$fn = 64;

// --- Parameters ---
rail_length = 600;       // Total length of the rail
rail_width = 40;         // Width of the rail against the wall
rail_depth = 12;         // Total thickness/depth of the rail
bevel_width = 5;         // Width of the dovetail chamfer
lap_length = 15;         // Length of the interlocking half-lap joint

hole_count = 6;          // Number of mounting holes
hole_spacing = 100;      // Distance between mounting holes
screw_dia = 5.5;         // Clearance hole for M5 screw
screw_head_dia = 10.5;   // Diameter of the countersink
screw_head_depth = 3;    // Depth of the countersink cone

// --- Main Model ---
difference() {
    // Main rail profile (Dovetail/French Cleat style)
    rotate([0, 90, 0])
    translate([0, 0, -rail_length / 2])
    linear_extrude(rail_length)
    polygon([
        [0, -rail_width / 2],
        [0, rail_width / 2],
        [-rail_depth, rail_width / 2 - bevel_width],
        [-rail_depth, -rail_width / 2 + bevel_width]
    ]);

    // Mounting holes distributed along the rail
    start_x = - (hole_spacing * (hole_count - 1)) / 2;
    for (i = [0 : hole_count - 1]) {
        translate([start_x + i * hole_spacing, 0, -1]) {
            // Clearance hole for screw thread
            cylinder(h = rail_depth + 2, d = screw_dia);
            
            // Countersink for screw head
            translate([0, 0, rail_depth - screw_head_depth + 1])
            cylinder(h = screw_head_depth + 0.01, d1 = screw_dia, d2 = screw_head_dia);
            
            // Counterbore to ensure screw head is fully recessed or flush
            translate([0, 0, rail_depth + 1])
            cylinder(h = 2, d = screw_head_dia);
        }
    }

    // Interlocking half-lap joint (Right End - Top Cut)
    // Allows seamless extension with multiple printed pieces
    translate([rail_length / 2 - lap_length, -rail_width, rail_depth / 2])
    cube([lap_length + 1, rail_width * 2, rail_depth]);

    // Interlocking half-lap joint (Left End - Bottom Cut)
    translate([-rail_length / 2 - 1, -rail_width, -1])
    cube([lap_length + 1, rail_width * 2, rail_depth / 2 + 1]);
}