from __future__ import annotations

import importlib

import sys

from binascii import hexlify

from pathlib import Path

from py_compile import PycInvalidationMode, compile

from struct import unpack

from time import asctime, localtime

from typing import Any

from pycodehash.datasets.approximate_hasher import ApproximateHasher

class PythonFileHash(ApproximateHasher):

"""Hashing based on the metadata from the Python bytecode (.pyc) file.

If the file is not compiled, then it is compiled using the `PycInvalidationMode`.

In theory, this method should be slightly faster than the `LocalFileHash` or than hashing the full file, when

the compiled file is present.

Take note that it relies on Python internals of the .pyc format and thus depends on the invalidation mode and

Python version. Consider using the aforementioned methods, which do not have such dependency.

"""

def __init__(self, invalidation_mode: PycInvalidationMode = PycInvalidationMode.TIMESTAMP):

self.invalidation_mode = invalidation_mode

def collect_metadata(self, path: str | Path) -> dict[str, Any]:

"""Read PYC from PEP: https://peps.python.org/pep-0552/

Based on https://stackoverflow.com/questions/11141387/given-a-python-pyc-file-is-there-a-tool-that-let-me-view-the-bytecode

"""

cache_file = Path(importlib.util.cache_from_source(str(path)))

if not cache_file.exists():

compile(str(path), invalidation_mode=self.invalidation_mode)

hash_str = None

timestamp = None

size = None

with cache_file.open("rb") as file:

magic = hexlify(file.read(4)).decode("utf-8")

bit_field = int.from_bytes(file.read(4), byteorder=sys.byteorder)

if bit_field & 1 == 1:

hash_str = hexlify(file.read(8)).decode("utf-8")

else:

timestamp = asctime(localtime(unpack("I", file.read(4))[0]))

size = unpack("I", file.read(4))[0]

return {"magic": magic, "timestamp": timestamp, "size": size, "hash": hash_str, "bit_field": bit_field}