from rest_framework.parsers import BaseParser, DataAndFiles
from django.http.multipartparser import MultiPartParserError
from rest_framework.exceptions import ParseError
from django.http.multipartparser import \
    MultiPartParser as DjangoMultiPartParser
from django.conf import settings
import json


class NestedJsonMultiPartParser(BaseParser):
    """
    Parser for multipart form data, which may include file data.
    """
    media_type = 'multipart/form-data'

    def parse(self, stream, media_type=None, parser_context=None):
        """
        Parses the incoming bytestream as a multipart encoded form,
        and returns a DataAndFiles object.
        The main difference with the parser from rest_framework.parsers
        is that it attempts to parse nested strings as json to fit with
        better with json payloads. I also ensure that a single file is
        passed per field instead of a list which was erroring out
        FieldFile.to_internal_value.

        `.data` will be a dict containing all the form parameters.
        `.files` will be a dict containing all the form files.
        """
        parser_context = parser_context or {}
        request = parser_context['request']
        encoding = parser_context.get('encoding', settings.DEFAULT_CHARSET)
        meta = request.META.copy()
        meta['CONTENT_TYPE'] = media_type
        upload_handlers = request.upload_handlers

        try:
            parser = DjangoMultiPartParser(meta,
                                           stream,
                                           upload_handlers,
                                           encoding)
            data, files = parser.parse()

            # Attempt to parse the multipart fields as json, this is not
            # demanding since multiparts exist exclusively for file uploads
            # which is much more demanding
            data_dict = {}
            for key in data.keys():
                values = data[key]
                try:
                    data_dict[key] = json.loads(values)
                except Exception as e:
                    data_dict[key] = values

            # Make sure the filenames become file names
            for filename in files.keys():
                uploaded_file = files[filename]
                hasfilename = hasattr(uploaded_file, '_name')
                hasname = hasattr(uploaded_file, 'name')
                if hasfilename and not hasname:
                    uploaded_file.name = uploaded_file._name

            # Turn the monstrous MultiValueDict into a normal dict so that
            # there is only a single uploaded file per field passed
            files_dict = {}
            for key in files.keys():
                uploaded_file = files[key]
                if isinstance(uploaded_file, list):
                    uploaded_file = uploaded_file[0]
                files_dict[key] = uploaded_file

            return DataAndFiles(data_dict, files_dict)
        except MultiPartParserError as exc:
            raise ParseError('Multipart form parse error - %s' % str(exc))