#!/usr/bin/env python3

import argparse
import os
import shutil
import subprocess
import sys
from pathlib import Path

SRC_DIR = Path('/usr/src')
BOOT_DIR = Path('/boot')


def update_config(old_dir: Path, new_dir: Path, make_cmd: list[str]) -> None:
	if old_dir == new_dir:
		return
	old_config = old_dir / '.config'
	new_config = new_dir / '.config'
	while new_config.is_file():
		response = input('New config present. Overwrite? [y/N]\n').strip().lower()
		if response == 'y':
			break
		elif response in ('', 'n'):
			return
		else:
			print('unrecognized option {}', response)
	print(f'Copying config from {old_config} to {new_config}')
	shutil.copy2(old_config, new_config)

	print(f'Setting symlink to {new_dir}')
	(SRC_DIR / 'linux').symlink_to(new_dir, target_is_directory=True)
	print('Migrating config options')
	migrate = [*make_cmd, '--directory', new_dir.as_posix(), 'oldconfig']
	subprocess.run(migrate, check=True)
	menuconfig = [*make_cmd, '--directory', new_dir.as_posix(), 'menuconfig']
	while True:
		subprocess.run(menuconfig, check=True)
		response = input('Stop editing? [Y/n]').strip().lower()
		if response in ('', 'y'):
			break
		elif response == 'n':
			continue
		else:
			print('unrecognized option {}', response)


def compile_kernel(new_dir: Path, make_cmd: list[str]) -> None:
	cc = [*make_cmd, '--directory', new_dir.as_posix()]
	subprocess.run(cc, check=True)


def install_kernel(kernel_dir: Path, make_cmd: list[str], kver: str) -> None:
	install_modules = [*make_cmd, '--directory', kernel_dir.as_posix(), 'modules_install']
	subprocess.run(install_modules, check=True)
	kver = kver[6:]  # drop "linux-" prefix
	# assumes proper dracut config in /etc, incl. signing keys
	dracut = ['dracut', f'--kver={kver}', '--force', '--no-machineid']
	res = subprocess.run(dracut, check=True)
	print(res)


def linux_folder(src_dir: Path, version: str) -> Path:
	revision = ''
	version = version.split('-')
	if len(version) > 1:
		revision = '-' + version[1]
	version = version[0]
	return src_dir / (f'linux-{version}-gentoo{revision}')


def update_kernel(args: argparse.Namespace) -> None:
	old_dir = linux_folder(SRC_DIR, args.old_version)
	new_dir = linux_folder(SRC_DIR, args.new_version)
	new_version = new_dir.name
	make_cmd = ['make', f'--jobs={len(os.sched_getaffinity(0))}']

	if args.llvm:
		# https://docs.kernel.org/kbuild/llvm.html
		make_cmd.extend(['LLVM=1'])
	none_selected = not any((args.config, args.compile, args.install))
	if none_selected:
		update_config(old_dir, new_dir, make_cmd)
		compile_kernel(new_dir, make_cmd)
		install_kernel(new_dir, make_cmd, new_version)
	if args.config:
		update_config(old_dir, new_dir, make_cmd)
	if args.compile:
		compile_kernel(new_dir, make_cmd)
	if args.install:
		install_kernel(new_dir, make_cmd, new_version)


def main() -> None:
	parser = argparse.ArgumentParser(description='Helper for manual kernel updates', usage=f'{sys.argv[0]}')
	parser.add_argument('--llvm', '-l', action='store_true', help='Use clang/llvm to compile kernel')
	parser.add_argument('--config', '-C', action='store_true', help='Migrate config from old kernel')
	parser.add_argument('--compile', '-c', action='store_true', help='Compile new kernel')
	parser.add_argument('--install', '-i', action='store_true', help='Install new kernel')
	parser.add_argument('old_version', help='Old kernel version (optional)', nargs='?', default=None)
	parser.add_argument('new_version', help='New kernel version (optional)', nargs='?', default=None)

	args = parser.parse_args()
	if args.old_version and not args.new_version:
		args.new_version = args.old_version
		args.old_version = None
	if not args.old_version:
		args.old_version = (SRC_DIR / 'linux').readlink().name.split('-')[1]
	if not args.new_version:
		subdirs = Path(SRC_DIR).glob('linux-*-gentoo*')  # too broad but good enough, blame fnmatch
		args.new_version = sorted(subdir.name for subdir in subdirs if subdir.is_dir())[-1].split('-')[1]
	update_kernel(args)


if __name__ == '__main__':
	main()