from rest_framework import viewsets, status, permissions
from rest_framework.decorators import action
from rest_framework.response import Response
from rest_framework.exceptions import MethodNotAllowed # <<<< 新增导入
# from django.shortcuts import get_object_or_404

from .models import Group, Membership, Post
from .serializers import (
    GroupSerializer,
    # MembershipSerializer,
    PostSerializer
)
from .permissions import IsAuthorOrReadOnly # 从自定义权限文件导入

class GroupViewSet(viewsets.ModelViewSet):
    queryset = Group.objects.all().order_by('-created_at')
    serializer_class = GroupSerializer

    def get_permissions(self):
        if self.action in ['list', 'retrieve']:
            permission_classes = [permissions.AllowAny]
        elif self.action in ['list_group_posts', 'create_group_post', 'join_group', 'leave_group', 'my_groups']:
            permission_classes = [permissions.IsAuthenticated]
        else: # create, update, partial_update, destroy (for groups)
            permission_classes = [permissions.IsAuthenticated]
        return [permission() for permission in permission_classes]

    def perform_create(self, serializer):
        group = serializer.save(creator=self.request.user)
        Membership.objects.create(user=self.request.user, group=group)

    @action(detail=True, methods=['post'], permission_classes=[permissions.IsAuthenticated])
    def join_group(self, request, pk=None):
        group = self.get_object()
        user = request.user
        if Membership.objects.filter(user=user, group=group).exists():
            return Response({'detail': '您已经是该小组成员。'}, status=status.HTTP_400_BAD_REQUEST)
        Membership.objects.create(user=user, group=group)
        return Response({'detail': '成功加入小组。'}, status=status.HTTP_200_OK)

    @action(detail=True, methods=['post'], permission_classes=[permissions.IsAuthenticated])
    def leave_group(self, request, pk=None):
        group = self.get_object()
        user = request.user
        try:
            membership = Membership.objects.get(user=user, group=group)
            membership.delete()
            return Response({'detail': '成功退出小组。'}, status=status.HTTP_200_OK)
        except Membership.DoesNotExist:
            return Response({'detail': '您不是该小组成员。'}, status=status.HTTP_400_BAD_REQUEST)

    @action(detail=False, methods=['get'], permission_classes=[permissions.IsAuthenticated], url_path='my-groups')
    def my_groups(self, request):
        user = request.user
        memberships = Membership.objects.filter(user=user).select_related('group')
        groups = [membership.group for membership in memberships]
        page = self.paginate_queryset(groups)
        if page is not None:
            serializer = self.get_serializer(page, many=True, context={'request': request})
            return self.get_paginated_response(serializer.data)
        serializer = self.get_serializer(groups, many=True, context={'request': request})
        return Response(serializer.data)

    @action(detail=True, methods=['get'], url_path='posts', url_name='group-posts-list')
    def list_group_posts(self, request, pk=None):
        group = self.get_object()
        posts_queryset = Post.objects.filter(group=group).order_by('-created_at')
        page = self.paginate_queryset(posts_queryset)
        if page is not None:
            serializer = PostSerializer(page, many=True, context={'request': request})
            return self.get_paginated_response(serializer.data)
        serializer = PostSerializer(posts_queryset, many=True, context={'request': request})
        return Response(serializer.data)

    @action(detail=True, methods=['post'], url_path='create-post', url_name='group-post-create')
    def create_group_post(self, request, pk=None):
        group = self.get_object()
        serializer = PostSerializer(data=request.data, context={'request': request})
        if serializer.is_valid():
            serializer.save(author=request.user, group=group)
            return Response(serializer.data, status=status.HTTP_201_CREATED)
        return Response(serializer.errors, status=status.HTTP_400_BAD_REQUEST)


class PostViewSet(viewsets.ModelViewSet):
    queryset = Post.objects.all().select_related('author', 'group').order_by('-created_at')
    serializer_class = PostSerializer

    def get_permissions(self):
        if self.action in ['list', 'retrieve']:
            permission_classes = [permissions.IsAuthenticated] # 或者 IsAuthenticatedOrReadOnly
        elif self.action in ['update', 'partial_update', 'destroy']:
            permission_classes = [permissions.IsAuthenticated, IsAuthorOrReadOnly]
        elif self.action == 'create':
            # 即使是Admin，我们也希望通过小组接口创建帖子，以确保group关联正确
            # 所以这里可以直接禁止，或者只允许特定调试场景
            permission_classes = [permissions.IsAdminUser] # 示例：只允许Admin（但会被perform_create阻止）
        else:
            permission_classes = [permissions.IsAuthenticated]
        return [permission() for permission in permission_classes]

    def perform_create(self, serializer): # <<<< 修改这里
        """
        通过此独立ViewSet创建帖子是不推荐的。
        应通过 /api/v1/groups/<group_pk>/create-post/ 创建。
        """
        raise MethodNotAllowed(
            method=self.request.method,
            detail="不推荐通过此接口创建帖子。请通过小组接口 /api/v1/groups/<group_pk>/create-post/ 创建。"
        )

    # perform_update 和 perform_destroy 由 IsAuthorOrReadOnly 权限类控制，无需显式覆盖默认行为
    # def perform_update(self, serializer):
    #     serializer.save() # DRF默认行为

    # def perform_destroy(self, instance):
    #     instance.delete() # DRF默认行为