"""Helpers for the student app. """
from datetime import datetime
import urllib

from pytz import UTC
from django.core.urlresolvers import reverse, NoReverseMatch

import third_party_auth
from lms.djangoapps.verify_student.models import VerificationDeadline, SoftwareSecurePhotoVerification
from course_modes.models import CourseMode


# Enumeration of per-course verification statuses
# we display on the student dashboard.
VERIFY_STATUS_NEED_TO_VERIFY = "verify_need_to_verify"
VERIFY_STATUS_SUBMITTED = "verify_submitted"
VERIFY_STATUS_APPROVED = "verify_approved"
VERIFY_STATUS_MISSED_DEADLINE = "verify_missed_deadline"
VERIFY_STATUS_NEED_TO_REVERIFY = "verify_need_to_reverify"

DISABLE_UNENROLL_CERT_STATES = [
    'generating',
    'ready',
]


def check_verify_status_by_course(user, course_enrollments):
    """
    Determine the per-course verification statuses for a given user.

    The possible statuses are:
        * VERIFY_STATUS_NEED_TO_VERIFY: The student has not yet submitted photos for verification.
        * VERIFY_STATUS_SUBMITTED: The student has submitted photos for verification,
          but has have not yet been approved.
        * VERIFY_STATUS_APPROVED: The student has been successfully verified.
        * VERIFY_STATUS_MISSED_DEADLINE: The student did not submit photos within the course's deadline.
        * VERIFY_STATUS_NEED_TO_REVERIFY: The student has an active verification, but it is
            set to expire before the verification deadline for the course.

    It is is also possible that a course does NOT have a verification status if:
        * The user is not enrolled in a verified mode, meaning that the user didn't pay.
        * The course does not offer a verified mode.
        * The user submitted photos but an error occurred while verifying them.
        * The user submitted photos but the verification was denied.

    In the last two cases, we rely on messages in the sidebar rather than displaying
    messages for each course.

    Arguments:
        user (User): The currently logged-in user.
        course_enrollments (list[CourseEnrollment]): The courses the user is enrolled in.

    Returns:
        dict: Mapping of course keys verification status dictionaries.
            If no verification status is applicable to a course, it will not
            be included in the dictionary.
            The dictionaries have these keys:
                * status (str): One of the enumerated status codes.
                * days_until_deadline (int): Number of days until the verification deadline.
                * verification_good_until (str): Date string for the verification expiration date.

    """
    status_by_course = {}

    # Retrieve all verifications for the user, sorted in descending
    # order by submission datetime
    verifications = SoftwareSecurePhotoVerification.objects.filter(user=user)

    # Check whether the user has an active or pending verification attempt
    # To avoid another database hit, we re-use the queryset we have already retrieved.
    has_active_or_pending = SoftwareSecurePhotoVerification.user_has_valid_or_pending(
        user, queryset=verifications
    )

    # Retrieve verification deadlines for the enrolled courses
    enrolled_course_keys = [enrollment.course_id for enrollment in course_enrollments]
    course_deadlines = VerificationDeadline.deadlines_for_courses(enrolled_course_keys)

    recent_verification_datetime = None

    for enrollment in course_enrollments:

        # If the user hasn't enrolled as verified, then the course
        # won't display state related to its verification status.
        if enrollment.mode in CourseMode.VERIFIED_MODES:

            # Retrieve the verification deadline associated with the course.
            # This could be None if the course doesn't have a deadline.
            deadline = course_deadlines.get(enrollment.course_id)

            relevant_verification = SoftwareSecurePhotoVerification.verification_for_datetime(deadline, verifications)

            # Picking the max verification datetime on each iteration only with approved status
            if relevant_verification is not None and relevant_verification.status == "approved":
                recent_verification_datetime = max(
                    recent_verification_datetime if recent_verification_datetime is not None
                    else relevant_verification.expiration_datetime,
                    relevant_verification.expiration_datetime
                )

            # By default, don't show any status related to verification
            status = None

            # Check whether the user was approved or is awaiting approval
            if relevant_verification is not None:
                if relevant_verification.status == "approved":
                    status = VERIFY_STATUS_APPROVED
                elif relevant_verification.status == "submitted":
                    status = VERIFY_STATUS_SUBMITTED

