import logging
from datetime import timedelta

import boto3
from celery import shared_task
from django.utils import timezone

from labs.models import LabInstance as DBLabInstance

logger = logging.getLogger(__name__)


AWS_REGIONS = [
    "us-west-2",
    "ap-northeast-1",
    "ap-southeast-1",
    "eu-central-1",
]


@shared_task
def aws_cloudformation_housekeeping():
    """
    Fallback cleanup task for AWS CloudFormation stacks.

    Purpose:
    - Acts as a safety net when a Lab Instance is not properly destroyed.
    - Scans configured regions and cleans up orphaned or expired stacks associated with lab instances.
    - Prevents unused resources from lingering and incurring unnecessary cost.

    Behavior:
    - Only targets stacks linked to a lab instance whose scheduled_terminate_at is in the past.
    - CREATE_COMPLETE or CREATE_FAILED: request deletion.
    - DELETE_FAILED: force deletion.
    - DELETE_IN_PROGRESS: skip.
    """
    for region in AWS_REGIONS:
        _aws_cloudformation_housekeeping(region)


def _aws_cloudformation_housekeeping(region: str):
    client = boto3.client("cloudformation", region_name=region)
    status_filter = [
        "CREATE_COMPLETE",
        "CREATE_FAILED",
        "DELETE_FAILED",
    ]
    paginator = client.get_paginator("list_stacks")
    for page in paginator.paginate(StackStatusFilter=status_filter):
        for stack in page.get("StackSummaries", []):
            stack_name = stack["StackName"]
            stack_status = stack["StackStatus"]

            try:
                DBLabInstance.objects.get(
                    unique_tag=stack_name,
                    scheduled_terminate_at__lt=timezone.now()
                    # subtract 10 minutes to give normal recycle task time to execute;
                    # this housekeeping task is a final safety net if recycle fails
                    - timedelta(minutes=10),
                )
            except DBLabInstance.DoesNotExist:
                continue

            match stack_status:
                case "DELETE_IN_PROGRESS":
                    # Already being deleted; skip and let it finish
                    continue
                case "CREATE_COMPLETE" | "CREATE_FAILED":
                    logger.info(
                        f"Housekeeping[{region}]: Deleting stack {stack_name} in status {stack_status}"
                    )
                    try:
                        client.delete_stack(StackName=stack_name)
                    except Exception as exc:
                        logger.warning(
                            f"Housekeeping[{region}]: Failed to delete {stack_name} in {stack_status}: {exc}"
                        )
                case "DELETE_FAILED":
                    logger.info(
                        f"Housekeeping[{region}]: DELETE_FAILED for {stack_name}, attempting to force delete"
                    )
                    try:
                        client.delete_stack(
                            StackName=stack_name, DeletionMode="FORCE_DELETE_STACK"
                        )
                    except Exception as exc:
                        logger.error(
                            f"Housekeeping[{region}]: Still failed to delete {stack_name}: {exc}"
                        )
                case _:
                    continue