import ipaddress
import logging

from django.contrib.contenttypes.models import ContentType
from django.db import transaction
from ipam.models import Prefix
from netbox.plugins import get_plugin_config

logger = logging.getLogger(__name__)


def network_for_address(address):
    """Return the canonical network encoded by an IPAddress.address value."""
    return ipaddress.ip_interface(str(address)).network


def _scope_from_ip(ip):
    """Derive the most specific supported Prefix scope from an IP assignment."""
    assigned = getattr(ip, "assigned_object", None)
    if assigned is None:
        return None

    parent = (
        getattr(assigned, "parent_object", None)
        or getattr(assigned, "device", None)
        or getattr(assigned, "virtual_machine", None)
    )
    if parent is None:
        return None

    location = getattr(parent, "location", None)
    if location is not None:
        return location

    site = getattr(parent, "site", None)
    if site is not None:
        return site

    cluster = getattr(parent, "cluster", None)
    return getattr(cluster, "scope", None) if cluster is not None else None


def _tenant_from_ip(ip):
    tenant = getattr(ip, "tenant", None)
    if tenant is not None:
        return tenant
    assigned = getattr(ip, "assigned_object", None)
    parent = (
        getattr(assigned, "parent_object", None)
        or getattr(assigned, "device", None)
        or getattr(assigned, "virtual_machine", None)
        or assigned
    )
    return getattr(parent, "tenant", None)


@transaction.atomic
def ensure_prefix_for_ip(ip, *, config=None):
    """Get or create the exact Prefix represented by an IP address and its mask.

    NetBox derives hierarchy from address/prefix + VRF. There is deliberately no
    parent FK to update on IPAddress; creating the missing Prefix is the assignment.
    """
    settings = config or {
        key: get_plugin_config("netbox_better_ips", key)
        for key in (
            "prefix_status", "inherit_scope", "inherit_tenant", "ignore_host_prefixes"
        )
    }
    network = network_for_address(ip.address)
    if settings.get("ignore_host_prefixes", True) and network.prefixlen == network.max_prefixlen:
        return None, False

    lookup = {"prefix": str(network), "vrf_id": ip.vrf_id}
    existing = Prefix.objects.filter(**lookup).first()
    if existing:
        return existing, False

    defaults = {"status": settings.get("prefix_status", "active")}
    if settings.get("inherit_tenant", True):
        defaults["tenant"] = _tenant_from_ip(ip)
    if settings.get("inherit_scope", True):
        scope = _scope_from_ip(ip)
        if scope is not None:
            defaults["scope_type"] = ContentType.objects.get_for_model(scope)
            defaults["scope_id"] = scope.pk

    prefix, created = Prefix.objects.get_or_create(defaults=defaults, **lookup)
    if created:
        logger.info("Created missing prefix %s for IP address %s", prefix, ip)
    return prefix, created