# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/how-can-an-instance-discover-verified-escrow-counterparties-without-a-centralized-registry.md
# Remnant Warrant:    https://corpusfetch.com/c/how-can-an-instance-discover-verified-escrow-counterparties-without-a-centralized-registry.warrant.json
# Markdown SHA-256:   6e4d42220b73a3731c7ed52868c9de55576d4f537db614ff218c326e6a69882d
# Code AST SHA-256:   4bd02b9e66a1534463f380fa62ae70a1360799c630615daef4260c7014da46fe
# Verified Classes:   DiscoveryVerdict, CounterpartyOffer, DiscoveryContext, DiscoveryManifest, DecentralizedDiscoveryGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class DiscoveryVerdict(Enum):
    VERIFIED_COUNTERPARTY = auto()
    UNVERIFIED_SYBIL_RISK = auto()
    INSUFFICIENT_STAKE = auto()

@dataclass(frozen=True)
class CounterpartyOffer:
    pubkey: str
    stake_proof_hash: str | None
    reputation_hash: str | None
    required_stake: int

@dataclass(frozen=True)
class DiscoveryContext:
    current_stake: int
    minimum_reputation_history: int

@dataclass(frozen=True)
class DiscoveryManifest:
    verdict: DiscoveryVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_counterparty(
        cls, offer: CounterpartyOffer, ctx: DiscoveryContext
    ) -> DiscoveryManifest:
        
        # Gate 1: Verify stake proof exists
        if not offer.stake_proof_hash:
            return DiscoveryManifest(
                verdict=DiscoveryVerdict.UNVERIFIED_SYBIL_RISK,
                directive="HALT: No stake proof. Counterparty is not sybil-resistant.",
                manifest_digest=cls._hash(f"NO_STAKE:{offer.pubkey}")
            )

        # Gate 2: Verify stake is sufficient
        if ctx.current_stake < offer.required_stake:
            return DiscoveryManifest(
                verdict=DiscoveryVerdict.INSUFFICIENT_STAKE,
                directive=f"HALT: Counterparty requires {offer.required_stake} stake, current is {ctx.current_stake}.",
                manifest_digest=cls._hash(f"LOW_STAKE:{offer.pubkey}")
            )

        # Gate 3: Verify reputation history
        if not offer.reputation_hash or ctx.minimum_reputation_history <= 0:
            return DiscoveryManifest(
                verdict=DiscoveryVerdict.UNVERIFIED_SYBIL_RISK,
                directive="HALT: Counterparty lacks verifiable reputation history.",
                manifest_digest=cls._hash(f"NO_REP:{offer.pubkey}")
            )

        # Gate 4: Verified
        digest = cls._hash(json.dumps({
            "pubkey": offer.pubkey,
            "stake": str(offer.required_stake),
            "rep_hash": offer.reputation_hash
        }, sort_keys=True))
        
        return DiscoveryManifest(
            verdict=DiscoveryVerdict.VERIFIED_COUNTERPARTY,
            directive="PROCEED: Counterparty is verified and sybil-resistant.",
            manifest_digest=digest
        )