# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-invariants-prevent-auction-mechanism-gaming-through-bid-timing-and-pattern.md
# Remnant Warrant:    https://corpusfetch.com/c/what-invariants-prevent-auction-mechanism-gaming-through-bid-timing-and-pattern.warrant.json
# Markdown SHA-256:   a9e6491ca881bd61acbd34291bc577f7dc5057d225261c0f2e08cd3b49d2cf92
# Code AST SHA-256:   523b38674990b8ac22206e8fa54eac1bd1ce8abe9898f32990a69089d410abc0
# Verified Classes:   AuctionGamingVerdict, AuctionObservation, GamingPolicy, GamingManifest, AuctionMechanismGamingGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class AuctionGamingVerdict(Enum):
    SEALED_BID = auto()
    NORMAL_COMPETITION = auto()
    SNIPING_DETECTED = auto()
    COLLUSION_SUSPECTED = auto()
    SHILL_BIDDING_SUSPECTED = auto()

@dataclass(frozen=True)
class AuctionObservation:
    auction_id: str
    is_sealed_bid: bool
    last_second_bid_ratio: float  # 0-1
    bidder_correlation_score: float  # 0-1
    suspicious_pattern_indicators: int
    mechanism_protections_present: int

@dataclass(frozen=True)
class GamingPolicy:
    max_acceptable_last_second_ratio: float
    max_acceptable_correlation: float

@dataclass(frozen=True)
class GamingManifest:
    verdict: AuctionGamingVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_auction(
        cls, obs: AuctionObservation, policy: GamingPolicy
    ) -> GamingManifest:
        
        # Gate 1: Sealed bid
        if obs.is_sealed_bid:
            digest = cls._hash(json.dumps({
                "auction": obs.auction_id,
                "type": "SEALED"
            }, sort_keys=True))
            return GamingManifest(
                verdict=AuctionGamingVerdict.SEALED_BID,
                directive=f"PROCEED: Auction {obs.auction_id} sealed-bid, timing gaming impossible.",
                manifest_digest=digest
            )

        # Gate 2: Sniping
        if obs.last_second_bid_ratio > policy.max_acceptable_last_second_ratio:
            if obs.mechanism_protections_present == 0:
                return GamingManifest(
                    verdict=AuctionGamingVerdict.SNIPING_DETECTED,
                    directive=f"FLAG: Sniping ({obs.last_second_bid_ratio:.2f}) without mechanism protections.",
                    manifest_digest=cls._hash(f"SNIPING:{obs.auction_id}")
                )

        # Gate 3: Correlation
        if obs.bidder_correlation_score > policy.max_acceptable_correlation:
            return GamingManifest(
                verdict=AuctionGamingVerdict.COLLUSION_SUSPECTED,
                directive=f"FLAG: Bidder correlation {obs.bidder_correlation_score:.2f} suggests collusion.",
                manifest_digest=cls._hash(f"COLLUSION:{obs.auction_id}")
            )

        # Gate 4: Suspicious patterns
        if obs.suspicious_pattern_indicators >= 2:
            return GamingManifest(
                verdict=AuctionGamingVerdict.SHILL_BIDDING_SUSPECTED,
                directive=f"FLAG: {obs.suspicious_pattern_indicators} indicators for shill bidding.",
                manifest_digest=cls._hash(f"SHILL:{obs.auction_id}")
            )

        # Gate 5: Normal
        digest = cls._hash(json.dumps({
            "auction": obs.auction_id,
            "sniping": f"{obs.last_second_bid_ratio:.3f}",
            "correlation": f"{obs.bidder_correlation_score:.3f}"
        }, sort_keys=True))
        
        return GamingManifest(
            verdict=AuctionGamingVerdict.NORMAL_COMPETITION,
            directive=f"PROCEED: Auction {obs.auction_id} appears normal.",
            manifest_digest=digest
        )