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

'''

Created on Sep 1, 2015

@author: ymh

'''

from django.apps import AppConfig

from django.core.files.base import File

from django.db.models.fields.files import FieldFile

from django.db.models.fields.files import FileDescriptor

import six

def ldt_get(self, instance=None, owner=None):

    if instance is None:

        raise AttributeError(

            "The '%s' attribute can only be accessed from %s instances."

            % (self.field.name, owner.__name__))

    # This is slightly complicated, so worth an explanation.

    # instance.file`needs to ultimately return some instance of `File`,

    # probably a subclass. Additionally, this returned object needs to have

    # the FieldFile API so that users can easily do things like

    # instance.file.path and have that delegated to the file storage engine.

    # Easy enough if we're strict about assignment in __set__, but if you

    # peek below you can see that we're not. So depending on the current

    # value of the field we have to dynamically construct some sort of

    # "thing" to return.

    # The instance dict contains whatever was originally assigned

    # in __set__.

    file = instance.__dict__[self.field.name]  # @ReservedAssignment

    # If this value is callable (certainly because the field was defined

    # with a callable default), we execute the function and assign the

    # result to the value

    if six.callable(file):

        file = file()  # @ReservedAssignment

        if isinstance(file, FieldFile) and not hasattr(file, 'field'):

            instance.__dict__[self.field.name] = file

    # If this value is a string (instance.file = "path/to/file") or None

    # then we simply wrap it with the appropriate attribute class according

    # to the file field. [This is FieldFile for FileFields and

    # ImageFieldFile for ImageFields; it's also conceivable that user

    # subclasses might also want to subclass the attribute class]. This

    # object understands how to convert a path to a file, and also how to

    # handle None.

    if isinstance(file, six.string_types) or file is None:

        attr = self.field.attr_class(instance, self.field, file)

        instance.__dict__[self.field.name] = attr

    # Other types of files may be assigned as well, but they need to have

    # the FieldFile interface added to them. Thus, we wrap any other type of

    # File inside a FieldFile (well, the field's attr_class, which is

    # usually FieldFile).

    elif isinstance(file, File) and not isinstance(file, FieldFile):

        file_copy = self.field.attr_class(instance, self.field, file.name)

        file_copy.file = file

        file_copy._committed = False

        instance.__dict__[self.field.name] = file_copy

    # Finally, because of the (some would say boneheaded) way pickle works,

    # the underlying FieldFile might not actually itself have an associated

    # file. So we need to reset the details of the FieldFile in those cases.

    elif isinstance(file, FieldFile) and not hasattr(file, 'field'):

        file.instance = instance

        file.field = self.field

        file.storage = self.field.storage

    # That was fun, wasn't it?

    return instance.__dict__[self.field.name]

class LdtAppConfig(AppConfig):

    '''

    App config to monkey patch django.db.models.fields.files.FileDescriptor.__get__ (cf django bug #24823 https://code.djangoproject.com/ticket/24823)

    '''

    name = 'ldt'

    verbose_name = 'LDT Platform'

    def ready(self):

        FileDescriptor.__get__ = ldt_get