"""Background 'Download to Library' jobs with progress tracking."""

import logging
import threading
import time
from pathlib import Path
from urllib.parse import urlparse

from django.conf import settings
from django.utils import timezone

from . import services
from .models import DownloadTask

logger = logging.getLogger(__name__)


def start_download_task(task_id):
    thread = threading.Thread(target=run_download_task, args=(task_id,), daemon=True)
    thread.start()


def run_download_task(task_id):
    task = DownloadTask.objects.filter(id=task_id).first()
    if task is None:
        return

    folder = Path(settings.WATCHED_FOLDER)
    name = (
        task.filename
        or Path(urlparse(task.url).path).name
        or f"post-{task.post_id or 'download'}"
    )
    destination = services.unique_destination(folder, name)

    state = {
        "progress_at": 0.0,
        "bytes_at": 0,
        "cancel_at": 0.0,
        "cancelled": False,
    }

    def should_cancel():
        now = time.monotonic()
        if now - state["cancel_at"] >= 1.0:
            state["cancelled"] = DownloadTask.objects.filter(
                id=task_id, cancelled=True
            ).exists()
            state["cancel_at"] = now
        return state["cancelled"]

    def on_progress(downloaded, total):
        now = time.monotonic()
        if now - state["progress_at"] < 0.5 and (total == 0 or downloaded < total):
            return
        elapsed = max(now - state["progress_at"], 0.001)
        speed = None
        if state["bytes_at"] > 0 and downloaded >= state["bytes_at"]:
            speed = (downloaded - state["bytes_at"]) / elapsed
        state["progress_at"] = now
        state["bytes_at"] = downloaded
        DownloadTask.objects.filter(id=task_id).update(
            downloaded=downloaded,
            total=total,
            progress=int(downloaded * 100 / total) if total else 0,
            speed=speed,
            updated_at=timezone.now(),
        )

    DownloadTask.objects.filter(id=task_id).update(
        status=DownloadTask.STATUS_DOWNLOADING, updated_at=timezone.now()
    )
    try:
        services.download_file(
            task.url,
            destination,
            progress_callback=on_progress,
            should_cancel=should_cancel,
        )
        item, _, location, _ = services.index_file(destination, folder)
        services.rename_location_to_j_id(item, location)

        update_fields = []
        if item.uploaded_by_id is None and task.user_id is not None:
            item.uploaded_by = task.user
            update_fields.append("uploaded_by")
        if task.e621_data:
            item.e621_post_id = task.post_id
            item.e621_data = task.e621_data
            update_fields += ["e621_post_id", "e621_data"]
            rating = (task.e621_data or {}).get("rating")
            if not item.rating and rating in {"s", "q", "e"}:
                item.rating = rating
                update_fields.append("rating")
        if update_fields:
            item.save(update_fields=update_fields + ["updated_at"])

        DownloadTask.objects.filter(id=task_id).update(
            status=DownloadTask.STATUS_COMPLETE,
            progress=100,
            speed=None,
            library_item=item,
            updated_at=timezone.now(),
        )
    except services.DownloadCancelled:
        destination.unlink(missing_ok=True)
        DownloadTask.objects.filter(id=task_id).update(
            status=DownloadTask.STATUS_CANCELLED,
            progress=0,
            downloaded=0,
            speed=None,
            updated_at=timezone.now(),
        )
    except Exception as exc:  # noqa: BLE001 - report background failures
        destination.unlink(missing_ok=True)
        logger.exception("Download task %s failed", task_id)
        DownloadTask.objects.filter(id=task_id).update(
            status=DownloadTask.STATUS_ERROR,
            error=str(exc),
            speed=None,
            updated_at=timezone.now(),
        )