from dal import autocomplete
from django.db.models import Q


class ModelSearch:
    """Basic search engine for models based on filtering.

    Subclasses should override the ``model`` class attribute and specify the list of
    search fields to be searched in.
    """

    model = None
    search_fields = []

    def get_queryset_filter(self, keywords):
        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):
        """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)