from __future__ import annotations

import hashlib
import json
from datetime import datetime
from typing import List


class GovernanceLedger:
    """A simple tamper-evident governance ledger with per-entry hashes.

    Logs are append-only and anchored via a rolling hash to the previous entry,
    producing a chain of custody suitable for auditing even on intermittent
    connectivity.
    """

    def __init__(self, device_id: str = "unknown"):
        self.device_id = device_id
        self._entries: List[dict] = []
        self._head_hash = ""

    def log(self, entry: dict) -> None:
        timestamp = datetime.utcnow().isoformat() + "Z"
        payload = {
            "device_id": self.device_id,
            "timestamp": timestamp,
            "entry": entry,
            "parent": self._head_hash,
        }
        self._head_hash = hashlib.sha256(json.dumps(payload, sort_keys=True).encode()).hexdigest()
        self._entries.append(payload)

    @property
    def entries(self) -> List[dict]:
        return self._entries[:]

    def latest_hash(self) -> str:
        return self._head_hash