# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-cost-attribution-invariants-must-survive-multi-hop-reference-propagation.md
# Remnant Warrant:    https://corpusfetch.com/c/what-cost-attribution-invariants-must-survive-multi-hop-reference-propagation.warrant.json
# Markdown SHA-256:   7d7799e7d01938bd8a0e758fa1e1d12e01827fe2e5beead0095d7a92ad28879b
# Code AST SHA-256:   60f9ca1a7b0e7a771fc37c897b0872b3ae5e10a386838f14f6c25d3bb2edb94c
# Verified Classes:   CostVerdict, HopCost, ReferenceChain, CostPolicy, CostManifest, ReferenceCostAttributionGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class CostVerdict(Enum):
    SINGLE_HOP = auto()
    COST_ATTRIBUTED = auto()
    POLICY_MISSING = auto()
    COST_ATTRIBUTION_INCOMPLETE = auto()

@dataclass(frozen=True)
class HopCost:
    hop_id: str
    cost_units: float
    cost_type: str  # "BANDWIDTH" | "COMPUTE" | "STORAGE"

@dataclass(frozen=True)
class ReferenceChain:
    reference_id: str
    hop_costs: tuple[HopCost, ...]
    attribution_policy: str | None  # "ORIGIN_PAYS" | "CONSUMER_PAYS" | "PROPAGATOR_PAYS"

@dataclass(frozen=True)
class CostPolicy:
    require_attribution_policy: bool

@dataclass(frozen=True)
class CostManifest:
    verdict: CostVerdict
    total_cost: float
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_chain(
        cls, chain: ReferenceChain, policy: CostPolicy
    ) -> CostManifest:
        
        # Gate 1: Single hop
        if len(chain.hop_costs) <= 1:
            total = sum(h.cost_units for h in chain.hop_costs)
            digest = cls._hash(json.dumps({
                "reference": chain.reference_id,
                "hops": str(len(chain.hop_costs)),
                "cost": f"{total:.2f}"
            }, sort_keys=True))
            return CostManifest(
                verdict=CostVerdict.SINGLE_HOP,
                total_cost=total,
                directive=f"PROCEED: Single hop, cost {total:.2f} attributed to hop.",
                manifest_digest=digest
            )

        # Gate 2: Policy presence
        if policy.require_attribution_policy and not chain.attribution_policy:
            return CostManifest(
                verdict=CostVerdict.POLICY_MISSING,
                total_cost=sum(h.cost_units for h in chain.hop_costs),
                directive=f"HALT: Multi-hop chain without attribution policy. Free-riding risk.",
                manifest_digest=cls._hash(f"NO_POLICY:{chain.reference_id}")
            )

        # Gate 3: Hop completeness
        if any(not h.hop_id for h in chain.hop_costs):
            return CostManifest(
                verdict=CostVerdict.COST_ATTRIBUTION_INCOMPLETE,
                total_cost=0.0,
                directive=f"HALT: Some hop costs lack hop attribution.",
                manifest_digest=cls._hash(f"INCOMPLETE:{chain.reference_id}")
            )

        # Gate 4: Attributed
        total = sum(h.cost_units for h in chain.hop_costs)
        digest = cls._hash(json.dumps({
            "reference": chain.reference_id,
            "hops": tuple(h.hop_id for h in chain.hop_costs),
            "total": f"{total:.2f}",
            "policy": chain.attribution_policy
        }, sort_keys=True))
        
        return CostManifest(
            verdict=CostVerdict.COST_ATTRIBUTED,
            total_cost=total,
            directive=f"PROCEED: Total cost {total:.2f} attributed across {len(chain.hop_costs)} hops per {chain.attribution_policy}.",
            manifest_digest=digest
        )