#!/usr/bin/env python3
"""
Given a hash checksum file, validate it's checksums

SPDX-License-Identifier: MIT
"""

import argparse
import hashlib
import os
import signal
import sys

__version__ = "0.0.1"


def parse_args():
    """Argument parsing routine"""
    parser = argparse.ArgumentParser(description="hashcheck")
    parser.add_argument(
        "--version", action="version", version=__version__, help="Display the version"
    )
    parser.add_argument(
        "-c", "--checksum", required=True, dest="checksum", help="Checksum file to read"
    )
    parser.add_argument(
        "-t",
        "--type",
        required=False,
        dest="type",
        default="auto",
        choices=["auto", "md5", "sha1", "sha224", "sha256", "sha384", "sha512"],
        help=(
            "Hash type: auto (default), md5, sha1, sha224, " "sha256, sha384, sha512"
        ),
    )
    return parser.parse_args()


def sigbye_handler(signal, frame):
    """Exit function triggered by caught signals"""
    sys.exit(0)


def guess_type(hstring):
    """Given an input string, guess the crypto hash based on length"""
    hexsize = {
        32: "md5",
        40: "sha1",
        56: "sha224",
        64: "sha256",
        96: "sha384",
        128: "sha512",
    }
    return hexsize.get(len(hstring.strip()), "NaN")


if __name__ == "__main__":
    """Main entry point for hashcheck"""
    # register a clean shutdown for the usual signals
    signal.signal(signal.SIGINT, sigbye_handler)
    signal.signal(signal.SIGQUIT, sigbye_handler)
    signal.signal(signal.SIGTERM, sigbye_handler)

    # parse cmdline arguments
    args = parse_args()

    # for each line in the checksum, calculate the hash of the file
    # and compare it against the digest it's supposed to be
    try:
        with open(args.checksum, "r") as csum:
            # a hash file 99.999% of the time has a relative path of the
            # file, so we'll attempt to cwd() there to help the user out
            startdir = os.getcwd()
            if os.path.dirname(args.checksum):
                # if already in the directory, dirname() returns '' which is
                # an exception result when used with chdir()
                os.chdir(os.path.dirname(args.checksum))

            # read our checksum and do the needful
            for line in csum:
                line = line.rstrip("\n")

                # hash checksum = "abcdef  file.name" where the second
                # "space" is actually one of: *, ?, ^, or ' ' (space)
                hparts = line.split(" ", 1)
                if len(hparts) != 2:
                    print("Invalid line, skipping.")
                    continue
                # hparts[0] = hash, hparts[1] = 1char type + name

                # in auto mode, we can try and guess the type of hash used
                # by the checksum length, which allows for mixed types of
                # hashes in one file; otherwise, we have to use what was
                # indicated on the cli
                htype = args.type
                if htype == "auto":
                    htype = guess_type(hparts[0])
                    if htype == "NaN":
                        print("Unable to guess hash type: {}".format(line))
                        continue

                # attempt to instantiate the hashlib.foo()
                try:
                    hasher = hashlib.new(htype)
                except AttributeError as error:
                    print("Python hashlib does not support hash: {}".format(args.type))
                    continue

                # calculate the hash of the file and compare
                try:
                    # could be hashin a 4G iso file, calculate in chunks
                    with open(hparts[1][1:], "rb") as hfile:
                        for chunk in iter(lambda: hfile.read(4096), b""):
                            hasher.update(chunk)
                    # simply compare our two values
                    if hasher.hexdigest() == hparts[0]:
                        print("Pass: {}".format(line))
                    else:
                        print("Fail: {}".format(line))
                except (IOError, OSError) as error:
                    # py2 = IOError, py3 = FileNotFound
                    print("Unable to open file: {}".format(hparts[1][1:]))
                    continue

            # usually python exits and leaves the user where they began,
            # trust but verify - doesn't hurt to make sure
            os.chdir(startdir)

    except (IOError, OSError) as error:
        # py2 = IOError, py3 = FileNotFound
        print("Unable to open checksum file: {}".format(args.checksum))
        sys.exit(1)

    sys.exit(0)