import math
import re
from django.contrib.auth import get_user_model
from django.db import transaction
from django.db.models import Q, Sum
from django.shortcuts import get_object_or_404
from rest_framework import status
from rest_framework.authentication import TokenAuthentication
from rest_framework.authtoken.models import Token
from rest_framework.permissions import BasePermission, 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 (
    AdminSupportMessageSerializer,
    AdminSupportRoomSerializer,
    SendSupportMessageSerializer,
    SupportMessageSerializer,
    SupportRoomSerializer,
    serialize_admin_chat_user,
)

User = get_user_model()


class IsSupportAdminPanelUser(BasePermission):
    """
    Allows access to users who can log into the admin panel (super_admin, admin, professor, staff).
    """

    def has_permission(self, request, view):
        user = request.user
        if not user or not user.is_authenticated:
            return False
        if getattr(user, 'is_superuser', False) or getattr(user, 'is_staff', False):
            return True
        if hasattr(user, 'can_access_admin_panel') and user.can_access_admin_panel():
            return True
        return getattr(user, 'user_type', None) in ('super_admin', 'admin', 'professor', 'consultant')


def cleanup_deleted_or_inactive_support_rooms() -> None:
    """
    Deletes SupportRooms belonging to users who have been soft-deleted or deactivated.
    """
    SupportRoom.objects.filter(
        Q(user__is_active=False)
        | Q(user__deleted_at__isnull=False)
        | Q(user__fullname__endswith=':deleted')
    ).delete()


def active_support_rooms_queryset():
    """
    Returns SupportRooms belonging only to active, non-deleted users (including active guest users)
    that have at least one message.
    """
    cleanup_deleted_or_inactive_support_rooms()
    return (
        SupportRoom.objects.filter(
            user__is_active=True,
            user__deleted_at__isnull=True,
            messages__isnull=False,
        )
        .exclude(user__fullname__endswith=':deleted')
        .distinct()
    )


def get_total_admin_unread_count() -> int:
    agg = (
        SupportRoom.objects.filter(
            user__is_active=True,
            user__deleted_at__isnull=True,
            messages__isnull=False,
        )
        .exclude(user__fullname__endswith=':deleted')
        .distinct()
        .aggregate(total=Sum('unread_by_admin'))
    )
    return int(agg.get('total') or 0)


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 the user is logged in, automatically checks for and merges any unmerged guest support room
    (from X-Guest-Token or Web IP+UA device_id).
    """
    user = request.user
    if not getattr(user, 'is_guest', False) and getattr(user, 'email', None):
        from apps.account.guest_merge import resolve_guest_users_from_request, merge_guest_user_data

        guest_candidates = resolve_guest_users_from_request(request)
        for guest_user in guest_candidates:
            if guest_user.id != user.id:
                merge_guest_user_data(guest_user, user)

    room = SupportRoom.objects.filter(user=user).first()
    if room:
        return 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,
        )


class AdminSupportRoomListView(APIView):
    """
    GET /api/support/admin/rooms/?page=1&per_page=20&search=...
    Lists all SupportRooms for the admin dashboard (`dovodi-panel`).
    """
    authentication_classes = [TokenAuthentication]
    permission_classes = [IsAuthenticated, IsSupportAdminPanelUser]

    def get(self, request, *args, **kwargs):
        try:
            page = max(1, int(request.query_params.get('page', 1)))
        except (TypeError, ValueError):
            page = 1

        try:
            per_page = max(1, min(100, int(request.query_params.get('per_page', 20))))
        except (TypeError, ValueError):
            per_page = 20

        search = (request.query_params.get('search') or '').strip()

        qs = active_support_rooms_queryset().select_related('user', 'assigned_to').order_by(
            '-last_message_at',
            '-updated_at',
            '-id',
        )

        if search:
            q_filter = (
                Q(user__fullname__icontains=search)
                | Q(user__email__icontains=search)
                | Q(user__phone_number__icontains=search)
                | Q(messages__content__icontains=search)
            )
            digits_match = re.search(r'(\d+)', search)
            if digits_match:
                num_val = int(digits_match.group(1))
                q_filter |= Q(id=num_val) | Q(user__id=num_val)
            elif search.lower() == 'guest':
                q_filter |= Q(user__email__isnull=True)

            qs = qs.filter(q_filter).distinct()

        total_rooms = qs.count()
        total_pages = max(1, math.ceil(total_rooms / per_page))
        offset = (page - 1) * per_page
        rooms_page = list(qs[offset:offset + per_page])

        serialized_rooms = AdminSupportRoomSerializer(
            rooms_page,
            many=True,
            context={'request': request},
        ).data

        return Response(
            {
                'status': 'success',
                'current_user': serialize_admin_chat_user(request.user, request=request),
                'room_messages': serialized_rooms,
                'total_pages': total_pages,
                'current_page': page,
                'per_page': per_page,
                'total_rooms': total_rooms,
                'total_unread_count': get_total_admin_unread_count(),
            },
            status=status.HTTP_200_OK,
        )


class AdminSupportRoomByUserView(APIView):
    """
    POST /api/support/admin/rooms/by-user/
    Body: { "user_id": <int> }
    Gets or creates a SupportRoom for a specific user when an admin starts a new chat from the panel.
    """
    authentication_classes = [TokenAuthentication]
    permission_classes = [IsAuthenticated, IsSupportAdminPanelUser]

    @transaction.atomic
    def post(self, request, *args, **kwargs):
        user_id = request.data.get('user_id') or request.data.get('recipient_id')
        target_user = get_object_or_404(User, pk=user_id)
        room, _ = SupportRoom.objects.get_or_create(
            user=target_user,
            defaults={'assigned_to': request.user},
        )

