$fn = 64;

// --- Parameters ---

// Stair Dimensions
step_width = 150;   // Total width of the display
step_depth = 40;    // Depth of each individual step
step_height = 30;   // Height of each individual step
num_steps = 3;      // Number of tiers

// Shell & Print Settings
wall_thickness = 2; // Thickness of the hollowed shell walls

// Grid Connection System (Bottom Holes)
grid_pitch = 30;    // Distance between grid holes
grid_offset_x = 15; // Starting X offset for grid
grid_offset_y = 15; // Starting Y offset for grid
hole_dia = 5.2;     // Diameter of connection holes (5mm peg + clearance)
hole_depth = 6;     // Depth of the connection holes
pillar_dia = 12;    // Diameter of the reinforcing pillar around each hole

// --- Main Geometry ---

difference() {
    union() {
        // Main hollow stair body
        difference() {
            // 1. Solid outer stairs (with slight overlap to ensure manifold geometry)
            for(i = [0 : num_steps - 1]) {
                translate([0, i * step_depth - (i > 0 ? 0.01 : 0), 0])
                    cube([step_width, step_depth + (i > 0 ? 0.01 : 0), step_height * (i + 1)]);
            }

            // 2. Hollow out the inside to save filament and prevent warping
            for(i = [0 : num_steps - 1]) {
                y_start = (i == 0) ? wall_thickness : i * step_depth - 0.1;
                y_end   = (i == num_steps - 1) ? num_steps * step_depth - wall_thickness : (i + 1) * step_depth + 0.1;
                y_len   = y_end - y_start;

                translate([wall_thickness, y_start, -0.1])
                    cube([step_width - 2 * wall_thickness, y_len, step_height * (i + 1) - wall_thickness + 0.1]);
            }
        }

        // 3. Reinforcement pillars for grid connections
        for(x = [grid_offset_x : grid_pitch : step_width - 0.1]) {
            for(y = [grid_offset_y : grid_pitch : num_steps * step_depth - 0.1]) {
                translate([x, y, 0])
                    cylinder(h = hole_depth + 2, d = pillar_dia);
            }
        }
    }

    // 4. Subtract the connection holes from the bottom
    for(x = [grid_offset_x : grid_pitch : step_width - 0.1]) {
        for(y = [grid_offset_y : grid_pitch : num_steps * step_depth - 0.1]) {
            translate([x, y, -0.1])
                cylinder(h = hole_depth + 0.1, d = hole_dia);
        }
    }
}