# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-message-ordering-invariants-must-survive-when-the-transport-lacks-ordering-guarantees.md
# Remnant Warrant:    https://corpusfetch.com/c/what-message-ordering-invariants-must-survive-when-the-transport-lacks-ordering-guarantees.warrant.json
# Markdown SHA-256:   a0418876e2b0b5eef7565821a18644da028883aa98ddee66f4e8eb0f17cdd791
# Code AST SHA-256:   7ffbef9a9328642924fe7726e4b6d3245d2a5f5d74545efd1b7c8bd2d236ef5c
# Verified Classes:   OrderingVerdict, OrderedMessage, ReceiverState, OrderingPolicy, OrderingManifest, CausalOrderingGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

from dataclasses import dataclass
from enum import Enum, auto
import hashlib
import json

class OrderingVerdict(Enum):
    PROCESS_IMMEDIATELY = auto()
    BUFFER_WAIT_FOR_ANTECEDENT = auto()
    ESCALATE_BROKEN_CHAIN = auto()
    ORDER_INDEPENDENT = auto()

@dataclass(frozen=True)
class OrderedMessage:
    message_id: str
    logical_clock: int
    causal_dependencies: frozenset[str]
    order_independent: bool

@dataclass(frozen=True)
class ReceiverState:
    processed_message_ids: frozenset[str]
    buffered_messages: tuple[str, ...]
    current_epoch: float
    buffer_start_epoch: dict[str, float]

@dataclass(frozen=True)
class OrderingPolicy:
    max_buffer_age_sec: float
    current_epoch: float

@dataclass(frozen=True)
class OrderingManifest:
    verdict: OrderingVerdict
    directive: str
    manifest_digest: str

class CausalOrderingGuard:
    @staticmethod
    def _hash(data: str) -> str:
        return hashlib.sha256(data.encode("utf-8")).hexdigest()

    @classmethod
    def evaluate_message(
        cls, msg: OrderedMessage, state: ReceiverState, policy: OrderingPolicy
    ) -> OrderingManifest:
        
        # Gate 1: Order independent
        if msg.order_independent:
            digest = cls._hash(json.dumps({
                "message": msg.message_id,
                "status": "ORDER_INDEPENDENT"
            }, sort_keys=True))
            return OrderingManifest(
                verdict=OrderingVerdict.ORDER_INDEPENDENT,
                directive=f"PROCEED: Message {msg.message_id} is order-independent.",
                manifest_digest=digest
            )

        # Gate 2: Antecedents present
        missing = msg.causal_dependencies - state.processed_message_ids
        if not missing:
            digest = cls._hash(json.dumps({
                "message": msg.message_id,
                "clock": str(msg.logical_clock),
                "antecedents": tuple(sorted(msg.causal_dependencies))
            }, sort_keys=True))
            return OrderingManifest(
                verdict=OrderingVerdict.PROCESS_IMMEDIATELY,
                directive=f"PROCEED: All antecedents present for {msg.message_id}.",
                manifest_digest=digest
            )

        # Gate 3: Buffer with timeout
        if msg.message_id in state.buffer_start_epoch:
            age = policy.current_epoch - state.buffer_start_epoch[msg.message_id]
            if age > policy.max_buffer_age_sec:
                return OrderingManifest(
                    verdict=OrderingVerdict.ESCALATE_BROKEN_CHAIN,
                    directive=f"HALT: Message {msg.message_id} buffered {age:.0f}s > {policy.max_buffer_age_sec:.0f}s. Chain broken.",
                    manifest_digest=cls._hash(f"BROKEN:{msg.message_id}")
                )

        # Gate 4: Buffer
        digest = cls._hash(json.dumps({
            "message": msg.message_id,
            "missing": tuple(sorted(missing))
        }, sort_keys=True))
        
        return OrderingManifest(
            verdict=OrderingVerdict.BUFFER_WAIT_FOR_ANTECEDENT,
            directive=f"BUFFER: {msg.message_id} waiting for {sorted(missing)}.",
            manifest_digest=digest
        )