from typing import Generic, Iterable, Type, TypeVar

from dal import autocomplete  # type: ignore
from django.db.models import Model, Q

M = TypeVar("M", bound=Model)


class ModelSearch(Generic[M]):
    """Basic search engine for models based on filtering.

    As the type hints indicate, the class is generic with respect to the model. This
    means that the ``search`` method only returns instances of the model specified as
    the ``model`` class attribute in subclasses.

    The ``search_fields`` attributes indicates which fields to search in during the
    search.

    Example:

    >>> from django.contrib.auth.models import User
    >>>
    >>> class UserSearch(ModelSearch):
    ...     model = User
    ...     search_fields = ["username", "first_name", "last_name"]
    >>>
    >>> user_search = UserSearch()  # has type ModelSearch[User]
    >>> user_search.search(["toto", "foo"])  # returns a queryset of Users
    """

    # This says that `model` is the class corresponding to the type variable M (or a
    # subclass).
    model: Type[M]
    search_fields: Iterable[str]

    def get_queryset_filter(self, keywords: Iterable[str]) -> Q:
        filter_q = Q()

        if not keywords:
            return filter_q

        for keyword in keywords:
            kw_filter = Q()
            for field in self.search_fields:
                kw_filter |= Q(**{"{}__icontains".format(field): keyword})
            filter_q &= kw_filter

        return filter_q

    def search(self, keywords: Iterable[str]) -> Iterable[M]:
        """Returns the queryset of model instances matching all the keywords.

        The semantic of the search is the following: a model instance appears in the
        search results iff all of the keywords given as arguments occur in at least one
        of the search fields.
        """

        return self.model.objects.filter(self.get_queryset_filter(keywords))


class Select2QuerySetView(ModelSearch, autocomplete.Select2QuerySetView):
    """Compatibility layer between ModelSearch and Select2QuerySetView."""

    def get_queryset(self):
        keywords = self.q.split()
        return super().search(keywords)