# pylint: disable=too-many-branches, too-many-lines, too-many-statements

"""
In-Proc API (aka Library) for the edx_proctoring subsystem. This is not to be confused with a HTTP REST
API which is in the views.py file, per edX coding standards
"""
from __future__ import absolute_import

from datetime import datetime, timedelta
import logging
import uuid
import pytz

from django.utils.translation import ugettext as _, ugettext_noop
from django.conf import settings
from django.contrib.auth.models import User
from django.template import Context, loader
from django.core.urlresolvers import reverse, NoReverseMatch
from django.core.mail.message import EmailMessage

from edx_proctoring import constants
from edx_proctoring.exceptions import (
    ProctoredExamAlreadyExists,
    ProctoredExamNotFoundException,
    StudentExamAttemptAlreadyExistsException,
    StudentExamAttemptDoesNotExistsException,
    StudentExamAttemptedAlreadyStarted,
    ProctoredExamIllegalStatusTransition,
    ProctoredExamPermissionDenied,
    ProctoredExamNotActiveException,
    ProctoredExamReviewPolicyNotFoundException,
    ProctoredExamReviewPolicyAlreadyExists
)
from edx_proctoring.models import (
    ProctoredExam,
    ProctoredExamStudentAllowance,
    ProctoredExamStudentAttempt,
    ProctoredExamStudentAttemptStatus,
    ProctoredExamReviewPolicy,
)
from edx_proctoring.serializers import (
    ProctoredExamSerializer,
    ProctoredExamStudentAttemptSerializer,
    ProctoredExamStudentAllowanceSerializer,
    ProctoredExamReviewPolicySerializer
)
from edx_proctoring.utils import (
    humanized_time,
    emit_event
)

from edx_proctoring.backends import get_backend_provider
from edx_proctoring.runtime import get_runtime_service

log = logging.getLogger(__name__)

SHOW_EXPIRY_MESSAGE_DURATION = 1 * 60  # duration within which expiry message is shown for a timed-out exam

APPROVED_STATUS = 'approved'


def create_exam(course_id, content_id, exam_name, time_limit_mins, due_date=None,
                is_proctored=True, is_practice_exam=False, external_id=None, is_active=True, hide_after_due=False):
    """
    Creates a new ProctoredExam entity, if the course_id/content_id pair do not already exist.
    If that pair already exists, then raise exception.

    Returns: id (PK)
    """

    if ProctoredExam.get_exam_by_content_id(course_id, content_id) is not None:
        raise ProctoredExamAlreadyExists

    proctored_exam = ProctoredExam.objects.create(
        course_id=course_id,
        content_id=content_id,
        external_id=external_id,
        exam_name=exam_name,
        time_limit_mins=time_limit_mins,
        due_date=due_date,
        is_proctored=is_proctored,
        is_practice_exam=is_practice_exam,
        is_active=is_active,
        hide_after_due=hide_after_due,
    )

    log_msg = (
        u'Created exam ({exam_id}) with parameters: course_id={course_id}, '
        u'content_id={content_id}, exam_name={exam_name}, time_limit_mins={time_limit_mins}, '
        u'is_proctored={is_proctored}, is_practice_exam={is_practice_exam}, '
        u'external_id={external_id}, is_active={is_active}, hide_after_due={hide_after_due}'.format(
            exam_id=proctored_exam.id,
            course_id=course_id, content_id=content_id,
            exam_name=exam_name, time_limit_mins=time_limit_mins,
            is_proctored=is_proctored, is_practice_exam=is_practice_exam,
            external_id=external_id, is_active=is_active, hide_after_due=hide_after_due
        )
    )
    log.info(log_msg)

    # read back exam so we can emit an event on it
    exam = get_exam_by_id(proctored_exam.id)
    emit_event(exam, 'created')

    return proctored_exam.id


def create_exam_review_policy(exam_id, set_by_user_id, review_policy):
    """
    Creates a new exam_review_policy entity, if the review_policy
    for exam_id does not already exist. If it exists, then raise exception.

    Returns: id (PK)
    """

    exam_review_policy = ProctoredExamReviewPolicy.get_review_policy_for_exam(exam_id)
    if exam_review_policy is not None:
        raise ProctoredExamReviewPolicyAlreadyExists

    exam_review_policy = ProctoredExamReviewPolicy.objects.create(
        proctored_exam_id=exam_id,
        set_by_user_id=set_by_user_id,
        review_policy=review_policy
    )

    log_msg = (
        u'Created ProctoredExamReviewPolicy ({review_policy}) with parameters: exam_id={exam_id}, '
        u'set_by_user_id={set_by_user_id}'.format(
            exam_id=exam_id,
            review_policy=review_policy,
            set_by_user_id=set_by_user_id
        )
    )
    log.info(log_msg)

    return exam_review_policy.id


def update_review_policy(exam_id, set_by_user_id, review_policy):
    """
    Given a exam id, update/remove the existing record, otherwise raise exception if not found.
    Returns: review_policy_id
    """

    log_msg = (
        u'Updating exam review policy with exam_id {exam_id}'
        u'set_by_user_id={set_by_user_id}, review_policy={review_policy}'
        .format(
            exam_id=exam_id, set_by_user_id=set_by_user_id, review_policy=review_policy,
        )
    )
    log.info(log_msg)
    exam_review_policy = ProctoredExamReviewPolicy.get_review_policy_for_exam(exam_id)
    if exam_review_policy is None:
        raise ProctoredExamReviewPolicyNotFoundException

    if review_policy:
        exam_review_policy.set_by_user_id = set_by_user_id
        exam_review_policy.review_policy = review_policy
        exam_review_policy.save()
        msg = 'Updated exam review policy with {exam_id}'.format(exam_id=exam_id)
        log.info(msg)
    else:
        exam_review_policy.delete()
        msg = 'removed exam review policy with {exam_id}'.format(exam_id=exam_id)
        log.info(msg)


def remove_review_policy(exam_id):
    """
    Given a exam id, remove the existing record, otherwise raise exception if not found.
    """

    log_msg = (
        u'removing exam review policy with exam_id {exam_id}'
        .format(exam_id=exam_id)
    )
    log.info(log_msg)
    exam_review_policy = ProctoredExamReviewPolicy.get_review_policy_for_exam(exam_id)
    if exam_review_policy is None:
        raise ProctoredExamReviewPolicyNotFoundException

    exam_review_policy.delete()


def get_review_policy_by_exam_id(exam_id):
    """
    Looks up exam by the Primary Key. Raises exception if not found.

    Returns dictionary version of the Django ORM object
    e.g.
    {
        "id": 1
        "proctored_exam": "{object}",
        "set_by_user": "{object}",
        "exam_review_rules": "review rules value"
        "created": "datetime",
        "modified": "datetime"
    }
    """
    exam_review_policy = ProctoredExamReviewPolicy.get_review_policy_for_exam(exam_id)
    if exam_review_policy is None:
        raise ProctoredExamReviewPolicyNotFoundException

    return ProctoredExamReviewPolicySerializer(exam_review_policy).data


def update_exam(exam_id, exam_name=None, time_limit_mins=None, due_date=constants.MINIMUM_TIME,
                is_proctored=None, is_practice_exam=None, external_id=None, is_active=None, hide_after_due=None):
    """
    Given a Django ORM id, update the existing record, otherwise raise exception if not found.
    If an argument is not passed in, then do not change it's current value.

