"""Tamper-evident ledger for test attestations (MVP).

Implements a simple hash-chain ledger suitable for signing and auditing
test results.
"""
from __future__ import annotations

import hashlib
import json
from dataclasses import dataclass, asdict, field
from typing import List, Dict, Any


@dataclass
class LedgerEntry:
    index: int
    payload: Dict[str, Any]
    prev_hash: str
    hash: str = field(init=False)

    def __post_init__(self):
        self.hash = self.compute_hash()

    def compute_hash(self) -> str:
        data = json.dumps({"index": self.index, "payload": self.payload, "prev_hash": self.prev_hash}, sort_keys=True)
        return hashlib.sha256(data.encode("utf-8")).hexdigest()


class Ledger:
    def __init__(self):
        self.entries: List[LedgerEntry] = []
        self._genesis_hash = "0" * 64

    def add_entry(self, payload: Dict[str, Any]) -> LedgerEntry:
        index = len(self.entries)
        prev_hash = self.entries[-1].hash if self.entries else self._genesis_hash
        entry = LedgerEntry(index=index, payload=payload, prev_hash=prev_hash)
        self.entries.append(entry)
        return entry

    def get_chain(self) -> List[Dict[str, Any]]:
        return [asdict(e) for e in self.entries]