from datetime import date, datetime
from typing import Optional

from django.contrib.auth.decorators import login_required
from django.core.exceptions import PermissionDenied
from django.db.models import Count, Exists, OuterRef, Q, Sum
from django.http import Http404, HttpRequest, HttpResponse
from django.shortcuts import get_object_or_404, redirect, render
from django.urls import reverse
from django.utils.translation import ugettext as _

from biscuit.apps.chronos.models import LessonPeriod
from biscuit.apps.chronos.util import CalendarWeek
from biscuit.core.models import Group, Person

from .forms import LessonDocumentationForm, PersonalNoteFormSet, SelectForm
from .models import LessonDocumentation, PersonalNote


@login_required
def lesson(request: HttpRequest, year: Optional[int] = None, week: Optional[int] = None, period_id: Optional[int] = None) -> HttpResponse:
    context = {}

    if year and week and period_id:
        # Get a specific lesson period if provided in URL
        lesson_period = LessonPeriod.objects.get(pk=period_id)
        wanted_week = CalendarWeek(year=year, week=week)
    else:
        # Determine current lesson by current date and time
        lesson_period = LessonPeriod.objects.at_time().filter_teacher(request.user.person).first()
        wanted_week = CalendarWeek()

        if lesson_period:
            return redirect('lesson_by_week_and_period', wanted_week.year, wanted_week.week, lesson_period.pk)
        else:
            raise Http404(_('You either selected an invalid lesson or there is currently no lesson in progress.'))

    if datetime.combine(wanted_week[lesson_period.period.weekday - 1], lesson_period.period.time_start) > datetime.now():
        raise PermissionDenied(_('You are not allowed to create a lesson documentation for a lesson in the future.'))

    context['lesson_period'] = lesson_period
    context['week'] = wanted_week
    context['day'] = wanted_week[lesson_period.period.weekday - 1]

    # Create or get lesson documentation object; can be empty when first opening lesson
    lesson_documentation, created = LessonDocumentation.objects.get_or_create(
        lesson_period=lesson_period, week=wanted_week.week)
    lesson_documentation_form = LessonDocumentationForm(
        request.POST or None, instance=lesson_documentation, prefix='leson_documentation')

    # Find all persons in the associated groups that do not yet have a personal note for this lesson
    missing_persons = Person.objects.annotate(
        no_personal_notes=~Exists(PersonalNote.objects.filter(
            week=wanted_week.week,
            lesson_period=lesson_period,
            person__pk=OuterRef('pk')
        ))
    ).filter(
        member_of__in=Group.objects.filter(pk__in=lesson_period.lesson.groups.all()),
        is_active=True,
        no_personal_notes=True
    )

    # Create all missing personal notes
    PersonalNote.objects.bulk_create([
        PersonalNote(person=person, lesson_period=lesson_period,
                     week=wanted_week.week) for person in missing_persons  # FIXME Respect year as well
    ])

    # Create a formset that holds all personal notes for all persons in this lesson
    persons_qs = PersonalNote.objects.select_related('person').filter(
        lesson_period=lesson_period, week=wanted_week.week)  # FIXME Respect year as well
    personal_note_formset = PersonalNoteFormSet(
        request.POST or None, queryset=persons_qs, prefix='personal_notes')

    if request.method == 'POST':
        if lesson_documentation_form.is_valid():
            lesson_documentation_form.save()
        if personal_note_formset.is_valid():
            personal_note_formset.save()

    context['lesson_documentation'] = lesson_documentation
    context['lesson_documentation_form'] = lesson_documentation_form
    context['personal_note_formset'] = personal_note_formset

    return render(request, 'alsijil/lesson.html', context)


@login_required
def week_view(request: HttpRequest, year: Optional[int] = None, week: Optional[int] = None) -> HttpResponse:
    context = {}

    if year and week:
        wanted_week = CalendarWeek(year=year, week=week)
    else:
        wanted_week = CalendarWeek()

    lesson_periods = LessonPeriod.objects.annotate(
            has_documentation=Exists(LessonDocumentation.objects.filter(
                ~Q(topic__exact=''),
                lesson_period=OuterRef('pk'),
                week=wanted_week.week
            ))
        ).in_week(wanted_week)

    if request.GET.get('group', None) or request.GET.get('teacher', None) or request.GET.get('room', None):
        lesson_periods = lesson_periods.filter_from_query(request.GET)
    elif hasattr(request, 'user') and hasattr(request.user, 'person'):
        group = request.user.person.owner_of.first()
        lesson_periods = lesson_periods.filter_group(group)
    else:
        lesson_periods = None

    if lesson_periods:
        # Aggregate all personal notes for this group and week
        persons = Person.objects.filter(
            is_active=True
        ).filter(
            Q(member_of=group) | Q(member_of__parent_groups=group)
        ).distinct().prefetch_related(
            'personal_notes'
        ).annotate(
            absences=Count('personal_notes__absent', filter=Q(
                personal_notes__lesson_period__in=lesson_periods,
                personal_notes__week=wanted_week.week,
                personal_notes__absent=True
            )),
            unexcused=Count('personal_notes__absent', filter=Q(
                personal_notes__lesson_period__in=lesson_periods,
                personal_notes__week=wanted_week.week,
                personal_notes__absent=True,
                personal_notes__excused=False
            )),
            tardiness=Sum('personal_notes__late', filter=Q(
                personal_notes__lesson_period__in=lesson_periods,
                personal_notes__week=wanted_week.week
            ))
        )
    else:
        persons = None

    # Add a form to filter the view
    select_form = SelectForm(request.GET or None)

    context['current_head'] = str(wanted_week)
    context['week'] = wanted_week
    context['lesson_periods'] = lesson_periods
    context['persons'] = persons
    context['select_form'] = select_form

    week_prev = wanted_week - 1
    week_next = wanted_week + 1
    context['url_prev'] = '%s?%s' % (reverse('week_view_by_week', args=[week_prev.year, week_prev.week]), request.GET.urlencode())
    context['url_next'] = '%s?%s' % (reverse('week_view_by_week', args=[week_next.year, week_next.week]), request.GET.urlencode())

    return render(request, 'alsijil/week_view.html', context)


@login_required
def full_register_group(request: HttpRequest, id_: int) -> HttpResponse:
    context = {}

    group = get_object_or_404(Group, pk=id_)

    # Get all lesson periods for the selected group
    lesson_periods = LessonPeriod.objects.annotate(
        has_documentation=Exists(LessonDocumentation.objects.filter(
            ~Q(topic__exact=''),
            lesson_period=OuterRef('pk'),
        ))
    ).within_dates(
        group.school.current_term.date_start,
        group.school.current_term.date_end
    ).filter_group(group).distinct()

    weeks = CalendarWeek.weeks_within(group.school.current_term.date_start, group.school.current_term.date_end)
    periods_by_day = {}
    for lesson_period in lesson_periods:
        for week in weeks:
            day = week[lesson_period.period.weekday - 1]

            if lesson_period.lesson.date_start <= day and lesson_period.lesson.date_end >= day:
                documentations = list(filter(lambda d: d.week == week.week, lesson_period.documentations.all()))
                notes = list(filter(lambda d: d.week == week.week, lesson_period.personal_notes.all()))
                substitution = lesson_period.get_substitution(week.week)

                periods_by_day.setdefault(day, []).append((lesson_period, documentations, notes, substitution))

    context['group'] = group
    context['weeks'] = weeks
    context['periods_by_day'] = periods_by_day
    context['today'] = date.today()

    return render(request, 'alsijil/print/full_register.html', context)