"""
DRF API ViewSets for Referrals app.
"""

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

from .models import Referral
from .serializers import (
    ReferralListSerializer, ReferralDetailSerializer,
    ReferralCreateSerializer, ReferralResponseSerializer,
)


class ReferralViewSet(viewsets.ModelViewSet):
    """
    API endpoint for Referral CRUD and workflow operations.
    
    list: Get list of referrals
    retrieve: Get referral details
    create: Create new referral
    update: Update referral
    destroy: Delete referral
    
    Custom actions:
    - accept: Accept referral
    - reject: Reject referral
    - complete: Complete referral
    - sent: Get sent referrals
    - received: Get received referrals
    """
    
    permission_classes = [IsAuthenticated]
    filter_backends = [DjangoFilterBackend, filters.SearchFilter, filters.OrderingFilter]
    filterset_fields = ['patient', 'from_clinic', 'to_clinic', 'status', 'urgency', 'is_internal']
    search_fields = ['patient__mrn', 'patient__first_name_en', 'reason']
    ordering_fields = ['created_at', 'urgency']
    ordering = ['-created_at']
    
    def get_queryset(self):
        """Filter by tenant."""
        return Referral.objects.filter(
            tenant=self.request.user.tenant
        ).select_related(
            'patient', 'from_clinic', 'to_clinic',
            'from_provider__user', 'to_provider__user'
        )
    
    def get_serializer_class(self):
        """Return appropriate serializer based on action."""
        if self.action == 'list':
            return ReferralListSerializer
        elif self.action == 'create':
            return ReferralCreateSerializer
        elif self.action in ['accept', 'reject']:
            return ReferralResponseSerializer
        return ReferralDetailSerializer
    
    def perform_create(self, serializer):
        """Set tenant and from_provider on create."""
        serializer.save(
            tenant=self.request.user.tenant,
            from_provider=self.request.user,
            status='PENDING'
        )
    
    @action(detail=True, methods=['post'])
    def accept(self, request, pk=None):
        """Accept a pending referral."""
        referral = self.get_object()
        
        if referral.status != 'PENDING':
            return Response(
                {'error': 'Only pending referrals can be accepted'},
                status=status.HTTP_400_BAD_REQUEST
            )
        
        serializer = ReferralResponseSerializer(data=request.data)
        if not serializer.is_valid():
            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
        
        referral.status = 'ACCEPTED'
        referral.response_notes = serializer.validated_data['response_notes']
        referral.responded_at = timezone.now()
        referral.save()
        
        detail_serializer = ReferralDetailSerializer(referral)
        return Response(detail_serializer.data)
    
    @action(detail=True, methods=['post'])
    def reject(self, request, pk=None):
        """Reject a pending referral."""
        referral = self.get_object()
        
        if referral.status != 'PENDING':
            return Response(
                {'error': 'Only pending referrals can be rejected'},
                status=status.HTTP_400_BAD_REQUEST
            )
        
        serializer = ReferralResponseSerializer(data=request.data)
        if not serializer.is_valid():
            return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)
        
        referral.status = 'REJECTED'
        referral.response_notes = serializer.validated_data['response_notes']
        referral.responded_at = timezone.now()
        referral.save()
        
        detail_serializer = ReferralDetailSerializer(referral)
        return Response(detail_serializer.data)
    
    @action(detail=True, methods=['post'])
    def complete(self, request, pk=None):
        """Complete an accepted referral."""
        referral = self.get_object()
        
        if referral.status != 'ACCEPTED':
            return Response(
                {'error': 'Only accepted referrals can be completed'},
                status=status.HTTP_400_BAD_REQUEST
            )
        
        referral.status = 'COMPLETED'
        referral.completed_at = timezone.now()
        referral.save()
        
        serializer = ReferralDetailSerializer(referral)
        return Response(serializer.data)
    
    @action(detail=False, methods=['get'])
    def sent(self, request):
        """Get referrals sent by current user's clinic."""
        # Get user's clinic(s)
        user_clinics = request.user.provider.specialties.all() if hasattr(request.user, 'provider') else []
        
        referrals = self.get_queryset().filter(
            from_clinic__in=user_clinics
        )
        
        serializer = ReferralListSerializer(referrals, many=True)
        return Response(serializer.data)
    
    @action(detail=False, methods=['get'])
    def received(self, request):
        """Get referrals received by current user's clinic."""
        # Get user's clinic(s)
        user_clinics = request.user.provider.specialties.all() if hasattr(request.user, 'provider') else []
        
        referrals = self.get_queryset().filter(
            to_clinic__in=user_clinics,
            is_internal=True
        )
        
        serializer = ReferralListSerializer(referrals, many=True)
        return Response(serializer.data)
    
    @action(detail=False, methods=['get'])
    def pending(self, request):
        """Get pending referrals."""
        referrals = self.get_queryset().filter(status='PENDING')
        serializer = ReferralListSerializer(referrals, many=True)
        return Response(serializer.data)
    
    @action(detail=False, methods=['get'])
    def urgent(self, request):
        """Get urgent referrals."""
        referrals = self.get_queryset().filter(
            urgency__in=['URGENT', 'EMERGENCY'],
            status='PENDING'
        )
        serializer = ReferralListSerializer(referrals, many=True)
        return Response(serializer.data)
    
    @action(detail=False, methods=['get'])
    def statistics(self, request):
        """Get referral statistics."""
        queryset = self.get_queryset()
        
        stats = {
            'total': queryset.count(),
            'by_status': dict(queryset.values('status').annotate(
                count=Count('id')
            ).values_list('status', 'count')),
            'by_urgency': dict(queryset.values('urgency').annotate(
                count=Count('id')
            ).values_list('urgency', 'count')),
            'internal': queryset.filter(is_internal=True).count(),
            'external': queryset.filter(is_internal=False).count(),
            'pending': queryset.filter(status='PENDING').count(),
            'urgent_pending': queryset.filter(
                urgency__in=['URGENT', 'EMERGENCY'],
                status='PENDING'
            ).count(),
        }
        
        return Response(stats)
    
    @action(detail=False, methods=['get'])
    def workflow(self, request):
        """Get referral workflow statistics."""
        queryset = self.get_queryset()
        
        workflow_stats = {
            'pending': queryset.filter(status='PENDING').count(),
            'accepted': queryset.filter(status='ACCEPTED').count(),
            'completed': queryset.filter(status='COMPLETED').count(),
            'rejected': queryset.filter(status='REJECTED').count(),
        }
        
        return Response(workflow_stats)