"""Backend factory - resolves ``SEARCH["BACKEND"]`` to a concrete strategy."""

from __future__ import annotations

from functools import cache

from django.conf import settings
from django.core.exceptions import ImproperlyConfigured

from apps.search.backends.base import SearchBackend

__all__ = ["SearchBackend", "get_search_backend"]


@cache
def get_search_backend(name: str | None = None) -> SearchBackend:
    """
    Return the configured backend.

    Cached because both implementations hold a connection pool that should be
    created once per process, not once per request.
    """
    backend = (name or settings.SEARCH["BACKEND"]).lower()

    if backend == "elasticsearch":
        from apps.search.backends.elastic import ElasticsearchBackend

        return ElasticsearchBackend()
    if backend == "postgres":
        from apps.search.backends.postgres import PostgresBackend

        return PostgresBackend()

    raise ImproperlyConfigured(
        f"Unknown SEARCH['BACKEND'] {backend!r}; expected 'elasticsearch' or 'postgres'."
    )