#!/usr/bin/env python

import argparse
import magic
import os
import shutil
import subprocess
import sys

from pathlib import Path
from typing import Any, Dict, List, Tuple

BOOT_FILES = {
	'config': Path('config-gentoo'),
	'initramfs': Path('initramfs-gentoo.img'),
	'kernel': Path('vmlinuz-gentoo'),
	'system_map': Path('System.map-gentoo'),
}

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


def backup_kernel(boot_dir: Path, files: Dict[str, Path]) -> None:
	for f in files.values():
		src = boot_dir/f
		dst = boot_dir/(f.name + '.old')
		print(f'Backing-up {src} to {dst}')
		shutil.copy2(src, dst)


def rollback_impl(boot_dir: Path, files: Dict[str, Path]) -> None:
	for f in files.values():
		src = boot_dir/(f.name + '.old')
		dst = boot_dir/f
		print(f'Restoring {src} to {dst}')
		shutil.copy2(src, dst)


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]').strip().lower()
		if response == 'y':
			break
		elif response == '' or response == '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}')
	subprocess.run(['eselect', 'kernel', 'set', new_dir.name])
	print(f'Migrating config options')
	migrate = make_cmd + ['-C', new_dir.as_posix(), 'oldconfig']
	subprocess.run(migrate)
	menuconfig = make_cmd + ['-C', new_dir.as_posix(), 'menuconfig']
	while True:
		subprocess.run(menuconfig)
		response = input('Stop editing? [Y/n]').strip().lower()
		if response == '' or response == '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 + ['-C', new_dir.as_posix()]
	subprocess.run(cc)


def install_kernel(kernel_dir: Path, boot_dir: Path, boot_files: Dict[str, Path], make_cmd: List[str]) -> None:
	make_files = {
		'config': Path('.config'),
		'system_map': Path('System.map'),
		'kernel': Path('arch/x86/boot/bzImage')
	}

	config = (kernel_dir/make_files['config']).as_posix()
	# subprocess.run(make_cmd.extend(['-C', kernel_dir, 'install'])) # this would create unwanted entries
	common_keys = make_files.keys() & boot_files.keys()
	for key in common_keys:
		src = kernel_dir/make_files[key]
		dst = boot_dir/boot_files[key]
		print(f'Installing {src} to {dst}')
		shutil.copy2(src, dst)

	install_modules = make_cmd + ['-C', kernel_dir.as_posix(), 'modules_install']
	subprocess.run(install_modules)

	genkernel = ['genkernel', f'--kernel-config={config}', '--microcode', 'initramfs']
	subprocess.run(genkernel)


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 module_check(boot_dir: Path, boot_files: Dict[str, Path]) -> Tuple[bool, Path]:
	kernel_name = boot_files['kernel'].name + '.old'
	old_kernel: Path = boot_dir/kernel_name
	magic_list = magic.from_file(old_kernel).split()
	version = Path(magic_list[magic_list.index('version') + 1])
	modules = Path('/lib/modules')/version
	if not modules.exists():
		return (False, version)
	return (True, version)

def rollback_kernel(boot_dir: Path, boot_files: Dict[str, Path], _args: Any) -> None:
	check = module_check(boot_dir, boot_files)
	if not check[0]:
		err = f'Module directory not found for {check[1]}.\nRefusing to proceed.'
		raise RuntimeError(err)
	rollback_impl(boot_dir, boot_files)

def update_kernel(boot_dir: Path, boot_files: Dict[str, Path], args: Any) -> 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'-j{len(os.sched_getaffinity(0))}']
	clang_env = ['CC=clang', 'LD=ld.lld', 'LLVM=1', 'LLVM_IAS=1']

	if args.llvm:
		make_cmd.extend(clang_env)
	none_selected = not (args.backup or args.config or args.compile or args.install or args.rollback)
	if none_selected:
		backup_kernel(BOOT_DIR, BOOT_FILES)
		update_config(old_dir, new_dir, make_cmd)
		compile_kernel(new_dir, make_cmd)
		install_kernel(new_dir, BOOT_DIR, BOOT_FILES, make_cmd)
	if args.backup:
		backup_kernel(BOOT_DIR, BOOT_FILES)
	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, BOOT_DIR, BOOT_FILES, make_cmd)

def main() -> None:
	parser = argparse.ArgumentParser(description='Convenience for manual kernel updates')
	subparsers = parser.add_subparsers()

	rollback = subparsers.add_parser('rollback')
	rollback.set_defaults(func=rollback_kernel)

	update = subparsers.add_parser('update',
		usage=f'{sys.argv[0]} update 5.15.12 5.16.3',
	)
	update.add_argument(
		'--llvm', '-l', action='store_true',
		help="Use clang/llvm to compile kernel")
	update.add_argument(
		'--backup', '-b', action='store_true',
		help="Backup old kernel files as .old")
	update.add_argument(
		'--rollback', '-r', action='store_true',
		help='Restore .old kernel files as main boot choice')
	update.add_argument(
		'--config', '-C', action='store_true',
		help='Migrate config from old kernel')
	update.add_argument(
		'--compile', '-c', action='store_true',
		help='Compile new kernel')
	update.add_argument(
		'--install', '-i', action='store_true',
		help='Install new kernel')
	update.add_argument('old_version', help='Old kernel version')
	update.add_argument('new_version', help='New kernel version')
	update.set_defaults(func=update_kernel)

	args = parser.parse_args()
	args.func(BOOT_DIR, BOOT_FILES, args)


if __name__ == "__main__":
	main()