from rest_framework import serializers
from rest_framework import exceptions as rest_exceptions

from rest_framework.views import exception_handler
from rest_framework.settings import api_settings
from rest_framework import exceptions

from django.core.exceptions import ValidationError


def create_serializer_class(name, fields):
    return type(name, (serializers.Serializer, ), fields)


def inline_serializer(*, fields, data=None, **kwargs):
    serializer_class = create_serializer_class(name='', fields=fields)

    if data is not None:
        return serializer_class(data=data, **kwargs)

    return serializer_class(**kwargs)


def get_first_matching_attr(obj, *attrs, default=None):
    for attr in attrs:
        if hasattr(obj, attr):
            return getattr(obj, attr)

    return default


def get_error_message(exc):
    if hasattr(exc, 'message_dict'):
        return exc.message_dict
    error_msg = get_first_matching_attr(exc, 'message', 'messages')

    if isinstance(error_msg, list):
        error_msg = ', '.join(error_msg)

    if error_msg is None:
        error_msg = str(exc)

    return error_msg


class ApiErrorsMixin:
    """
    Mixin that transforms Django and Python exceptions into rest_framework ones.
    without the mixin, they return 500 status code which is not desired.
    """
    expected_exceptions = {
        ValueError: rest_exceptions.ValidationError,
        ValidationError: rest_exceptions.ValidationError,
        PermissionError: rest_exceptions.PermissionDenied
    }

    def handle_exception(self, exc):
        if isinstance(exc, tuple(self.expected_exceptions.keys())):
            drf_exception_class = self.expected_exceptions[exc.__class__]
            drf_exception = drf_exception_class(get_error_message(exc))

            return super().handle_exception(drf_exception)

        return super().handle_exception(exc)


class ErrorsFormatter:
    """
    The current formatter gets invalid serializer errors,
    uses DRF standart for code and messaging
    and then parses it to the following format:

    {
        "errors": [
            {
                "message": "Error message",
                "code": "Some code",
                "field": "field_name"
            },
            {
                "message": "Error message",
                "code": "Some code",
                "field": "nested.field_name"
            },
            ...
        ]
    }
    """
    FIELD = 'field'
    MESSAGE = 'message'
    CODE = 'code'
    ERRORS = 'errors'

    def __init__(self, exception):
        self.exception = exception

    def __call__(self):
        if hasattr(self.exception, 'get_full_details'):
            formatted_errors = self._get_response_json_from_drf_errors(
                serializer_errors=self.exception.get_full_details()
            )
        else:
            formatted_errors = self._get_response_json_from_error_message(message=str(self.exception))

        return formatted_errors

    def _get_response_json_from_drf_errors(self, serializer_errors=None):
        if serializer_errors is None:
            serializer_errors = {}

        if type(serializer_errors) is list:
            serializer_errors = {
                api_settings.NON_FIELD_ERRORS_KEY: serializer_errors
            }

        list_of_errors = self._get_list_of_errors(errors_dict=serializer_errors)

        response_data = {
            self.ERRORS: list_of_errors
        }

        return response_data

    def _get_response_json_from_error_message(self, *, message='', field=None, code='error'):
        response_data = {
            self.ERRORS: [
                {
                    self.MESSAGE: message,
                    self.CODE: code
                }
            ]
        }

        if field:
            response_data[self.ERRORS][self.FIELD] = field

        return response_data

    def _unpack(self, obj):
        if type(obj) is list and len(obj) == 1:
            return obj[0]

        return obj

    def _get_list_of_errors(self, field_path='', errors_dict=None):
        """
        Error_dict is in the following format:
        {
            'field1': {
                'message': 'some message..'
                'code' 'some code...'
            },
            'field2: ...'
        }
        """
        if errors_dict is None:
            return []

        message_value = errors_dict.get(self.MESSAGE, None)

        # Note: If 'message' is name of a field we don't want to stop the recursion here!
        if message_value is not None and\
           (type(message_value) in {str, exceptions.ErrorDetail}):
            if field_path:
                errors_dict[self.FIELD] = field_path
            return [errors_dict]

        errors_list = []
        for key, value in errors_dict.items():
            new_field_path = '{0}.{1}'.format(field_path, key) if field_path else key
            key_is_non_field_errors = key == api_settings.NON_FIELD_ERRORS_KEY

            if type(value) is list:
                current_level_error_list = []
                new_value = value

                for error in new_value:
                    # if the type of field_error is list we need to unpack it
                    field_error = self._unpack(error)

                    if not key_is_non_field_errors:
                        field_error[self.FIELD] = new_field_path

                    current_level_error_list.append(field_error)
            else:
                path = field_path if key_is_non_field_errors else new_field_path

                current_level_error_list = self._get_list_of_errors(field_path=path, errors_dict=value)

            errors_list += current_level_error_list

        return errors_list


def exception_errors_format_handler(exc, context):
    response = exception_handler(exc, context)

    # If unexpected error occurs (server error, etc.)
    if response is None:
        return response

    formatter = ErrorsFormatter(exc)

    response.data = formatter()

    return response