"""ViewSets для API модуля закупок."""

from django.db.models import Q
from django.utils import timezone
from django_filters.rest_framework import DjangoFilterBackend
from drf_spectacular.utils import extend_schema
from rest_framework import filters, permissions, status, viewsets
from rest_framework.decorators import action
from rest_framework.response import Response

from employees.models import Department
from procurement.constants import (
    ProcurementStatus,
)
from procurement.models import (
    Budget,
    ProcurementRequest,
)

from ..serializers import (
    BudgetSerializer,
    ProcurementDepartmentStatsSerializer,
    ProcurementOverviewStatsSerializer,
)


class ProcurementStatsViewSet(viewsets.ViewSet):
    """ViewSet для статистики закупок."""

    permission_classes = [permissions.IsAuthenticated]

    @extend_schema(
        tags=["Procurement"],
        summary="Получить общую статистику закупок",
        responses=ProcurementOverviewStatsSerializer,
    )
    @action(detail=False, methods=["get"])
    def overview(self, request):
        """Общая статистика закупок."""
        from django.db.models import Count, Sum
        from django.utils import timezone

        now = timezone.now()
        month_start = now.replace(day=1, hour=0, minute=0, second=0)
        year_start = now.replace(month=1, day=1, hour=0, minute=0, second=0)

        user = request.user

        # Базовый queryset зависит от прав пользователя
        if user.is_superuser or user.is_staff:
            base_qs = ProcurementRequest.objects.all()
        else:
            base_qs = ProcurementRequest.objects.filter(
                Q(requestor=user) | Q(department__in=user.departments.all())
            )

        # Подсчёт по статусам
        by_status = dict(
            base_qs.values("status")
            .annotate(count=Count("id"))
            .values_list("status", "count")
        )

        # Подсчёт по срочности
        by_urgency = dict(
            base_qs.values("urgency")
            .annotate(count=Count("id"))
            .values_list("urgency", "count")
        )

        # Общие метрики
        total = base_qs.count()
        pending = base_qs.filter(status=ProcurementStatus.PENDING).count()
        approved_month = base_qs.filter(
            status=ProcurementStatus.APPROVED, updated_at__gte=month_start
        ).count()
        completed_month = base_qs.filter(
            status=ProcurementStatus.COMPLETED, completed_at__gte=month_start
        ).count()

        # Сумма потраченного за год
        spent_year = (
            base_qs.filter(
                status=ProcurementStatus.COMPLETED, completed_at__gte=year_start
            ).aggregate(total=Sum("actual_cost"))["total"]
            or 0
        )

        return Response(
            {
                "total_requests": total,
                "pending_requests": pending,
                "approved_this_month": approved_month,
                "completed_this_month": completed_month,
                "total_spent_this_year": str(spent_year),
                "by_status": by_status,
                "by_urgency": by_urgency,
            }
        )

    @extend_schema(
        tags=["Procurement"],
        summary="Получить статистику закупок по отделам",
        responses=ProcurementDepartmentStatsSerializer(many=True),
    )
    @action(detail=False, methods=["get"], url_path="by-department")
    def by_department(self, request):
        """Статистика по отделам."""
        from django.db.models import Sum

        user = request.user

        # Только для staff/superuser или руководителей
        if not (user.is_superuser or user.is_staff):
            if not user.headed_departments.exists():
                return Response(
                    {"detail": "Нет доступа к статистике по отделам."},
                    status=status.HTTP_403_FORBIDDEN,
                )
            departments = user.headed_departments.all()
        else:
            departments = Department.objects.all()

        result = []
        for dept in departments:
            requests = ProcurementRequest.objects.filter(department=dept)
            total = requests.count()
            spent = (
                requests.filter(status=ProcurementStatus.COMPLETED).aggregate(
                    total=Sum("actual_cost")
                )["total"]
                or 0
            )

            result.append(
                {
                    "department": {"id": dept.id, "name": dept.name},
                    "total_requests": total,
                    "total_spent": str(spent),
                }
            )

        return Response(result)


class BudgetViewSet(viewsets.ReadOnlyModelViewSet):
    """ViewSet для просмотра бюджетов отдела."""

    queryset = Budget.objects.select_related("department")
    serializer_class = BudgetSerializer
    filter_backends = [DjangoFilterBackend, filters.OrderingFilter]
    filterset_fields = ["department", "year", "quarter"]
    ordering = ["-year", "-quarter", "department__name"]

    def get_permissions(self):
        return [permissions.IsAuthenticated()]

    def get_queryset(self):
        queryset = super().get_queryset()
        user = self.request.user

        if user.is_superuser or user.is_staff:
            return queryset

        headed_departments = user.headed_departments.all()
        if headed_departments.exists():
            return queryset.filter(department__in=headed_departments)

        if self.action == "my_department":
            return queryset

        return queryset.none()

    def list(self, request, *args, **kwargs):
        user = request.user
        if not (user.is_superuser or user.is_staff or user.headed_departments.exists()):
            return Response(
                {"detail": "Нет доступа к бюджетам отделов."},
                status=status.HTTP_403_FORBIDDEN,
            )
        return super().list(request, *args, **kwargs)

    @action(detail=False, methods=["get"], url_path="my-department")
    def my_department(self, request):
        """Бюджет текущего отдела пользователя на текущий квартал."""
        user_departments = request.user.departments.all()
        department = user_departments.first()
        if department is None:
            return Response(
                {"detail": "Пользователь не состоит ни в одном отделе."},
                status=status.HTTP_404_NOT_FOUND,
            )

        now = timezone.now()
        quarter = (now.month - 1) // 3 + 1
        budget = (
            self.get_queryset()
            .filter(
                department=department,
                year=now.year,
                quarter=quarter,
            )
            .first()
        )
        if budget is None:
            return Response(
                {"detail": "Бюджет на текущий квартал не найден."},
                status=status.HTTP_404_NOT_FOUND,
            )

        serializer = self.get_serializer(budget)
        return Response(serializer.data)