sub inverse_color {
    my $color = shift;
    die "Missing argument to inverse_color()" unless $color;

    state $color_names;
    if ( not $color_names ) {
	#set_default_namespace("www");
	$color_names = available_names();
    }
    $color =~ s/^\s+//;
    $color =~ s/\s+$//;
    
    if ( $color =~ /^#[[:xdigit:]]{3}$/ ) {
	$color =~ s/#//;
	my $n = hex $color;
	my $i = 0xFFF - $n;
	my $inverse = sprintf "#%03x", $i;
	return $inverse;	    	    
    } elsif ( $color =~ /^#[[:xdigit:]]{6}$/ ) {
	$color =~ s/#//;
	my $n = hex $color;
	my $i = 0xFFFFFF - $n;
	my $inverse = sprintf "#%06x", $i;
	return $inverse;
    } elsif ( $color =~ /rgb \s* \( \s* ([0-9]+) \s* , \s* ([0-9]+) , \s* ([0-9]+) \s* \) /x ) {
	my ($r, $g, $b) = ($1, $2, $3);
	my $n = $r * 65536 + $g * 256 + $b;
	printf "converted %s to %06x\n", $color, $n    if $verbose;
	my $i = 0xFFFFFF - $n;
	my $inverse = sprintf "#%06x", $i;
	return $inverse;	    	    
    } elsif ( $color =~ /rgba \s* \( \s* ([0-9]+) \s* , \s* ([0-9]+) , \s* ([0-9]+) \s* , \s* ([0-9.]+) \s* \) /x ) {
	my ($r, $g, $b, $alpha) = ($1, $2, $3, $4);
	my $inverse = sprintf "rgba( %d, %d, %d, %0.2f )", 255 - $r, 255 - $g, 255 - $b, 1 - $alpha;
	return $inverse;
    } elsif ( $color =~ /hsl \s* \( \s*  ([0-9]+) \s* , \s* ([0-9]+)% , \s* ([0-9]+)% \s* \) /x ) {
	my ( $hue, $saturation, $lightness ) = ($1, $2, $3);
	my $hue2 = ($hue + 180) % 360;
	my $sat2 = 100 - $saturation;
	my $light2 = 100 - $lightness;
	my $inverse = sprintf "hsl( %d, %d%%, %d%% )", $hue2, $sat2, $light2;
	return $inverse;
    } elsif ( $color =~ /hsla \s* \( \s*  ([0-9]+) \s* , \s* ([0-9]+)% , \s* ([0-9]+)% \s* , \s* ([0-9.]+) \s* \) /x ) {
	my ( $hue, $saturation, $lightness, $alpha ) = ($1, $2, $3, $4);
	my $hue2 = ($hue + 180) % 360;
	my $sat2 = 100 - $saturation;
	my $light2 = 100 - $lightness;
	my $alpha2 = 1 - $alpha;
	my $inverse = sprintf "hsl( %d, %d%%, %d%%, %0.2f )", $hue2, $sat2, $light2, $alpha2;
	return $inverse;
    } elsif ( $color =~ /currentcolor/i ) {
	warn "Should have removed currentcolor in fix_css_colors()";
    } elsif ( $color =~ /inherit/i ) {
        return "inherit";
    } elsif ( $color_names->{ "www:". $color} or $color_names->{ $color} ) {
	my $hexcolor = name2rgb( $color );
	if ( not $hexcolor ) {
	    $hexcolor = name2rgb( "www:" . $color );
	    if ( not $hexcolor ) {
		die "Can't resolve color name $color";
	    }
	}
	    
	$hexcolor =~ s/#//;
	my $i = 0xFFFFFF - hex($hexcolor);
	my $inverse = sprintf "#%06x", $i;
	return $inverse;
    }  else  {
	die "Color format not implemented: $color";
    }
}


sub fix_css_colors {
    my ($csstext, $css_fn, $epub_fn) = @_;
    return if not $csstext;
    my $errors = 0;
    my $corrections = 0;
    my $printed_filename = 0;

    say "Checking $epub_fn:$css_fn for bad colors\n" if $verbose;
    
    # this might be a good use of negative lookbehind?
    my @css_blocks = split /(})/, $csstext;
    for my $block ( @css_blocks ) {
	if ( $block =~ m/color: \s* ( [^;]+ ) \s* (?:;|$) /x ) {
	    my $fgcolor = $1;
	    print "found color: $fgcolor\n" if $verbose;

	    if ( $fgcolor =~ m/currentcolor/i ) {
		$block =~ s/(color: \s* currentcolor \s* ;? \s* ) \n* //xi;
		print "Stripping out $1 as it is a pleonasm\n"  if $verbose;
		$corrections++;
		next;
	    }
	    
	    if ( $block !~ m/background-color:/ ) {
		my $bgcolor = inverse_color( $fgcolor );
		$block =~ s/(color: \s* [^;}]+ \s* (?:;|$) )/background-color: $bgcolor;\n$1/x;
		print "corrected block:\n$block\n}\n" if $verbose;
   	        $corrections++;
	    }
	}
    }

    if ( $corrections ) {
	my $new_css_text = join "", @css_blocks;
	return $new_css_text;
    } else {
	return undef;
    }    
}