"""
Celery-Tasks für die PDF-Erzeugung.
"""
from __future__ import annotations

import csv
import io
import logging
import tempfile
from pathlib import Path

from celery import shared_task
from django.core.files import File
from django.utils import timezone

from .models import JobLogEntry, MailMergeJob
from .services.docx_renderer import docx_to_pdf, render_docx
from .services.pdf_merge import merge_pdfs

logger = logging.getLogger(__name__)


def _log(job: MailMergeJob, level: str, msg: str) -> None:
    JobLogEntry.objects.create(job=job, level=level, message=msg)
    logger.log(getattr(logging, level.upper(), logging.INFO), "[job %s] %s", job.id, msg)


@shared_task(bind=True)
def run_mailmerge(self, job_id: str) -> str:
    job = MailMergeJob.objects.select_related("template").get(pk=job_id)
    job.status = MailMergeJob.Status.RUNNING
    job.started_at = timezone.now()
    job.save(update_fields=["status", "started_at"])
    _log(job, "info", f"Job gestartet (task={self.request.id}).")

    try:
        # CSV einlesen
        raw = job.recipients_csv.read().decode("utf-8-sig")
        reader = csv.DictReader(io.StringIO(raw))
        rows = list(reader)
        job.total_rows = len(rows)
        job.save(update_fields=["total_rows"])
        _log(job, "info", f"{len(rows)} Empfänger gefunden.")

        if not rows:
            raise ValueError("CSV enthält keine Datenzeilen.")

        # CSV-Felder vs. Template-Platzhalter prüfen
        csv_fields = set(reader.fieldnames or [])
        placeholders = set(job.template.placeholders or [])
        missing = placeholders - csv_fields
        if missing:
            _log(job, "warning",
                 f"CSV fehlen Spalten: {', '.join(sorted(missing))}")

        # Jeden Brief rendern, alle zu einem PDF zusammenführen
        with tempfile.TemporaryDirectory(prefix="mailmerge-") as tmpdir:
            tmp = Path(tmpdir)
            pdfs: list[Path] = []
            template_path = Path(job.template.file.path)

            for idx, row in enumerate(rows, start=1):
                docx_out = tmp / f"letter_{idx:05d}.docx"
                render_docx(template_path, row, docx_out)
                pdf = docx_to_pdf(docx_out, tmp / "pdf")
                pdfs.append(pdf)
                job.processed_rows = idx
                job.save(update_fields=["processed_rows"])

            merged = tmp / f"serienbrief_{job.id}.pdf"
            merge_pdfs(pdfs, merged)
            with merged.open("rb") as f:
                job.result_pdf.save(merged.name, File(f), save=False)

        job.status = MailMergeJob.Status.DONE
        job.finished_at = timezone.now()
        job.save()
        _log(job, "info", "Job erfolgreich abgeschlossen.")
        return str(job.id)

    except Exception as exc:  # noqa: BLE001
        job.status = MailMergeJob.Status.FAILED
        job.error_message = str(exc)
        job.finished_at = timezone.now()
        job.save()
        _log(job, "error", f"Job fehlgeschlagen: {exc}")
        raise