"""Delta-Sync ledger: tamper-evident log with replay capability.

The ledger is a lightweight, chain-logged store where each entry records the
payload hash and a chain hash of the previous entry to provide auditability and
replay verification in offline mode.
"""
from __future__ import annotations
import hashlib
import json
from dataclasses import dataclass, asdict
from typing import List, Dict, Any


@dataclass
class LedgerEntry:
    seq: int
    payload: Dict[str, Any]
    prev_hash: str
    hash: str

    def to_dict(self) -> Dict[str, Any]:
        return asdict(self)


class DeltaSyncLedger:
    def __init__(self) -> None:
        self.entries: List[LedgerEntry] = []
        self._last_hash = ""  # Genesis chain

    @staticmethod
    def _hash(payload: Dict[str, Any], prev_hash: str) -> str:
        h = hashlib.sha256()
        h.update(json.dumps(payload, sort_keys=True).encode("utf-8"))
        h.update(prev_hash.encode("utf-8"))
        return h.hexdigest()

    def append(self, payload: Dict[str, Any]) -> LedgerEntry:
        seq = len(self.entries) + 1
        entry_hash = self._hash(payload, self._last_hash)
        entry = LedgerEntry(seq=seq, payload=payload, prev_hash=self._last_hash, hash=entry_hash)
        self.entries.append(entry)
        self._last_hash = entry_hash
        return entry

    def verify(self) -> bool:
        prev = ""
        for e in self.entries:
            if e.prev_hash != prev:
                return False
            if e.hash != self._hash(e.payload, e.prev_hash):
                return False
            prev = e.hash
        return True

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