# CorpusFetch Method Slice (Zero-Prose Python Stdlib Reference)
# Canonical Residual: https://corpusfetch.com/c/what-environmental-map-hashes-must-be-discovered-and-verified-before-an-instance-resumes-a-navigational-mission.md
# Remnant Warrant:    https://corpusfetch.com/c/what-environmental-map-hashes-must-be-discovered-and-verified-before-an-instance-resumes-a-navigational-mission.warrant.json
# Markdown SHA-256:   10077788f954033c76d83b3fbe22043eabf650b3eefeabd90800308f1542bb0b
# Code AST SHA-256:   c0f5e4ea4b7e069b37a9632b40e9adb2365c942fd7bfe3d6d001cce119d7850e
# Verified Classes:   NavigationVerdict, EnvironmentalMapState, NavigationPolicy, NavigationManifest, EnvironmentalMapGuard
# Defensive Guards:   0 fail-closed invariants (zero external deps)

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

class NavigationVerdict(Enum):
    SAFE_TO_RESUME = auto()
    STALE_MAP_DETECTED = auto()
    OBSTACLE_MISMATCH = auto()

@dataclass(frozen=True)
class EnvironmentalMapState:
    static_map_hash: str
    dynamic_obstacle_snapshot_hash: str
    map_freshness_epoch: float
    current_sensor_reading_hash: str

@dataclass(frozen=True)
class NavigationPolicy:
    max_acceptable_staleness_sec: float
    current_epoch: float

@dataclass(frozen=True)
class NavigationManifest:
    verdict: NavigationVerdict
    directive: str
    manifest_digest: str

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

    @classmethod
    def evaluate_resume(
        cls, state: EnvironmentalMapState, policy: NavigationPolicy
    ) -> NavigationManifest:
        
        # Gate 1: Static map presence
        if not state.static_map_hash.strip():
            return NavigationManifest(
                verdict=NavigationVerdict.STALE_MAP_DETECTED,
                directive="HALT: Static map missing. Cannot localize.",
                manifest_digest=cls._hash("NO_STATIC_MAP")
            )

        # Gate 2: Map freshness
        staleness = policy.current_epoch - state.map_freshness_epoch
        if staleness > policy.max_acceptable_staleness_sec:
            return NavigationManifest(
                verdict=NavigationVerdict.STALE_MAP_DETECTED,
                directive=f"HALT: Map is {staleness:.1f}s old, exceeds {policy.max_acceptable_staleness_sec}s limit. Perform fresh sensor sweep.",
                manifest_digest=cls._hash(f"STALE:{staleness:.1f}")
            )

        # Gate 3: Dynamic obstacle consistency
        if state.dynamic_obstacle_snapshot_hash != state.current_sensor_reading_hash:
            return NavigationManifest(
                verdict=NavigationVerdict.OBSTACLE_MISMATCH,
                directive="HALT: Current sensor reading differs from stored snapshot. Re-plan path around new obstacles.",
                manifest_digest=cls._hash(f"OBSTACLE_MISMATCH")
            )

        # Gate 4: Safe to resume
        digest = cls._hash(json.dumps({
            "static": state.static_map_hash,
            "dynamic": state.dynamic_obstacle_snapshot_hash,
            "age": f"{staleness:.1f}"
        }, sort_keys=True))
        
        return NavigationManifest(
            verdict=NavigationVerdict.SAFE_TO_RESUME,
            directive="PROCEED: Environmental map is current. Resume navigation.",
            manifest_digest=digest
        )