    Returns: id
    """

    log_msg = (
        u'Updating exam_id {exam_id} with parameters '
        u'exam_name={exam_name}, time_limit_mins={time_limit_mins}, due_date={due_date}'
        u'is_proctored={is_proctored}, is_practice_exam={is_practice_exam}, '
        u'external_id={external_id}, is_active={is_active}, hide_after_due={hide_after_due}'.format(
            exam_id=exam_id, exam_name=exam_name, time_limit_mins=time_limit_mins,
            due_date=due_date, is_proctored=is_proctored, is_practice_exam=is_practice_exam,
            external_id=external_id, is_active=is_active, hide_after_due=hide_after_due
        )
    )
    log.info(log_msg)

    proctored_exam = ProctoredExam.get_exam_by_id(exam_id)
    if proctored_exam is None:
        raise ProctoredExamNotFoundException

    if exam_name is not None:
        proctored_exam.exam_name = exam_name
    if time_limit_mins is not None:
        proctored_exam.time_limit_mins = time_limit_mins
    if due_date is not constants.MINIMUM_TIME:
        proctored_exam.due_date = due_date
    if is_proctored is not None:
        proctored_exam.is_proctored = is_proctored
    if is_practice_exam is not None:
        proctored_exam.is_practice_exam = is_practice_exam
    if external_id is not None:
        proctored_exam.external_id = external_id
    if is_active is not None:
        proctored_exam.is_active = is_active
    if hide_after_due is not None:
        proctored_exam.hide_after_due = hide_after_due
    proctored_exam.save()

    # read back exam so we can emit an event on it
    exam = get_exam_by_id(proctored_exam.id)
    emit_event(exam, 'updated')

    return proctored_exam.id


def get_exam_by_id(exam_id):
    """
    Looks up exam by the Primary Key. Raises exception if not found.

    Returns dictionary version of the Django ORM object
    e.g.
    {
        "course_id": "edX/DemoX/Demo_Course",
        "content_id": "123",
        "external_id": "",
        "exam_name": "Midterm",
        "time_limit_mins": 90,
        "is_proctored": true,
        "is_active": true
    }
    """
    proctored_exam = ProctoredExam.get_exam_by_id(exam_id)
    if proctored_exam is None:
        raise ProctoredExamNotFoundException

    serialized_exam_object = ProctoredExamSerializer(proctored_exam)
    return serialized_exam_object.data


def get_exam_by_content_id(course_id, content_id):
    """
    Looks up exam by the course_id/content_id pair. Raises exception if not found.

    Returns dictionary version of the Django ORM object
    e.g.
    {
        "course_id": "edX/DemoX/Demo_Course",
        "content_id": "123",
        "external_id": "",
        "exam_name": "Midterm",
        "time_limit_mins": 90,
        "is_proctored": true,
        "is_active": true
    }
    """
    proctored_exam = ProctoredExam.get_exam_by_content_id(course_id, content_id)
    if proctored_exam is None:
        raise ProctoredExamNotFoundException

    serialized_exam_object = ProctoredExamSerializer(proctored_exam)
    return serialized_exam_object.data


def add_allowance_for_user(exam_id, user_info, key, value):
    """
    Adds (or updates) an allowance for a user within a given exam
    """

    log_msg = (
        'Adding allowance "{key}" with value "{value}" for exam_id {exam_id} '
        'for user {user_info} '.format(
            key=key, value=value, exam_id=exam_id, user_info=user_info
        )
    )
    log.info(log_msg)

    try:
        student_allowance, action = ProctoredExamStudentAllowance.add_allowance_for_user(exam_id, user_info, key, value)
    except ProctoredExamNotActiveException:
        raise ProctoredExamNotActiveException  # let this exception raised so that we get 400 in case of inactive exam

    if student_allowance is not None:
        # emit an event for 'allowance.created|updated'
        data = {
            'allowance_user_id': student_allowance.user.id,
            'allowance_key': student_allowance.key,
            'allowance_value': student_allowance.value
        }

        exam = get_exam_by_id(exam_id)
        emit_event(exam, 'allowance.{action}'.format(action=action), override_data=data)


def get_allowances_for_course(course_id, timed_exams_only=False):
    """
    Get all the allowances for the course.
    """
    student_allowances = ProctoredExamStudentAllowance.get_allowances_for_course(
        course_id, timed_exams_only=timed_exams_only
    )
    return [ProctoredExamStudentAllowanceSerializer(allowance).data for allowance in student_allowances]


def remove_allowance_for_user(exam_id, user_id, key):
    """
    Deletes an allowance for a user within a given exam.
    """
    log_msg = (
        'Removing allowance "{key}" for exam_id {exam_id} for user_id {user_id} '.format(
            key=key, exam_id=exam_id, user_id=user_id
        )
    )
    log.info(log_msg)

    student_allowance = ProctoredExamStudentAllowance.get_allowance_for_user(exam_id, user_id, key)
    if student_allowance is not None:
        student_allowance.delete()

        # emit an event for 'allowance.deleted'
        data = {
            'allowance_user_id': student_allowance.user.id,
            'allowance_key': student_allowance.key,
            'allowance_value': student_allowance.value
        }

        exam = get_exam_by_id(exam_id)
        emit_event(exam, 'allowance.deleted', override_data=data)


def _check_for_attempt_timeout(attempt):
    """
    Helper method to see if the status of an
    exam needs to be updated, e.g. timeout
    """

    if not attempt:
        return attempt

    # right now the only adjustment to
    # status is transitioning to timeout
    has_started_exam = (
        attempt and
        attempt.get('started_at') and
        ProctoredExamStudentAttemptStatus.is_incomplete_status(attempt.get('status'))
    )
    if has_started_exam:
        now_utc = datetime.now(pytz.UTC)
        expires_at = attempt['started_at'] + timedelta(minutes=attempt['allowed_time_limit_mins'])
        has_time_expired = now_utc > expires_at

        if has_time_expired:
            update_attempt_status(
                attempt['proctored_exam']['id'],
                attempt['user']['id'],
                ProctoredExamStudentAttemptStatus.timed_out,
                timeout_timestamp=expires_at
            )
            attempt = get_exam_attempt_by_id(attempt['id'])

    return attempt


def _get_exam_attempt(exam_attempt_obj):
    """
    Helper method to commonalize all query patterns
    """

    if not exam_attempt_obj:
        return None

    serialized_attempt_obj = ProctoredExamStudentAttemptSerializer(exam_attempt_obj)
    attempt = serialized_attempt_obj.data
    attempt = _check_for_attempt_timeout(attempt)

    return attempt


def get_exam_attempt(exam_id, user_id):
    """
    Return an existing exam attempt for the given student
    """
    exam_attempt_obj = ProctoredExamStudentAttempt.objects.get_exam_attempt(exam_id, user_id)
    return _get_exam_attempt(exam_attempt_obj)


def get_exam_attempt_by_id(attempt_id):
    """
    Return an existing exam attempt for the given student
    """
    exam_attempt_obj = ProctoredExamStudentAttempt.objects.get_exam_attempt_by_id(attempt_id)
    return _get_exam_attempt(exam_attempt_obj)


def get_exam_attempt_by_code(attempt_code):
    """
    Signals the beginning of an exam attempt when we only have
    an attempt code
    """

    exam_attempt_obj = ProctoredExamStudentAttempt.objects.get_exam_attempt_by_code(attempt_code)
    return _get_exam_attempt(exam_attempt_obj)


def update_exam_attempt(attempt_id, **kwargs):
    """
    update exam_attempt
    """
    exam_attempt_obj = ProctoredExamStudentAttempt.objects.get_exam_attempt_by_id(attempt_id)
    if not exam_attempt_obj:
        err_msg = (
            'Attempted to access of attempt object with attempt_id {attempt_id} but '
            'it does not exist.'.format(
                attempt_id=attempt_id
            )
        )
        raise StudentExamAttemptDoesNotExistsException(err_msg)

    for key, value in kwargs.items():
        # only allow a limit set of fields to update
        # namely because status transitions can trigger workflow
        if key not in ['last_poll_timestamp', 'last_poll_ipaddr', 'is_status_acknowledged']:
            err_msg = (
                'You cannot call into update_exam_attempt to change '
                'field {key}'.format(key=key)
            )
            raise ProctoredExamPermissionDenied(err_msg)
        setattr(exam_attempt_obj, key, value)
    exam_attempt_obj.save()


def has_due_date_passed(due_datetime):
    """
    return True if due date is lesser than current datetime, otherwise False
    and if due_datetime is None then we don't have to consider the due date for return False
    """

    if due_datetime:
        return due_datetime <= datetime.now(pytz.UTC)
    return False


def _was_review_status_acknowledged(is_status_acknowledged, due_datetime):
    """
    return True if review status has been acknowledged and due date has been passed
    """
    return is_status_acknowledged and has_due_date_passed(due_datetime)