        # Mark any unread messages from this user as read
        if room.unread_by_admin > 0:
            SupportMessage.objects.filter(
                room=room,
                sender_type=SupportMessage.SenderType.USER,
                is_read=False,
            ).update(is_read=True)
            room.unread_by_admin = 0
            room.save(update_fields=['unread_by_admin', 'updated_at'])

        messages_qs = room.messages.select_related('sender').order_by('id')
        messages_list = list(messages_qs)

        return Response(
            {
                'status': 'success',
                'room': AdminSupportRoomSerializer(room, context={'request': request}).data,
                'messages': AdminSupportMessageSerializer(
                    messages_list,
                    many=True,
                    context={'request': request},
                ).data,
                'current_user': serialize_admin_chat_user(request.user, request=request),
                'total_pages': 1,
                'current_page': 1,
                'per_page': max(20, len(messages_list)),
                'total_messages': len(messages_list),
                'total_unread_count': get_total_admin_unread_count(),
            },
            status=status.HTTP_200_OK,
        )


class AdminSupportRoomMessagesView(APIView):
    """
    GET  /api/support/admin/rooms/<int:room_id>/messages/?after_id=<id>
         Returns messages for a SupportRoom and marks unread user messages as read.
    POST /api/support/admin/rooms/<int:room_id>/messages/
         Sends a reply from the admin/specialist (`sender_type='support'`).
    """
    authentication_classes = [TokenAuthentication]
    permission_classes = [IsAuthenticated, IsSupportAdminPanelUser]

    def get(self, request, room_id: int, *args, **kwargs):
        room = get_object_or_404(
            active_support_rooms_queryset().select_related('user', 'assigned_to'),
            pk=room_id,
        )

        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 user messages as read when admin views the room
        if room.unread_by_admin > 0 or any(
            m.sender_type == SupportMessage.SenderType.USER and not m.is_read
            for m in messages_list
        ):
            SupportMessage.objects.filter(
                room=room,
                sender_type=SupportMessage.SenderType.USER,
                is_read=False,
            ).update(is_read=True)
            if room.unread_by_admin != 0:
                room.unread_by_admin = 0
                room.save(update_fields=['unread_by_admin', 'updated_at'])

        total_messages = room.messages.count()

        return Response(
            {
                'status': 'success',
                'room': AdminSupportRoomSerializer(room, context={'request': request}).data,
                'messages': AdminSupportMessageSerializer(
                    messages_list,
                    many=True,
                    context={'request': request},
                ).data,
                'current_user': serialize_admin_chat_user(request.user, request=request),
                'total_pages': 1,
                'current_page': 1,
                'per_page': max(50, total_messages),
                'total_messages': total_messages,
                'total_unread_count': get_total_admin_unread_count(),
            },
            status=status.HTTP_200_OK,
        )

    @transaction.atomic
    def post(self, request, room_id: int, *args, **kwargs):
        room = get_object_or_404(
            active_support_rooms_queryset().select_related('user', 'assigned_to'),
            pk=room_id,
        )
        serializer = SendSupportMessageSerializer(data=request.data)
        serializer.is_valid(raise_exception=True)

        if not room.assigned_to_id:
            room.assigned_to = request.user
            room.save(update_fields=['assigned_to', 'updated_at'])

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

        return Response(
            {
                'status': 'success',
                'room': AdminSupportRoomSerializer(room, context={'request': request}).data,
                'message': AdminSupportMessageSerializer(
                    message,
                    context={'request': request},
                ).data,
                'current_user': serialize_admin_chat_user(request.user, request=request),
                'total_unread_count': get_total_admin_unread_count(),
            },
            status=status.HTTP_201_CREATED,
        )


class AdminSupportMessageDetailView(APIView):
    """
    PATCH  /api/support/admin/messages/<int:message_id>/
           Updates the content of a support message.
    DELETE /api/support/admin/messages/<int:message_id>/
           Deletes a support message.
    """
    authentication_classes = [TokenAuthentication]
    permission_classes = [IsAuthenticated, IsSupportAdminPanelUser]

    @transaction.atomic
    def patch(self, request, message_id: int, *args, **kwargs):
        message = get_object_or_404(
            SupportMessage.objects.select_related('room', 'sender'),
            pk=message_id,
        )
        serializer = SendSupportMessageSerializer(data=request.data)
        serializer.is_valid(raise_exception=True)

        message.content = serializer.validated_data['content']
        message.save(update_fields=['content'])

        return Response(
            {
                'status': 'success',
                'room_id': message.room_id,
                'message': AdminSupportMessageSerializer(
                    message,
                    context={'request': request},
                ).data,
                'total_unread_count': get_total_admin_unread_count(),
            },
            status=status.HTTP_200_OK,
        )

    @transaction.atomic
    def delete(self, request, message_id: int, *args, **kwargs):
        message = get_object_or_404(
            SupportMessage.objects.select_related('room'),
            pk=message_id,
        )
        room = message.room
        deleted_id = message.id
        message.delete()

        last_msg = room.messages.order_by('-id').first()
        room.last_message_at = last_msg.created_at if last_msg else None
        room.save(update_fields=['last_message_at', 'updated_at'])

        return Response(
            {
                'status': 'success',
                'room_id': room.id,
                'deleted_message_id': deleted_id,
                'room': AdminSupportRoomSerializer(room, context={'request': request}).data,
                'total_unread_count': get_total_admin_unread_count(),
            },
            status=status.HTTP_200_OK,
        )