# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-decommissioning-invariants-prevent-orphaned-references-when-agents-retire.md
# Remnant Warrant:    https://corpusfetch.com/c/what-decommissioning-invariants-prevent-orphaned-references-when-agents-retire.warrant.json
# Markdown SHA-256:   3b7701778d693995bcafc65a1963a26acca6de3716e5537087e903053388a6cb
# Code AST SHA-256:   c5000a7a873549fccc69c31d27b734563d7391bf643ea204aefe171d34e80865
# Verified Classes:   DecommissionVerdict, DecommissionState, DecommissionPolicy, DecommissionManifest, DecommissioningGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class DecommissionVerdict(Enum):
    NOT_DECOMMISSIONING = auto()
    GRACEFUL_DECOMMISSION = auto()
    UNSAFE_TERMINATION = auto()
    REDIRECTED = auto()

@dataclass(frozen=True)
class DecommissionState:
    agent_id: str
    is_decommissioning: bool
    announcement_sent: bool
    deadline_epoch: float
    current_epoch: float
    active_consumers: tuple[str, ...]
    consumers_migrated: frozenset[str]
    successor_available: bool
    successor_redirection_active: bool

@dataclass(frozen=True)
class DecommissionPolicy:
    min_lead_time_sec: float
    require_all_consumers_migrated: bool

@dataclass(frozen=True)
class DecommissionManifest:
    verdict: DecommissionVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_decommission(
        cls, state: DecommissionState, policy: DecommissionPolicy
    ) -> DecommissionManifest:
        
        # Gate 1: Not decommissioning
        if not state.is_decommissioning:
            digest = cls._hash(json.dumps({
                "agent": state.agent_id,
                "status": "ACTIVE"
            }, sort_keys=True))
            return DecommissionManifest(
                verdict=DecommissionVerdict.NOT_DECOMMISSIONING,
                directive=f"PROCEED: Agent {state.agent_id} active.",
                manifest_digest=digest
            )

        # Gate 2: Successor redirection
        if state.successor_available and state.successor_redirection_active:
            digest = cls._hash(json.dumps({
                "agent": state.agent_id,
                "successor": "AVAILABLE",
                "redirection": "ACTIVE"
            }, sort_keys=True))
            return DecommissionManifest(
                verdict=DecommissionVerdict.REDIRECTED,
                directive=f"PROCEED: Consumers redirected to successor, safe to retire.",
                manifest_digest=digest
            )

        # Gate 3: Announcement lead time
        lead_time = state.deadline_epoch - state.current_epoch
        if state.announcement_sent and lead_time < policy.min_lead_time_sec:
            # Less lead time than policy requires
            if not state.active_consumers or all(c in state.consumers_migrated for c in state.active_consumers):
                pass  # All migrated, fine
            else:
                return DecommissionManifest(
                    verdict=DecommissionVerdict.UNSAFE_TERMINATION,
                    directive=f"HALT: Only {lead_time:.0f}s lead time < {policy.min_lead_time_sec:.0f}s with unmigrated consumers.",
                    manifest_digest=cls._hash(f"SHORT_LEAD:{lead_time:.0f}")
                )

        # Gate 4: All consumers migrated
        if policy.require_all_consumers_migrated:
            unmigrated = [c for c in state.active_consumers if c not in state.consumers_migrated]
            if unmigrated:
                return DecommissionManifest(
                    verdict=DecommissionVerdict.UNSAFE_TERMINATION,
                    directive=f"HALT: {len(unmigrated)} consumers not migrated.",
                    manifest_digest=cls._hash(f"UNMIGRATED:{len(unmigrated)}")
                )

        # Gate 5: Graceful
        digest = cls._hash(json.dumps({
            "agent": state.agent_id,
            "consumers": str(len(state.active_consumers)),
            "migrated": str(len(state.consumers_migrated)),
            "lead_time": f"{lead_time:.0f}"
        }, sort_keys=True))
        
        return DecommissionManifest(
            verdict=DecommissionVerdict.GRACEFUL_DECOMMISSION,
            directive=f"PROCEED: Graceful decommission of {state.agent_id} ({len(state.consumers_migrated)}/{len(state.active_consumers)} migrated).",
            manifest_digest=digest
        )