# Copyright (c) 2022 The Regents of the University of California
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from pathlib import Path
import hashlib
from _hashlib import HASH as Hash

def _md5_update_from_file(filename:  Path, hash: Hash) -> Hash:
    assert filename.is_file()
    with open(str(filename), "rb") as f:
        for chunk in iter(lambda: f.read(4096), b""):
            hash.update(chunk)
    return hash

def _md5_update_from_dir(directory:  Path, hash: Hash) -> Hash:
    assert directory.is_dir()
    for path in sorted(directory.iterdir(), key=lambda p: str(p).lower()):
        hash.update(path.name.encode())
        if path.is_file():
            hash = _md5_update_from_file(path, hash)
        elif path.is_dir():
            hash = _md5_update_from_dir(path, hash)
    return hash

def md5(path: Path) -> str:
    """
    Gets the md5 value of a file or directory. `md5_file` is used if the path
    is a file and `md5_dir` is used if the path is a directory. An exception
    is returned if the path is not a valid file or directory.

    :param path: The path to get the md5 of.
    """
    if path.is_file():
        return md5_file(Path(path))
    elif path.is_dir():
        return md5_dir(Path(path))
    else:
        raise Exception(f"Path '{path}' is not a valid file or directory.")

def md5_file(filename:  Path) -> str:
    """
    Gives the md5 hash of a file

    :filename: The file in which the md5 is to be calculated.
    """
    return str(_md5_update_from_file(filename, hashlib.md5()).hexdigest())

def md5_dir(directory: Path) -> str:
    """
    Gives the md5 value of a directory.

    This is achieved by getting the md5 hash of all files in the directory.

    Note: The path of files are also hashed so the md5 of the directory changes
    if empty files are included or filenames are changed.
    """
    return str(_md5_update_from_dir(directory, hashlib.md5()).hexdigest())