"""
CourseEnrollment related signal handlers.
"""

import datetime
import logging

from django.db.models.signals import post_save
from django.dispatch import receiver
from edx_ace.utils import date

from common.djangoapps.course_modes.models import CourseMode
from lms.djangoapps.courseware.models import (
    CourseDynamicUpgradeDeadlineConfiguration,
    DynamicUpgradeDeadlineConfiguration,
    OrgDynamicUpgradeDeadlineConfiguration
)
from openedx.core.djangoapps.content.course_overviews.signals import COURSE_START_DATE_CHANGED
from openedx.core.djangoapps.schedules.content_highlights import course_has_highlights_from_store
from openedx.core.djangoapps.schedules.models import ScheduleExperience
from openedx.core.djangoapps.schedules.utils import reset_self_paced_schedule
from common.djangoapps.student.models import CourseEnrollment
from common.djangoapps.student.signals import ENROLLMENT_TRACK_UPDATED  # lint-amnesty, pylint: disable=unused-import
from .models import Schedule
from .tasks import update_course_schedules

log = logging.getLogger(__name__)


@receiver(post_save, sender=CourseEnrollment, dispatch_uid='create_schedule_for_enrollment')
def create_schedule(sender, **kwargs):  # pylint: disable=unused-argument
    """
    When a CourseEnrollment is created, create a Schedule if configured.
    """
    try:
        enrollment = kwargs.get('instance')
        enrollment_created = kwargs.get('created')

        schedule_details = _create_schedule(enrollment, enrollment_created)

        if schedule_details:
            log.debug(  # lint-amnesty, pylint: disable=logging-not-lazy
                'Schedules: created a new schedule starting at ' +
                '%s with an upgrade deadline of %s and experience type: %s',
                schedule_details['content_availability_date'],
                schedule_details['upgrade_deadline'],
                ScheduleExperience.EXPERIENCES[schedule_details['experience_type']]
            )
    except Exception:  # pylint: disable=broad-except
        # We do not want to block the creation of a CourseEnrollment because of an error in creating a Schedule.
        # No Schedule is acceptable, but no CourseEnrollment is not.
        log.exception('Encountered error in creating a Schedule for CourseEnrollment for user {} in course {}'.format(
            enrollment.user.id if (enrollment and enrollment.user) else None,
            enrollment.course_id if enrollment else None
        ))


@receiver(COURSE_START_DATE_CHANGED)
def update_schedules_on_course_start_changed(sender, updated_course_overview, previous_start_date, **kwargs):   # pylint: disable=unused-argument
    """
    Updates all course schedules start and upgrade_deadline dates based off of
    the new course overview start date.
    """
    upgrade_deadline = _calculate_upgrade_deadline(
        updated_course_overview.id,
        content_availability_date=updated_course_overview.start,
    )
    update_course_schedules.apply_async(
        kwargs=dict(
            course_id=str(updated_course_overview.id),
            new_start_date_str=date.serialize(updated_course_overview.start),
            new_upgrade_deadline_str=date.serialize(upgrade_deadline),
        ),
    )


@receiver(ENROLLMENT_TRACK_UPDATED)
def reset_schedule_on_mode_change(sender, user, course_key, mode, **kwargs):  # pylint: disable=unused-argument
    """
    When a CourseEnrollment's mode is changed, reset the user's schedule if self-paced.
    """
    # If switching to audit, reset to when the user got access to course. This is for the case where a user
    # upgrades to verified (resetting their date), then later refunds the order and goes back to audit. We want
    # to make sure that audit users go back to their normal audit schedule access.
    use_availability_date = mode in CourseMode.AUDIT_MODES
    reset_self_paced_schedule(user, course_key, use_availability_date=use_availability_date)


def _calculate_upgrade_deadline(course_id, content_availability_date):  # lint-amnesty, pylint: disable=missing-function-docstring
    upgrade_deadline = None

    delta = _get_upgrade_deadline_delta_setting(course_id)
    if delta is not None:
        upgrade_deadline = content_availability_date + datetime.timedelta(days=delta)
        if upgrade_deadline is not None:
            # The content availability-based deadline should never occur
            # after the verified mode's expiration date, if one is set.
            try:
                verified_mode = CourseMode.verified_mode_for_course(course_id)
            except CourseMode.DoesNotExist:
                pass
            else:
                if verified_mode:
                    course_mode_upgrade_deadline = verified_mode.expiration_datetime
                    if course_mode_upgrade_deadline is not None:
                        upgrade_deadline = min(upgrade_deadline, course_mode_upgrade_deadline)

    return upgrade_deadline


def _get_upgrade_deadline_delta_setting(course_id):  # lint-amnesty, pylint: disable=missing-function-docstring
    delta = None

    global_config = DynamicUpgradeDeadlineConfiguration.current()
    if global_config.enabled:
        # Use the default from this model whether or not the feature is enabled
        delta = global_config.deadline_days

    # Check if the org has a deadline
    org_config = OrgDynamicUpgradeDeadlineConfiguration.current(course_id.org)
    if org_config.opted_in():
        delta = org_config.deadline_days
    elif org_config.opted_out():
        delta = None

    # Check if the course has a deadline
    course_config = CourseDynamicUpgradeDeadlineConfiguration.current(course_id)
    if course_config.opted_in():
        delta = course_config.deadline_days
    elif course_config.opted_out():
        delta = None

    return delta


def _create_schedule(enrollment, enrollment_created):
    """
    Checks configuration and creates Schedule with ScheduleExperience for this enrollment.
    """
    if not enrollment_created:
        # only create schedules when enrollment records are created
        return

    # This represents the first date at which the learner can access the content. This will be the latter of
    # either the enrollment date or the course's start date.
    content_availability_date = max(enrollment.created, enrollment.course_overview.start)
    upgrade_deadline = _calculate_upgrade_deadline(enrollment.course_id, content_availability_date)
    experience_type = _get_experience_type(enrollment)

    schedule = Schedule.objects.create(
        enrollment=enrollment,
        start_date=content_availability_date,
        upgrade_deadline=upgrade_deadline
    )

    ScheduleExperience(schedule=schedule, experience_type=experience_type).save()

    return {
        'content_availability_date': content_availability_date,
        'upgrade_deadline': upgrade_deadline,
        'experience_type': experience_type,
    }


def _get_experience_type(enrollment):
    """
    Returns the ScheduleExperience type for the given enrollment.

    Schedules will receive the Course Updates experience if the course has any section highlights defined.
    """
    has_highlights = enrollment.course_overview.has_highlights
    if has_highlights is None:  # old course that doesn't have this info cached in the overview
        has_highlights = course_has_highlights_from_store(enrollment.course_id)

    if has_highlights:
        return ScheduleExperience.EXPERIENCES.course_updates
    else:
        return ScheduleExperience.EXPERIENCES.default