$fn = 64;

// --- Parameters ---
cols = 6;                  // Number of columns (width)
rows = 3;                  // Number of rows (depth)
hole_diameter = 16;        // Diameter of the slots (16mm fits most standard markers/pens)
hole_depth = 60;           // Depth of the slots
wall_thickness = 2.5;      // Thickness of walls between slots
base_thickness = 3;        // Thickness of the bottom base

// --- Calculated Dimensions ---
width = cols * hole_diameter + (cols + 1) * wall_thickness;
depth = rows * hole_diameter + (rows + 1) * wall_thickness;
height = hole_depth + base_thickness;

// --- Main Object ---
union() {
    // Main Holder Body
    difference() {
        // Solid block
        cube([width, depth, height]);

        // Subtract grid of holes
        for (c = [0 : cols - 1]) {
            for (r = [0 : rows - 1]) {
                x_pos = wall_thickness + hole_diameter/2 + c * (hole_diameter + wall_thickness);
                y_pos = wall_thickness + hole_diameter/2 + r * (hole_diameter + wall_thickness);

                // Main hole (extends slightly above top to ensure a clean cut)
                translate([x_pos, y_pos, base_thickness])
                    cylinder(h = hole_depth + 1, d = hole_diameter);
            }
        }
    }

    // Mounting Bracket (Universal Cleat / Rail Style)
    // Designed with 45-degree angles for support-free 3D printing
    // Shifted slightly into the main body (-0.1 in Y) to ensure manifold geometry
    translate([0, depth - 0.1, 0]) {
        // Top mounting hook
        hull() {
            // Overlaps back of the body
            translate([0, 0, height - 20])
                cube([width, 0.2, 20]);
            // Outward extension forming the downward hook
            translate([0, 0, height - 10])
                cube([width, 10.1, 10]);
        }

        // Bottom spacer to keep the holder vertical against the wall
        hull() {
            // Overlaps back of the body
            translate([0, 0, 0])
                cube([width, 0.2, 10]);
            // Outward extension forming the spacer
            translate([0, 0, 0])
                cube([width, 10.1, 5]);
        }
    }
}