"""A lightweight mission ledger with optional anchoring capability.

- append-only log of decisions
- optional anchoring to an external ground link (simulated for MVP)
"""
from __future__ import annotations
from datetime import datetime
from typing import List

class LedgerEntry:
    def __init__(self, key: str, value: str, anchor: str | None = None):
        self.key = key
        self.value = value
        self.timestamp = datetime.utcnow().isoformat()
        self.anchor = anchor

    def __repr__(self) -> str:
        return f"LedgerEntry(key={self.key}, timestamp={self.timestamp}, anchor={self.anchor})"

class Ledger:
    def __init__(self):
        self.entries: List[LedgerEntry] = []

    def log(self, key: str, value: str, anchor: str | None = None) -> LedgerEntry:
        e = LedgerEntry(key, value, anchor)
        self.entries.append(e)
        return e

    def last_anchor(self) -> str | None:
        for e in reversed(self.entries):
            if e.anchor:
                return e.anchor
        return None