#! /usr/bin/python3
# amend HEAD commit to contain acab in its hash, it does so by repeatedly
# amending the commit with a new date.

import argparse
import hashlib
import os
import subprocess
import sys
import time

parser = argparse.ArgumentParser()
parser.add_argument('--start', type=str, default='commit', help='now or commit')
parser.add_argument('--prefix', action='store_true')
parser.add_argument('--suffix', action='store_true')
parser.add_argument('-q', '--quiet', action='store_true')
args = parser.parse_args()


def amend_commit(start_timestamp):
    t0 = time.time()
    counter = 0
    cat_file = subprocess.run(['git', 'cat-file', 'commit', 'HEAD'], capture_output=True).stdout
    cat_file_lines = cat_file.splitlines()
    cat_file_lines[2] = cat_file_lines[2].replace(cat_file_lines[2].rsplit(b' ', 2)[1], b'$AUTHOR__$')
    cat_file_lines[3] = cat_file_lines[3].replace(cat_file_lines[3].rsplit(b' ', 2)[1], b'$COMMITER$')
    hashed_bytes_template = b'commit %s\0%s\n' % (
        str(len(b'\n'.join(cat_file_lines)) + 1).encode(),
        b'\n'.join(cat_file_lines),
    )
    authored_timestamp = start_timestamp
    base_env = os.environ
    last_print = 0
    while True:
        authored_timestamp -= 1
        for committed_timestamp in range(start_timestamp, authored_timestamp, -1):
            counter += 1
            if not args.quiet and time.time() - last_print > 0.05:
                last_print = time.time()
                print(
                    '%5d - %s - %s - [%s:%02d]'
                    % (
                        counter,
                        time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(authored_timestamp)),
                        time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(committed_timestamp)),
                        int((time.time() - t0) // 60),
                        int((time.time() - t0) % 60),
                    ),
                    end='\r',
                )

            hashed_bytes = hashed_bytes_template.replace(
                b'$AUTHOR__$', str(authored_timestamp).encode()
            ).replace(b'$COMMITER$', str(committed_timestamp).encode())
            new_hash = hashlib.sha1(hashed_bytes).hexdigest()
            if args.prefix and not new_hash.startswith('acab'):
                continue
            if args.suffix and not new_hash.endswith('acab'):
                continue
            if 'acab' not in new_hash:
                continue
            base_env['GIT_COMMITTER_DATE'] = time.strftime(
                '%Y-%m-%d %H:%M:%S', time.localtime(committed_timestamp)
            )
            subprocess.run(
                [
                    'git',
                    'commit',
                    '--no-verify',
                    '--amend',
                    '--no-edit',
                    '--date=%s' % time.strftime('%Y-%m-%d %H:%M:%S', time.localtime(authored_timestamp)),
                ],
                capture_output=True,
                env=base_env,
            )
            return


if args.start == 'commit':
    p = subprocess.run(['git', 'show', '--format=format:%at'], capture_output=True)
    start_timestamp = int(p.stdout[: p.stdout.index(b'\n')])
elif args.start == 'now':
    start_timestamp = int(time.time())
else:
    sys.stderr('unknown value for --start')
    sys.exit(1)

amend_commit(start_timestamp)

if not args.quiet:
    p = subprocess.run(['git', 'rev-parse', 'HEAD'], capture_output=True)
    print('\ngot %s 🔥🚓' % p.stdout.decode().strip())