#![allow(unused)]
fn main() {
struct Tank {
    speed: f32,
}

fn drive(ctx: &mut Ctx) {
    ctx.world
        .query::<(&mut Transform2D, &Tank)>()
        .for_each(|(t, tank)| t.position.x += tank.speed);
}

#[test]
fn turrets_ride_on_tanks() {
    let mut turret = None;
    let world = Game::new("tanks", 800, 600)
        .sim_system(drive)
        .sim_system(follow_attachments) // after the systems that move things
        .run_headless(10, |ctx| {
            let tank = ctx.world.spawn((Transform2D::at(vec2(0.0, 0.0)), Tank { speed: 1.0 }));
            let on_top = Attached::to(tank).offset(vec2(0.0, -4.0));
            turret = Some(ctx.world.spawn((Transform2D::default(), on_top)));
        });
    assert_eq!(position(&world, turret.unwrap()), vec2(10.0, -4.0));
}
}

struct Tank { float speed; };

static void turrets_ride_on_tanks() {
    crabby::entity turret = 0;
    auto world = crabby::game("tanks", 800, 600)
        .sim_system([](crabby::ctx& ctx) {
            ctx.world().each([](crabby::transform2d& t, const Tank& tank) { t.position.x += tank.speed; });
        }, "drive")
        .follow_attachments() // after the systems that move things
        .run_headless(10, [&](crabby::ctx& ctx) {
            auto w = ctx.world();
            const auto tank = w.spawn(crabby::transform_at({0, 0}), Tank{1});
            turret = w.spawn(crabby::transform_at({0, 0}), crabby::attach_to(tank, {0, -4}));
        });
    const auto at = world.get<crabby::transform2d>(turret).position;
    if (at != crabby::vec2{10, -4}) { std::fprintf(stderr, "turret at %f,%f\n", double(at.x), double(at.y)); std::abort(); }
}