module pill(length, bevel) {
    hull() {
        translate([0, 0, (-length / 2) + bevel]) sphere(r = bevel);
        translate([0, 0, (length / 2) - bevel]) sphere(r = bevel);
    }
}

module box_face(length, width, wall_thickness, bevel) {
    center_width = width - bevel * 2;
    center_length = length - bevel * 2;

    hull() {
        translate([-center_width / 2, -center_length / 2, 0])
            pill(wall_thickness, bevel);
        translate([center_width / 2, -center_length / 2, 0])
            pill(wall_thickness, bevel);
        translate([center_width / 2, center_length / 2, 0])
            pill(wall_thickness, bevel);
        translate([-center_width / 2, center_length / 2, 0])
            pill(wall_thickness, bevel);
    }
}

module channel(length, width, height) {
    union() {
        translate([0, 0, -height / 2 + wall_thickness / 2])
            box_face(length, width, wall_thickness, bevel);
        translate([-width / 2 + wall_thickness / 2, 0, 0]) rotate([0, 90, 0])
            box_face(length, height, wall_thickness, bevel);
        translate([width / 2 - wall_thickness / 2, 0, 0]) rotate([0, 90, 0])
            box_face(length, height, wall_thickness, bevel);
    }
}

module box(length, width, height) {
    union() {
        channel(length, width, height);

        translate([0, -length / 2 + wall_thickness / 2, 0]) rotate([90, 0, 0])
            box_face(height, width, wall_thickness, bevel);

        translate([0, length / 2 - wall_thickness / 2, 0]) rotate([90, 0, 0])
            box_face(height, width, wall_thickness, bevel);
    }
}