$fn = 64;

// --- PARAMETERS ---
// Dimensions of the bin's outer top rim
bin_length = 150.0;
bin_width = 100.0;
bin_corner_radius = 10.0;

// Lid configuration
wall_thickness = 2.0;
skirt_height = 15.0;
clearance = 0.4;        // Tolerance gap between bin and lid for easy fit
snap_depth = 0.8;       // How far the snap ridge protrudes inward to grip the bin
snap_height = 5.0;      // Total vertical space taken by the snap ridge profile

// --- CALCULATED DIMENSIONS ---
outer_l = bin_length + (2 * clearance) + (2 * wall_thickness);
outer_w = bin_width + (2 * clearance) + (2 * wall_thickness);
outer_h = skirt_height + wall_thickness;
outer_r = bin_corner_radius + clearance + wall_thickness;

inner_l = bin_length + (2 * clearance);
inner_w = bin_width + (2 * clearance);
inner_r = bin_corner_radius + clearance;

// --- MODULES ---
module rounded_box(l, w, h, r) {
    safe_r = max(0.01, min(r, l/2, w/2));
    hull() {
        for(x = [-l/2 + safe_r, l/2 - safe_r]) {
            for(y = [-w/2 + safe_r, w/2 - safe_r]) {
                translate([x, y, 0]) cylinder(r=safe_r, h=h);
            }
        }
    }
}

// --- MAIN GEOMETRY ---
difference() {
    // Main solid lid body
    rounded_box(outer_l, outer_w, outer_h, outer_r);

    // Subtract the inner cavity (bin volume + snap mechanism)
    union() {
        // 1. Main inner cavity above the snap ridge
        translate([0, 0, snap_height])
            rounded_box(inner_l, inner_w, skirt_height - snap_height, inner_r);

        // 2. Top chamfer of the snap ridge (locking face)
        hull() {
            translate([0, 0, snap_height])
                rounded_box(inner_l, inner_w, 0.01, inner_r);
            translate([0, 0, snap_height / 2])
                rounded_box(inner_l - (2 * snap_depth), inner_w - (2 * snap_depth), 0.01, max(0.1, inner_r - snap_depth));
        }

        // 3. Bottom chamfer of the snap ridge (slide-on entry face)
        hull() {
            translate([0, 0, snap_height / 2])
                rounded_box(inner_l - (2 * snap_depth), inner_w - (2 * snap_depth), 0.01, max(0.1, inner_r - snap_depth));
            // Extend slightly below 0 to ensure a clean manifold cut
            translate([0, 0, -0.1])
                rounded_box(inner_l, inner_w, 0.01, inner_r);
        }
    }
}