$fn = 64;

// --- Parameters ---
num_slots = 6;
slot_spacing = 35;
slot_width = 8;
slot_depth = 25;
shelf_depth = 40;
back_height = 35;
thickness = 4.5;
hole_diameter = 4.5;

rack_width = num_slots * slot_spacing;

// --- Main Object ---
difference() {
    union() {
        // Back mounting plate
        cube([rack_width, thickness, back_height]);

        // Horizontal shelf
        // Overlapped slightly into the back plate to ensure manifold geometry
        translate([0, thickness - 0.1, back_height - thickness])
            cube([rack_width, shelf_depth + 0.1, thickness]);

        // Support gussets
        gusset(0);                                      // Left
        gusset((rack_width / 2) - (thickness / 2));     // Center
        gusset(rack_width - thickness);                 // Right
    }

    // Screwdriver slots
    for (i = [0 : num_slots - 1]) {
        x_pos = (i * slot_spacing) + (slot_spacing / 2);
        translate([x_pos, thickness + shelf_depth - slot_depth, back_height - thickness - 1])
            slot_cutout();
    }

    // Mounting holes
    mount_hole(slot_spacing / 2);
    mount_hole(rack_width - (slot_spacing / 2));
}

// --- Modules ---

module gusset(x_pos) {
    translate([x_pos, thickness - 0.1, 0])
    hull() {
        // Base against back plate
        cube([thickness, 0.1, back_height]);
        // Tip under the front of the shelf
        translate([0, shelf_depth - 0.1, back_height - thickness])
            cube([thickness, 0.1, thickness]);
    }
}

module slot_cutout() {
    // Back rounded edge of the slot
    cylinder(d=slot_width, h=thickness + 2);
    
    // Straight channel
    translate([-slot_width / 2, 0, 0])
        cube([slot_width, slot_depth + 5, thickness + 2]);
        
    // Flared opening to easily slide screwdrivers in
    translate([0, slot_depth, 0])
        hull() {
            translate([-slot_width / 2, 0, 0])
                cube([slot_width, 0.1, thickness + 2]);
            translate([-slot_width * 1.5, 5, 0])
                cube([slot_width * 3, 0.1, thickness + 2]);
        }
}

module mount_hole(x_pos) {
    translate([x_pos, -1, back_height / 2])
        rotate([-90, 0, 0]) {
            // Main screw hole
            cylinder(d=hole_diameter, h=thickness + 2);
            // Countersink for screw head
            translate([0, 0, thickness - 1.5])
                cylinder(d1=hole_diameter, d2=hole_diameter * 2.5, h=3);
        }
}