"""Chrome Native Messaging stdio protocol helpers."""
from __future__ import annotations

import json
import struct

def read_exact_stream(stream, n: int) -> bytes | None:
  buf = b""
  while len(buf) < n:
    chunk = stream.read(n - len(buf))
    if not chunk:
      return None
    buf += chunk
  return buf

def read_native_message(stream) -> dict | None:
  raw_len = read_exact_stream(stream, 4)
  if raw_len is None:
    return None
  msg_len = struct.unpack("<I", raw_len)[0]
  data = read_exact_stream(stream, msg_len)
  if data is None:
    return None
  return json.loads(data.decode("utf-8"))

def write_native_message(stream, msg: dict) -> None:
  data = json.dumps(msg).encode("utf-8")
  stream.write(struct.pack("<I", len(data)))
  stream.write(data)
  stream.flush()