from django.db import DataError
from django.db.models import Model
from rest_framework import exceptions, serializers
from rest_framework.exceptions import ValidationError
from rest_framework.validators import qs_exists, qs_filter, UniqueTogetherValidator

from desecapi.permissions import TokenHasRRsetPermission


def qs_exclude(queryset, **kwargs):
    try:
        return queryset.exclude(**kwargs)
    except (TypeError, ValueError, DataError):
        return queryset.none()


class ExclusionConstraintValidator(UniqueTogetherValidator):
    """
    Validator that implements ExclusionConstraints, currently very basic with support for one field only.
    Should be applied to the serializer class, not to an individual field.
    No-op if parent serializer is a list serializer (many=True). We expect the list serializer to assure exclusivity.
    """

    message = "This field violates an exclusion constraint."

    def __init__(self, queryset, fields, exclusion_condition, message=None):
        super().__init__(queryset, fields, message)
        self.exclusion_condition = exclusion_condition

    def filter_queryset(self, attrs, queryset, serializer):
        qs = super().filter_queryset(attrs, queryset, serializer)

        # Determine the exclusion filters and prepare the queryset.
        field_name = self.exclusion_condition[0]
        value = self.exclusion_condition[1]
        source = serializer.fields[field_name].source
        if serializer.instance is not None:
            if source not in attrs:
                attrs[source] = getattr(serializer.instance, source)
        exclusion_method = qs_exclude if attrs[source] == value else qs_filter
        return exclusion_method(qs, **{field_name: value})

    def __call__(self, attrs, serializer, *args, **kwargs):
        # Ignore validation if the many flag is set
        if getattr(serializer.root, "many", False):
            return

        self.enforce_required_fields(attrs, serializer)
        queryset = self.queryset
        queryset = self.filter_queryset(attrs, queryset, serializer)
        queryset = self.exclude_current_instance(attrs, queryset, serializer.instance)

        # Ignore validation if any field is None
        checked_values = [
            value for field, value in attrs.items() if field in self.fields
        ]
        if None not in checked_values and qs_exists(queryset):
            types = queryset.values_list("type", flat=True)
            types = ", ".join(types)
            message = self.message.format(types=types)
            raise ValidationError(message, code="exclusive")


class PermissionValidator:
    """
    Validator that checks write permission for an RRset.
    """

    requires_context = True

    def __call__(self, attrs, serializer):
        # On the RRsetDetail apex endpoint, subname is not in attrs
        subname = attrs.get("subname")
        if subname is None:
            subname = serializer.context["view"].kwargs["subname"]
        # On the RRsetDetail endpoint, the type is not in attrs
        type_ = attrs.get("type") or serializer.instance.type

        rrset = serializer.Meta.model(
            domain=serializer.domain, subname=subname, type=type_
        )
        permission = TokenHasRRsetPermission()
        if not permission.has_object_permission(
            serializer.context.get("request"), None, rrset
        ):
            raise exceptions.PermissionDenied(
                detail=getattr(permission, "message", None),
                code=getattr(permission, "code", None),
            )


class Validator:
    message = "This field did not pass validation."

    def __init__(self, message=None):
        self.field_name = None
        self.message = message or self.message
        self.instance = None

    def __call__(self, value):
        raise NotImplementedError

    def __repr__(self):
        return "<%s>" % self.__class__.__name__


class ReadOnlyOnUpdateValidator(Validator):
    message = "Can only be written on create."
    requires_context = True

    def __call__(self, value, serializer_field):
        field_name = serializer_field.source_attrs[-1]
        instance = getattr(serializer_field.parent, "instance", None)
        if isinstance(instance, Model) and value != getattr(instance, field_name):
            raise serializers.ValidationError(self.message, code="read-only-on-update")