$fn = 64;

// --- PARAMETERS ---
track_length = 120;     // Total length of the runner
track_width = 30;       // Outer width of the base track
track_height = 20;      // Outer height of the base track
wall_thickness = 2;     // Thickness of the walls
clearance = 0.2;        // Tolerance for snap fit
overlap = 6;            // How far the cover overlaps the base walls
num_holes = 3;          // Number of mounting screw holes

// --- RENDER ---
// Base track
base();

// Cover (placed next to base, oriented flat on the bed for printing)
cw = track_width + 2 * clearance + 2 * wall_thickness;
ch = overlap + wall_thickness;
translate([cw + track_width + 10, track_length, ch])
    rotate([0, 180, 0])
    rotate([-90, 0, 0])
    linear_extrude(height = track_length)
        cover_profile();

// --- MODULES ---
module base() {
    difference() {
        rotate([-90, 0, 0])
            linear_extrude(height = track_length)
                base_profile();

        // Screw mounting holes
        for (i = [1 : num_holes]) {
            translate([track_width / 2, i * track_length / (num_holes + 1), 0])
                screw_hole();
        }
    }
}

module base_profile() {
    difference() {
        square([track_width, track_height]);
        // Inner channel cutout
        translate([wall_thickness, wall_thickness])
            square([track_width - 2 * wall_thickness, track_height]);
    }
    // Snap lips (outer)
    translate([0, track_height - 4])
        polygon([[0,0], [-0.8, 1.5], [0, 3]]);
    translate([track_width, track_height - 4])
        polygon([[0,0], [0.8, 1.5], [0, 3]]);
}

module cover_profile() {
    cw = track_width + 2 * clearance + 2 * wall_thickness;
    ch = overlap + wall_thickness;
    
    difference() {
        square([cw, ch]);
        // Inner channel cutout
        translate([wall_thickness, -0.1])
            square([cw - 2 * wall_thickness, overlap + 0.1]);
    }
    // Snap lips (inner)
    translate([wall_thickness, overlap - 4])
        polygon([[0,0], [0.8, 1.5], [0, 3]]);
    translate([cw - wall_thickness, overlap - 4])
        polygon([[0,0], [-0.8, 1.5], [0, 3]]);
}

module screw_hole() {
    // Hole for screw shaft
    translate([0, 0, -1])
        cylinder(h = wall_thickness + 2, d = 4.5);
    // Clearance space for screw head
    translate([0, 0, wall_thickness])
        cylinder(h = track_height, d = 9);
}