from rest_framework import viewsets, permissions
from .models import Project, Task
from .serializers import ProjectSerializer, ProjectDetailSerializer, TaskSerializer, TaskDetailSerializer
from accounts.permissions import IsAdmin, IsTeacher, IsStudentReadOnly
from rest_framework.exceptions import PermissionDenied

class ProjectViewSet(viewsets.ModelViewSet):
    """
    CRUD for Projects.
    - list/retrieve: Admin, Teacher, Student
    - create/update/destroy: Admin, Teacher (but Teacher can only update/destroy their own)
    """
    # Base permissions. Object-level is handled in check_object_permissions or via queryset
    permission_classes = [permissions.IsAuthenticated]

    def get_queryset(self):
        # Filter by tenant
        return Project.objects.tenant(self.request.tenant).select_related('created_by').order_by('-created_at')

    def get_serializer_class(self):
        if self.action in ['retrieve']:
            return ProjectDetailSerializer
        return ProjectSerializer

    def perform_create(self, serializer):
        # Auto-set the tenant and creator
        serializer.save(tenant=self.request.tenant, created_by=self.request.user)

    def check_permissions(self, request):
        super().check_permissions(request)
        if request.user.role == 'student' and request.method not in permissions.SAFE_METHODS:
            raise PermissionDenied("Students cannot modify projects.")

    def check_object_permissions(self, request, obj):
        super().check_object_permissions(request, obj)
        if request.method not in permissions.SAFE_METHODS:
            if request.user.role == 'teacher' and obj.created_by != request.user:
                raise PermissionDenied("You can only modify projects you created.")

class TaskViewSet(viewsets.ModelViewSet):
    """
    CRUD for Tasks nested under a Project.
    """
    permission_classes = [permissions.IsAuthenticated]
    pagination_class = None  # Return all tasks as list, not paginated

    def get_queryset(self):
        # The URL captures project_pk
        project_id = self.kwargs.get('project_pk')
        return Task.objects.tenant(self.request.tenant).filter(project_id=project_id).select_related('assigned_to', 'project').order_by('-created_at')

    def get_serializer_class(self):
        if self.action in ['retrieve', 'create', 'update', 'partial_update']:
            return TaskDetailSerializer
        return TaskSerializer

    def perform_create(self, serializer):
        project_id = self.kwargs.get('project_pk')
        try:
            project = Project.objects.get(id=project_id)
        except Project.DoesNotExist:
            raise serializers.ValidationError("Project does not exist.")
        
        # Check permissions before allowing to create task
        if self.request.user.role == 'teacher' and project.created_by != self.request.user:
           raise PermissionDenied("You can only add tasks to projects you created.")

        assigned_to_id = self.request.data.get('assigned_to_id')
        
        serializer.save(tenant=self.request.tenant, project=project, assigned_to_id=assigned_to_id)
    
    def perform_update(self, serializer):
        assigned_to_id = self.request.data.get('assigned_to_id')
        if 'assigned_to_id' in self.request.data:
            serializer.save(assigned_to_id=assigned_to_id)
        else:
            serializer.save()

    def check_permissions(self, request):
        super().check_permissions(request)
        if request.user.role == 'student' and request.method not in permissions.SAFE_METHODS:
            raise PermissionDenied("Students cannot modify tasks.")

    def check_object_permissions(self, request, obj):
        super().check_object_permissions(request, obj)
        if request.method not in permissions.SAFE_METHODS:
            if request.user.role == 'teacher' and obj.project.created_by != request.user:
                raise PermissionDenied("You can only modify tasks in projects you created.")