// Under-desk cable tray: sheet-metal U-channel with inward return lips
// Units: mm. Z up, part rests on Z=0, length runs along X.

/* [Sheet] */
thickness = 1.2;        // [0.5:0.1:3]
inside_radius = 1.2;    // [0.5:0.1:5]
k_factor = 0.44;        // [0.3:0.01:0.5]

/* [Channel (outside dimensions)] */
length = 250;           // [100:1:600]
width = 42;             // [20:1:120]
height = 30;            // [15:1:100]
lip = 8;                // [4:0.5:20] return lip, measured from outer wall face

/* [Holes] */
hole_d = 5;             // [3:0.5:10]
hole_count = 6;         // [1:1:12]
hole_pitch = 40;        // [10:1:100]

/* [Output] */
mode = "folded";        // [folded, flat]

/* [Hidden] */
$fn = 64;
T = thickness; R = inside_radius; K = k_factor;
S = R + T;                          // outside setback for 90 deg bend
BA = (PI/2) * (R + K*T);            // bend allowance per 90 deg bend
base_flat = width - 2*S;
wall_flat = height - 2*S;
lip_flat  = lip - S;
flat_w = base_flat + 2*wall_flat + 2*lip_flat + 4*BA;
hole_x = [for (i=[0:hole_count-1]) length/2 + (i - (hole_count-1)/2)*hole_pitch];

echo(str("BA=",BA," flat=",length," x ",flat_w));

// annulus sector, center c=[y,z], from angle a0 to a1 (deg)
module sector(c, a0, a1) {
    translate(c) intersection() {
        difference() { circle(r=R+T); circle(r=R); }
        polygon(concat([[0,0]],
            [for (a=[a0:(a1-a0)/32:a1]) 2*(R+T)*[cos(a), sin(a)]]));
    }
}

// cross-section in (Y,Z)
module profile() {
    // base
    translate([S, 0]) square([base_flat, T]);
    // bottom bends
    sector([S, S], 180, 270);
    sector([width - S, S], 270, 360);
    // walls
    translate([0, S]) square([T, wall_flat]);
    translate([width - T, S]) square([T, wall_flat]);
    // top bends
    sector([S, height - S], 90, 180);
    sector([width - S, height - S], 0, 90);
    // return lips
    translate([S, height - T]) square([lip_flat, T]);
    translate([width - S - lip_flat, height - T]) square([lip_flat, T]);
}

module folded() {
    difference() {
        rotate([90, 0, 90]) linear_extrude(length) profile();
        for (x = hole_x) translate([x, width/2, -1]) cylinder(d=hole_d, h=T+2);
    }
}

// flat pattern: X = length, Y = developed width, base centred on Y = flat_w/2
module flat() {
    difference() {
        square([length, flat_w]);
        for (x = hole_x) translate([x, flat_w/2]) circle(d=hole_d);
    }
}

if (mode == "flat") flat(); else folded();