"""
Provides Python APIs exposed from Grades models.
"""


from opaque_keys.edx.keys import CourseKey, UsageKey

from lms.djangoapps.grades.models import PersistentCourseGrade as _PersistentCourseGrade
from lms.djangoapps.grades.models import PersistentSubsectionGrade as _PersistentSubsectionGrade
from lms.djangoapps.grades.models import PersistentSubsectionGradeOverride as _PersistentSubsectionGradeOverride
from lms.djangoapps.grades.models import VisibleBlocks as _VisibleBlocks
from lms.djangoapps.utils import _get_key


def prefetch_grade_overrides_and_visible_blocks(user, course_key):
    _PersistentSubsectionGradeOverride.prefetch(user.id, course_key)
    _VisibleBlocks.bulk_read(user.id, course_key)


def prefetch_course_grades(course_key, users):
    _PersistentCourseGrade.prefetch(course_key, users)


def prefetch_course_and_subsection_grades(course_key, users):
    _PersistentCourseGrade.prefetch(course_key, users)
    _PersistentSubsectionGrade.prefetch(course_key, users)


def clear_prefetched_course_grades(course_key):
    _PersistentCourseGrade.clear_prefetched_data(course_key)
    _PersistentSubsectionGrade.clear_prefetched_data(course_key)


def clear_prefetched_course_and_subsection_grades(course_key):
    _PersistentCourseGrade.clear_prefetched_data(course_key)


def get_recently_modified_grades(course_keys, start_date, end_date, users=None):
    """
    Returns a QuerySet of PersistentCourseGrade objects filtered by the input
    parameters and ordered by modified date.
    """
    grade_filter_args = {}
    if course_keys:
        grade_filter_args['course_id__in'] = course_keys
    if start_date:
        grade_filter_args['modified__gte'] = start_date
    if end_date:
        grade_filter_args['modified__lte'] = end_date
    if users:
        grade_filter_args['user_id__in'] = [u.id for u in users]

    return _PersistentCourseGrade.objects.filter(**grade_filter_args).order_by('modified')


def update_or_create_override(grade, **kwargs):
    """
    Update or creates a subsection override.
    """
    kwargs['subsection_grade_model'] = grade
    return _PersistentSubsectionGradeOverride.update_or_create_override(**kwargs)


def get_subsection_grade(user_id, course_key_or_id, usage_key_or_id):
    """
    Find and return the earned subsection grade for user
    """
    course_key = _get_key(course_key_or_id, CourseKey)
    usage_key = _get_key(usage_key_or_id, UsageKey)

    return _PersistentSubsectionGrade.objects.get(
        user_id=user_id,
        course_id=course_key,
        usage_key=usage_key
    )


def get_subsection_grades(user_id, course_key_or_id):
    """
    Return dictionary of grades for user_id.
    """
    course_key = _get_key(course_key_or_id, CourseKey)
    grades = {}
    for grade in _PersistentSubsectionGrade.bulk_read_grades(user_id, course_key):
        grades[grade.usage_key] = grade
    return grades


def get_subsection_grade_override(user_id, course_key_or_id, usage_key_or_id):
    """
    Finds the subsection grade for user and returns the override for that grade if it exists

    If override does not exist, returns None. If subsection grade does not exist, will raise an exception.
    """
    usage_key = _get_key(usage_key_or_id, UsageKey)

    # Verify that a corresponding subsection grade exists for the given user and usage_key
    # Raises PersistentSubsectionGrade.DoesNotExist if it does not exist.
    _ = get_subsection_grade(user_id, course_key_or_id, usage_key_or_id)

    return _PersistentSubsectionGradeOverride.get_override(user_id, usage_key)