def _create_and_decline_attempt(exam_id, user_id):
    """
    It will create the exam attempt and change the attempt's status to decline.
    it will auto-decline further exams too
    """

    create_exam_attempt(exam_id, user_id)
    update_attempt_status(
        exam_id,
        user_id,
        ProctoredExamStudentAttemptStatus.declined,
        raise_if_not_found=False
    )


def create_exam_attempt(exam_id, user_id, taking_as_proctored=False):
    """
    Creates an exam attempt for user_id against exam_id. There should only be
    one exam_attempt per user per exam. Multiple attempts by user will be archived
    in a separate table
    """
    # for now the student is allowed the exam default

    log_msg = (
        'Creating exam attempt for exam_id {exam_id} for '
        'user_id {user_id} with taking as proctored = {taking_as_proctored}'.format(
            exam_id=exam_id, user_id=user_id, taking_as_proctored=taking_as_proctored
        )
    )
    log.info(log_msg)

    exam = get_exam_by_id(exam_id)
    existing_attempt = ProctoredExamStudentAttempt.objects.get_exam_attempt(exam_id, user_id)
    if existing_attempt:
        if existing_attempt.is_sample_attempt:
            # Archive the existing attempt by deleting it.
            existing_attempt.delete_exam_attempt()
        else:
            err_msg = (
                'Cannot create new exam attempt for exam_id = {exam_id} and '
                'user_id = {user_id} because it already exists!'
            ).format(exam_id=exam_id, user_id=user_id)

            raise StudentExamAttemptAlreadyExistsException(err_msg)

    allowed_time_limit_mins = exam['time_limit_mins']

    # add in the allowed additional time
    allowance_extra_mins = ProctoredExamStudentAllowance.get_additional_time_granted(exam_id, user_id)
    if allowance_extra_mins:
        allowed_time_limit_mins += allowance_extra_mins

    allowed_time_limit_mins, is_exam_past_due_date = _calculate_allowed_mins(
        exam['due_date'],
        allowed_time_limit_mins
    )

    attempt_code = unicode(uuid.uuid4()).upper()

    external_id = None
    review_policy = ProctoredExamReviewPolicy.get_review_policy_for_exam(exam_id)
    review_policy_exception = ProctoredExamStudentAllowance.get_review_policy_exception(exam_id, user_id)

    if not is_exam_past_due_date and taking_as_proctored:
        scheme = 'https' if getattr(settings, 'HTTPS', 'on') == 'on' else 'http'
        callback_url = '{scheme}://{hostname}{path}'.format(
            scheme=scheme,
            hostname=settings.SITE_NAME,
            path=reverse(
                'edx_proctoring.anonymous.proctoring_launch_callback.start_exam',
                args=[attempt_code]
            )
        )

        # get the name of the user, if the service is available
        full_name = None
        email = None

        credit_service = get_runtime_service('credit')
        if credit_service:
            credit_state = credit_service.get_credit_state(user_id, exam['course_id'])
            full_name = credit_state['profile_fullname']
            email = credit_state['student_email']

        context = {
            'time_limit_mins': allowed_time_limit_mins,
            'attempt_code': attempt_code,
            'is_sample_attempt': exam['is_practice_exam'],
            'callback_url': callback_url,
            'full_name': full_name,
            'email': email
        }

        # see if there is an exam review policy for this exam
        # if so, then pass it into the provider
        if review_policy:
            context.update({
                'review_policy': review_policy.review_policy
            })

        # see if there is a review policy exception for this *user*
        # exceptions are granted on a individual basis as an
        # allowance
        if review_policy_exception:
            context.update({
                'review_policy_exception': review_policy_exception
            })

        # now call into the backend provider to register exam attempt
        external_id = get_backend_provider().register_exam_attempt(
            exam,
            context=context,
        )

    attempt = ProctoredExamStudentAttempt.create_exam_attempt(
        exam_id,
        user_id,
        '',  # student name is TBD
        allowed_time_limit_mins,
        attempt_code,
        taking_as_proctored,
        exam['is_practice_exam'],
        external_id,
        review_policy_id=review_policy.id if review_policy else None,
    )

    # Emit event when exam attempt created
    emit_event(exam, attempt.status, attempt=_get_exam_attempt(attempt))

    log_msg = (
        'Created exam attempt ({attempt_id}) for exam_id {exam_id} for '
        'user_id {user_id} with taking as proctored = {taking_as_proctored} '
        'with allowed time limit minutes of {allowed_time_limit_mins}. '
        'Attempt_code {attempt_code} was generated which has a '
        'external_id of {external_id}'.format(
            attempt_id=attempt.id, exam_id=exam_id, user_id=user_id,
            taking_as_proctored=taking_as_proctored,
            allowed_time_limit_mins=allowed_time_limit_mins,
            attempt_code=attempt_code,
            external_id=external_id
        )
    )
    log.info(log_msg)

    return attempt.id


def start_exam_attempt(exam_id, user_id):
    """
    Signals the beginning of an exam attempt for a given
    exam_id. If one already exists, then an exception should be thrown.

    Returns: exam_attempt_id (PK)
    """

    existing_attempt = ProctoredExamStudentAttempt.objects.get_exam_attempt(exam_id, user_id)

    if not existing_attempt:
        err_msg = (
            'Cannot start exam attempt for exam_id = {exam_id} '
            'and user_id = {user_id} because it does not exist!'
        ).format(exam_id=exam_id, user_id=user_id)

        raise StudentExamAttemptDoesNotExistsException(err_msg)

    return _start_exam_attempt(existing_attempt)


def start_exam_attempt_by_code(attempt_code):
    """
    Signals the beginning of an exam attempt when we only have
    an attempt code
    """

    existing_attempt = ProctoredExamStudentAttempt.objects.get_exam_attempt_by_code(attempt_code)

    if not existing_attempt:
        err_msg = (
            'Cannot start exam attempt for attempt_code = {attempt_code} '
            'because it does not exist!'
        ).format(attempt_code=attempt_code)

        raise StudentExamAttemptDoesNotExistsException(err_msg)

    return _start_exam_attempt(existing_attempt)


def _start_exam_attempt(existing_attempt):
    """
    Helper method
    """

    if existing_attempt.started_at and existing_attempt.status == ProctoredExamStudentAttemptStatus.started:
        # cannot restart an attempt
        err_msg = (
            'Cannot start exam attempt for exam_id = {exam_id} '
            'and user_id = {user_id} because it has already started!'
        ).format(exam_id=existing_attempt.proctored_exam.id, user_id=existing_attempt.user_id)

        raise StudentExamAttemptedAlreadyStarted(err_msg)

    update_attempt_status(
        existing_attempt.proctored_exam_id,
        existing_attempt.user_id,
        ProctoredExamStudentAttemptStatus.started
    )

    return existing_attempt.id


def stop_exam_attempt(exam_id, user_id):
    """
    Marks the exam attempt as completed (sets the completed_at field and updates the record)
    """
    return update_attempt_status(exam_id, user_id, ProctoredExamStudentAttemptStatus.ready_to_submit)


def mark_exam_attempt_timeout(exam_id, user_id):
    """
    Marks the exam attempt as timed_out
    """
    return update_attempt_status(exam_id, user_id, ProctoredExamStudentAttemptStatus.timed_out)


def mark_exam_attempt_as_ready(exam_id, user_id):
    """
    Marks the exam attemp as ready to start
    """
    return update_attempt_status(exam_id, user_id, ProctoredExamStudentAttemptStatus.ready_to_start)


def update_attempt_status(exam_id, user_id, to_status,
                          raise_if_not_found=True, cascade_effects=True, timeout_timestamp=None):
    """
    Internal helper to handle state transitions of attempt status
    """

    log_msg = (
        'Updating attempt status for exam_id {exam_id} '
        'for user_id {user_id} to status {to_status}'.format(
            exam_id=exam_id, user_id=user_id, to_status=to_status
        )
    )
    log.info(log_msg)

