"""Dynamic slot generation.

Slots are generated from runtime settings (working hours, slot duration,
default capacity) and per-day `FacilitySchedule` overrides (capacity for the
day, days off). Generation is idempotent — re-running updates existing slots
instead of duplicating them.
"""
from datetime import datetime, timedelta

from apps.core.settings_service import SettingsService
from apps.reservations.models import FacilitySchedule, Slot


class SlotService:
    def generate_slots(self, facility, day, line=None) -> int:
        schedule = FacilitySchedule.objects.filter(facility=facility, date=day).first()
        if schedule is not None and not schedule.is_open:
            return 0  # day off

        service = SettingsService()
        if schedule is not None and schedule.start_time:
            start_str = schedule.start_time.strftime("%H:%M")
        else:
            start_str = service.get("reservation.working_hours_start", "08:00")
        if schedule is not None and schedule.end_time:
            end_str = schedule.end_time.strftime("%H:%M")
        else:
            end_str = service.get("reservation.working_hours_end", "17:00")
        duration = int(service.get("reservation.slot_duration_minutes", 30))
        if schedule is not None:
            capacity = schedule.capacity
        else:
            capacity = int(service.get("reservation.default_capacity", 2))

        if duration <= 0:
            raise ValueError("Slot duration must be positive.")

        start_t = datetime.strptime(start_str, "%H:%M").time()
        end_t = datetime.strptime(end_str, "%H:%M").time()
        current = datetime.combine(day, start_t)
        end_dt = datetime.combine(day, end_t)

        created = 0
        while current + timedelta(minutes=duration) <= end_dt:
            slot_end = (current + timedelta(minutes=duration)).time()
            _, was_created = Slot.objects.update_or_create(
                facility=facility,
                line=line,
                date=day,
                start_time=current.time(),
                defaults={"end_time": slot_end, "capacity": capacity},
            )
            if was_created:
                created += 1
            current += timedelta(minutes=duration)
        return created