$fn=64;

// --- Parameters ---
columns = 3;
rows = 2;
cell_top_width = 40;
cell_bottom_width = 28;
cell_height = 50;
wall_thickness = 1.2;
drain_hole_dia = 8;
lip_width = 3;
lip_height = 3;
corner_radius = 4;

// --- Modules ---
module rounded_square(w, r) {
    safe_r = max(0.01, min(r, w/2 - 0.01));
    hull() {
        translate([ w/2-safe_r,  w/2-safe_r]) circle(safe_r);
        translate([-w/2+safe_r,  w/2-safe_r]) circle(safe_r);
        translate([ w/2-safe_r, -w/2+safe_r]) circle(safe_r);
        translate([-w/2+safe_r, -w/2+safe_r]) circle(safe_r);
    }
}

module cell_outer() {
    hull() {
        linear_extrude(0.01) 
            rounded_square(cell_bottom_width, corner_radius);
        translate([0, 0, cell_height - 0.01]) 
            linear_extrude(0.01) 
                rounded_square(cell_top_width, corner_radius);
    }
}

module cell_inner() {
    hull() {
        translate([0, 0, wall_thickness]) 
            linear_extrude(0.01) 
                rounded_square(cell_bottom_width - 2*wall_thickness, max(0.1, corner_radius - wall_thickness));
        translate([0, 0, cell_height + 1]) 
            linear_extrude(0.01) 
                rounded_square(cell_top_width - 2*wall_thickness, max(0.1, corner_radius - wall_thickness));
    }
}

module starter_tray() {
    difference() {
        // Main Body
        union() {
            // Individual tapered cells
            for(x=[0:columns-1], y=[0:rows-1]) {
                translate([x*cell_top_width, y*cell_top_width, 0])
                    cell_outer();
            }
            
            // Top deck / lip (chamfered for support-free 3D printing)
            hull() {
                // Base of the lip
                for(x=[0, columns-1], y=[0, rows-1]) {
                    translate([x*cell_top_width, y*cell_top_width, cell_height - lip_height])
                        linear_extrude(0.01)
                            rounded_square(cell_top_width, corner_radius);
                }
                // Top edge of the lip
                for(x=[0, columns-1], y=[0, rows-1]) {
                    translate([x*cell_top_width, y*cell_top_width, cell_height - 0.01])
                        linear_extrude(0.01)
                            rounded_square(cell_top_width + 2*lip_width, corner_radius + lip_width);
                }
            }
        }
        
        // Hollow out cells and add drainage holes
        for(x=[0:columns-1], y=[0:rows-1]) {
            translate([x*cell_top_width, y*cell_top_width, 0]) {
                cell_inner();
                // Drainage hole
                translate([0, 0, -1])
                    cylinder(h=wall_thickness + 2, d=drain_hole_dia);
            }
        }
    }
}

// Center the tray on the origin
translate([-(columns-1)*cell_top_width/2, -(rows-1)*cell_top_width/2, 0])
    starter_tray();