# Try to set the locale from the system configuration if we did not inherit any. One case where this
# can happen is a linux with systemd where the user logs in via getty (e.g., on the system console).
# See https://github.com/fish-shell/fish-shell/issues/3092. This isn't actually our job, so there's
# a bunch of edge-cases we are unlikely to handle properly. If we get a value for _any_ language
# variable, we assume we've inherited something sensible so we skip this to allow the user to set it
# at runtime without mucking with config files.
#
# NOTE: This breaks the expectation that an empty LANG will be the same as LANG=POSIX, but an empty
# LANG seems more likely to be caused by a missing or misconfigured locale configuration.

function __fish_set_locale
    set -l LOCALE_VARS
    set LOCALE_VARS $LOCALE_VARS LANG LANGUAGE LC_CTYPE LC_NUMERIC LC_TIME LC_COLLATE
    set LOCALE_VARS $LOCALE_VARS LC_MONETARY LC_MESSAGES LC_PAPER LC_NAME LC_ADDRESS
    set LOCALE_VARS $LOCALE_VARS LC_TELEPHONE LC_MEASUREMENT LC_IDENTIFICATION

    # We check LC_ALL to figure out if we have a locale but we don't set it later. That is because
    # locale.conf doesn't allow it so we should not set it.
    for locale_var in $LOCALE_VARS LC_ALL
        if set -q $locale_var
            return 0
        end
    end

    # Unset all variables - they are empty anyway and this makes merging easier.
    for locale_var in $LOCALE_VARS
        set -e $locale_var
    end

    # Try to extract the locale from the kernel boot commandline. The splitting here is a bit weird,
    # but we operate under the assumption that the locale can't include whitespace. Other whitespace
    # shouldn't concern us, but a quoted "locale.LANG=SOMETHING" as a value to something else might.
    # Here the last definition of a variable takes precedence.
    if test -r /proc/cmdline
        for var in (string match -ra 'locale.[^=]+=\S+' < /proc/cmdline)
            set -l kv (string replace 'locale.' '' -- $var | string split '=')
            # Only set locale variables, not other stuff contained in these files - this also
            # automatically ignores comments.
            if contains -- $kv[1] $LOCALE_VARS
                and set -q kv[2]
                set -gx $kv[1] (string trim -c '\'"' -- $kv[2])
            end
        end
    end

    # Now read the config files we know are used by various OS distros.
    #
    # /etc/sysconfig/i18n is for old Red Hat derivatives (and possibly of no use anymore).
    #
    # /etc/env.d/02locale is from OpenRC.
    #
    # The rest are systemd inventions but also used elsewhere (e.g. Void Linux). systemd's
    # documentation is a bit unclear on this. We merge all the config files (and the commandline),
    # which seems to be what systemd itself does. (I.e. the value for a variable will be taken from
    # the highest-precedence source) We read the systemd files first since they are a newer
    # invention and therefore the rest are likely to be accumulated cruft.
    #
    # NOTE: Slackware puts the locale in /etc/profile.d/lang.sh, which we can't use because it's a
    # full POSIX-shell script.
    set -l user_cfg_dir (set -q XDG_CONFIG_HOME; and echo $XDG_CONFIG_HOME; or echo ~/.config)
    for f in $user_cfg_dir/locale.conf /etc/locale.conf /etc/env.d/02locale /etc/sysconfig/i18n
        if test -r $f
            while read -l kv
                set kv (string split '=' -- $kv)
                if contains -- $kv[1] $LOCALE_VARS
                    and set -q kv[2]
                    # Do not set already set variables again - this makes the merging happen.
                    if not set -q $kv[1]
                        set -gx $kv[1] (string trim -c '\'"' -- $kv[2])
                    end
                end
            end <$f
        end
    end

    # If we really cannot get anything, at least set character encoding to UTF-8.
    for locale_var in $LOCALE_VARS LC_ALL
        if set -q $locale_var
            return 0
        end
    end
    set -gx LC_CTYPE en_US.UTF-8
end