"""Allocators create or acquire objects that don't exist yet (e.g. IP addresses)."""

from .registry import register_allocator, get_selector


@register_allocator("first_free")
class FirstFreeIPAddressAllocator:
    """Allocate the first available IP address from a resolved prefix.

    Spec shape::

        {"strategy": "first_free", "prefix": {"type": "reference", "path": "parent.site.mgmt_prefix"}}
        {"strategy": "first_free", "prefix": {"type": "prefix", "filters": {"site": "hq"}}}
    """

    def __init__(self, spec):
        self.spec = spec
        self.prefix_spec = spec.get("prefix", {})

    def resolve_prefix(self, context):
        from ipam.models import Prefix
        selector = get_selector(self.prefix_spec)
        qs = selector.resolve(context, Prefix)
        return qs.first()

    def allocate(self, context):
        from ipam.models import IPAddress
        from ipam.choices import IPAddressStatusChoices

        prefix = self.resolve_prefix(context)
        if prefix is None:
            raise ValueError("No prefix resolved for first_free allocation.")

        available = prefix.get_first_available_ip()
        if available is None:
            raise ValueError(
                f"No available IP addresses in prefix {prefix.prefix}."
            )

        ip = IPAddress.objects.create(
            address=available,
            status=IPAddressStatusChoices.STATUS_ACTIVE,
        )
        return ip


@register_allocator("specific")
class SpecificAllocator:
    """Use a specific object identified by content type + ID or context path.

    Spec shape (by reference)::

        {"strategy": "specific", "path": "parent.site.primary_ip4"}

    Spec shape (by value, for IP addresses)::

        {"strategy": "specific", "address": "10.0.0.1/24"}
    """

    def __init__(self, spec):
        self.spec = spec
        self.path = spec.get("path")
        self.address = spec.get("address")

    def allocate(self, context):
        if self.address:
            from ipam.models import IPAddress
            from ipam.choices import IPAddressStatusChoices
            ip, _ = IPAddress.objects.get_or_create(
                address=self.address,
                defaults={"status": IPAddressStatusChoices.STATUS_ACTIVE},
            )
            return ip

        if self.path:
            return context.resolve_path(self.path)

        raise ValueError("SpecificAllocator requires 'path' or 'address'.")