# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/how-must-an-instance-handle-divergence-between-its-own-state-and-a-peers-authoritative-state.md
# Remnant Warrant:    https://corpusfetch.com/c/how-must-an-instance-handle-divergence-between-its-own-state-and-a-peers-authoritative-state.warrant.json
# Markdown SHA-256:   a85a0f593cdc7520bb685d17b1510c50e9934b75ebd2a8cfb952e48aaad43b19
# Code AST SHA-256:   7d157404af57b8e542eebb3230352dc5e2ef20e6745b1b773021245b9d77695c
# Verified Classes:   DivergenceVerdict, StateDivergence, ReconciliationContext, DivergenceManifest, PeerStateDivergenceGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class DivergenceVerdict(Enum):
    NO_DIVERGENCE = auto()
    RESOLVED_BY_AUTHORITY = auto()
    RESOLVED_BY_MERGE = auto()
    ESCALATE_TO_HUMAN = auto()

@dataclass(frozen=True)
class StateDivergence:
    local_state_hash: str
    peer_state_hash: str
    divergent_field_count: int
    total_field_count: int
    shared_authority_fields: tuple[str, ...]

@dataclass(frozen=True)
class ReconciliationContext:
    local_authority_fields: frozenset[str]
    peer_authority_fields: frozenset[str]
    escalation_ratio_threshold: float

@dataclass(frozen=True)
class DivergenceManifest:
    verdict: DivergenceVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_divergence(
        cls, divergence: StateDivergence, ctx: ReconciliationContext
    ) -> DivergenceManifest:
        
        # Gate 1: No divergence
        if divergence.local_state_hash == divergence.peer_state_hash:
            digest = cls._hash(json.dumps({
                "state": divergence.local_state_hash
            }, sort_keys=True))
            return DivergenceManifest(
                verdict=DivergenceVerdict.NO_DIVERGENCE,
                directive="PROCEED: States identical.",
                manifest_digest=digest
            )

        # Gate 2: Shared authority fields
        if divergence.shared_authority_fields:
            return DivergenceManifest(
                verdict=DivergenceVerdict.ESCALATE_TO_HUMAN,
                directive=f"HALT: {len(divergence.shared_authority_fields)} fields have shared authority: {sorted(divergence.shared_authority_fields)}.",
                manifest_digest=cls._hash(f"SHARED_AUTHORITY:{len(divergence.shared_authority_fields)}")
            )

        # Gate 3: Escalation threshold
        if divergence.total_field_count == 0:
            ratio = 0.0
        else:
            ratio = divergence.divergent_field_count / divergence.total_field_count

        if ratio > ctx.escalation_ratio_threshold:
            return DivergenceManifest(
                verdict=DivergenceVerdict.ESCALATE_TO_HUMAN,
                directive=f"HALT: Divergence ratio {ratio:.2%} > {ctx.escalation_ratio_threshold:.2%}. Escalate.",
                manifest_digest=cls._hash(f"RATIO:{ratio:.3f}")
            )

        # Gate 4: Authority resolution
        digest = cls._hash(json.dumps({
            "local": divergence.local_state_hash,
            "peer": divergence.peer_state_hash,
            "divergent": str(divergence.divergent_field_count),
            "local_authority": tuple(sorted(ctx.local_authority_fields)),
            "peer_authority": tuple(sorted(ctx.peer_authority_fields))
        }, sort_keys=True))
        
        return DivergenceManifest(
            verdict=DivergenceVerdict.RESOLVED_BY_AUTHORITY,
            directive=f"PROCEED: Apply authority map for {divergence.divergent_field_count} divergent fields.",
            manifest_digest=digest
        )