import os

from django.conf import settings

from django.core import signals

from django.core.exceptions import ImproperlyConfigured

from django.utils.functional import curry

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

if not settings.DATABASE_ENGINE:

    settings.DATABASE_ENGINE = 'dummy'

try:

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

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

    _import_path = 'django.db.backends.'

    backend = __import__('%s%s.base' % (_import_path, settings.DATABASE_ENGINE), {}, {}, [''])

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:

        _import_path = ''

        backend = __import__('%s.base' % settings.DATABASE_ENGINE, {}, {}, [''])

    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 not f.startswith('_') and not f.startswith('.') and not f.endswith('.py') and not f.endswith('.pyc')]

        except EnvironmentError:

            available_backends = []

        available_backends.sort()

        if settings.DATABASE_ENGINE not in available_backends:

            raise ImproperlyConfigured, "%r isn't an available database backend. Available options are: %s\nError was: %s" % \

                (settings.DATABASE_ENGINE, ", ".join(map(repr, available_backends)), e_user)

        else:

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

# Convenient aliases for backend bits.

connection = backend.DatabaseWrapper(**settings.DATABASE_OPTIONS)

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)