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(dimensions, bevel = 0) {
    x = dimensions[0];
    y = dimensions[1];
    z = dimensions[2];

    if (bevel > 0) {
        translate([0, 0, z / 2])
        hull() {
            pill(z, bevel);
            translate([x, 0, 0])
                pill(z, bevel);
            translate([x, y, 0])
                pill(z, bevel);
            translate([0, y, 0])
                pill(z, bevel);
        }
    } else {
        cube(dimensions);
    }
}

module channel(length, width, height, bevel) {
    union() {
        box_face([length, width, wall_thickness], bevel);

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

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

module box(length, width, height, bevel = 0) {
    union() {
        channel(length, width, height, bevel);

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