$fn = 64;

// --- Parameters ---
hook_width = 15;        // Width of the hook
thickness = 6;          // Thickness of the hook (sturdy for 1.5kg capacity)
inner_radius = 12;      // Inner radius of the hook curve
back_height = 45;       // Height of the mounting backplate
upturn_length = 15;     // Length of the 30-degree upturn
hole_diameter = 4.5;    // Screw hole diameter (M4 clearance)
head_diameter = 8.5;    // Screw countersink head diameter

// Derived parameter
outer_radius = inner_radius + thickness;

module j_hook_2d() {
    union() {
        // Vertical backplate
        translate([-outer_radius, -0.01])
            square([thickness, back_height + 0.01]);
            
        // Rounded top of the backplate
        translate([-outer_radius + thickness/2, back_height])
            circle(d=thickness);

        // Bottom curved section (180 to 300 degrees)
        difference() {
            circle(r=outer_radius);
            circle(r=inner_radius);
            
            // Remove the top half (y > 0)
            translate([-(outer_radius + 1), 0])
                square([(outer_radius + 1)*2, outer_radius + 1]);
                
            // Remove the section from 300 to 360 degrees
            // A square rotated by 300 (-60) degrees covers exactly 300 to 30 degrees
            rotate(300)
                square(outer_radius + 1);
        }

        // 30-degree upturn lip
        rotate(300) {
            // Straight tangent extension
            translate([inner_radius, -0.01])
                square([thickness, upturn_length + 0.01]);
                
            // Rounded tip of the upturn
            translate([inner_radius + thickness/2, upturn_length])
                circle(d=thickness);
        }
    }
}

// Extrude the 2D profile and cut mounting holes
difference() {
    // Main body
    linear_extrude(height=hook_width)
        j_hook_2d();

    // Countersunk mounting holes
    for (y_pos = [10, back_height - 5]) {
        translate([-outer_radius + thickness + 0.1, y_pos, hook_width/2])
            rotate([0, -90, 0]) {
                // Screw shaft
                cylinder(h=thickness + 0.2, d=hole_diameter);
                // Screw countersink
                cylinder(h=2.5, d1=head_diameter, d2=hole_diameter);
            }
    }
}