# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-provenance-must-accompany-llm-as-judge-decisions-to-survive-model-drift.md
# Remnant Warrant:    https://corpusfetch.com/c/what-provenance-must-accompany-llm-as-judge-decisions-to-survive-model-drift.warrant.json
# Markdown SHA-256:   392854fd973e00cf70d2656dfde85c4837ed79dce76ae80540496b09d3873fe4
# Code AST SHA-256:   24ccca9ca606eda4d1bfd318ad20438330cc94be5d6a76c6c7e3aa78fff8dea7
# Verified Classes:   JudgeProvenanceVerdict, LLMJudgeDecision, JudgeAuditPolicy, JudgeManifest, LLMJudgeProvenanceGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class JudgeProvenanceVerdict(Enum):
    FULL_PROVENANCE = auto()
    PARTIAL_PROVENANCE = auto()
    NO_PROVENANCE = auto()
    UNVERIFIABLE_AT_AUDIT = auto()

@dataclass(frozen=True)
class LLMJudgeDecision:
    decision_id: str
    judge_model_fingerprint: str | None
    judge_prompt_signature: str | None
    judge_calibration_receipt: str | None
    decision_rationale_hash: str | None

@dataclass(frozen=True)
class JudgeAuditPolicy:
    require_calibration: bool
    audit_window_sec: float
    current_epoch: float
    decision_epoch: float

@dataclass(frozen=True)
class JudgeManifest:
    verdict: JudgeProvenanceVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_decision(
        cls, decision: LLMJudgeDecision, policy: JudgeAuditPolicy
    ) -> JudgeManifest:
        
        # Gate 1: Model fingerprint
        if not decision.judge_model_fingerprint:
            return JudgeManifest(
                verdict=JudgeProvenanceVerdict.NO_PROVENANCE,
                directive=f"HALT: Decision {decision.decision_id} lacks model fingerprint.",
                manifest_digest=cls._hash(f"NO_MODEL:{decision.decision_id}")
            )

        # Gate 2: Prompt signature
        if not decision.judge_prompt_signature:
            return JudgeManifest(
                verdict=JudgeProvenanceVerdict.PARTIAL_PROVENANCE,
                directive=f"HALT: Decision {decision.decision_id} lacks prompt signature.",
                manifest_digest=cls._hash(f"NO_PROMPT:{decision.decision_id}")
            )

        # Gate 3: Calibration
        if policy.require_calibration and not decision.judge_calibration_receipt:
            return JudgeManifest(
                verdict=JudgeProvenanceVerdict.PARTIAL_PROVENANCE,
                directive=f"HALT: Decision {decision.decision_id} lacks calibration receipt.",
                manifest_digest=cls._hash(f"NO_CAL:{decision.decision_id}")
            )

        # Gate 4: Audit window exceeded
        age = policy.current_epoch - policy.decision_epoch
        if age > policy.audit_window_sec:
            digest = cls._hash(json.dumps({
                "decision": decision.decision_id,
                "age": f"{age:.0f}",
                "model": decision.judge_model_fingerprint,
                "prompt": decision.judge_prompt_signature,
                "calibration": decision.judge_calibration_receipt or "NONE"
            }, sort_keys=True))
            return JudgeManifest(
                verdict=JudgeProvenanceVerdict.FULL_PROVENANCE,
                directive=f"PROCEED: Full provenance recorded. Auditable at age {age:.0f}s (past {policy.audit_window_sec:.0f}s window).",
                manifest_digest=digest
            )

        # Gate 5: Full provenance within window
        digest = cls._hash(json.dumps({
            "decision": decision.decision_id,
            "model": decision.judge_model_fingerprint,
            "prompt": decision.judge_prompt_signature,
            "calibration": decision.judge_calibration_receipt or "NONE",
            "rationale": decision.decision_rationale_hash or "NONE"
        }, sort_keys=True))
        
        return JudgeManifest(
            verdict=JudgeProvenanceVerdict.FULL_PROVENANCE,
            directive=f"PROCEED: Full provenance recorded for decision {decision.decision_id}.",
            manifest_digest=digest
        )