import datetime

import functools

import json

class Rate:

    FIELDS = [

        'base',

        'disclaimer',

        'license',

        'rates',

        'timestamp',

    ]

    @classmethod

    def walk_fields(cls, get_field, transform_prefix):

        for fieldname in cls.FIELDS:

            value = get_field(fieldname)

            if value is not None:

                try:

                    transformer = getattr(cls, '{}_{}'.format(transform_prefix, fieldname))

                except AttributeError:

                    pass

                else:

                    value = transformer(value)

            yield (fieldname, value)

    def __init__(self, base, rates, **kwargs):

        for key, value in self.walk_fields(kwargs.get, 'deserialize'):

            setattr(self, key, value)

        self.base = base

        self.rates = rates

    @classmethod

    def deserialize_timestamp(cls, value):

        return datetime.datetime.fromtimestamp(value)

    @classmethod

    def serialize_timestamp(cls, value):

        return int(value.timestamp())

    @classmethod

    def from_json_file(cls, json_file):

        response = json.load(json_file)

        return cls(**response)

    def serialize(self):

        return dict(self.walk_fields(functools.partial(getattr, self), 'serialize'))