import ipaddress
import logging

import netaddr
from django.db import transaction
from ipam.models import IPRange
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 _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_range_for_ip(ip, *, config=None):
    """Get or create the usable-host IPRange represented by an IP and its mask."""
    settings = config or {
        key: get_plugin_config("netbox_better_ips", key)
        for key in ("range_status", "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

    first = int(network.network_address)
    last = int(network.broadcast_address)
    if network.version == 4 and network.prefixlen < 31:
        first += 1
        last -= 1
    elif network.version == 6 and network.prefixlen < 127:
        first += 1

    # IPRange.save() performs arithmetic on the field values before Django's
    # field conversion runs, so these must be netaddr objects rather than strings.
    start_address = netaddr.IPNetwork(f"{ipaddress.ip_address(first)}/{network.prefixlen}")
    end_address = netaddr.IPNetwork(f"{ipaddress.ip_address(last)}/{network.prefixlen}")
    lookup = {
        "start_address": start_address,
        "end_address": end_address,
        "vrf_id": ip.vrf_id,
    }
    existing = IPRange.objects.filter(**lookup).first()
    if existing:
        return existing, False

    defaults = {"status": settings.get("range_status", "active")}
    if settings.get("inherit_tenant", True):
        defaults["tenant"] = _tenant_from_ip(ip)

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