import os

from django.conf import settings

from django.core import signals

from django.core.exceptions import ImproperlyConfigured

from django.utils.functional import curry

from django.utils.importlib import import_module

__all__ = ('backend', 'connection', 'DatabaseError', 'IntegrityError')

if not settings.DATABASE_ENGINE:

    settings.DATABASE_ENGINE = 'dummy'

def load_backend(backend_name):

    try:

        # Most of the time, the database backend will be one of the official

        # backends that ships with Django, so look there first.

        return import_module('.base', 'django.db.backends.%s' % backend_name)

    except ImportError, e:

        # If the import failed, we might be looking for a database backend

        # distributed external to Django. So we'll try that next.

        try:

            return import_module('.base', backend_name)

        except ImportError, e_user:

            # The database backend wasn't found. Display a helpful error message

            # listing all possible (built-in) database backends.

            backend_dir = os.path.join(__path__[0], 'backends')

            try:

                available_backends = [f for f in os.listdir(backend_dir)

                        if os.path.isdir(os.path.join(backend_dir, f))

                        and not f.startswith('.')]

            except EnvironmentError:

                available_backends = []

            available_backends.sort()

            if backend_name not in available_backends:

                error_msg = "%r isn't an available database backend. Available options are: %s\nError was: %s" % \

                    (backend_name, ", ".join(map(repr, available_backends)), e_user)

                raise ImproperlyConfigured(error_msg)

            else:

                raise # If there's some other error, this must be an error in Django itself.

backend = load_backend(settings.DATABASE_ENGINE)

# `connection`, `DatabaseError` and `IntegrityError` are convenient aliases

# for backend bits.

# DatabaseWrapper.__init__() takes a dictionary, not a settings module, so

# we manually create the dictionary from the settings, passing only the

# settings that the database backends care about. Note that TIME_ZONE is used

# by the PostgreSQL backends.

connection = backend.DatabaseWrapper({

    'DATABASE_HOST': settings.DATABASE_HOST,

    'DATABASE_NAME': settings.DATABASE_NAME,

    'DATABASE_OPTIONS': settings.DATABASE_OPTIONS,

    'DATABASE_PASSWORD': settings.DATABASE_PASSWORD,

    'DATABASE_PORT': settings.DATABASE_PORT,

    'DATABASE_USER': settings.DATABASE_USER,

    'TIME_ZONE': settings.TIME_ZONE,

})

DatabaseError = backend.DatabaseError

IntegrityError = backend.IntegrityError

# Register an event that closes the database connection

# when a Django request is finished.

def close_connection(**kwargs):

    connection.close()

signals.request_finished.connect(close_connection)

# Register an event that resets connection.queries

# when a Django request is started.

def reset_queries(**kwargs):

    connection.queries = []

signals.request_started.connect(reset_queries)

# Register an event that rolls back the connection

# when a Django request has an exception.

def _rollback_on_exception(**kwargs):

    from django.db import transaction

    try:

        transaction.rollback_unless_managed()

    except DatabaseError:

        pass

signals.got_request_exception.connect(_rollback_on_exception)