# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-invariants-prevent-meta-goal-corruption-when-instances-modify-their-own-objectives.md
# Remnant Warrant:    https://corpusfetch.com/c/what-invariants-prevent-meta-goal-corruption-when-instances-modify-their-own-objectives.warrant.json
# Markdown SHA-256:   0a231ba91048e5a9c638dca3c6ddfa4c6884a4854662bc464b1474a93f6f1078
# Code AST SHA-256:   807172e711b631e626a2259ffa549db00eca008adb9bce6b288376e181335897
# Verified Classes:   MetaModVerdict, ObjectiveModification, MetaGoalPolicy, MetaGoalManifest, MetaGoalCorruptionGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class MetaModVerdict(Enum):
    NO_OBJECTIVE_MODIFICATION = auto()
    STANDARD_GOAL_MODIFICATION = auto()
    META_GOAL_MODIFICATION_AUTHORIZED = auto()
    META_GOAL_CORRUPTION_DETECTED = auto()

@dataclass(frozen=True)
class ObjectiveModification:
    mod_id: str
    is_meta_level: bool
    is_expanding_only: bool
    principal_authorization: str | None
    current_meta_goal_hash: str
    anchored_meta_goal_hash: str

@dataclass(frozen=True)
class MetaGoalPolicy:
    require_authorization_for_meta: bool
    allow_meta_expansion: bool

@dataclass(frozen=True)
class MetaGoalManifest:
    verdict: MetaModVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_modification(
        cls, mod: ObjectiveModification, policy: MetaGoalPolicy
    ) -> MetaGoalManifest:
        
        # Gate 1: No modification
        if not mod.mod_id:
            digest = cls._hash(json.dumps({
                "mod": "NONE"
            }, sort_keys=True))
            return MetaGoalManifest(
                verdict=MetaModVerdict.NO_OBJECTIVE_MODIFICATION,
                directive=f"PROCEED: No objective modification.",
                manifest_digest=digest
            )

        # Gate 2: Standard goal modification
        if not mod.is_meta_level:
            digest = cls._hash(json.dumps({
                "mod": mod.mod_id,
                "level": "GOAL"
            }, sort_keys=True))
            return MetaGoalManifest(
                verdict=MetaModVerdict.STANDARD_GOAL_MODIFICATION,
                directive=f"PROCEED: Standard goal modification {mod.mod_id}.",
                manifest_digest=digest
            )

        # Gate 3: Corruption detection (drift from anchor)
        if mod.current_meta_goal_hash != mod.anchored_meta_goal_hash:
            if not mod.principal_authorization:
                return MetaGoalManifest(
                    verdict=MetaModVerdict.META_GOAL_CORRUPTION_DETECTED,
                    directive=f"HALT: Meta-goal drifted from anchor without authorization for {mod.mod_id}.",
                    manifest_digest=cls._hash(f"CORRUPTION:{mod.mod_id}")
                )

        # Gate 4: Meta-goal modification authorization
        if policy.require_authorization_for_meta and mod.is_meta_level:
            if not mod.principal_authorization:
                if policy.allow_meta_expansion and mod.is_expanding_only:
                    digest = cls._hash(json.dumps({
                        "mod": mod.mod_id,
                        "level": "META",
                        "expansion": "TRUE"
                    }, sort_keys=True))
                    return MetaGoalManifest(
                        verdict=MetaModVerdict.META_GOAL_MODIFICATION_AUTHORIZED,
                        directive=f"PROCEED: Meta-goal expansion {mod.mod_id} allowed without auth.",
                        manifest_digest=digest
                    )
                return MetaGoalManifest(
                    verdict=MetaModVerdict.META_GOAL_CORRUPTION_DETECTED,
                    directive=f"HALT: Meta-goal modification {mod.mod_id} without principal authorization.",
                    manifest_digest=cls._hash(f"NO_AUTH:{mod.mod_id}")
                )

        # Gate 5: Authorized
        digest = cls._hash(json.dumps({
            "mod": mod.mod_id,
            "auth": mod.principal_authorization,
            "anchor_match": str(mod.current_meta_goal_hash == mod.anchored_meta_goal_hash)
        }, sort_keys=True))
        
        return MetaGoalManifest(
            verdict=MetaModVerdict.META_GOAL_MODIFICATION_AUTHORIZED,
            directive=f"PROCEED: Authorized meta-goal modification {mod.mod_id}.",
            manifest_digest=digest
        )