            # If the user didn't submit at all, then tell them they need to verify
            # If the deadline has already passed, then tell them they missed it.
            # If they submitted but something went wrong (error or denied),
            # then don't show any messaging next to the course, since we already
            # show messages related to this on the left sidebar.
            submitted = (
                relevant_verification is not None and
                relevant_verification.status not in ["created", "ready"]
            )
            if status is None and not submitted:
                if deadline is None or deadline > datetime.now(UTC):
                    if has_active_or_pending:
                        # The user has an active verification, but the verification
                        # is set to expire before the deadline.  Tell the student
                        # to reverify.
                        status = VERIFY_STATUS_NEED_TO_REVERIFY
                    else:
                        status = VERIFY_STATUS_NEED_TO_VERIFY
                else:
                    # If a user currently has an active or pending verification,
                    # then they may have submitted an additional attempt after
                    # the verification deadline passed.  This can occur,
                    # for example, when the support team asks a student
                    # to reverify after the deadline so they can receive
                    # a verified certificate.
                    # In this case, we still want to show them as "verified"
                    # on the dashboard.
                    if has_active_or_pending:
                        status = VERIFY_STATUS_APPROVED

                    # Otherwise, the student missed the deadline, so show
                    # them as "honor" (the kind of certificate they will receive).
                    else:
                        status = VERIFY_STATUS_MISSED_DEADLINE

            # Set the status for the course only if we're displaying some kind of message
            # Otherwise, leave the course out of the dictionary.
            if status is not None:
                days_until_deadline = None

                now = datetime.now(UTC)
                if deadline is not None and deadline > now:
                    days_until_deadline = (deadline - now).days

                status_by_course[enrollment.course_id] = {
                    'status': status,
                    'days_until_deadline': days_until_deadline
                }

    if recent_verification_datetime:
        for key, value in status_by_course.iteritems():  # pylint: disable=unused-variable
            status_by_course[key]['verification_good_until'] = recent_verification_datetime.strftime("%m/%d/%Y")

    return status_by_course


def auth_pipeline_urls(auth_entry, redirect_url=None):
    """Retrieve URLs for each enabled third-party auth provider.

    These URLs are used on the "sign up" and "sign in" buttons
    on the login/registration forms to allow users to begin
    authentication with a third-party provider.

    Optionally, we can redirect the user to an arbitrary
    url after auth completes successfully.  We use this
    to redirect the user to a page that required login,
    or to send users to the payment flow when enrolling
    in a course.

    Args:
        auth_entry (string): Either `pipeline.AUTH_ENTRY_LOGIN` or `pipeline.AUTH_ENTRY_REGISTER`

    Keyword Args:
        redirect_url (unicode): If provided, send users to this URL
            after they successfully authenticate.

    Returns:
        dict mapping provider IDs to URLs

    """
    if not third_party_auth.is_enabled():
        return {}

    return {
        provider.provider_id: third_party_auth.pipeline.get_login_url(
            provider.provider_id, auth_entry, redirect_url=redirect_url
        ) for provider in third_party_auth.provider.Registry.accepting_logins()
    }


# Query string parameters that can be passed to the "finish_auth" view to manage
# things like auto-enrollment.
POST_AUTH_PARAMS = ('course_id', 'enrollment_action', 'course_mode', 'email_opt_in')


def get_next_url_for_login_page(request):
    """
    Determine the URL to redirect to following login/registration/third_party_auth

    The user is currently on a login or registration page.
    If 'course_id' is set, or other POST_AUTH_PARAMS, we will need to send the user to the
    /account/finish_auth/ view following login, which will take care of auto-enrollment in
    the specified course.

    Otherwise, we go to the ?next= query param or to the dashboard if nothing else is
    specified.
    """
    redirect_to = request.GET.get('next', None)
    if not redirect_to:
        try:
            redirect_to = reverse('dashboard')
        except NoReverseMatch:
            redirect_to = reverse('home')
    if any(param in request.GET for param in POST_AUTH_PARAMS):
        # Before we redirect to next/dashboard, we need to handle auto-enrollment:
        params = [(param, request.GET[param]) for param in POST_AUTH_PARAMS if param in request.GET]
        params.append(('next', redirect_to))  # After auto-enrollment, user will be sent to payment page or to this URL
        redirect_to = '{}?{}'.format(reverse('finish_auth'), urllib.urlencode(params))
        # Note: if we are resuming a third party auth pipeline, then the next URL will already
        # be saved in the session as part of the pipeline state. That URL will take priority
        # over this one.
    return redirect_to
