from __future__ import annotations

import json
import urllib.error
import urllib.request
from dataclasses import dataclass
from typing import Any

from django.conf import settings
from django.core.mail import send_mail
from django.utils import timezone

from .models import BackupRun, NotificationDelivery, NotificationTarget


TERMINAL_RUN_STATUSES = {
    BackupRun.Status.SUCCESS,
    BackupRun.Status.WARNING,
    BackupRun.Status.FAILED,
    BackupRun.Status.CANCELLED,
}


@dataclass(frozen=True)
class DeliveryResult:
    target: NotificationTarget
    delivery: NotificationDelivery
    sent: bool


def notify_backup_run_completed(run: BackupRun) -> list[DeliveryResult]:
    if run.status not in TERMINAL_RUN_STATUSES:
        return []

    targets = [target for target in NotificationTarget.objects.filter(enabled=True) if _target_wants_status(target, run.status)]
    return [_notify_target(target=target, run=run) for target in targets]


def _target_wants_status(target: NotificationTarget, status: str) -> bool:
    statuses = target.statuses
    if not isinstance(statuses, list):
        return False
    return status in {str(item) for item in statuses}


def _notify_target(*, target: NotificationTarget, run: BackupRun) -> DeliveryResult:
    payload = _run_payload(run)
    delivery, created = NotificationDelivery.objects.get_or_create(
        target=target,
        run=run,
        defaults={
            "status": NotificationDelivery.Status.SKIPPED,
            "payload": payload,
        },
    )
    if not created:
        return DeliveryResult(target=target, delivery=delivery, sent=False)

    try:
        if target.channel == NotificationTarget.Channel.EMAIL:
            _send_email(target=target, run=run, payload=payload)
        elif target.channel == NotificationTarget.Channel.WEBHOOK:
            _send_webhook(target=target, payload=payload)
        else:
            raise ValueError(f"Unsupported notification channel: {target.channel}")
    except Exception as exc:
        delivery.status = NotificationDelivery.Status.FAILED
        delivery.error = str(exc)
        delivery.save(update_fields=["status", "error"])
        target.last_status = NotificationDelivery.Status.FAILED
        target.last_error = str(exc)
        target.save(update_fields=["last_status", "last_error", "updated_at"])
        return DeliveryResult(target=target, delivery=delivery, sent=False)

    delivery.status = NotificationDelivery.Status.SENT
    delivery.save(update_fields=["status"])
    target.last_status = NotificationDelivery.Status.SENT
    target.last_error = ""
    target.last_sent_at = timezone.now()
    target.save(update_fields=["last_status", "last_error", "last_sent_at", "updated_at"])
    return DeliveryResult(target=target, delivery=delivery, sent=True)


def _send_email(*, target: NotificationTarget, run: BackupRun, payload: dict[str, Any]) -> None:
    recipients = [line.strip() for line in target.email_to.replace(",", "\n").splitlines() if line.strip()]
    if not recipients:
        raise ValueError("Email notification target has no recipients.")

    subject = f"pobsync {run.status}: {run.host.host} run {run.id}"
    message = _email_message(payload)
    from_email = getattr(settings, "DEFAULT_FROM_EMAIL", "") or "pobsync@localhost"
    sent = send_mail(subject, message, from_email, recipients, fail_silently=False)
    if sent == 0:
        raise ValueError("Django email backend reported zero sent messages.")


def _send_webhook(*, target: NotificationTarget, payload: dict[str, Any]) -> None:
    if not target.webhook_url:
        raise ValueError("Webhook notification target has no URL.")

    headers = {"Content-Type": "application/json", **_string_headers(target.webhook_headers)}
    request = urllib.request.Request(
        target.webhook_url,
        data=json.dumps(payload).encode("utf-8"),
        headers=headers,
        method="POST",
    )
    try:
        with urllib.request.urlopen(request, timeout=10) as response:
            if response.status >= 400:
                raise ValueError(f"Webhook returned HTTP {response.status}.")
    except urllib.error.HTTPError as exc:
        raise ValueError(f"Webhook returned HTTP {exc.code}.") from exc


def _string_headers(headers: object) -> dict[str, str]:
    if not isinstance(headers, dict):
        return {}
    return {str(key): str(value) for key, value in headers.items() if str(key).strip()}


def _run_payload(run: BackupRun) -> dict[str, Any]:
    result = run.result if isinstance(run.result, dict) else {}
    failure = result.get("failure") if isinstance(result.get("failure"), dict) else {}
    prune = result.get("prune") if isinstance(result.get("prune"), dict) else {}
    return {
        "event": "backup_run.completed",
        "run": {
            "id": run.id,
            "host": run.host.host,
            "type": run.run_type,
            "status": run.status,
            "started_at": run.started_at.isoformat() if run.started_at else None,
            "ended_at": run.ended_at.isoformat() if run.ended_at else None,
            "snapshot": run.snapshot_path,
            "rsync_exit_code": run.rsync_exit_code,
        },
        "failure": {
            "category": failure.get("category"),
            "message": failure.get("message") or result.get("error"),
            "hint": failure.get("hint"),
        },
        "prune": {
            "ok": prune.get("ok") if prune else None,
            "error": prune.get("error") if prune else "",
        },
    }


def _email_message(payload: dict[str, Any]) -> str:
    run = payload["run"]
    lines = [
        f"Host: {run['host']}",
        f"Run: {run['id']}",
        f"Type: {run['type']}",
        f"Status: {run['status']}",
        f"Started: {run['started_at'] or '-'}",
        f"Ended: {run['ended_at'] or '-'}",
        f"Snapshot: {run['snapshot'] or '-'}",
        f"Rsync exit code: {run['rsync_exit_code'] if run['rsync_exit_code'] is not None else '-'}",
    ]
    failure = payload.get("failure") if isinstance(payload.get("failure"), dict) else {}
    if failure.get("message"):
        lines.extend(["", f"Failure: {failure['message']}"])
    prune = payload.get("prune") if isinstance(payload.get("prune"), dict) else {}
    if prune.get("error"):
        lines.extend(["", f"Retention: {prune['error']}"])
    return "\n".join(lines)