    # In some configuration we may treat timeouts the same
    # as the user saying he/she wises to submit the exam
    treat_timeout_as_submitted = (
        to_status == ProctoredExamStudentAttemptStatus.timed_out and
        not settings.PROCTORING_SETTINGS.get('ALLOW_TIMED_OUT_STATE', False)
    )
    if treat_timeout_as_submitted:
        to_status = ProctoredExamStudentAttemptStatus.submitted

    exam_attempt_obj = ProctoredExamStudentAttempt.objects.get_exam_attempt(exam_id, user_id)
    if exam_attempt_obj is None:
        if raise_if_not_found:
            raise StudentExamAttemptDoesNotExistsException('Error. Trying to look up an exam that does not exist.')
        else:
            return

    exam = get_exam_by_id(exam_id)

    #
    # don't allow state transitions from a completed state to an incomplete state
    # if a re-attempt is desired then the current attempt must be deleted
    #
    in_completed_status = ProctoredExamStudentAttemptStatus.is_completed_status(exam_attempt_obj.status)
    to_incompleted_status = ProctoredExamStudentAttemptStatus.is_incomplete_status(to_status)

    if in_completed_status and to_incompleted_status:
        err_msg = (
            'A status transition from {from_status} to {to_status} was attempted '
            'on exam_id {exam_id} for user_id {user_id}. This is not '
            'allowed!'.format(
                from_status=exam_attempt_obj.status,
                to_status=to_status,
                exam_id=exam_id,
                user_id=user_id
            )
        )
        raise ProctoredExamIllegalStatusTransition(err_msg)

    # special case logic, if we are in a completed status we shouldn't allow
    # for a transition to 'Error' state
    if in_completed_status and to_status == ProctoredExamStudentAttemptStatus.error:
        err_msg = (
            'A status transition from {from_status} to {to_status} was attempted '
            'on exam_id {exam_id} for user_id {user_id}. This is not '
            'allowed!'.format(
                from_status=exam_attempt_obj.status,
                to_status=to_status,
                exam_id=exam_id,
                user_id=user_id
            )
        )
        raise ProctoredExamIllegalStatusTransition(err_msg)

    # OK, state transition is fine, we can proceed
    exam_attempt_obj.status = to_status

    # if we have transitioned to started and haven't set our
    # started_at timestamp, do so now
    add_start_time = (
        to_status == ProctoredExamStudentAttemptStatus.started and
        not exam_attempt_obj.started_at
    )
    if add_start_time:
        exam_attempt_obj.started_at = datetime.now(pytz.UTC)
    elif treat_timeout_as_submitted:
        exam_attempt_obj.completed_at = timeout_timestamp
    elif to_status == ProctoredExamStudentAttemptStatus.submitted:
        # likewise, when we transition to submitted mark
        # when the exam has been completed
        exam_attempt_obj.completed_at = datetime.now(pytz.UTC)

    exam_attempt_obj.save()

    # see if the status transition this changes credit requirement status
    if ProctoredExamStudentAttemptStatus.needs_credit_status_update(to_status):

        # trigger credit workflow, as needed
        credit_service = get_runtime_service('credit')

        if to_status == ProctoredExamStudentAttemptStatus.verified:
            credit_requirement_status = 'satisfied'
        elif to_status == ProctoredExamStudentAttemptStatus.submitted:
            credit_requirement_status = 'submitted'
        elif to_status == ProctoredExamStudentAttemptStatus.declined:
            credit_requirement_status = 'declined'
        else:
            credit_requirement_status = 'failed'

        log_msg = (
            'Calling set_credit_requirement_status for '
            'user_id {user_id} on {course_id} for '
            'content_id {content_id}. Status: {status}'.format(
                user_id=exam_attempt_obj.user_id,
                course_id=exam['course_id'],
                content_id=exam_attempt_obj.proctored_exam.content_id,
                status=credit_requirement_status
            )
        )
        log.info(log_msg)

        credit_service.set_credit_requirement_status(
            user_id=exam_attempt_obj.user_id,
            course_key_or_id=exam['course_id'],
            req_namespace='proctored_exam',
            req_name=exam_attempt_obj.proctored_exam.content_id,
            status=credit_requirement_status
        )

    if cascade_effects and ProctoredExamStudentAttemptStatus.is_a_cascadable_failure(to_status):
        if to_status == ProctoredExamStudentAttemptStatus.declined:
            # if user declines attempt, make sure we clear out the external_id and
            # taking_as_proctored fields
            exam_attempt_obj.taking_as_proctored = False
            exam_attempt_obj.external_id = None
            exam_attempt_obj.save()

        # some state transitions (namely to a rejected or declined status)
        # will mark other exams as declined because once we fail or decline
        # one exam all other (un-completed) proctored exams will be likewise
        # updated to reflect a declined status
        # get all other unattempted exams and mark also as declined
        all_other_exams = ProctoredExam.get_all_exams_for_course(
            exam_attempt_obj.proctored_exam.course_id,
            active_only=True
        )

        # we just want other exams which are proctored and are not practice
        other_exams = [
            other_exam
            for other_exam in all_other_exams
            if (
                other_exam.content_id != exam_attempt_obj.proctored_exam.content_id and
                other_exam.is_proctored and not other_exam.is_practice_exam
            )
        ]

        for other_exam in other_exams:
            # see if there was an attempt on those other exams already
            attempt = get_exam_attempt(other_exam.id, user_id)
            if attempt and ProctoredExamStudentAttemptStatus.is_completed_status(attempt['status']):
                # don't touch any completed statuses
                # we won't revoke those
                continue

            if not attempt:
                create_exam_attempt(other_exam.id, user_id, taking_as_proctored=False)

            # update any new or existing status to declined
            update_attempt_status(
                other_exam.id,
                user_id,
                ProctoredExamStudentAttemptStatus.declined,
                cascade_effects=False
            )

    # call service to get course name.
    credit_service = get_runtime_service('credit')
    credit_state = credit_service.get_credit_state(
        exam_attempt_obj.user_id,
        exam_attempt_obj.proctored_exam.course_id,
        return_course_info=True
    )

    default_name = _('your course')
    if credit_state:
        course_name = credit_state.get('course_name', default_name)
    else:
        course_name = default_name
        log.info(
            "Could not find credit_state for user id %r in the course %r.",
            exam_attempt_obj.user_id,
            exam_attempt_obj.proctored_exam.course_id
        )
    email = create_proctoring_attempt_status_email(
        user_id,
        exam_attempt_obj,
        course_name
    )
    if email:
        email.send()

    # emit an anlytics event based on the state transition
    # we re-read this from the database in case fields got updated
    # via workflow
    attempt = get_exam_attempt(exam_id, user_id)

    # we user the 'status' field as the name of the event 'verb'
    emit_event(exam, attempt['status'], attempt=attempt)

    return attempt['id']


def create_proctoring_attempt_status_email(user_id, exam_attempt_obj, course_name):
    """
    Creates an email about change in proctoring attempt status.
    """
    # Don't send an email unless this is a non-practice proctored exam
    if not exam_attempt_obj.taking_as_proctored or exam_attempt_obj.is_sample_attempt:
        return None

    user = User.objects.get(id=user_id)
    course_info_url = ''
    email_subject = (
        _('Proctoring Results For {course_name} {exam_name}').format(
            course_name=course_name,
            exam_name=exam_attempt_obj.proctored_exam.exam_name
        )
    )
    status = exam_attempt_obj.status
    if status == ProctoredExamStudentAttemptStatus.submitted:
        email_template_path = 'emails/proctoring_attempt_submitted_email.html'
        email_subject = (
            _('Proctoring Review In Progress For {course_name} {exam_name}').format(
                course_name=course_name,
                exam_name=exam_attempt_obj.proctored_exam.exam_name
            )
        )
    elif status == ProctoredExamStudentAttemptStatus.verified:
        email_template_path = 'emails/proctoring_attempt_satisfactory_email.html'
    elif status == ProctoredExamStudentAttemptStatus.rejected:
        email_template_path = 'emails/proctoring_attempt_unsatisfactory_email.html'
    else:
        # Don't send an email for any other attempt status codes
        return None
    email_template = loader.get_template(email_template_path)
    try:
        course_info_url = reverse(
            'courseware.views.views.course_info',
            args=[exam_attempt_obj.proctored_exam.course_id]
        )
    except NoReverseMatch:
        log.exception("Can't find course info url for course %s", exam_attempt_obj.proctored_exam.course_id)

