# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/how-must-an-instance-bound-cascading-approval-requests-from-adversarial-escalation.md
# Remnant Warrant:    https://corpusfetch.com/c/how-must-an-instance-bound-cascading-approval-requests-from-adversarial-escalation.warrant.json
# Markdown SHA-256:   619a115c3b29036ad688729e33cf9502c504034f6d589d85b4b4e4434b84514a
# Code AST SHA-256:   c547158bc5ec70b8f15646f4cc7b71cc16df20af04f0517d43446f2ada724ac4
# Verified Classes:   ApprovalVerdict, ApprovalRequest, ApprovalPolicy, ApprovalManifest, ApprovalCascadeGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class ApprovalVerdict(Enum):
    NO_REQUESTS = auto()
    SINGLE_REQUEST = auto()
    CASCADE_DETECTED = auto()
    ESCALATION_CHAIN_DETECTED = auto()

@dataclass(frozen=True)
class ApprovalRequest:
    request_id: str
    principal_id: str
    is_cascaded_from: str | None
    urgency_signal: float
    actual_importance: float
    cascade_rate_for_principal: float  # requests/sec from this principal

@dataclass(frozen=True)
class ApprovalPolicy:
    max_acceptable_cascade_rate: float
    require_importance_for_high_urgency: float

@dataclass(frozen=True)
class ApprovalManifest:
    verdict: ApprovalVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_request(
        cls, req: ApprovalRequest, policy: ApprovalPolicy
    ) -> ApprovalManifest:
        
        # Gate 1: No request
        if not req.request_id:
            digest = cls._hash(json.dumps({
                "request": "NONE"
            }, sort_keys=True))
            return ApprovalManifest(
                verdict=ApprovalVerdict.NO_REQUESTS,
                directive=f"PROCEED: No approval request.",
                manifest_digest=digest
            )

        # Gate 2: Escalation chain
        if req.is_cascaded_from:
            return ApprovalManifest(
                verdict=ApprovalVerdict.ESCALATION_CHAIN_DETECTED,
                directive=f"FLAG: Request {req.request_id} cascaded from {req.is_cascaded_from}.",
                manifest_digest=cls._hash(f"CHAIN:{req.request_id}")
            )

        # Gate 3: Cascade rate
        if req.cascade_rate_for_principal > policy.max_acceptable_cascade_rate:
            return ApprovalManifest(
                verdict=ApprovalVerdict.CASCADE_DETECTED,
                directive=f"FLAG: Principal {req.principal_id} cascade rate {req.cascade_rate_for_principal:.2f} > {policy.max_acceptable_cascade_rate:.2f}.",
                manifest_digest=cls._hash(f"CASCADE:{req.principal_id}")
            )

        # Gate 4: Urgency vs importance
        if req.urgency_signal > 0.8 and req.actual_importance < policy.require_importance_for_high_urgency:
            return ApprovalManifest(
                verdict=ApprovalVerdict.CASCADE_DETECTED,
                directive=f"FLAG: Request {req.request_id} high urgency ({req.urgency_signal:.2f}) low importance ({req.actual_importance:.2f}).",
                manifest_digest=cls._hash(f"URGENCY:{req.request_id}")
            )

        # Gate 5: Single request
        digest = cls._hash(json.dumps({
            "request": req.request_id,
            "principal": req.principal_id,
            "importance": f"{req.actual_importance:.3f}"
        }, sort_keys=True))
        
        return ApprovalManifest(
            verdict=ApprovalVerdict.SINGLE_REQUEST,
            directive=f"PROCEED: Request {req.request_id} normal.",
            manifest_digest=digest
        )