#!/usr/bin/env python3
"""Build the latest kernel but only if need be"""
import os
import shutil
import subprocess

EMERGE = os.environ["EMERGE"].split()
USEPKG = os.environ["USEPKG"].split()


def get_latest_available_kernel():
    kernel = os.environ["KERNEL"]
    package_name = "sys-kernel/{}".format(kernel)
    popen = subprocess.Popen(
        ["portageq", "best_visible", "/", package_name], stdout=subprocess.PIPE
    )
    cpv = popen.stdout.read().decode().strip()

    return cpv.rpartition("-")[2]


def get_current_kernel():
    """what kernel does /boot/vmlinuz point to"""
    vmlinuz = "/boot/vmlinuz"

    if not os.path.islink(vmlinuz):
        return None

    filename = os.path.basename(os.path.realpath(vmlinuz))
    assert filename.startswith("vmlinuz")
    part_after_vmlinuz = filename[8:]

    # may have "-gentoo" or whatever in the name
    version = part_after_vmlinuz.rpartition("-")[0]

    return version


def install_kernel_package_deps():
    kernel = os.environ["KERNEL"]
    package_name = "sys-kernel/{}".format(kernel)
    cmd = EMERGE + USEPKG + ["--onlydeps", "--oneshot", "--noreplace", package_name]

    subprocess.check_call(cmd)


def copy_kernel_config():
    filename = "/root/kernel.config"

    shutil.copy(filename, "/usr/src/linux/.config")


def build_kernel():
    makeopts = os.environ.get("MAKEOPTS", "")

    subprocess.check_call(
        ["make", "-C", "/usr/src/linux", "MAKEOPTS=" + makeopts, "oldconfig"]
    )
    subprocess.check_call(["make", "-C", "/usr/src/linux", "MAKEOPTS=" + makeopts])


def remove_old_kernels():
    kernel_files = ["vmlinuz-", "System.map-", "config-"]

    for filename in os.listdir("/boot"):
        for kernel_file in kernel_files:
            if filename.startswith(kernel_file):
                path = os.path.join("/boot", filename)
                os.unlink(path)

    if os.path.exists("/boot/vmlinuz"):
        os.unlink("/boot/vmlinuz")

    ##shutil.rmtree("/lib/modules", ignore_errors=True)


def install_kernel():
    makeopts = os.environ.get("MAKEOPTS", "")
    modules_install = False

    for line in open("/usr/src/linux/.config"):
        if "CONFIG_MODULES=y" in line:
            modules_install = True
            break

    if modules_install:
        subprocess.check_call([
            'make', '-C', '/usr/src/linux', 'MAKEOPTS=' + makeopts, 'install',
            'modules_install'
        ])
    else:
        subprocess.check_call([
            'make', '-C', '/usr/src/linux', 'MAKEOPTS=' + makeopts, 'install'
        ])

    # create the symlink.  /sbin/installkernel claims this is not used on
    # "modern" distributions and doesn't create it (unless it already
    # exists).  I still do this however.
    for filename in os.listdir("/boot"):
        if filename.startswith("vmlinuz-"):
            if os.path.lexists("/boot/vmlinuz"):
                os.unlink("/boot/vmlinuz")
            os.symlink(filename, "/boot/vmlinuz")
            break


def uninstall_kernel_package_deps():
    subprocess.check_call(EMERGE + USEPKG + ["--depclean", "--with-bdeps=n"])


def backup_kernel_config():
    shutil.copy("/usr/src/linux/.config", "/root/kernel.config")


def main():
    latest_kernel = get_latest_available_kernel()
    current_kernel = get_current_kernel()

    if current_kernel == latest_kernel:
        return

    install_kernel_package_deps()
    ##copy_kernel_config()
    build_kernel()
    remove_old_kernels()
    install_kernel()
    backup_kernel_config()

    uninstall_kernel_package_deps()


main()