"""
Enrollment API for creating, updating, and deleting enrollments. Also provides access to enrollment information at a
course level, such as available course modes.

"""
from django.utils import importlib
import logging
from django.conf import settings
from django.core.cache import cache
from enrollment import errors

log = logging.getLogger(__name__)

DEFAULT_DATA_API = 'enrollment.data'


def get_enrollments(user_id):
    """Retrieves all the courses a user is enrolled in.

    Takes a user and retrieves all relative enrollments. Includes information regarding how the user is enrolled
    in the the course.

    Args:
        user_id (str): The username of the user we want to retrieve course enrollment information for.

    Returns:
        A list of enrollment information for the given user.

    Examples:
        >>> get_enrollments("Bob")
        [
            {
                "created": "2014-10-20T20:18:00Z",
                "mode": "honor",
                "is_active": True,
                "user": "Bob",
                "course": {
                    "course_id": "edX/DemoX/2014T2",
                    "enrollment_end": "2014-12-20T20:18:00Z",
                    "enrollment_start": "2014-10-15T20:18:00Z",
                    "course_start": "2015-02-03T00:00:00Z",
                    "course_end": "2015-05-06T00:00:00Z",
                    "course_modes": [
                        {
                            "slug": "honor",
                            "name": "Honor Code Certificate",
                            "min_price": 0,
                            "suggested_prices": "",
                            "currency": "usd",
                            "expiration_datetime": null,
                            "description": null,
                            "sku": null
                        }
                    ],
                    "invite_only": False
                }
            },
            {
                "created": "2014-10-25T20:18:00Z",
                "mode": "verified",
                "is_active": True,
                "user": "Bob",
                "course": {
                    "course_id": "edX/edX-Insider/2014T2",
                    "enrollment_end": "2014-12-20T20:18:00Z",
                    "enrollment_start": "2014-10-15T20:18:00Z",
                    "course_start": "2015-02-03T00:00:00Z",
                    "course_end": "2015-05-06T00:00:00Z",
                    "course_modes": [
                        {
                            "slug": "honor",
                            "name": "Honor Code Certificate",
                            "min_price": 0,
                            "suggested_prices": "",
                            "currency": "usd",
                            "expiration_datetime": null,
                            "description": null,
                            "sku": null
                        }
                    ],
                    "invite_only": True
                }
            }
        ]

    """
    return _data_api().get_course_enrollments(user_id)


def get_enrollment(user_id, course_id):
    """Retrieves all enrollment information for the user in respect to a specific course.

    Gets all the course enrollment information specific to a user in a course.

    Args:
        user_id (str): The user to get course enrollment information for.
        course_id (str): The course to get enrollment information for.

    Returns:
        A serializable dictionary of the course enrollment.

    Example:
        >>> get_enrollment("Bob", "edX/DemoX/2014T2")
        {
            "created": "2014-10-20T20:18:00Z",
            "mode": "honor",
            "is_active": True,
            "user": "Bob",
            "course": {
                "course_id": "edX/DemoX/2014T2",
                "enrollment_end": "2014-12-20T20:18:00Z",
                "enrollment_start": "2014-10-15T20:18:00Z",
                "course_start": "2015-02-03T00:00:00Z",
                "course_end": "2015-05-06T00:00:00Z",
                "course_modes": [
                    {
                        "slug": "honor",
                        "name": "Honor Code Certificate",
                        "min_price": 0,
                        "suggested_prices": "",
                        "currency": "usd",
                        "expiration_datetime": null,
                        "description": null,
                        "sku": null
                    }
                ],
                "invite_only": False
            }
        }

    """
    return _data_api().get_course_enrollment(user_id, course_id)


def add_enrollment(user_id, course_id, mode='honor', is_active=True):
    """Enrolls a user in a course.

    Enrolls a user in a course. If the mode is not specified, this will default to 'honor'.

    Arguments:
        user_id (str): The user to enroll.
        course_id (str): The course to enroll the user in.

    Keyword Arguments:
        mode (str): Optional argument for the type of enrollment to create. Ex. 'audit', 'honor', 'verified',
            'professional'. If not specified, this defaults to 'honor'.
        is_active (boolean): Optional argument for making the new enrollment inactive. If not specified, is_active
            defaults to True.

    Returns:
        A serializable dictionary of the new course enrollment.

