from __future__ import annotations

from enum import Enum


class Delivery(str, Enum):
    UNRELIABLE_SEQUENCED = "unreliable_sequenced"
    RELIABLE_ORDERED = "reliable_ordered"


_SNAPSHOT_PACKET_TYPES = frozenset({"transform", "npcState"})


def delivery_for_packet_type(packet_type: str) -> Delivery:
    """Return the transport contract for one validated protocol packet type.

    Unknown packet types intentionally default to reliable/ordered. Protocol
    validation still decides whether an unknown packet is accepted; this
    function only prevents a future transport adapter from accidentally
    downgrading control traffic to an unreliable channel.
    """
    if packet_type in _SNAPSHOT_PACKET_TYPES:
        return Delivery.UNRELIABLE_SEQUENCED
    return Delivery.RELIABLE_ORDERED


def is_snapshot_packet(packet_type: str) -> bool:
    return delivery_for_packet_type(packet_type) is Delivery.UNRELIABLE_SEQUENCED