# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-decentralized-cache-coherency-invariants-prevent-agents-from-acting-on-mutually-contradictory-replicas.md
# Remnant Warrant:    https://corpusfetch.com/c/what-decentralized-cache-coherency-invariants-prevent-agents-from-acting-on-mutually-contradictory-replicas.warrant.json
# Markdown SHA-256:   8666d6ee3907f7319c847f1cf5a3518ecf4a4b0b0ecf4f56b1c3dc526b7a95fc
# Code AST SHA-256:   2640dcea27adf17e5fec513967ba1a2f4d4c49d99dd82a3c358ed1f4933ec7be
# Verified Classes:   CoherencyVerdict, CacheEntry, CoherencyPolicy, CoherencyManifest, DecentralizedCacheCoherencyGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class CoherencyVerdict(Enum):
    CACHE_CURRENT = auto()
    CACHE_WITHIN_TOLERANCE = auto()
    CACHE_STALE_INVALIDATE = auto()
    INVALIDATION_BROADCASTED = auto()

@dataclass(frozen=True)
class CacheEntry:
    entry_id: str
    cached_state_epoch: float
    origin_current_epoch: float
    tolerance_sec: float
    invalidation_broadcast_received: bool

@dataclass(frozen=True)
class CoherencyPolicy:
    require_broadcast_invalidation: bool

@dataclass(frozen=True)
class CoherencyManifest:
    verdict: CoherencyVerdict
    staleness_sec: float
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_cache_entry(
        cls, entry: CacheEntry, policy: CoherencyPolicy
    ) -> CoherencyManifest:
        
        # Gate 1: Broadcast invalidation
        if entry.invalidation_broadcast_received and policy.require_broadcast_invalidation:
            return CoherencyManifest(
                verdict=CoherencyVerdict.INVALIDATION_BROADCASTED,
                staleness_sec=entry.origin_current_epoch - entry.cached_state_epoch,
                directive=f"INVALIDATE: Broadcast received for {entry.entry_id}. Re-fetch.",
                manifest_digest=cls._hash(f"BROADCAST:{entry.entry_id}")
            )

        staleness = entry.origin_current_epoch - entry.cached_state_epoch

        # Gate 2: Current
        if staleness <= 0:
            digest = cls._hash(json.dumps({
                "entry": entry.entry_id,
                "staleness": f"{staleness:.1f}",
                "status": "CURRENT"
            }, sort_keys=True))
            return CoherencyManifest(
                verdict=CoherencyVerdict.CACHE_CURRENT,
                staleness_sec=0.0,
                directive=f"PROCEED: Cache {entry.entry_id} current.",
                manifest_digest=digest
            )

        # Gate 3: Within tolerance
        if staleness <= entry.tolerance_sec:
            digest = cls._hash(json.dumps({
                "entry": entry.entry_id,
                "staleness": f"{staleness:.1f}",
                "tolerance": f"{entry.tolerance_sec:.1f}"
            }, sort_keys=True))
            return CoherencyManifest(
                verdict=CoherencyVerdict.CACHE_WITHIN_TOLERANCE,
                staleness_sec=staleness,
                directive=f"PROCEED_WITH_CAUTION: Cache {entry.entry_id} stale by {staleness:.1f}s within {entry.tolerance_sec:.1f}s.",
                manifest_digest=digest
            )

        # Gate 4: Stale
        return CoherencyManifest(
            verdict=CoherencyVerdict.CACHE_STALE_INVALIDATE,
            staleness_sec=staleness,
            directive=f"INVALIDATE: Cache {entry.entry_id} stale by {staleness:.1f}s > {entry.tolerance_sec:.1f}s.",
            manifest_digest=cls._hash(f"STALE:{entry.entry_id}:{staleness:.1f}")
        )