    Example:
        >>> add_enrollment("Bob", "edX/DemoX/2014T2", mode="audit")
        {
            "created": "2014-10-20T20:18:00Z",
            "mode": "honor",
            "is_active": True,
            "user": "Bob",
            "course": {
                "course_id": "edX/DemoX/2014T2",
                "enrollment_end": "2014-12-20T20:18:00Z",
                "enrollment_start": "2014-10-15T20:18:00Z",
                "course_start": "2015-02-03T00:00:00Z",
                "course_end": "2015-05-06T00:00:00Z",
                "course_modes": [
                    {
                        "slug": "honor",
                        "name": "Honor Code Certificate",
                        "min_price": 0,
                        "suggested_prices": "",
                        "currency": "usd",
                        "expiration_datetime": null,
                        "description": null,
                        "sku": null
                    }
                ],
                "invite_only": False
            }
        }
    """
    _validate_course_mode(course_id, mode, is_active=is_active)
    return _data_api().create_course_enrollment(user_id, course_id, mode, is_active)


def update_enrollment(user_id, course_id, mode=None, is_active=None, enrollment_attributes=None):
    """Updates the course mode for the enrolled user.

    Update a course enrollment for the given user and course.

    Arguments:
        user_id (str): The user associated with the updated enrollment.
        course_id (str): The course associated with the updated enrollment.

    Keyword Arguments:
        mode (str): The new course mode for this enrollment.
        is_active (bool): Sets whether the enrollment is active or not.
        enrollment_attributes (list): Attributes to be set the enrollment.

    Returns:
        A serializable dictionary representing the updated enrollment.

    Example:
        >>> update_enrollment("Bob", "edX/DemoX/2014T2", "honor")
        {
            "created": "2014-10-20T20:18:00Z",
            "mode": "honor",
            "is_active": True,
            "user": "Bob",
            "course": {
                "course_id": "edX/DemoX/2014T2",
                "enrollment_end": "2014-12-20T20:18:00Z",
                "enrollment_start": "2014-10-15T20:18:00Z",
                "course_start": "2015-02-03T00:00:00Z",
                "course_end": "2015-05-06T00:00:00Z",
                "course_modes": [
                    {
                        "slug": "honor",
                        "name": "Honor Code Certificate",
                        "min_price": 0,
                        "suggested_prices": "",
                        "currency": "usd",
                        "expiration_datetime": null,
                        "description": null,
                        "sku": null
                    }
                ],
                "invite_only": False
            }
        }

    """
    if mode is not None:
        _validate_course_mode(course_id, mode, is_active=is_active)
    enrollment = _data_api().update_course_enrollment(user_id, course_id, mode=mode, is_active=is_active)
    if enrollment is None:
        msg = u"Course Enrollment not found for user {user} in course {course}".format(user=user_id, course=course_id)
        log.warn(msg)
        raise errors.EnrollmentNotFoundError(msg)
    else:
        if enrollment_attributes is not None:
            set_enrollment_attributes(user_id, course_id, enrollment_attributes)

    return enrollment


def get_course_enrollment_details(course_id, include_expired=False):
    """Get the course modes for course. Also get enrollment start and end date, invite only, etc.

    Given a course_id, return a serializable dictionary of properties describing course enrollment information.

    Args:
        course_id (str): The Course to get enrollment information for.

        include_expired (bool): Boolean denoting whether expired course modes
        should be included in the returned JSON data.

    Returns:
        A serializable dictionary of course enrollment information.

    Example:
        >>> get_course_enrollment_details("edX/DemoX/2014T2")
        {
            "course_id": "edX/DemoX/2014T2",
            "enrollment_end": "2014-12-20T20:18:00Z",
            "enrollment_start": "2014-10-15T20:18:00Z",
            "course_start": "2015-02-03T00:00:00Z",
            "course_end": "2015-05-06T00:00:00Z",
            "course_modes": [
                {
                    "slug": "honor",
                    "name": "Honor Code Certificate",
                    "min_price": 0,
                    "suggested_prices": "",
                    "currency": "usd",
                    "expiration_datetime": null,
                    "description": null,
                    "sku": null
                }
            ],
            "invite_only": False
        }

