$fn=64;

// --- Parameters ---
bp_width = 45;         // Backplate width
bp_height = 60;        // Backplate height
bp_thick = 5;          // Backplate thickness
corner_radius = 5;     // Backplate corner radius

prong_spacing = 18;    // Gap between prongs (accommodates pliers hinge)
prong_width = 8;       // Width of each prong
prong_length = 45;     // Outward extension from the wall
prong_lift = 14;       // Upward curve at the tip
prong_drop = -4;       // Downward dip to create a resting saddle

hole_dia = 4.5;        // Screw hole diameter
head_dia = 8.5;        // Screw head diameter
hole_spacing = 44;     // Distance between top and bottom screw holes

// --- Modules ---
module backplate() {
    difference() {
        // Main plate with rounded corners
        hull() {
            translate([-bp_width/2 + corner_radius, -bp_height/2 + corner_radius, 0]) 
                cylinder(r=corner_radius, h=bp_thick);
            translate([bp_width/2 - corner_radius, -bp_height/2 + corner_radius, 0]) 
                cylinder(r=corner_radius, h=bp_thick);
            translate([-bp_width/2 + corner_radius, bp_height/2 - corner_radius, 0]) 
                cylinder(r=corner_radius, h=bp_thick);
            translate([bp_width/2 - corner_radius, bp_height/2 - corner_radius, 0]) 
                cylinder(r=corner_radius, h=bp_thick);
        }
        
        // Mounting holes
        for (y = [-hole_spacing/2, hole_spacing/2]) {
            translate([0, y, -1]) {
                // Main screw shaft clearance
                cylinder(d=hole_dia, h=bp_thick + 2);
                // Countersink
                translate([0, 0, bp_thick - 2.5 + 1]) 
                    cylinder(d1=hole_dia, d2=head_dia, h=2.51);
                // Screw head clearance
                translate([0, 0, bp_thick + 1]) 
                    cylinder(d=head_dia, h=10);
            }
        }
    }
}

module hook_profile() {
    // Defines the contoured side profile of a single prong
    z0 = bp_thick;
    y0 = 0;
    d0 = 14; // Thicker base for strength
    
    z1 = bp_thick + prong_length * 0.4;
    y1 = prong_drop; 
    d1 = 10; // Tapered mid-section
    
    z2 = bp_thick + prong_length;
    y2 = prong_lift;
    d2 = 8;  // Rounded tip
    
    hull() {
        translate([0, y0, z0]) 
            rotate([0, 90, 0]) cylinder(d=d0, h=prong_width, center=true);
        translate([0, y1, z1]) 
            rotate([0, 90, 0]) cylinder(d=d1, h=prong_width, center=true);
    }
    hull() {
        translate([0, y1, z1]) 
            rotate([0, 90, 0]) cylinder(d=d1, h=prong_width, center=true);
        translate([0, y2, z2]) 
            rotate([0, 90, 0]) cylinder(d=d2, h=prong_width, center=true);
    }
}

// --- Assembly ---
difference() {
    union() {
        backplate();
        
        // Left Prong
        translate([-prong_spacing/2 - prong_width/2, 0, 0]) 
            hook_profile();
            
        // Right Prong
        translate([prong_spacing/2 + prong_width/2, 0, 0]) 
            hook_profile();
    }
    
    // Cleanly slice off anything extending behind the backplate
    // (caused by the circular base of the prongs)
    translate([0, 0, -50]) 
        cube([100, 100, 100], center=true);
}