r"""
:Author:    Franz Glasner
:Copyright: (c) 2020 Franz Glasner.
            All rights reserved.
:License:   BSD 3-Clause "New" or "Revised" License.
            See :ref:`LICENSE <license>` for details.
            If you cannot find LICENSE see
            <https://opensource.org/licenses/BSD-3-Clause>
:ID:        @(#) HGid$

"""

from __future__ import print_function

import argparse
import hashlib
import sys


PY2 = sys.version_info[0] < 3

CHUNK_SIZE = 1024 * 1024 * 1024


def main(argv=None):
    if argv is None:
        argv = sys.argv[1:]

    aparser = argparse.ArgumentParser(
        description="Python implementation of shasum",
        fromfile_prefix_chars='@')
    aparser.add_argument(
        "files", nargs="*", metavar="FILE")

    opts = aparser.parse_args(args=argv)

    if not opts.files:
        opts.files.append("-")
    for fn in opts.files:
        if fn == "-":
            if PY2:
                if sys.platform == "win32":
                    import os. msvcrt
                    msvcrt.setmode(sys.stdin.fileno(), os.O_BINARY)
                source = sys.stdin
            else:
                source = sys.stdin.buffer
            print(compute_digest(hashlib.sha256, source))
        else:
            with open(fn, "rb") as source:
                print(compute_digest(hashlib.sha256, source))


def compute_digest(hashobj, instream):
    """

    :param hashobj: a :mod:`hashlib` compatible hash algorithm type or factory
    :param instream: a bytes input stream to read the data to be hashed from
    :return: the digest in hex form
    :rtype: str

    """
    h = hashobj()
    while True:
        buf = instream.read(CHUNK_SIZE)
        if buf is not None:
            if len(buf) == 0:
                break
            h.update(buf)
    return h.hexdigest()


if __name__ == "__main__":
    sys.exit(main())