import random
import logging

from django.conf import settings

from xmodule import graders
from xmodule.graders import Score
from models import StudentModule

_log = logging.getLogger("mitx.courseware")


def grade_sheet(student, course, grader, student_module_cache):
    """
    This pulls a summary of all problems in the course. It returns a dictionary with two datastructures:

    - courseware_summary is a summary of all sections with problems in the course. It is organized as an array of chapters,
    each containing an array of sections, each containing an array of scores. This contains information for graded and ungraded
    problems, and is good for displaying a course summary with due dates, etc.

    - grade_summary is the output from the course grader. More information on the format is in the docstring for CourseGrader.

    Arguments:
        student: A User object for the student to grade
        course: An XModule containing the course to grade
        student_module_cache: A StudentModuleCache initialized with all instance_modules for the student
    """
    totaled_scores = {}
    chapters = []
    for c in course.get_children():
        sections = []
        for s in c.get_children():
            def yield_descendents(module):
                yield module
                for child in module.get_display_items():
                    for module in yield_descendents(child):
                        yield module

            graded = s.metadata.get('graded', False)
            scores = []
            for module in yield_descendents(s):
                (correct, total) = get_score(student, module, student_module_cache)

                if correct is None and total is None:
                    continue

                if settings.GENERATE_PROFILE_SCORES:
                    if total > 1:
                        correct = random.randrange(max(total - 2, 1), total + 1)
                    else:
                        correct = total

                if not total > 0:
                    #We simply cannot grade a problem that is 12/0, because we might need it as a percentage
                    graded = False

                scores.append(Score(correct, total, graded, module.metadata.get('display_name')))

            section_total, graded_total = graders.aggregate_scores(scores, s.metadata.get('display_name'))
            #Add the graded total to totaled_scores
            format = s.metadata.get('format', "")
            if format and graded_total.possible > 0:
                format_scores = totaled_scores.get(format, [])
                format_scores.append(graded_total)
                totaled_scores[format] = format_scores

            sections.append({
                'section': s.metadata.get('display_name'),
                'scores': scores,
                'section_total': section_total,
                'format': format,
                'due': s.metadata.get("due", ""),
                'graded': graded,
            })

        chapters.append({'course': course.metadata.get('display_name'),
                         'chapter': c.metadata.get('display_name'),
                         'sections': sections})

    grade_summary = grader.grade(totaled_scores)

    return {'courseware_summary': chapters,
            'grade_summary': grade_summary}


def get_score(user, problem, cache):
    """
    Return the score for a user on a problem

    user: a Student object
    problem: an XModule
    cache: A StudentModuleCache
    """
    correct = 0.0

    # If the ID is not in the cache, add the item
    instance_module = cache.lookup(problem.category, problem.id)
    if instance_module is None:
        instance_module = StudentModule(module_type=problem.category,
                                        module_state_key=problem.id,
                                        student=user,
                                        state=None,
                                        grade=0,
                                        max_grade=problem.max_score(),
                                        done='i')
        cache.append(instance_module)
        instance_module.save()

    # If this problem is ungraded/ungradable, bail
    if instance_module.max_grade is None:
        return (None, None)

    correct = instance_module.grade if instance_module.grade is not None else 0
    total = instance_module.max_grade

    if correct is not None and total is not None:
        #Now we re-weight the problem, if specified
        weight = getattr(problem, 'weight', 1)
        if weight != 1:
            correct = correct * weight / total
            total = weight

    return (correct, total)
