"""
Simple utility functions for computing access.
It allows us to share code between access.py and block transformers.
"""

from __future__ import absolute_import

from datetime import datetime, timedelta
from logging import getLogger

from django.conf import settings
from django.utils.translation import ugettext as _
from pytz import UTC

from courseware.access_response import AccessResponse, StartDateError
from courseware.masquerade import get_course_masquerade, is_masquerading_as_student
from openedx.core.djangoapps.util.user_messages import PageLevelMessages
from openedx.core.djangolib.markup import HTML
from openedx.features.course_experience import COURSE_PRE_START_ACCESS_FLAG
from student.roles import CourseBetaTesterRole
from xmodule.util.xmodule_django import get_current_request_hostname

DEBUG_ACCESS = False
log = getLogger(__name__)

ACCESS_GRANTED = AccessResponse(True)
ACCESS_DENIED = AccessResponse(False)


def debug(*args, **kwargs):
    """
    Helper function for local debugging.
    """
    # to avoid overly verbose output, this is off by default
    if DEBUG_ACCESS:
        log.debug(*args, **kwargs)


def adjust_start_date(user, days_early_for_beta, start, course_key):
    """
    If user is in a beta test group, adjust the start date by the appropriate number of
    days.

    Returns:
        A datetime.  Either the same as start, or earlier for beta testers.
    """
    if days_early_for_beta is None:
        # bail early if no beta testing is set up
        return start

    if CourseBetaTesterRole(course_key).has_user(user):
        debug(u"Adjust start time: user in beta role for %s", course_key)
        delta = timedelta(days_early_for_beta)
        effective = start - delta
        return effective

    return start


def check_start_date(user, days_early_for_beta, start, course_key, display_error_to_user=True):
    """
    Verifies whether the given user is allowed access given the
    start date and the Beta offset for the given course.

    Arguments:
        display_error_to_user: If True, display this error to users in the UI.

    Returns:
        AccessResponse: Either ACCESS_GRANTED or StartDateError.
    """
    start_dates_disabled = settings.FEATURES['DISABLE_START_DATES']
    masquerading_as_student = is_masquerading_as_student(user, course_key)

    if start_dates_disabled and not masquerading_as_student:
        return ACCESS_GRANTED
    else:
        now = datetime.now(UTC)
        if start is None or in_preview_mode() or get_course_masquerade(user, course_key):
            return ACCESS_GRANTED

        effective_start = adjust_start_date(user, days_early_for_beta, start, course_key)
        if now > effective_start:
            return ACCESS_GRANTED

        return StartDateError(start, display_error_to_user=display_error_to_user)


def in_preview_mode():
    """
    Returns whether the user is in preview mode or not.
    """
    hostname = get_current_request_hostname()
    preview_lms_base = settings.FEATURES.get('PREVIEW_LMS_BASE', None)
    return bool(preview_lms_base and hostname and hostname.split(':')[0] == preview_lms_base.split(':')[0])


def check_course_open_for_learner(user, course):
    """
    Check if the course is open for learners based on the start date.

    Returns:
        AccessResponse: Either ACCESS_GRANTED or StartDateError.
    """
    if COURSE_PRE_START_ACCESS_FLAG.is_enabled():
        return ACCESS_GRANTED
    return check_start_date(user, course.days_early_for_beta, course.start, course.id)