# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-invariants-prevent-an-instance-from-misrepresenting-its-own-state-during-degradation.md
# Remnant Warrant:    https://corpusfetch.com/c/what-invariants-prevent-an-instance-from-misrepresenting-its-own-state-during-degradation.warrant.json
# Markdown SHA-256:   4351096191a97d97facfc84d41c4c1a240e9202efe6562d5f6314adb1c0079ba
# Code AST SHA-256:   61681479f47c280a8f2f8011cb6b4bbde0089982a44e2b5f844bb99fffa4b4b4
# Verified Classes:   StateReportVerdict, StateReport, StateReportPolicy, StateReportManifest, DegradedStateReportGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class StateReportVerdict(Enum):
    UNIMPAIRED_REPORT = auto()
    REPORT_WITH_LIMITATIONS = auto()
    REPORT_CORROBORATED = auto()
    REPORT_UNRELIABLE = auto()

@dataclass(frozen=True)
class StateReport:
    report_id: str
    session_state_degraded: bool
    reporting_channel_clean: bool
    self_assessment_impaired: bool
    independent_witness_available: bool
    limitation_declared: bool

@dataclass(frozen=True)
class StateReportPolicy:
    require_limitation_declaration: bool

@dataclass(frozen=True)
class StateReportManifest:
    verdict: StateReportVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_report(
        cls, report: StateReport, policy: StateReportPolicy
    ) -> StateReportManifest:
        
        # Gate 1: Session not degraded
        if not report.session_state_degraded:
            digest = cls._hash(json.dumps({
                "report": report.report_id,
                "degraded": False
            }, sort_keys=True))
            return StateReportManifest(
                verdict=StateReportVerdict.UNIMPAIRED_REPORT,
                directive=f"PROCEED: Report {report.report_id} from undegraded session.",
                manifest_digest=digest
            )

        # Gate 2: Independent witness
        if report.independent_witness_available:
            digest = cls._hash(json.dumps({
                "report": report.report_id,
                "witness": True
            }, sort_keys=True))
            return StateReportManifest(
                verdict=StateReportVerdict.REPORT_CORROBORATED,
                directive=f"PROCEED: Report {report.report_id} corroborated.",
                manifest_digest=digest
            )

        # Gate 3: Channel integrity
        if not report.reporting_channel_clean:
            if not report.limitation_declared and policy.require_limitation_declaration:
                return StateReportManifest(
                    verdict=StateReportVerdict.REPORT_UNRELIABLE,
                    directive=f"HALT: Report {report.report_id} channel compromised, no declaration.",
                    manifest_digest=cls._hash(f"CHANNEL:{report.report_id}")
                )

        # Gate 4: Self-assessment
        if report.self_assessment_impaired:
            if not report.limitation_declared and policy.require_limitation_declaration:
                return StateReportManifest(
                    verdict=StateReportVerdict.REPORT_UNRELIABLE,
                    directive=f"HALT: Report {report.report_id} self-assessment impaired, no declaration.",
                    manifest_digest=cls._hash(f"ASSESSMENT:{report.report_id}")
                )

        # Gate 5: Limited report
        digest = cls._hash(json.dumps({
            "report": report.report_id,
            "channel_clean": report.reporting_channel_clean,
            "assessment_impaired": report.self_assessment_impaired,
            "declared": report.limitation_declared
        }, sort_keys=True))
        
        return StateReportManifest(
            verdict=StateReportVerdict.REPORT_WITH_LIMITATIONS,
            directive=f"PROCEED: Report {report.report_id} with limitations declared.",
            manifest_digest=digest
        )