githook_for_black

#! /usr/bin/env python

import subprocess
from datetime import datetime
from dateutil import parser
import os.path as op
import pytz

FORMATTER_ADOPTION_DATE = pytz.UTC.localize(datetime(2018, 7, 1))

EXECUTABLES = (
    ("black", [],),
)


def git(args):
    args = ["git"] + args
    git_cmd = subprocess.Popen(args, stdout=subprocess.PIPE)
    details = git_cmd.stdout.read()
    details = details.decode("utf-8").strip()
    return details


def is_python(filename):
    return op.splitext(filename)[1] == ".py"


def get_modified_files():
    files = git(["diff-index", "-z", "--cached", "HEAD", "--name-only"])
    for f in files.rstrip("\0").split("\0"):
        yield f


def get_creation_date_for(filename):
    datestr = git(
        ["log", "--diff-filter=A", "--follow", "--format=%aD", "-1", "--", filename]
    )
    return parser.parse(datestr).replace(tzinfo=pytz.UTC)


def process(f):
    for binary, args in EXECUTABLES:
        subprocess.call([binary, f, *args])


def should_process(filename):
    dt = get_creation_date_for(f)
    return dt > FORMATTER_ADOPTION_DATE and is_python(filename)


def main():
    for f in get_modified_files():
        if should_process(f):
            process(f)


if __name__ == "__main__":
    main()