module side_piece(
    arch_width,
    arch_base,
    arch_angle,
    pillar_height
) {

    module arch(
        arch_width,
        arch_base,
        arch_angle,
        pillar_height
    ) {
        
        arch_radius = arch_width / (2 - 2 * cos(arch_angle) );

        module basic_shape() {
            union(){
                translate( [0, -arch_base / 2] )
                square( arch_base );
                
                translate( [arch_base, 0] )
                circle( d = arch_base * 3 / 5, $fn = 18);
            }
        }

        translate( [0, 0, pillar_height] )
        for (m = [0:1])
        mirror( [m, 0, 0] )
        difference(){
            translate( [cos(arch_angle) * arch_radius, 0, 0] )
            union(){
                rotate( [-90, 0, 0])
                rotate_extrude( angle = arch_angle, $fn = 100 )
                translate( [-arch_radius, 0] )
                basic_shape();

                translate( [0, 0, -pillar_height] )
                linear_extrude( height = pillar_height )
                translate( [-arch_radius, 0] )
                basic_shape();
            }   
           
            translate([
                0, 
                -arch_base, 
                sin(arch_angle) * arch_radius - 5 * arch_base
            ])
            cube( 5 * arch_base);
        }
    }

    // main arch
    arch(
        arch_width,
        arch_base,
        arch_angle,
        pillar_height
    );

    width_factor = 2 / 3;
    base_factor  = 3 / 5;

    // inner arches
    displacement_x1 = 
        (arch_width -
         arch_width * width_factor - 
         arch_base / 2) / 2;

    for(v = [-1:2:1])
    translate( [displacement_x1*v, 0, 0] )
    arch(
        arch_width * width_factor,
        arch_base * base_factor,
        arch_angle * 0.82,
        pillar_height
    );

    // inner side arches
    displacement_x2 = 
        (arch_width - 
         arch_width * (1 - width_factor) - 
         arch_base / 2) / 2;

    for(v = [-1:2:1])
    translate( [displacement_x2*v, 0, 0] )
    arch(
        arch_width * (1 - width_factor),
        arch_base * base_factor,
        arch_angle * 0.58,
        pillar_height
    );

}



arch_width    = 60;
arch_base     = 5;
arch_angle    = 50;
pillar_height = 75;

bottom_thickness = 1;
border_height    = 5;
border_thickness = 3;

cylinder_dm     = 50;
cylinder_height = 100;
cylinder_walls  = 2;

hexagonal_height = arch_width / ( 2 * tan(30) );
hexagonal_radius = arch_width / ( 2 * sin(30) );

for (r = [0:60:359])
rotate( [0, 0, r] )
translate( [0, hexagonal_height - arch_base / 2, 0] )
union() {
    side_piece(
        arch_width,
        arch_base,
        arch_angle,
        pillar_height
    );
    
    // bottom plate
    translate( [-arch_width / 2, -hexagonal_height, 0] )
    cube( [arch_width, hexagonal_height, bottom_thickness] );

    // border
    translate( [-arch_width / 2, -border_thickness / 2, 0] )
    cube( [arch_width, border_thickness, border_height] );    
}

// center cylinder
difference() {
    cylinder( d = cylinder_dm, h = cylinder_height ,$fn = 50);
    
    translate( [0, 0, bottom_thickness] )
    cylinder( 
        d = cylinder_dm - 2 * cylinder_walls, 
        h = cylinder_height ,
        $fn = 50
    );
}

// inner walls
for (r = [0:60:359])
rotate( [0, 0, r] )
translate( [cylinder_dm/2 - 0.1, -cylinder_walls / 2, 0] )
cube([
    hexagonal_radius - cylinder_dm/2 - arch_base / 2, 
    cylinder_walls,
    pillar_height
]);