import types

__all__ = ('Field', 'Food')

class Field(object):
    """A field in a resource enforcing the type of its value"""
    def __init__(self, field_type, doc=None, default=None):
        self._field_type = field_type
        if not isinstance(default, (self._field_type, types.NoneType)):
            raise TypeError(default.__class__)
        self._default_value = default
        if not doc:
            doc = self._field_type.__doc__
        elif isinstance(doc, unicode):
            doc = doc.decode('utf-8')
        self.__doc__ = '%r: %s' % (self._field_type, doc)

    def _set_field_name(self, name):
        self._field_name = name

    def __get__(self, obj, type=None):
        return getattr(obj, self._field_name, self._default_value)

    def __set__(self, obj, value):
        # if someone gives str and we want unicode (or viceversa) handle the
        # conversion automagically, this simplifies a lot
        if self._field_type is unicode and isinstance(value, str):
            value = value.decode('utf-8')
        elif self._field_type is str and isinstance(value, unicode):
            value = value.encode('utf-8')
        elif not isinstance(value, (self._field_type, types.NoneType)):
            raise TypeError('Expected %r, got %r' % (self._field_type,
                    value.__class__))
        setattr(obj, self._field_name, value)


class Food(object):
    """A single resource"""
    def __new__(cls, **kwargs):
        obj = super(Food, cls).__new__(cls)
        fields = []
        for xcls in cls.mro():
            for k,v in xcls.__dict__.iteritems():
                if isinstance(v, Field):
                    field_name = '__field_%s' % k
                    v._set_field_name(field_name)
                    fields.append(k)
        obj._fields = tuple(fields)
        return obj

    def __init__(self, **kwargs):
        super(Food, self).__init__()
        for k,v in kwargs.iteritems():
            if k in self._fields:
                setattr(self, k, v)


    @property
    def kind(self):
        """Kind is not a Field"""
        return self._kind

    def values(self):
        d = dict(zip(self._fields, (getattr(self, k) for k in self._fields)))
        # kind is not a Field, but still it should be present on avery Food
        d['kind'] = self.kind
        return d

    def __str__(self):
        return str(self.values())

    def __eq__(self, other):
        return self.values() == other.values()