$fn=64;

// --- Parameters ---
columns = 4;
rows = 3;

// Inside dimensions of a single cell
cell_top_width = 38;
cell_bottom_width = 25;
cell_depth = 50;

// Thickness and features
wall_thickness = 1.2;
lip_height = 2;
lip_overhang = 3;
drainage_hole_diameter = 6;
corner_radius = 3;

// --- Calculated Values ---
spacing = cell_top_width + wall_thickness;
outer_top_w = cell_top_width + wall_thickness * 2;
outer_bot_w = cell_bottom_width + wall_thickness * 2;

// --- Modules ---
module rounded_square(w, r) {
    offset(r=r) square(w - 2*r, center=true);
}

module tapered_cell(w_bot, w_top, h, r) {
    hull() {
        linear_extrude(0.01) rounded_square(w_bot, r);
        translate([0, 0, h - 0.01])
            linear_extrude(0.01) rounded_square(w_top, r);
    }
}

module top_lip() {
    w_lip = outer_top_w + lip_overhang * 2;
    r_lip = corner_radius + wall_thickness;
    
    translate([0, 0, cell_depth - lip_height])
        linear_extrude(lip_height)
            hull() {
                translate([0, 0]) rounded_square(w_lip, r_lip);
                translate([(columns - 1) * spacing, 0]) rounded_square(w_lip, r_lip);
                translate([0, (rows - 1) * spacing]) rounded_square(w_lip, r_lip);
                translate([(columns - 1) * spacing, (rows - 1) * spacing]) rounded_square(w_lip, r_lip);
            }
}

// --- Main Object ---
difference() {
    // Solid Tray Body
    union() {
        // Outer cell bodies
        for(x = [0 : columns - 1]) {
            for(y = [0 : rows - 1]) {
                translate([x * spacing, y * spacing, 0])
                    tapered_cell(outer_bot_w, outer_top_w, cell_depth, corner_radius + wall_thickness);
            }
        }

        // Top reinforcing lip
        top_lip();
    }

    // Hollow out cells and add drainage holes
    for(x = [0 : columns - 1]) {
        for(y = [0 : rows - 1]) {
            // Hollow core (shifted up to leave the bottom wall, naturally protrudes out the top)
            translate([x * spacing, y * spacing, wall_thickness])
                tapered_cell(cell_bottom_width, cell_top_width, cell_depth, corner_radius);

            // Drainage hole
            translate([x * spacing, y * spacing, -1])
                cylinder(d=drainage_hole_diameter, h=wall_thickness + 2);
        }
    }
}