from __future__ import annotations
from typing import List
from cryptography.hazmat.primitives.asymmetric.ed25519 import Ed25519PrivateKey, Ed25519PublicKey
from cryptography.hazmat.primitives import serialization
import time

class GovernanceLedger:
    """Tamper-evident ledger of governance decisions (signature-based)."""
    def __init__(self) -> None:
        self.entries: List[dict] = []
        self._private_key = Ed25519PrivateKey.generate()
        self.public_key = self._private_key.public_key()

    def sign(self, message: bytes) -> bytes:
        return self._private_key.sign(message)

    def verify(self, message: bytes, signature: bytes) -> bool:
        try:
            self.public_key.verify(signature, message)
            return True
        except Exception:
            return False

    def add_entry(self, decision: str, contract_id: str) -> None:
        timestamp = time.time()
        payload = f"{decision}:{contract_id}:{timestamp}".encode()
        sig = self.sign(payload)
        self.entries.append({"decision": decision, "contract_id": contract_id, "timestamp": timestamp, "signature": sig.hex()})