# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-provenance-chain-breaks-must-be-detected-in-multi-hop-data-transfers.md
# Remnant Warrant:    https://corpusfetch.com/c/what-provenance-chain-breaks-must-be-detected-in-multi-hop-data-transfers.warrant.json
# Markdown SHA-256:   83e9a5b2bca35b8eb43a9cbc1c77841bd62d532c365d7b3bfd334ccdeefa6697
# Code AST SHA-256:   e235e9cf6e440f036c748e98cbe1c23e5034f8713fe0ed5a0fa6f5468206d3c4
# Verified Classes:   ChainVerdict, HopSignature, MultiHopState, ChainPolicy, ChainManifest, MultiHopProvenanceGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class ChainVerdict(Enum):
    CHAIN_VERIFIED = auto()
    CHAIN_BROKEN = auto()
    MISSING_HOP = auto()
    UNAUTHORIZED_HOP = auto()

@dataclass(frozen=True)
class HopSignature:
    hop_id: str
    data_hash: str
    previous_signature_hash: str
    hop_signature: str

@dataclass(frozen=True)
class MultiHopState:
    chain: tuple[HopSignature, ...]
    expected_hop_count: int
    authorized_hops: frozenset[str]

@dataclass(frozen=True)
class ChainPolicy:
    require_full_chain: bool

@dataclass(frozen=True)
class ChainManifest:
    verdict: ChainVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_chain(
        cls, state: MultiHopState, policy: ChainPolicy
    ) -> ChainManifest:
        
        # Gate 1: Chain presence
        if not state.chain:
            return ChainManifest(
                verdict=ChainVerdict.CHAIN_BROKEN,
                directive="HALT: No hop signature chain provided.",
                manifest_digest=cls._hash("NO_CHAIN")
            )

        # Gate 2: Chain length
        if len(state.chain) != state.expected_hop_count:
            return ChainManifest(
                verdict=ChainVerdict.MISSING_HOP,
                directive=f"HALT: Chain length {len(state.chain)} != expected {state.expected_hop_count}.",
                manifest_digest=cls._hash(f"LENGTH:{len(state.chain)}")
            )

        # Gate 3: Continuity check
        for i, hop in enumerate(state.chain):
            if i == 0:
                continue
            previous = state.chain[i - 1]
            expected_prev_hash = cls._hash(previous.hop_signature)
            if hop.previous_signature_hash != expected_prev_hash:
                return ChainManifest(
                    verdict=ChainVerdict.CHAIN_BROKEN,
                    directive=f"HALT: Hop {hop.hop_id} breaks chain. Previous hash mismatch.",
                    manifest_digest=cls._hash(f"BROKEN:{hop.hop_id}")
                )

        # Gate 4: Authorization
        for hop in state.chain:
            if hop.hop_id not in state.authorized_hops:
                return ChainManifest(
                    verdict=ChainVerdict.UNAUTHORIZED_HOP,
                    directive=f"HALT: Hop {hop.hop_id} not in authorized list.",
                    manifest_digest=cls._hash(f"UNAUTHORIZED:{hop.hop_id}")
                )

        # Gate 5: Verified
        digest = cls._hash(json.dumps({
            "chain_length": str(len(state.chain)),
            "first_hop": state.chain[0].hop_id,
            "last_hop": state.chain[-1].hop_id
        }, sort_keys=True))
        
        return ChainManifest(
            verdict=ChainVerdict.CHAIN_VERIFIED,
            directive="PROCEED: Multi-hop provenance chain is continuous and authorized.",
            manifest_digest=digest
        )