$fn = 64;

// --- Parameters ---
// Outer dimensions of the bin (Default: 84x84mm for standard 2x2 modular bins)
bin_width = 84.0;
bin_length = 84.0;
corner_radius = 4.0;

// Lid dimensions
wall_thickness = 1.6;
top_thickness = 1.6;
skirt_height = 8.0;

// Fitment and snap mechanics
clearance = 0.25;
snap_lip = 0.5;

// --- Modules ---
module rounded_box(w, l, h, r) {
    safe_r = min(r, w/2, l/2);
    if (safe_r > 0) {
        hull() {
            translate([-w/2+safe_r, -l/2+safe_r, 0]) cylinder(r=safe_r, h=h);
            translate([ w/2-safe_r, -l/2+safe_r, 0]) cylinder(r=safe_r, h=h);
            translate([-w/2+safe_r,  l/2-safe_r, 0]) cylinder(r=safe_r, h=h);
            translate([ w/2-safe_r,  l/2-safe_r, 0]) cylinder(r=safe_r, h=h);
        }
    } else {
        translate([-w/2, -l/2, 0]) cube([w, l, h]);
    }
}

// --- Main Geometry ---
difference() {
    // Outer shell
    rounded_box(
        bin_width + 2*clearance + 2*wall_thickness,
        bin_length + 2*clearance + 2*wall_thickness,
        skirt_height + top_thickness,
        corner_radius + clearance + wall_thickness
    );

    // Inner cavity - Main clearance area
    translate([0, 0, 1.49])
    rounded_box(
        bin_width + 2*clearance,
        bin_length + 2*clearance,
        skirt_height - 1.49,
        corner_radius + clearance
    );

    // Inner cavity - 45-degree chamfer for printable snap fit
    hull() {
        translate([0, 0, 0.49])
        rounded_box(
            bin_width + 2*clearance - 2*snap_lip,
            bin_length + 2*clearance - 2*snap_lip,
            0.01,
            corner_radius + clearance - snap_lip
        );
        translate([0, 0, 1.5])
        rounded_box(
            bin_width + 2*clearance,
            bin_length + 2*clearance,
            0.01,
            corner_radius + clearance
        );
    }

    // Inner cavity - Bottom lip area (snaps under the rim)
    translate([0, 0, -0.01])
    rounded_box(
        bin_width + 2*clearance - 2*snap_lip,
        bin_length + 2*clearance - 2*snap_lip,
        0.51,
        corner_radius + clearance - snap_lip
    );
}