import logging

from app.core.config import settings
from app.services.backends.base import AbstractStorageBackend
from app.services.backends.local import LocalFSBackend
from app.services.backends.s3 import S3Backend
from app.services.backends.webdav import WebDAVBackend

logger = logging.getLogger(__name__)

_active_backend: AbstractStorageBackend | None = None


def build_backend(driver: str, config: dict) -> AbstractStorageBackend:
    """Construct a backend instance from a driver name + config dict."""
    if driver == "local":
        return LocalFSBackend(data_dir=config.get("data_dir", settings.DATA_DIR))
    if driver == "s3":
        return S3Backend(
            endpoint_url=config.get("endpoint_url", ""),
            access_key=config.get("access_key", ""),
            secret_key=config.get("secret_key", ""),
            region=config.get("region", "us-east-1"),
        )
    if driver == "webdav":
        return WebDAVBackend(
            url=config.get("url", ""),
            username=config.get("username", ""),
            password=config.get("password", ""),
            root_path=config.get("root_path", "/"),
        )
    raise ValueError(f"Unknown driver: {driver!r}. Valid options: local, s3, webdav")


def initialize_backend() -> None:
    """Build the initial backend from environment variables at startup."""
    global _active_backend
    driver = settings.STORAGE_BACKEND
    config: dict = {}
    if driver == "s3":
        config = {
            "endpoint_url": settings.S3_ENDPOINT_URL,
            "access_key": settings.S3_ACCESS_KEY,
            "secret_key": settings.S3_SECRET_KEY,
            "region": settings.S3_REGION,
        }
    elif driver == "webdav":
        config = {
            "url": settings.WEBDAV_URL,
            "username": settings.WEBDAV_USERNAME,
            "password": settings.WEBDAV_PASSWORD,
            "root_path": settings.WEBDAV_ROOT_PATH,
        }
    # local needs no extra config — DATA_DIR is read from settings inside build_backend
    _active_backend = build_backend(driver, config)
    logger.info("Storage backend initialized: %s", driver)


def get_backend() -> AbstractStorageBackend:
    if _active_backend is None:
        raise RuntimeError("Backend not initialized — call initialize_backend() at startup")
    return _active_backend


def switch_backend(new_backend: AbstractStorageBackend) -> None:
    """Replace the active backend. Called by the migration job after all data is verified."""
    global _active_backend
    old_name = _active_backend.driver_name if _active_backend else "none"
    _active_backend = new_backend
    logger.info("Storage backend switched: %s → %s", old_name, new_backend.driver_name)