import itertools

from django.db.models import Count, Min

from symposion.schedule.models import Room, Slot, SlotRoom


class TimeTable(object):

    def __init__(self, day):
        self.day = day
        self.slots_qs = Slot.objects.filter(day=day)\
            .select_related('kind', 'content_ptr__speaker__user')\
            .prefetch_related('content_ptr__additional_speakers')
        self._times = sorted(
            set(itertools.chain(*self.slots_qs.values_list("start", "end")))
        )

    def slots(self):
        if not hasattr(self, '_slots'):
            filters = {
                "room_count": Count("slotroom"),
                "order": Min("slotroom__room__order")
            }
            self._slots = self.slots_qs.annotate(**filters).order_by("order")
        return self._slots

    def rooms(self):
        if not hasattr(self, '_rooms'):
            self._rooms = Room.objects\
                .filter(slotroom__slot__in=self.slots_qs)\
                .distinct()\
                .order_by("order")
        return self._rooms

    def __iter__(self):
        slots = self.slots()

        row = []
        total_room_count = self.rooms().count()
        for time, next_time in pairwise(self._times):
            row = {"time": time, "end": next_time, "slots": []}
            row_slots = [ slot for slot in slots if slot.start == time]
            for slot in row_slots:
                slot.rowspan = TimeTable.rowspan(self._times, slot.start, slot.end)
                slot.colspan = slot.room_count if not slot.exclusive else total_room_count
                row["slots"].append(slot)
            if row["slots"] or next_time is None:
                yield row

    @staticmethod
    def rowspan(times, start, end):
        return times.index(end) - times.index(start)


def pairwise(iterable):
    a, b = itertools.tee(iterable)
    next(b)
    return itertools.zip_longest(a, b)