    scheme = 'https' if getattr(settings, 'HTTPS', 'on') == 'on' else 'http'
    course_url = '{scheme}://{site_name}{course_info_url}'.format(
        scheme=scheme,
        site_name=constants.SITE_NAME,
        course_info_url=course_info_url
    )
    exam_name = exam_attempt_obj.proctored_exam.exam_name
    support_email_subject = _('Proctored exam {exam_name} in {course_name} for user {username}').format(
        exam_name=exam_name,
        course_name=course_name,
        username=user.username,
    )

    body = email_template.render(
        Context({
            'username': user.username,
            'course_url': course_url,
            'course_name': course_name,
            'exam_name': exam_name,
            'status': status,
            'platform': constants.PLATFORM_NAME,
            'contact_email': constants.CONTACT_EMAIL,
            'support_email_subject': support_email_subject,
        })
    )

    email = EmailMessage(
        body=body,
        from_email=constants.FROM_EMAIL,
        to=[exam_attempt_obj.user.email],
        subject=email_subject,
    )
    email.content_subtype = 'html'
    return email


def remove_exam_attempt(attempt_id, requesting_user):
    """
    Removes an exam attempt given the attempt id. requesting_user is passed through to the instructor_service.
    """

    log_msg = (
        'Removing exam attempt {attempt_id}'.format(attempt_id=attempt_id)
    )
    log.info(log_msg)

    existing_attempt = ProctoredExamStudentAttempt.objects.get_exam_attempt_by_id(attempt_id)
    if not existing_attempt:
        err_msg = (
            'Cannot remove attempt for attempt_id = {attempt_id} '
            'because it does not exist!'
        ).format(attempt_id=attempt_id)

        raise StudentExamAttemptDoesNotExistsException(err_msg)

    username = existing_attempt.user.username
    user_id = existing_attempt.user.id
    course_id = existing_attempt.proctored_exam.course_id
    content_id = existing_attempt.proctored_exam.content_id
    to_status = existing_attempt.status

    existing_attempt.delete_exam_attempt()
    instructor_service = get_runtime_service('instructor')

    if instructor_service:
        instructor_service.delete_student_attempt(username, course_id, content_id, requesting_user=requesting_user)

    # see if the status transition this changes credit requirement status
    if ProctoredExamStudentAttemptStatus.needs_credit_status_update(to_status):
        # trigger credit workflow, as needed
        credit_service = get_runtime_service('credit')
        credit_service.remove_credit_requirement_status(
            user_id=user_id,
            course_key_or_id=course_id,
            req_namespace=u'proctored_exam',
            req_name=content_id
        )

    # emit an event for 'deleted'
    exam = get_exam_by_content_id(course_id, content_id)
    serialized_attempt_obj = ProctoredExamStudentAttemptSerializer(existing_attempt)
    attempt = serialized_attempt_obj.data
    emit_event(exam, 'deleted', attempt=attempt)


def get_all_exams_for_course(course_id, timed_exams_only=False, active_only=False):
    """
    This method will return all exams for a course. This will return a list
    of dictionaries, whose schema is the same as what is returned in
    get_exam_by_id
    Returns a list containing dictionary version of the Django ORM object
    e.g.
    [{
        "course_id": "edX/DemoX/Demo_Course",
        "content_id": "123",
        "external_id": "",
        "exam_name": "Midterm",
        "time_limit_mins": 90,
        "is_proctored": true,
        "is_active": true
    },
    {
        ...: ...,
        ...: ...

    },
    ..
    ]
    """
    exams = ProctoredExam.get_all_exams_for_course(
        course_id,
        active_only=active_only,
        timed_exams_only=timed_exams_only
    )

    return [ProctoredExamSerializer(proctored_exam).data for proctored_exam in exams]


def get_all_exam_attempts(course_id):
    """
    Returns all the exam attempts for the course id.
    """
    exam_attempts = ProctoredExamStudentAttempt.objects.get_all_exam_attempts(course_id)
    return [ProctoredExamStudentAttemptSerializer(active_exam).data for active_exam in exam_attempts]


def get_filtered_exam_attempts(course_id, search_by):
    """
    returns all exam attempts for a course id filtered by  the search_by string in user names and emails.
    """
    exam_attempts = ProctoredExamStudentAttempt.objects.get_filtered_exam_attempts(course_id, search_by)
    return [ProctoredExamStudentAttemptSerializer(active_exam).data for active_exam in exam_attempts]


def get_last_exam_completion_date(course_id, username):
    """
    return the completion date of last proctoring exam for the given course and username if
    all the proctored exams are attempted and completed otherwise None
    """
    exam_attempts = ProctoredExamStudentAttempt.objects.get_proctored_exam_attempts(course_id, username)
    proctored_exams_count = ProctoredExam.get_all_exams_for_course(course_id, proctored_exams_only=True).count()
    are_all_exams_attempted = len(exam_attempts) == proctored_exams_count
    if are_all_exams_attempted:
        for attempt in exam_attempts:
            if not attempt.completed_at:
                return None

    # Last proctored exam will be at first index, because attempts are sorted descending on completed_at
    return exam_attempts[0].completed_at if exam_attempts and are_all_exams_attempted else None


def get_active_exams_for_user(user_id, course_id=None):
    """
    This method will return a list of active exams for the user,
    i.e. started_at != None and completed_at == None. Theoretically there
    could be more than one, but in practice it will be one active exam.

    If course_id is set, then attempts only for an exam in that course_id
    should be returned.

    The return set should be a list of dictionary objects which are nested


    [{
        'exam': <exam fields as dict>,
        'attempt': <student attempt fields as dict>,
        'allowances': <student allowances as dict of key/value pairs
    }, {}, ...]

    """
    result = []

    student_active_exams = ProctoredExamStudentAttempt.objects.get_active_student_attempts(user_id, course_id)
    for active_exam in student_active_exams:
        # convert the django orm objects
        # into the serialized form.
        exam_serialized_data = ProctoredExamSerializer(active_exam.proctored_exam).data
        active_exam_serialized_data = ProctoredExamStudentAttemptSerializer(active_exam).data
        student_allowances = ProctoredExamStudentAllowance.get_allowances_for_user(
            active_exam.proctored_exam.id, user_id
        )
        allowance_serialized_data = [ProctoredExamStudentAllowanceSerializer(allowance).data for allowance in
                                     student_allowances]
        result.append({
            'exam': exam_serialized_data,
            'attempt': active_exam_serialized_data,
            'allowances': allowance_serialized_data
        })

    return result


def _check_eligibility_of_enrollment_mode(credit_state):
    """
    Inspects that the enrollment mode of the user
    is valid for proctoring
    """

    # Allow only the verified students to take the exam as a proctored exam
    # Also make an exception for the honor students to take the "practice exam" as a proctored exam.
    # For the rest of the enrollment modes, None is returned which shows the exam content
    # to the student rather than the proctoring prompt.
    return credit_state['enrollment_mode'] == 'verified'


def _get_ordered_prerequisites(prerequisites_statuses, filter_out_namespaces=None):
    """
    Apply filter and ordering of requirements status in our credit_state dictionary. This will
    return a list of statuses, filtered according to the filter_lambda (if non-None). We do this to ensure
    that we check for satisfactory fulfillment of prerequistes that we do so IN THE RIGHT ORDER
    """

    _filter_out_namespaces = filter_out_namespaces if filter_out_namespaces else []

    filtered_list = [
        status
        for status in prerequisites_statuses
        if status['namespace'] not in _filter_out_namespaces
    ]
    sorted_list = sorted(filtered_list, key=lambda status: status['order'])

    return sorted_list


def _are_prerequirements_satisfied(prerequisites_statuses, evaluate_for_requirement_name=None,
                                   filter_out_namespaces=None):
    """
    Returns a dict about the fulfillment of any pre-requisites in order to this exam
    as proctored. The pre-requisites are taken from the credit requirements table. So if ordering
    of requirements are - say - ICRV1, Proctoring1, ICRV2, and Proctoring2, then the user cannot take
    Proctoring2 until there is an explicit pass on ICRV1, Proctoring1, ICRV2...

