from django.db import transaction
from rest_framework import status
from rest_framework.authentication import TokenAuthentication
from rest_framework.authtoken.models import Token
from rest_framework.permissions import IsAuthenticated
from rest_framework.response import Response
from rest_framework.views import APIView

from apps.support.models import SupportMessage, SupportRoom
from apps.support.serializers import (
    SendSupportMessageSerializer,
    SupportMessageSerializer,
    SupportRoomSerializer,
)


def resolve_user_support_room(request, create_if_missing: bool = False):
    """
    Resolves the SupportRoom for request.user (works for both logged-in and guest users).
    If a logged-in user does not yet have a room, checks the optional X-Guest-Token header
    to seamlessly migrate their existing guest support conversation.
    """
    user = request.user
    room = SupportRoom.objects.filter(user=user).first()
    if room:
        return room

    # Check if user recently logged in from a guest session that already had a support chat
    guest_token_key = request.headers.get('X-Guest-Token', '').strip()
    if guest_token_key and not getattr(user, 'is_guest', False):
        guest_token_obj = (
            Token.objects.select_related('user')
            .filter(key=guest_token_key)
            .first()
        )
        if guest_token_obj and guest_token_obj.user_id != user.id:
            guest_room = SupportRoom.objects.filter(user=guest_token_obj.user).first()
            if guest_room:
                guest_room.user = user
                guest_room.save(update_fields=['user', 'updated_at'])
                return guest_room

    if create_if_missing:
        room, _ = SupportRoom.objects.get_or_create(user=user)
        return room

    return None


class SupportChatMessagesView(APIView):
    """
    GET  /api/support/messages/?after_id=<id>
         Returns the user's support room and messages (all or after `after_id` for short polling).
    POST /api/support/messages/
         Sends a new message from the user (or guest user) to support.
    """
    authentication_classes = [TokenAuthentication]
    permission_classes = [IsAuthenticated]

    def get(self, request, *args, **kwargs):
        room = resolve_user_support_room(request, create_if_missing=False)
        if not room:
            return Response(
                {
                    'room': None,
                    'messages': [],
                },
                status=status.HTTP_200_OK,
            )

        after_id_param = request.query_params.get('after_id')
        messages_qs = room.messages.select_related('sender').order_by('id')

        if after_id_param is not None:
            try:
                after_id = int(after_id_param)
                if after_id > 0:
                    messages_qs = messages_qs.filter(id__gt=after_id)
            except (TypeError, ValueError):
                pass

        messages_list = list(messages_qs)

        # Mark support replies as read when user fetches messages in open chat
        mark_read = request.query_params.get('mark_read', 'true').lower() != 'false'
        if mark_read and (room.unread_by_user > 0 or any(
            m.sender_type == SupportMessage.SenderType.SUPPORT and not m.is_read
            for m in messages_list
        )):
            SupportMessage.objects.filter(
                room=room,
                sender_type=SupportMessage.SenderType.SUPPORT,
                is_read=False,
            ).update(is_read=True)
            if room.unread_by_user != 0:
                room.unread_by_user = 0
                room.save(update_fields=['unread_by_user', 'updated_at'])

        return Response(
            {
                'room': SupportRoomSerializer(room).data,
                'messages': SupportMessageSerializer(messages_list, many=True).data,
            },
            status=status.HTTP_200_OK,
        )

    @transaction.atomic
    def post(self, request, *args, **kwargs):
        serializer = SendSupportMessageSerializer(data=request.data)
        serializer.is_valid(raise_exception=True)

        room = resolve_user_support_room(request, create_if_missing=True)
        message = SupportMessage.objects.create(
            room=room,
            sender_type=SupportMessage.SenderType.USER,
            sender=request.user,
            content=serializer.validated_data['content'],
        )
        room.refresh_from_db()

        return Response(
            {
                'room': SupportRoomSerializer(room).data,
                'message': SupportMessageSerializer(message).data,
            },
            status=status.HTTP_201_CREATED,
        )


class SupportUnreadCountView(APIView):
    """
    GET /api/support/unread/
    Lightweight endpoint to check if the user has unread support specialist replies.
    """
    authentication_classes = [TokenAuthentication]
    permission_classes = [IsAuthenticated]

    def get(self, request, *args, **kwargs):
        room = resolve_user_support_room(request, create_if_missing=False)
        return Response(
            {
                'unread_count': room.unread_by_user if room else 0,
                'status': room.status if room else None,
            },
            status=status.HTTP_200_OK,
        )