    """
    cache_key = u'enrollment.course.details.{course_id}.{include_expired}'.format(
        course_id=course_id,
        include_expired=include_expired
    )
    cached_enrollment_data = None
    try:
        cached_enrollment_data = cache.get(cache_key)
    except Exception:
        # The cache backend could raise an exception (for example, memcache keys that contain spaces)
        log.exception(u"Error occurred while retrieving course enrollment details from the cache")

    if cached_enrollment_data:
        log.info(u"Get enrollment data for course %s (cached)", course_id)
        return cached_enrollment_data

    course_enrollment_details = _data_api().get_course_enrollment_info(course_id, include_expired)

    try:
        cache_time_out = getattr(settings, 'ENROLLMENT_COURSE_DETAILS_CACHE_TIMEOUT', 60)
        cache.set(cache_key, course_enrollment_details, cache_time_out)
    except Exception:
        # Catch any unexpected errors during caching.
        log.exception(u"Error occurred while caching course enrollment details for course %s", course_id)
        raise errors.CourseEnrollmentError(u"An unexpected error occurred while retrieving course enrollment details.")

    log.info(u"Get enrollment data for course %s", course_id)
    return course_enrollment_details


def set_enrollment_attributes(user_id, course_id, attributes):
    """Set enrollment attributes for the enrollment of given user in the
    course provided.

    Args:
        course_id (str): The Course to set enrollment attributes for.
        user_id (str): The User to set enrollment attributes for.
        attributes (list): Attributes to be set.

    Example:
        >>>set_enrollment_attributes(
            "Bob",
            "course-v1-edX-DemoX-1T2015",
            [
                {
                    "namespace": "credit",
                    "name": "provider_id",
                    "value": "hogwarts",
                },
            ]
        )
    """
    _data_api().add_or_update_enrollment_attr(user_id, course_id, attributes)


def get_enrollment_attributes(user_id, course_id):
    """Retrieve enrollment attributes for given user for provided course.

    Args:
        user_id: The User to get enrollment attributes for
        course_id (str): The Course to get enrollment attributes for.

    Example:
        >>>get_enrollment_attributes("Bob", "course-v1-edX-DemoX-1T2015")
        [
            {
                "namespace": "credit",
                "name": "provider_id",
                "value": "hogwarts",
            },
        ]

    Returns: list
    """
    return _data_api().get_enrollment_attributes(user_id, course_id)


def _validate_course_mode(course_id, mode, is_active=None):
    """Checks to see if the specified course mode is valid for the course.

    If the requested course mode is not available for the course, raise an error with corresponding
    course enrollment information.

    'honor' is special cased. If there are no course modes configured, and the specified mode is
    'honor', return true, allowing the enrollment to be 'honor' even if the mode is not explicitly
    set for the course.

    Arguments:
        course_id (str): The course to check against for available course modes.
        mode (str): The slug for the course mode specified in the enrollment.

    Keyword Arguments:
        is_active (bool): Whether the enrollment is to be activated or deactivated.

    Returns:
        None

    Raises:
        CourseModeNotFound: raised if the course mode is not found.
    """
    # If the client has requested an enrollment deactivation, we want to include expired modes
    # in the set of available modes. This allows us to unenroll users from expired modes.
    include_expired = not is_active if is_active is not None else False

    course_enrollment_info = _data_api().get_course_enrollment_info(course_id, include_expired=include_expired)
    course_modes = course_enrollment_info["course_modes"]
    available_modes = [m['slug'] for m in course_modes]
    if mode not in available_modes:
        msg = (
            u"Specified course mode '{mode}' unavailable for course {course_id}.  "
            u"Available modes were: {available}"
        ).format(
            mode=mode,
            course_id=course_id,
            available=", ".join(available_modes)
        )
        log.warn(msg)
        raise errors.CourseModeNotFoundError(msg, course_enrollment_info)


def _data_api():
    """Returns a Data API.
    This relies on Django settings to find the appropriate data API.

    """
    # We retrieve the settings in-line here (rather than using the
    # top-level constant), so that @override_settings will work
    # in the test suite.
    api_path = getattr(settings, "ENROLLMENT_DATA_API", DEFAULT_DATA_API)

    try:
        return importlib.import_module(api_path)
    except (ImportError, ValueError):
        log.exception(u"Could not load module at '{path}'".format(path=api_path))
        raise errors.EnrollmentApiLoadError(api_path)
