from django.db.backends.signals import connection_created
from django.db.models import CharField, Transform
from django.dispatch import receiver
from rest_framework.filters import SearchFilter

SQLITE_CASEFOLD_FUNCTION = "EUSRR_CASEFOLD"


def _casefold(value):
    return None if value is None else str(value).casefold()


@receiver(connection_created, dispatch_uid="commerce.sqlite_unicode_casefold")
def register_sqlite_casefold(sender, connection, **kwargs):
    if connection.vendor != "sqlite":
        return
    connection.connection.create_function(
        SQLITE_CASEFOLD_FUNCTION,
        1,
        _casefold,
        deterministic=True,
    )


class UnicodeCasefold(Transform):
    lookup_name = "unicode_casefold"
    function = "LOWER"
    output_field = CharField()

    def as_sqlite(self, compiler, connection, **extra_context):
        return super().as_sql(
            compiler,
            connection,
            function=SQLITE_CASEFOLD_FUNCTION,
            **extra_context,
        )


CharField.register_lookup(UnicodeCasefold)


class UnicodeCasefoldSearchFilter(SearchFilter):
    """DRF substring search with Unicode-aware case normalization."""

    def get_search_terms(self, request):
        return [term.casefold() for term in super().get_search_terms(request)]