# Copyright 2014-2015 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
"""
Methods to check whether Portage is going to write to read-only filesystems.
Since the methods are not portable across different OSes, each OS needs its
own method. To expand RO checking for different OSes, add a method which
accepts a list of directories and returns a list of mounts which need to be
remounted RW, then add "elif ostype == (the ostype value for your OS)" to
get_ro_checker().
"""
import logging
import os

from portage import _encodings
from portage.util import writemsg_level
from portage.localization import _
from portage.data import ostype


def get_ro_checker():
    """
    Uses the system type to find an appropriate method for testing whether Portage
    is going to write to any read-only filesystems.

    @return:
    1. A method for testing for RO filesystems appropriate to the current system.
    """
    return _CHECKERS.get(ostype, empty_ro_checker)


def linux_ro_checker(dir_list):
    """
    Use /proc/self/mountinfo to check that no directories installed by the
    ebuild are set to be installed to a read-only filesystem.

    @param dir_list: A list of directories installed by the ebuild.
    @type dir_list: List
    @return:
    1. A list of filesystems which are both set to be written to and are mounted
    read-only, may be empty.
    """
    ro_filesystems = set()
    invalids = []

    try:
        with open(
            "/proc/self/mountinfo",
            encoding=_encodings["content"],
            errors="replace",
            newline="\n",
        ) as f:
            for line in f:
                # we're interested in dir and both attr fields which always
                # start with either 'ro' or 'rw'
                # example line:
                # 14 1 8:3 / / rw,noatime - ext3 /dev/root rw,errors=continue,commit=5,barrier=1,data=writeback
                #       _dir ^ ^ attr1                     ^ attr2
                # there can be a variable number of fields
                # to the left of the ' - ', after the attr's, so split it there
                mount = line.split(" - ", 1)
                try:
                    _dir, attr1 = mount[0].split(" ")[4:6]
                except ValueError:
                    # If it raises ValueError we can simply ignore the line.
                    invalids.append(line)
                    continue
                # check for situation with invalid entries for /home and /root in /proc/self/mountinfo
                # root path is missing sometimes on WSL
                # for example: 16 1 0:16 / /root rw,noatime - lxfs  rw
                if len(mount) > 1:
                    try:
                        attr2 = mount[1].split(" ")[2]
                    except IndexError:
                        try:
                            attr2 = mount[1].split(" ")[1]
                        except IndexError:
                            invalids.append(line)
                            continue
                else:
                    invalids.append(line)
                    continue
                if attr1.startswith("ro") or attr2.startswith("ro"):
                    ro_filesystems.add(_dir)

    # If /proc/self/mountinfo can't be read, assume that there are no RO
    # filesystems and return.
    except OSError:
        writemsg_level(
            _("!!! /proc/self/mountinfo cannot be read"),
            level=logging.WARNING,
            noiselevel=-1,
        )
        return []

    for line in invalids:
        writemsg_level(
            _("!!! /proc/self/mountinfo contains unrecognized line: %s\n")
            % line.rstrip(),
            level=logging.WARNING,
            noiselevel=-1,
        )

    ro_devs = {}
    for x in ro_filesystems:
        try:
            ro_devs[os.stat(x).st_dev] = x
        except OSError:
            pass

    ro_filesystems.clear()
    for x in set(dir_list):
        try:
            dev = os.stat(x).st_dev
        except OSError:
            pass
        else:
            try:
                ro_filesystems.add(ro_devs[dev])
            except KeyError:
                pass

    return ro_filesystems


def empty_ro_checker(dir_list):
    """
    Always returns [], this is the fallback function if the system does not have
    an ro_checker method defined.
    """
    return []


# _CHECKERS is a map from ostype output to the appropriate function to return
# in get_ro_checker.
_CHECKERS = {
    "Linux": linux_ro_checker,
}