$fs = 0.1;
$fa = 0.1;


// A5 = 148
page_size_width = 210; // [105, 148, 210]
page_size_height = sqrt(2)*page_size_width;

notebook_thickness = 3;
hinge_radius = 10;
hinge_hole_radius = 6;
number_of_hinge_segments = 5;
hinge_gap = 2;
notebook_open_angle = 0; // [0:180]
// notebook_open_angle = $t*180;

cover_material_colour = [128/255, 165/255, 0];
addtional_cover_material_colour = [255/255, 165/255, 0];
hinge_colour_even = [255/255, 0, 0];
hinge_colour_odd = [255/255, 0, 1];

hinge_segments_length = (page_size_height - hinge_gap * (number_of_hinge_segments - 1)) / number_of_hinge_segments;
hinge_offset = [-page_size_width/2-hinge_radius, page_size_height / 2 - hinge_segments_length / 2, hinge_radius - notebook_thickness/2];

function ALTERNATE(i, thing_1, thing_2) = (thing_1*(i % 2) + thing_2*(-(i % 2)+1));

echo(str("page size = ", page_size_height, "x", page_size_width, "mm"));


translate([page_size_width/2+hinge_radius, 0, -hinge_radius+notebook_thickness/2])
union(){
    color(cover_material_colour) 
    cube(size=[page_size_width, page_size_height, notebook_thickness], center=true);

    color(addtional_cover_material_colour)
    translate([-page_size_width/2 - hinge_radius/2 , 0, 0])        
    cube(size=[hinge_radius, page_size_height, notebook_thickness], center=true);

    translate(hinge_offset){
        for (i=[1:2:number_of_hinge_segments - 1]) {
            translate([0, -i*(hinge_segments_length+hinge_gap), 0]) 
            rotate([90, 0, 0])
            color(hinge_colour_odd) 
            difference() {
                cylinder(r=hinge_radius, h=hinge_segments_length, center=true);
                cylinder(r=hinge_hole_radius, h=hinge_segments_length*2, center=true);
            }
        }
    }
}

rotate([0, -notebook_open_angle, 0])
translate([page_size_width/2+hinge_radius, 0, -hinge_radius+notebook_thickness/2])
union(){
    translate([0, 0, hinge_radius*2 - notebook_thickness]){
        color(cover_material_colour) 
        cube(size=[page_size_width, page_size_height, notebook_thickness], center=true);

        color(addtional_cover_material_colour)
        translate([-page_size_width/2 - hinge_radius/2 , 0, 0])        
        cube(size=[hinge_radius, page_size_height, notebook_thickness], center=true);
    }

    translate(hinge_offset){
        for (i=[0:2:number_of_hinge_segments - 1]) {
            translate([0, -i*(hinge_segments_length+hinge_gap), 0]) 
            rotate([90, 0, 0])
            color(hinge_colour_even) 

            difference() {
                cylinder(r=hinge_radius, h=hinge_segments_length, center=true);
                cylinder(r=hinge_hole_radius, h=hinge_segments_length*2, center=true);
            }
        }
    }

}