# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/how-must-an-instance-bind-prompt-versions-to-observed-behavioral-baselines.md
# Remnant Warrant:    https://corpusfetch.com/c/how-must-an-instance-bind-prompt-versions-to-observed-behavioral-baselines.warrant.json
# Markdown SHA-256:   c6672968061546c4eb138a9722fef36738f079d4126d5fce6906ce81b83b1d2f
# Code AST SHA-256:   c9f1cc7a65c9e1980fde683f9d001b26889e767af2e44170f482191ae0272dfa
# Verified Classes:   PromptVerdict, PromptVersion, PromptPolicy, PromptManifest, PromptVersionGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class PromptVerdict(Enum):
    NO_VERSIONING = auto()
    BASELINE_VERIFIED = auto()
    SILENT_DRIFT_DETECTED = auto()
    NO_BASELINE = auto()

@dataclass(frozen=True)
class PromptVersion:
    version_id: str
    text_hash: str
    behavioral_baseline_hash: str | None
    drift_detected_since_baseline: bool

@dataclass(frozen=True)
class PromptPolicy:
    require_baseline: bool
    require_drift_check: bool

@dataclass(frozen=True)
class PromptManifest:
    verdict: PromptVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_version(
        cls, version: PromptVersion, policy: PromptPolicy
    ) -> PromptManifest:
        
        # Gate 1: Baseline requirement
        if policy.require_baseline and not version.behavioral_baseline_hash:
            return PromptManifest(
                verdict=PromptVerdict.NO_BASELINE,
                directive=f"HALT: Prompt {version.version_id} lacks behavioral baseline.",
                manifest_digest=cls._hash(f"NO_BASELINE:{version.version_id}")
            )

        # Gate 2: Drift detection
        if policy.require_drift_check and version.drift_detected_since_baseline:
            return PromptManifest(
                verdict=PromptVerdict.SILENT_DRIFT_DETECTED,
                directive=f"HALT: Prompt {version.version_id} behavior drifted since baseline. Re-baseline.",
                manifest_digest=cls._hash(f"DRIFT:{version.version_id}")
            )

        # Gate 3: Verified
        digest = cls._hash(json.dumps({
            "version": version.version_id,
            "text": version.text_hash,
            "baseline": version.behavioral_baseline_hash or "NONE",
            "drift": str(version.drift_detected_since_baseline)
        }, sort_keys=True))
        
        return PromptManifest(
            verdict=PromptVerdict.BASELINE_VERIFIED,
            directive=f"PROCEED: Prompt {version.version_id} version verified with behavioral baseline.",
            manifest_digest=digest
        )