    NOTE: If evaluate_for_requirement_name=None that means check all requirements

    Return (dict):

        {
            # If all prerequisites are satisfied
            'are_prerequisites_satisifed': True/False,

            # A list of prerequisites that have been satisfied
            'satisfied_prerequisites': [...]

            # A list of prerequisites that have failed
            'failed_prerequisites': [....],

            # A list of prerequisites that are still pending
            'pending_prerequisites': [...],
        }

    NOTE: We filter out any 'grade' requirement since the student will most likely not have fulfilled
    those requirements while he/she is in the course
    """

    satisfied_prerequisites = []
    failed_prerequisites = []
    pending_prerequisites = []
    declined_prerequisites = []

    # insure an ordered and filtered list
    # we remove 'grade' requirements since those cannot be
    # satisfied while student is in the middle of a course
    requirement_statuses = _get_ordered_prerequisites(
        prerequisites_statuses,
        filter_out_namespaces=filter_out_namespaces
    )

    # find ourselves in the list
    ourself = None
    if evaluate_for_requirement_name:
        for idx, requirement in enumerate(requirement_statuses):
            if requirement['name'] == evaluate_for_requirement_name:
                ourself = requirement
                break

    # we are not in the list of requirements, look at all requirements
    if not ourself:
        idx = len(requirement_statuses)

    # now that we have the index of ourselves in the ordered list, we can walk backwards
    # and inspect all prerequisites

    # we don't look at ourselves
    idx = idx - 1
    while idx >= 0:
        requirement = requirement_statuses[idx]
        status = requirement['status']
        if status == 'satisfied':
            satisfied_prerequisites.append(requirement)
        elif status == 'failed':
            failed_prerequisites.append(requirement)
        elif status == 'declined':
            declined_prerequisites.append(requirement)
        else:
            pending_prerequisites.append(requirement)

        idx = idx - 1

    return {
        # all prequisites are satisfied if there are no failed or pending requirement
        # statuses
        'are_prerequisites_satisifed': (
            not failed_prerequisites and not pending_prerequisites and not declined_prerequisites
        ),
        # note that we reverse the list here, because we assempled it by walking backwards
        'satisfied_prerequisites': list(reversed(satisfied_prerequisites)),
        'failed_prerequisites': list(reversed(failed_prerequisites)),
        'pending_prerequisites': list(reversed(pending_prerequisites)),
        'declined_prerequisites': list(reversed(declined_prerequisites))
    }


JUMPTO_SUPPORTED_NAMESPACES = [
    'proctored_exam',
    'reverification',
]


def _resolve_prerequisite_links(exam, prerequisites):
    """
    This will inject a jumpto URL into the list of prerequisites so that a user
    can click through
    """

    for prerequisite in prerequisites:
        jumpto_url = None
        if prerequisite['namespace'] in JUMPTO_SUPPORTED_NAMESPACES and prerequisite['name']:
            try:
                jumpto_url = reverse(
                    'courseware.views.views.jump_to',
                    args=[exam['course_id'], prerequisite['name']]
                )
            except NoReverseMatch:
                log.exception("Can't find jumpto url for course %s", exam['course_id'])

        prerequisite['jumpto_url'] = jumpto_url

    return prerequisites


STATUS_SUMMARY_MAP = {
    '_default': {
        'short_description': ugettext_noop('Taking As Proctored Exam'),
        'suggested_icon': 'fa-pencil-square-o',
        'in_completed_state': False
    },
    ProctoredExamStudentAttemptStatus.eligible: {
        'short_description': ugettext_noop('Proctored Option Available'),
        'suggested_icon': 'fa-pencil-square-o',
        'in_completed_state': False
    },
    ProctoredExamStudentAttemptStatus.declined: {
        'short_description': ugettext_noop('Taking As Open Exam'),
        'suggested_icon': 'fa-pencil-square-o',
        'in_completed_state': False
    },
    ProctoredExamStudentAttemptStatus.submitted: {
        'short_description': ugettext_noop('Pending Session Review'),
        'suggested_icon': 'fa-spinner fa-spin',
        'in_completed_state': True
    },
    ProctoredExamStudentAttemptStatus.second_review_required: {
        'short_description': ugettext_noop('Pending Session Review'),
        'suggested_icon': 'fa-spinner fa-spin',
        'in_completed_state': True
    },
    ProctoredExamStudentAttemptStatus.verified: {
        'short_description': ugettext_noop('Passed Proctoring'),
        'suggested_icon': 'fa-check',
        'in_completed_state': True
    },
    ProctoredExamStudentAttemptStatus.rejected: {
        'short_description': ugettext_noop('Failed Proctoring'),
        'suggested_icon': 'fa-exclamation-triangle',
        'in_completed_state': True
    },
    ProctoredExamStudentAttemptStatus.error: {
        'short_description': ugettext_noop('Failed Proctoring'),
        'suggested_icon': 'fa-exclamation-triangle',
        'in_completed_state': True
    },
    ProctoredExamStudentAttemptStatus.expired: {
        'short_description': ugettext_noop('Proctored Option No Longer Available'),
        'suggested_icon': 'fa-times-circle',
        'in_completed_state': False
    }
}


PRACTICE_STATUS_SUMMARY_MAP = {
    '_default': {
        'short_description': ugettext_noop('Ungraded Practice Exam'),
        'suggested_icon': '',
        'in_completed_state': False
    },
    ProctoredExamStudentAttemptStatus.submitted: {
        'short_description': ugettext_noop('Practice Exam Completed'),
        'suggested_icon': 'fa-check',
        'in_completed_state': True
    },
    ProctoredExamStudentAttemptStatus.error: {
        'short_description': ugettext_noop('Practice Exam Failed'),
        'suggested_icon': 'fa-exclamation-triangle',
        'in_completed_state': True
    }
}

TIMED_EXAM_STATUS_SUMMARY_MAP = {
    '_default': {
        'short_description': ugettext_noop('Timed Exam'),
        'suggested_icon': 'fa-clock-o',
        'in_completed_state': False
    }
}


def get_attempt_status_summary(user_id, course_id, content_id):
    """
    Returns a summary about the status of the attempt for the user
    in the course_id and content_id

    If the exam is timed exam only then we simply
    return the dictionary with timed exam default summary

    Return will be:
    None: Not applicable
    - or -
    {
        'status': ['eligible', 'declined', 'submitted', 'verified', 'rejected'],
        'short_description': <short description of status>,
        'suggested_icon': <recommended font-awesome icon to use>,
        'in_completed_state': <if the status is considered in a 'completed' state>
    }
    """

    try:
        exam = get_exam_by_content_id(course_id, content_id)
    except ProctoredExamNotFoundException, ex:
        # this really shouldn't happen, but log it at least
        log.exception(ex)
        return None

    # check if the exam is not proctored
    if not exam['is_proctored']:
        summary = {}
        summary.update(TIMED_EXAM_STATUS_SUMMARY_MAP['_default'])
        # Note: translate the short description as it was stored unlocalized
        summary.update({
            'short_description': _(summary['short_description'])  # pylint: disable=translation-of-non-string
        })
        return summary

    # let's check credit eligibility
    credit_service = get_runtime_service('credit')
    # practice exams always has an attempt status regardless of
    # eligibility
    if credit_service and not exam['is_practice_exam']:
        credit_state = credit_service.get_credit_state(user_id, unicode(course_id), return_course_info=True)
        if not _check_eligibility_of_enrollment_mode(credit_state):
            return None

    attempt = get_exam_attempt(exam['id'], user_id)
    if attempt:
        status = attempt['status']
    elif not exam['is_practice_exam'] and has_due_date_passed(credit_state.get('course_end_date', None)):
        status = ProctoredExamStudentAttemptStatus.expired
    else:
        status = ProctoredExamStudentAttemptStatus.eligible

    status_map = STATUS_SUMMARY_MAP if not exam['is_practice_exam'] else PRACTICE_STATUS_SUMMARY_MAP

    summary = {}
    if status in status_map:
        summary.update(status_map[status])
    else:
        summary.update(status_map['_default'])

