): 

    """Tri-state value: on, off or auto """ 

    ON  = True      # state is on == do it 

    OFF = False     # state is off == don't do it 

    AUTO = -1       # autodetect == do if possible 

 

    # We accept true as alias for on and false as alias for off 

    _VALID_NAMES = [ 'on', 'off', 'true', 'false', 'auto' ] 

 

    def __init__(self, val): 

        if type(val) in [ type(t) for t in (True, 1) ]: 

            if val > 0: 

                self._state = self.ON 

            elif val < 0: 

                self._state = self.AUTO 

            else: 

                self._state = self.OFF 

        elif type(val) in [ type(t) for t in ("", u"") ]: 

            if val.lower() in [ 'on', 'true' ]: 

                self._state = self.ON 

            elif val.lower() in [ 'auto' ]: 

                self._state = self.AUTO 

            else: 

                self._state = self.OFF 

        elif type(val) is Tristate: 

            self._state = val.state 

        else: 

            raise TypeError 

 

    def __repr__(self): 

        """ 

        >>> Tristate('on').__repr__() 

        'on' 

        >>> Tristate(True).__repr__() 

        'on' 

        >>> Tristate(False).__repr__() 

        'off' 

        >>> Tristate('auto').__repr__() 

        'auto' 

        """ 

        if self._state == self.ON: 

            return 'on' 

        elif self._state == self.AUTO: 

            return 'auto' 

        else: 

            return 'off' 

 

    @property 

    def state(self): 

        """Get current state""" 

        return self._state 

 

    def is_auto(self): 

        return [False, True][self._state == self.AUTO] 

 

    def is_on(self): 

        return [False, True][self._state == self.ON] 

 

    def is_off(self): 

        return [False, True][self._state == self.OFF] 

 

    def do(self, function, *args, **kwargs): 

        """ 

        Run function if tristate is on or auto, only report a failure if 

        tristate is on since failing is o.k. for autodetect. 

        """ 

        if self.is_off(): 

            return True 

 

        success = function(*args, **kwargs) 

        if not success: 

            return [True, False][self.is_on()] 

 

        return True