import dataclasses
import datetime
from collections.abc import Iterable

from django.http import HttpRequest, HttpResponse
from django.utils import timezone

from django_q.conf import Conf
from django_q.models import Schedule, Task
from django_q.status import Stat


@dataclasses.dataclass
class CheckResult:
    message: str
    ok: bool


@dataclasses.dataclass
class CheckResultOk(CheckResult):
    message: str
    ok: bool = True


@dataclasses.dataclass
class CheckResultFailure(CheckResult):
    message: str
    ok: bool = False


def _check_clusters() -> CheckResult:
    clusters = Stat.get_all()
    happy_clusters = [
        cluster for cluster in clusters if cluster.status in [Conf.IDLE, Conf.WORKING]
    ]

    if not len(clusters):
        return CheckResultFailure("No clusters running!")
    elif len(happy_clusters) != len(clusters):
        return CheckResultFailure(f"{len(happy_clusters)}/{len(clusters)} clusters up")
    else:
        return CheckResultOk(f"{len(happy_clusters)}/{len(clusters)} clusters up")


def _check_task(now: datetime.datetime, schedule: Schedule) -> CheckResult:
    if not schedule.task:
        return CheckResultFailure(f"Scheduled task {schedule} has never run!")

    else:
        try:
            task = Task.objects.get(id=schedule.task)
        except Task.DoesNotExist:
            if now - schedule.next_run > datetime.timedelta(minutes=5):
                return CheckResultFailure(
                    f"Scheduled task {schedule}'s last task doesn't exist, and is probably not still running!"
                )
            else:
                return CheckResultOk(
                    f"Schedule {schedule} has no task, but probably running now"
                )

        if not task.success:
            return CheckResultFailure(
                f"Scheduled task {schedule} failed at {task.started}"
            )
        elif now - schedule.next_run > datetime.timedelta(hours=2):
            return CheckResultFailure(
                f"Scheduled task {schedule} stale, last run at {task.started}"
            )
        else:
            return CheckResultOk(
                f"Scheduled task {schedule} ok, last run at {task.started}"
            )


def _check_tasks() -> Iterable[CheckResult]:
    now = timezone.now()
    for schedule in Schedule.objects.all():
        yield _check_task(now, schedule)


def healthcheck(request: HttpRequest):
    checks: list[CheckResult] = [_check_clusters(), *_check_tasks()]

    all_ok = all(check.ok for check in checks)
    messages = (check.message for check in sorted(checks, key=lambda c: c.ok))

    return HttpResponse(
        ("OK: " if all_ok else "CRITICAL: ") + "\n".join(messages),
        content_type="text/plain",
        status=200 if all_ok else 500,
    )