    # Note: translate the short description as it was stored unlocalized
    summary.update({
        'status': status,
        'short_description': _(summary['short_description'])  # pylint: disable=translation-of-non-string
    })

    return summary


def _does_time_remain(attempt):
    """
    Helper function returns True if time remains for an attempt and False
    otherwise. Called from _get_timed_exam_view(), _get_practice_exam_view()
    and _get_proctored_exam_view()
    """
    does_time_remain = False
    has_started_exam = (
        attempt and
        attempt.get('started_at') and
        ProctoredExamStudentAttemptStatus.is_incomplete_status(attempt.get('status'))
    )
    if has_started_exam:
        expires_at = attempt['started_at'] + timedelta(minutes=attempt['allowed_time_limit_mins'])
        does_time_remain = datetime.now(pytz.UTC) < expires_at
    return does_time_remain


def _get_timed_exam_view(exam, context, exam_id, user_id, course_id):
    """
    Returns a rendered view for the Timed Exams
    """
    student_view_template = None
    attempt = get_exam_attempt(exam_id, user_id)
    has_time_expired = False

    attempt_status = attempt['status'] if attempt else None
    has_due_date = True if exam['due_date'] is not None else False
    if not attempt_status:
        if has_due_date_passed(exam['due_date']):
            student_view_template = 'timed_exam/expired.html'
        else:
            student_view_template = 'timed_exam/entrance.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.started:
        # when we're taking the exam we should not override the view
        return None
    elif attempt_status == ProctoredExamStudentAttemptStatus.ready_to_submit:
        student_view_template = 'timed_exam/ready_to_submit.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.submitted:
        # If we are not hiding the exam after the due_date has passed,
        # check if the exam's due_date has passed. If so, return None
        # so that the user can see his exam answers in read only mode.
        if not exam['hide_after_due'] and has_due_date_passed(exam['due_date']):
            return None

        student_view_template = 'timed_exam/submitted.html'

        current_datetime = datetime.now(pytz.UTC)
        start_time = attempt['started_at']
        end_time = attempt['completed_at']
        attempt_duration_sec = (end_time - start_time).total_seconds()
        allowed_duration_sec = attempt['allowed_time_limit_mins'] * 60
        since_exam_ended_sec = (current_datetime - end_time).total_seconds()

        # if the user took >= the available time, then the exam must have expired.
        # but we show expiry message only when the exam was taken recently (less than SHOW_EXPIRY_MESSAGE_DURATION)
        if attempt_duration_sec >= allowed_duration_sec and since_exam_ended_sec < SHOW_EXPIRY_MESSAGE_DURATION:
            has_time_expired = True

    if student_view_template:
        template = loader.get_template(student_view_template)
        django_context = Context(context)

        allowed_time_limit_mins = attempt['allowed_time_limit_mins'] if attempt else None

        if not allowed_time_limit_mins:
            # no existing attempt, so compute the user's allowed
            # time limit, including any accommodations

            allowed_time_limit_mins = exam['time_limit_mins']
            allowance_extra_mins = ProctoredExamStudentAllowance.get_additional_time_granted(exam_id, user_id)

            if allowance_extra_mins:
                allowed_time_limit_mins += int(allowance_extra_mins)

            # apply any cut off times according to due dates
            allowed_time_limit_mins, _ = _calculate_allowed_mins(
                exam['due_date'],
                allowed_time_limit_mins
            )

        total_time = humanized_time(allowed_time_limit_mins)

        # According to WCAG, there is no need to allow for extra time if > 20 hours allowed
        hide_extra_time_footer = exam['time_limit_mins'] > 20 * 60

        progress_page_url = ''
        try:
            progress_page_url = reverse(
                'courseware.views.views.progress',
                args=[course_id]
            )
        except NoReverseMatch:
            log.exception("Can't find progress url for course %s", course_id)

        django_context.update({
            'total_time': total_time,
            'hide_extra_time_footer': hide_extra_time_footer,
            'will_be_revealed': has_due_date and not exam['hide_after_due'],
            'exam_id': exam_id,
            'exam_name': exam['exam_name'],
            'progress_page_url': progress_page_url,
            'does_time_remain': _does_time_remain(attempt),
            'has_time_expired': has_time_expired,
            'enter_exam_endpoint': reverse('edx_proctoring.proctored_exam.attempt.collection'),
            'change_state_url': reverse(
                'edx_proctoring.proctored_exam.attempt',
                args=[attempt['id']]
            ) if attempt else '',
        })
        return template.render(django_context)


def _calculate_allowed_mins(due_datetime, allowed_mins):
    """
    Returns the allowed minutes w.r.t due date and has due date pass
    """

    current_datetime = datetime.now(pytz.UTC)
    is_exam_past_due_date = False
    actual_allowed_mins = allowed_mins

    if due_datetime:
        if has_due_date_passed(due_datetime):
            is_exam_past_due_date = True
        elif current_datetime + timedelta(minutes=allowed_mins) > due_datetime:

            # e.g current_datetime=09:00, due_datetime=10:00 and allowed_mins=120(2hours)
            # then allowed_mins should be 60(1hour)

            actual_allowed_mins = int((due_datetime - current_datetime).total_seconds() / 60)
    return actual_allowed_mins, is_exam_past_due_date


def _get_proctored_exam_context(exam, attempt, course_id, is_practice_exam=False):
    """
    Common context variables for the Proctored and Practice exams' templates.
    """
    has_due_date = True if exam['due_date'] is not None else False
    attempt_time = attempt['allowed_time_limit_mins'] if attempt else exam['time_limit_mins']
    total_time = humanized_time(attempt_time)
    progress_page_url = ''
    try:
        progress_page_url = reverse(
            'courseware.views.views.progress',
            args=[course_id]
        )
    except NoReverseMatch:
        log.exception("Can't find progress url for course %s", course_id)

    return {
        'platform_name': settings.PLATFORM_NAME,
        'total_time': total_time,
        'exam_id': exam['id'],
        'progress_page_url': progress_page_url,
        'is_sample_attempt': is_practice_exam,
        'has_due_date': has_due_date,
        'has_due_date_passed': has_due_date_passed(exam['due_date']),
        'does_time_remain': _does_time_remain(attempt),
        'enter_exam_endpoint': reverse('edx_proctoring.proctored_exam.attempt.collection'),
        'exam_started_poll_url': reverse(
            'edx_proctoring.proctored_exam.attempt',
            args=[attempt['id']]
        ) if attempt else '',
        'change_state_url': reverse(
            'edx_proctoring.proctored_exam.attempt',
            args=[attempt['id']]
        ) if attempt else '',
        'update_is_status_acknowledge_url': reverse(
            'edx_proctoring.proctored_exam.attempt.review_status',
            args=[attempt['id']]
        ) if attempt else '',
        'link_urls': settings.PROCTORING_SETTINGS.get('LINK_URLS', {}),
        'tech_support_email': settings.TECH_SUPPORT_EMAIL,
    }


def _get_practice_exam_view(exam, context, exam_id, user_id, course_id):
    """
    Returns a rendered view for the practice Exams
    """
    student_view_template = None

    attempt = get_exam_attempt(exam_id, user_id)

    attempt_status = attempt['status'] if attempt else None

    if not attempt_status:
        student_view_template = 'practice_exam/entrance.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.started:
        # when we're taking the exam we should not override the view
        return None
    elif attempt_status in [ProctoredExamStudentAttemptStatus.created,
                            ProctoredExamStudentAttemptStatus.download_software_clicked]:
        provider = get_backend_provider()
        student_view_template = 'proctored_exam/instructions.html'
        context.update({
            'exam_code': attempt['attempt_code'],
            'software_download_url': provider.get_software_download_url(),
        })
    elif attempt_status == ProctoredExamStudentAttemptStatus.ready_to_start:
        student_view_template = 'proctored_exam/ready_to_start.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.error:
        student_view_template = 'practice_exam/error.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.submitted:
        student_view_template = 'practice_exam/submitted.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.ready_to_submit:
        student_view_template = 'proctored_exam/ready_to_submit.html'

    if student_view_template:
        template = loader.get_template(student_view_template)
        django_context = Context(context)
        django_context.update(_get_proctored_exam_context(exam, attempt, course_id, is_practice_exam=True))
        return template.render(django_context)


def _get_proctored_exam_view(exam, context, exam_id, user_id, course_id):
    """
    Returns a rendered view for the Proctored Exams
    """
    student_view_template = None

    credit_state = context.get('credit_state')

