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                    i_am_root_or_die
                   );
our %EXPORT_TAGS = ( ALL => [ @EXPORT_OK ] );

                 ####################################
                 #            SUBROUTINES           #
                 ####################################

sub have_prerequisites {

    # Return 1 if we are running on a Linux OS and have sudo, OpenSSH, and
    # btrfs-progs installed.

    return 0 unless $^O =~ /linux/i;
    return 0 unless 0 == system('which btrfs >/dev/null 2>&1');
    return 0 unless `ssh -V 2>&1` =~ /^OpenSSH/;
    return 0 unless 0 == system('which sudo >/dev/null 2>&1');

    return 1;
}

sub have_prerequisites_or_die {

    # Like &have_prerequisites except die if the prerequisites are not met.

    unless ($^O =~ /linux/i) {
        die "yabsm: internal error: not a Linux OS, this is a '$^O' OS\n";
    }

    unless (0 == system('which btrfs >/dev/null 2>&1')) {
        die 'yabsm: internal error: btrfs-progs not installed'."\n";
    }

    unless (`ssh -V 2>&1` =~ /^OpenSSH/) {
        die 'yabsm: internal error: OpenSSH not installed'."\n";
    }

    unless (0 == system('which sudo >/dev/null 2>&1')) {
        die 'yabsm: internal error: sudo not installed'."\n";
    }

    return 1;
}

sub arg_count_or_die {

    # Carp::Confess unless $num_args is in range $lower-$upper. If $lower equals
    # '_' then it is assumed to be 0 and if $upper equals '_' it is assumed to
    # be infinity.

    my $lower    = shift;
    my $upper    = shift;
    my $num_args = scalar @_;

    $lower = 0 if $lower eq '_';

    my $lower_ok = $lower <= $num_args;
    my $upper_ok = $upper eq '_' ? 1 : $upper >= $num_args;

    unless ($lower_ok && $upper_ok) {
        my $caller    = ( caller(1) )[3];
        my $error_msg = "yabsm: internal error: called '$caller' with $num_args args but it expects";
        my $range_msg;
        if    ($upper eq '_')    { $range_msg = "at least $lower args" }
        elsif ($lower == $upper) { $range_msg = "$lower args"          }
        else                     { $range_msg = "$lower-$upper args"   }
        confess("$error_msg $range_msg");
    }

    return 1;
}

sub with_error_catch_log {

    # Call $sub with @args within a Feature::Compat::Try try/catch block to catch
    # any exception and log it to /var/log/yabsm instead of killing the program.

    my $sub  = shift;
    my @args = @_;

    try {
        $sub->(@args);
    }
    catch ($e) {
        if (-f '/var/log/yabsm' && open(my $fh, '>>', '/var/log/yabsm')) {
            $e =~ s/^\s+|\s+$//g;
            my $t = localtime();
            my ($yr, $mon, $day, $hr, $min) = map { sprintf '%02d', $_ } $t->year, $t->mon, $t->mday, $t->hour, $t->min;
            say $fh "[${yr}_${mon}_${day}_$hr:$min]: $e";
            close $fh;
        }
    }
}

sub have_sudo_access_to_btrfs {

    # Return 1 if we can run 'btrfs' with 'sudo -n' and return 0 otherwise.

    arg_count_or_die(0, 0, @_);

    return 0+(0 == system('sudo -n btrfs --help >/dev/null 2>&1'));
}

sub have_sudo_access_to_btrfs_or_die {

    # Wrapper around have_sudo_access_to_btrfs() that Carp::Confess's if it
    # returns false.

    arg_count_or_die(0, 0, @_);

    my $username = getpwuid $<;

    have_sudo_access_to_btrfs() ? return 1 : die("yabsm: internal error: no sudo access rights to 'btrfs' while running as user '$username'");
}

sub is_btrfs_dir {

    # Return 1 if $dir is a directory residing on a btrfs subvolume
    # and return 0 otherwise.

    arg_count_or_die(1, 1, @_);