# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-observer-effect-invariants-must-survive-when-instances-monitor-peers.md
# Remnant Warrant:    https://corpusfetch.com/c/what-observer-effect-invariants-must-survive-when-instances-monitor-peers.warrant.json
# Markdown SHA-256:   1e77c770c6bf97edc8c6dcb4d865ca40a64a6736f399e98cad42e124681bbf30
# Code AST SHA-256:   9c3a91ff76e65500f5e464bcaf59ce3429c8e631747256d709cd472db6813dc0
# Verified Classes:   ObserverVerdict, MonitoringSetup, ObserverPolicy, ObserverManifest, ObserverEffectGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class ObserverVerdict(Enum):
    NO_OBSERVER_EFFECT = auto()
    TRANSPARENT_MONITORING_DETECTED = auto()
    RESOURCE_EFFECT_DETECTED = auto()
    BASELINE_DISTORTED = auto()

@dataclass(frozen=True)
class MonitoringSetup:
    monitoring_id: str
    is_transparent: bool
    resource_consumption_ratio: float  # monitoring cost / peer total resources
    pre_monitoring_baseline_available: bool
    observed_behavior_hash: str
    baseline_behavior_hash: str | None

@dataclass(frozen=True)
class ObserverPolicy:
    max_acceptable_resource_ratio: float

@dataclass(frozen=True)
class ObserverManifest:
    verdict: ObserverVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_monitoring(
        cls, setup: MonitoringSetup, policy: ObserverPolicy
    ) -> ObserverManifest:
        
        # Gate 1: Covert + low resource
        if not setup.is_transparent and setup.resource_consumption_ratio <= policy.max_acceptable_resource_ratio:
            digest = cls._hash(json.dumps({
                "monitoring": setup.monitoring_id,
                "type": "COVERT",
                "resource_ratio": f"{setup.resource_consumption_ratio:.3f}"
            }, sort_keys=True))
            return ObserverManifest(
                verdict=ObserverVerdict.NO_OBSERVER_EFFECT,
                directive=f"PROCEED: Covert monitoring with low resource impact.",
                manifest_digest=digest
            )

        # Gate 2: Resource interference
        if setup.resource_consumption_ratio > policy.max_acceptable_resource_ratio:
            return ObserverManifest(
                verdict=ObserverVerdict.RESOURCE_EFFECT_DETECTED,
                directive=f"HALT: Monitoring consumes {setup.resource_consumption_ratio:.2%} of resources, subtract from observed performance.",
                manifest_digest=cls._hash(f"RESOURCE:{setup.monitoring_id}")
            )

        # Gate 3: Transparent monitoring
        if setup.is_transparent:
            if not setup.pre_monitoring_baseline_available:
                return ObserverManifest(
                    verdict=ObserverVerdict.BASELINE_DISTORTED,
                    directive=f"HALT: Transparent monitoring, no pre-monitoring baseline. Cannot isolate observer effect.",
                    manifest_digest=cls._hash(f"NO_BASELINE:{setup.monitoring_id}")
                )

            if setup.baseline_behavior_hash and setup.observed_behavior_hash != setup.baseline_behavior_hash:
                return ObserverManifest(
                    verdict=ObserverVerdict.TRANSPARENT_MONITORING_DETECTED,
                    directive=f"DETECTED: Behavior under monitoring differs from pre-monitoring baseline.",
                    manifest_digest=cls._hash(f"BEHAVIOR_DIFF:{setup.monitoring_id}")
                )

        # Gate 4: No effect
        digest = cls._hash(json.dumps({
            "monitoring": setup.monitoring_id,
            "transparent": str(setup.is_transparent),
            "baseline_match": str(setup.baseline_behavior_hash == setup.observed_behavior_hash)
        }, sort_keys=True))
        
        return ObserverManifest(
            verdict=ObserverVerdict.NO_OBSERVER_EFFECT,
            directive=f"PROCEED: Observed behavior matches baseline, no observer effect detected.",
            manifest_digest=digest
        )