123123

use specs::{Builder, Component, ReadStorage, System, VecStorage, World, WorldExt, RunNow, EntityBuilder};

// =========================================================================================
#[derive(Debug)]
struct Position {
    x: f32,
    y: f32,
}

impl Component for Position {
    type Storage = VecStorage<Self>;
}

#[derive(Debug)]
struct Velocity {
    x: f32,
    y: f32,
}

impl Component for Velocity {
    type Storage = VecStorage<Self>;
}

// =========================================================================================

trait ComponentHandler{
    fn move_component_to<'a>(&mut self, builder: EntityBuilder<'a>) -> EntityBuilder<'a>;
}

struct ComponentHandlerImpl<T: Component> {
    pub component: Option<T>
}

impl<T: Component + Send + Sync> ComponentHandler for ComponentHandlerImpl<T> {
    fn move_component_to<'a>(&mut self, builder: EntityBuilder<'a>) -> EntityBuilder<'a> {
        if let Some(comp) = std::mem::replace(&mut self.component, None) {
            builder.with(comp)
        } else {
            builder
        }
    }
}

// =========================================================================================

struct PrintPositionSystem;

impl<'a> System<'a> for PrintPositionSystem {
    type SystemData = ReadStorage<'a, Position>;

    fn run(&mut self, position: Self::SystemData) {
        use specs::Join;

        for position in position.join() {
            println!("Hello, Pos {:?}", &position);
        }
    }
}

struct PrintVelocitySystem;

impl<'a> System<'a> for PrintVelocitySystem {
    type SystemData = ReadStorage<'a, Velocity>;

    fn run(&mut self, velocity: Self::SystemData) {
        use specs::Join;

        for position in velocity.join() {
            println!("Hello, Vel {:?}", &position);
        }
    }
}

// =========================================================================================

fn main() {
    let mut world = World::new();
    world.register::<Position>();
    world.register::<Velocity>();

    let mut vec: Vec<Box<dyn ComponentHandler>> = vec![
        Box::new(ComponentHandlerImpl { component: Some(Position { x: 1.0, y: 2.0 }) }),
        Box::new(ComponentHandlerImpl { component: Some(Velocity { x: 3.0, y: 4.0 }) }),
    ];

    for component_handler in vec.iter_mut() {
        component_handler.move_component_to(world.create_entity()).build();
    }

    let mut print_position_system = PrintPositionSystem;
    print_position_system.run_now(&world);

    let mut velocity_position_system = PrintVelocitySystem;
    velocity_position_system.run_now(&world);

    world.maintain();
}