#!/usr/bin/env python3
# SPDX-License-Identifier: GPL-3.0-or-later
"""Offline parser for the bounded Phase-1.0DM snapshot stream."""
from __future__ import annotations
from dataclasses import dataclass
import hashlib,struct

MAGIC=b"CHS10DM1";FRAME=struct.Struct("<8sIIiiQQQQq");MAX_BYTES=64*1024*1024
BEGIN=1;END=2;ERROR=3
class ProtocolError(ValueError):pass
@dataclass(frozen=True)
class SnapshotResult:
 data:bytes
 sha256:str
 size:int
 device:int
 inode:int
 mtime:int

def _frame(data:bytes):
 if len(data)!=64:raise ProtocolError("frame size")
 values=FRAME.unpack(data)
 if values[0]!=MAGIC or values[1]!=1:raise ProtocolError("frame identity")
 return values

def parse_stream(raw:bytes)->SnapshotResult:
 if not isinstance(raw,bytes) or len(raw)<128:raise ProtocolError("stream truncated")
 begin=_frame(raw[:64]);kind,status,saved,size,sent,dev,ino,mtime=begin[2:]
 if kind==ERROR:raise ProtocolError(f"target error {status}")
 if kind!=BEGIN or status!=0 or saved!=0 or sent!=0 or not 0<size<=MAX_BYTES:raise ProtocolError("begin invalid")
 if len(raw)!=64+size+64:raise ProtocolError("stream length")
 payload=raw[64:64+size];end=_frame(raw[64+size:]);ekind,estatus,esaved,esize,esent,edev,eino,emtime=end[2:]
 if ekind!=END or estatus!=0 or esaved!=0 or esize!=size or esent!=size or (edev,eino,emtime)!=(dev,ino,mtime):raise ProtocolError("terminal invalid")
 if payload[:16]!=b"SQLite format 3\x00":raise ProtocolError("not sqlite")
 return SnapshotResult(payload,hashlib.sha256(payload).hexdigest(),size,dev,ino,mtime)