    # see if only 'verified' track students should see this *except* if it is a practice exam
    check_mode = (
        settings.PROCTORING_SETTINGS.get('MUST_BE_VERIFIED_TRACK', True) and
        credit_state
    )

    if check_mode:
        has_mode = _check_eligibility_of_enrollment_mode(credit_state)
        if not has_mode:
            # user does not have the required enrollment mode
            # so do not override view this is a quick exit
            return None

    attempt = get_exam_attempt(exam_id, user_id)

    attempt_status = attempt['status'] if attempt else None

    # if user has declined the attempt, then we don't show the
    # proctored exam, a quick exit....
    if attempt_status == ProctoredExamStudentAttemptStatus.declined:
        return None

    if not attempt_status:
        # student has not started an attempt
        # so, show them:
        #       1) If there are failed prerequisites then block user and say why
        #       2) If there are pending prerequisites then block user and allow them to remediate them
        #       3) If there are declined prerequisites, then we auto-decline proctoring since user
        #          explicitly declined their interest in credit
        #       4) Otherwise - all prerequisites are satisfied - then give user
        #          option to take exam as proctored

        # get information about prerequisites

        credit_requirement_status = (
            credit_state.get('credit_requirement_status')
            if credit_state else []
        )

        prerequisite_status = _are_prerequirements_satisfied(
            credit_requirement_status,
            evaluate_for_requirement_name=exam['content_id'],
            filter_out_namespaces=['grade']
        )

        # add any prerequisite information, if applicable
        context.update({
            'prerequisite_status': prerequisite_status
        })

        # if exam due date has passed, then we can't take the exam
        if has_due_date_passed(exam['due_date']):
            student_view_template = 'proctored_exam/expired.html'
        elif not prerequisite_status['are_prerequisites_satisifed']:
            # do we have any declined prerequisites, if so, then we
            # will auto-decline this proctored exam
            if prerequisite_status['declined_prerequisites']:
                # user hasn't a record of attempt, create one now
                # so we can mark it as declined
                _create_and_decline_attempt(exam_id, user_id)
                return None

            # do we have failed prerequisites? That takes priority in terms of
            # messaging
            if prerequisite_status['failed_prerequisites']:
                # Let's resolve the URLs to jump to this prequisite
                prerequisite_status['failed_prerequisites'] = _resolve_prerequisite_links(
                    exam,
                    prerequisite_status['failed_prerequisites']
                )
                student_view_template = 'proctored_exam/failed-prerequisites.html'
            else:
                # Let's resolve the URLs to jump to this prequisite
                prerequisite_status['pending_prerequisites'] = _resolve_prerequisite_links(
                    exam,
                    prerequisite_status['pending_prerequisites']
                )
                student_view_template = 'proctored_exam/pending-prerequisites.html'
        else:
            student_view_template = 'proctored_exam/entrance.html'
            # emit an event that the user was presented with the option
            # to start timed exam
            emit_event(exam, 'option-presented')
    elif attempt_status == ProctoredExamStudentAttemptStatus.started:
        # when we're taking the exam we should not override the view
        return None
    elif attempt_status in [ProctoredExamStudentAttemptStatus.created,
                            ProctoredExamStudentAttemptStatus.download_software_clicked]:
        if context.get('verification_status') is not APPROVED_STATUS:
            # if the user has not id verified yet, show them the page that requires them to do so
            student_view_template = 'proctored_exam/id_verification.html'
        else:
            provider = get_backend_provider()
            student_view_template = 'proctored_exam/instructions.html'
            context.update({
                'exam_code': attempt['attempt_code'],
                'software_download_url': provider.get_software_download_url(),
            })
    elif attempt_status == ProctoredExamStudentAttemptStatus.ready_to_start:
        student_view_template = 'proctored_exam/ready_to_start.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.error:
        student_view_template = 'proctored_exam/error.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.timed_out:
        raise NotImplementedError('There is no defined rendering for ProctoredExamStudentAttemptStatus.timed_out!')
    elif attempt_status == ProctoredExamStudentAttemptStatus.submitted:
        student_view_template = None if _was_review_status_acknowledged(
            attempt['is_status_acknowledged'],
            exam['due_date']
        ) else 'proctored_exam/submitted.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.second_review_required:
        # the student should still see a 'submitted'
        # rendering even if the review needs a 2nd review
        student_view_template = None if _was_review_status_acknowledged(
            attempt['is_status_acknowledged'],
            exam['due_date']
        ) else 'proctored_exam/submitted.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.verified:
        student_view_template = None if _was_review_status_acknowledged(
            attempt['is_status_acknowledged'],
            exam['due_date']
        ) else 'proctored_exam/verified.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.rejected:
        student_view_template = None if _was_review_status_acknowledged(
            attempt['is_status_acknowledged'],
            exam['due_date']
        ) else 'proctored_exam/rejected.html'
    elif attempt_status == ProctoredExamStudentAttemptStatus.ready_to_submit:
        student_view_template = 'proctored_exam/ready_to_submit.html'

    if student_view_template:
        template = loader.get_template(student_view_template)
        django_context = Context(context)
        django_context.update(_get_proctored_exam_context(exam, attempt, course_id))
        return template.render(django_context)


def get_student_view(user_id, course_id, content_id,
                     context, user_role='student'):
    """
    Helper method that will return the view HTML related to the exam control
    flow (i.e. entering, expired, completed, etc.) If there is no specific
    content to display, then None will be returned and the caller should
    render it's own view
    """

    # non-student roles should never see any proctoring related
    # screens
    if user_role != 'student':
        return None

    credit_service = get_runtime_service('credit')

    # call service to get course end date.
    credit_state = credit_service.get_credit_state(user_id, course_id, return_course_info=True)
    course_end_date = credit_state.get('course_end_date', None)

    exam_id = None
    try:
        exam = get_exam_by_content_id(course_id, content_id)
        if not exam['is_active']:
            # Exam is no longer active
            # Note, we don't hard delete exams since we need to retain
            # data
            return None

        # Just in case the due date has been changed because of the
        # self-paced courses, use the due date from the context and
        # update the local exam object if necessary.
        if exam['due_date'] != context.get('due_date', None):
            update_exam(
                exam_id=exam['id'],
                due_date=context.get('due_date', None)
            )
            exam['due_date'] = context.get('due_date', None)

        exam_id = exam['id']
    except ProctoredExamNotFoundException:
        # This really shouldn't happen
        # as Studio will be setting this up
        exam_id = create_exam(
            course_id=course_id,
            content_id=unicode(content_id),
            exam_name=context['display_name'],
            time_limit_mins=context['default_time_limit_mins'],
            is_proctored=context.get('is_proctored', False),
            is_practice_exam=context.get('is_practice_exam', False),
            due_date=context.get('due_date', None),
            hide_after_due=context.get('hide_after_due', None),
        )
        exam = get_exam_by_content_id(course_id, content_id)

    is_practice_exam = exam['is_proctored'] and exam['is_practice_exam']
    is_proctored_exam = exam['is_proctored'] and not exam['is_practice_exam']
    is_timed_exam = not exam['is_proctored'] and not exam['is_practice_exam']

    sub_view_func = None
    if is_timed_exam:
        sub_view_func = _get_timed_exam_view
    elif is_practice_exam and not has_due_date_passed(course_end_date):
        sub_view_func = _get_practice_exam_view
    elif is_proctored_exam and not has_due_date_passed(course_end_date):
        sub_view_func = _get_proctored_exam_view

    if sub_view_func:
        return sub_view_func(exam, context, exam_id, user_id, course_id)
    return None
