import importlib
import os
from contextlib import contextmanager

from flask import g


class BaseBackend:
    instance = None

    def __init__(self, config):
        BaseBackend.instance = self
        self.register_models()

    @classmethod
    def get(cls):
        return cls.instance

    def init_app(self, app):
        @app.before_request
        def before_request():
            return self.setup()

        @app.after_request
        def after_request(response):
            self.teardown()
            return response

    @contextmanager
    def session(self):
        yield self.setup()
        self.teardown()

    @classmethod
    def install(self):
        """
        This methods prepares the database to host canaille data.
        """
        raise NotImplementedError()

    def setup(self):
        """
        This method will be called before each http request,
        it should open the connection to the backend.
        """
        raise NotImplementedError()

    def teardown(self):
        """
        This method will be called after each http request,
        it should close the connections to the backend.
        """
        raise NotImplementedError()

    @classmethod
    def validate(cls, config):
        """
        This method should validate the config part dedicated to the backend.
        It should raise :class:`~canaille.configuration.ConfigurationError` when
        errors are met.
        """
        raise NotImplementedError()

    def has_account_lockability(self):
        """
        Indicates wether the backend supports locking user accounts.
        """
        raise NotImplementedError()

    def register_models(self):
        from canaille.app import models

        module = ".".join(self.__class__.__module__.split(".")[:-1] + ["models"])
        try:
            backend_models = importlib.import_module(module)
        except ModuleNotFoundError:
            return

        model_names = [
            "AuthorizationCode",
            "Client",
            "Consent",
            "Group",
            "Token",
            "User",
        ]
        for model_name in model_names:
            models.register(getattr(backend_models, model_name))


def setup_backend(app, backend):
    if not backend:
        backend_name = list(app.config.get("BACKENDS", {"memory": {}}).keys())[
            0
        ].lower()
        module = importlib.import_module(f"canaille.backends.{backend_name}.backend")
        backend_class = getattr(module, "Backend")
        backend = backend_class(app.config)
        backend.init_app(app)

    with app.app_context():
        g.backend = backend
        app.backend = backend

    if app.debug:
        backend.install(app.config, True)


def available_backends():
    return {
        elt.name
        for elt in os.scandir(os.path.dirname(__file__))
        if elt.is_dir() and os.path.exists(os.path.join(elt, "backend.py"))
    }