from datetime import timedelta

from django.utils.translation import gettext_lazy as _
from rest_framework import serializers

from apps.bookings.models import Booking, BookingStatus
from apps.salons.models import StaffAvailability, StaffProfile


def validate_booking_request(service, staff, start_time, end_time):
    if staff is None:
        raise serializers.ValidationError({"staff": _("Staff is required for booking")})

    if isinstance(staff, StaffProfile) and staff.salon_id != service.salon_id:
        raise serializers.ValidationError({"staff": _("Selected staff does not belong to this salon")})

    if start_time >= end_time:
        raise serializers.ValidationError({"end_time": _("End time must be after start time")})

    expected_end = start_time + timedelta(minutes=service.duration_minutes)
    if expected_end != end_time:
        raise serializers.ValidationError({"end_time": _("End time must match service duration")})

    availability_qs = StaffAvailability.objects.filter(
        staff=staff,
        day_of_week=start_time.weekday(),
        is_active=True,
    )

    if availability_qs.exists():
        within_window = availability_qs.filter(
            start_time__lte=start_time.time(),
            end_time__gte=end_time.time(),
        ).exists()
        if not within_window:
            raise serializers.ValidationError({"start_time": _("Booking is outside staff availability")})

    overlap_exists = Booking.objects.filter(
        staff=staff,
        status__in=[BookingStatus.PENDING, BookingStatus.CONFIRMED],
        start_time__lt=end_time,
        end_time__gt=start_time,
    ).exists()
    if overlap_exists:
        raise serializers.ValidationError({"start_time": _("Booking overlaps an existing appointment")})