from __future__ import annotations

from dataclasses import dataclass

from django.conf import settings
from django.db import transaction
from django.utils import timezone, translation
from django.utils.translation import gettext_lazy as _

from apps.accounts.services.otp import PROVIDERS as OTP_PROVIDERS
from apps.bookings.models import Booking, BookingStatus
from apps.notifications.models import (
    Notification,
    NotificationChannel,
    NotificationEvent,
    NotificationStatus,
)


@dataclass
class NotificationSendResult:
    status: str
    payload: dict
    error_message: str = ""


def _get_provider():
    provider_key = getattr(settings, "NOTIFICATION_PROVIDER", settings.OTP_PROVIDER)
    provider_cls = OTP_PROVIDERS.get(provider_key)
    if not provider_cls:
        raise ValueError(_("Unknown notification provider: %(provider)s") % {"provider": provider_key})
    return provider_cls(), provider_key


def _format_start_time(booking: Booking) -> str:
    start_local = timezone.localtime(booking.start_time)
    return start_local.strftime("%Y-%m-%d %H:%M")


def _build_message(booking: Booking, event: str) -> str:
    start_text = _format_start_time(booking)
    service_name = booking.service.name
    salon_name = booking.salon.name

    if event == NotificationEvent.BOOKING_CREATED:
        return _(
            "Your booking request is received for %(service)s at %(salon)s on %(start)s."
        ) % {
            "service": service_name,
            "salon": salon_name,
            "start": start_text,
        }
    if event == NotificationEvent.BOOKING_CONFIRMED:
        return _(
            "Your booking is confirmed for %(service)s at %(salon)s on %(start)s."
        ) % {
            "service": service_name,
            "salon": salon_name,
            "start": start_text,
        }
    if event == NotificationEvent.BOOKING_CANCELLED:
        return _(
            "Your booking was cancelled for %(service)s at %(salon)s on %(start)s."
        ) % {
            "service": service_name,
            "salon": salon_name,
            "start": start_text,
        }

    return _("Booking update for %(service)s at %(salon)s on %(start)s.") % {
        "service": service_name,
        "salon": salon_name,
        "start": start_text,
    }


def _send_message(phone_number: str, channel: str, message: str) -> NotificationSendResult:
    provider, _ = _get_provider()
    try:
        if channel == NotificationChannel.SMS:
            provider.send_sms(phone_number, message)
        elif channel == NotificationChannel.WHATSAPP:
            provider.send_whatsapp(phone_number, message)
        else:
            raise ValueError(_("Unsupported notification channel"))
    except Exception as exc:  # pragma: no cover - provider failures are environment specific
        return NotificationSendResult(status=NotificationStatus.FAILED, payload={}, error_message=str(exc))

    return NotificationSendResult(status=NotificationStatus.SENT, payload={}, error_message="")


def _notification_channel() -> str:
    return getattr(settings, "NOTIFICATION_DEFAULT_CHANNEL", NotificationChannel.SMS)


def send_booking_notification(booking: Booking, recipient, event: str) -> Notification:
    channel = _notification_channel()
    phone_number = getattr(recipient, "phone_number", None) or ""

    # Render the message in the recipient's preferred language.
    with translation.override(getattr(recipient, "preferred_language", None)):
        message = _build_message(booking, event)

    with transaction.atomic():
        notification, created = Notification.objects.get_or_create(
            booking=booking,
            recipient=recipient,
            event=event,
            channel=channel,
            defaults={
                "phone_number": phone_number,
                "message": message,
            },
        )

        if not created and notification.status == NotificationStatus.SENT:
            return notification

        if not phone_number:
            # Record the skip for auditability when we cannot deliver.
            notification.status = NotificationStatus.SKIPPED
            notification.error_message = "Recipient has no phone number"
            notification.save(update_fields=["status", "error_message"])
            return notification

        notification.phone_number = phone_number
        notification.message = message
        send_result = _send_message(phone_number, channel, message)
        notification.status = send_result.status
        notification.provider = getattr(settings, "NOTIFICATION_PROVIDER", settings.OTP_PROVIDER)
        notification.provider_payload = send_result.payload
        notification.error_message = send_result.error_message
        notification.sent_at = timezone.now() if send_result.status == NotificationStatus.SENT else None
        notification.save(
            update_fields=[
                "phone_number",
                "message",
                "status",
                "provider",
                "provider_payload",
                "error_message",
                "sent_at",
            ]
        )

    return notification


def notify_booking_lifecycle(booking: Booking, event: str) -> list[Notification]:
    recipients = [booking.customer]
    if booking.staff and booking.staff.user:
        recipients.append(booking.staff.user)

    notifications = []
    for recipient in recipients:
        notifications.append(send_booking_notification(booking, recipient, event))

    return notifications


def notify_on_status_change(booking: Booking, previous_status: str) -> list[Notification]:
    if booking.status == previous_status:
        return []

    # Only notify for lifecycle transitions we explicitly support today.
    if booking.status == BookingStatus.CONFIRMED:
        return notify_booking_lifecycle(booking, NotificationEvent.BOOKING_CONFIRMED)
    if booking.status == BookingStatus.CANCELLED:
        return notify_booking_lifecycle(booking, NotificationEvent.BOOKING_CANCELLED)

    return []