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#!/usr/bin/env python

# -*- coding: utf-8 -*-

"""

@author: Gordeev Andrey <gordeev.and.and@gmail.com>

Specification provide recombination business logic by

chaining together using boolean logic

"""

from abc import abstractmethod

class Specification(object):

def and_specification(self, candidate):

raise NotImplementedError()

def or_specification(self, candidate):

raise NotImplementedError()

def not_specification(self):

raise NotImplementedError()

@abstractmethod

def is_satisfied_by(self, candidate):

pass

class CompositeSpecification(Specification):

@abstractmethod

def is_satisfied_by(self, candidate):

pass

def and_specification(self, candidate):

return AndSpecification(self, candidate)

def or_specification(self, candidate):

return OrSpecification(self, candidate)

def not_specification(self):

return NotSpecification(self)

class AndSpecification(CompositeSpecification):

_one = Specification()

_other = Specification()

def __init__(self, one, other):

self._one = one

self._other = other

def is_satisfied_by(self, candidate):

return bool(self._one.is_satisfied_by(candidate) and

self._other.is_satisfied_by(candidate))

class OrSpecification(CompositeSpecification):

_one = Specification()

_other = Specification()

def __init__(self, one, other):

self._one = one

self._other = other

def is_satisfied_by(self, candidate):

return bool(self._one.is_satisfied_by(candidate) or

self._other.is_satisfied_by(candidate))

class NotSpecification(CompositeSpecification):

_wrapped = Specification()

def __init__(self, wrapped):

self._wrapped = wrapped

def is_satisfied_by(self, candidate):

return bool(not self._wrapped.is_satisfied_by(candidate))

class User(object):

def __init__(self, super_user=False):

self.super_user = super_user

class UserSpecification(CompositeSpecification):

def is_satisfied_by(self, candidate):

return isinstance(candidate, User)

class SuperUserSpecification(CompositeSpecification):

def is_satisfied_by(self, candidate):

return getattr(candidate, 'super_user', False)

if __name__ == '__main__':

print('Specification')

andrey = User()

ivan = User(super_user=True)

vasiliy = 'not User instance'

root_specification = UserSpecification().\

and_specification(SuperUserSpecification())

print(root_specification.is_satisfied_by(andrey))

print(root_specification.is_satisfied_by(ivan))

print(root_specification.is_satisfied_by(vasiliy))

### OUTPUT ###

# Specification

# False

# True

# False