// Library
use specs::{Join, Read, ReadStorage, System, WriteStorage};

// Crate
use crate::{
    comp::phys::{Pos, Vel},
    state::DeltaTime,
};

// Basic ECS physics system
pub struct Sys;

impl<'a> System<'a> for Sys {
    type SystemData = (
        WriteStorage<'a, Pos>,
        ReadStorage<'a, Vel>,
        Read<'a, DeltaTime>,
    );

    fn run(&mut self, (mut positions, velocities, dt): Self::SystemData) {
        (&mut positions, &velocities)
            .join() // this can be parallelized with par_join()
            .for_each(|(pos, vel)| pos.0 += vel.0 * dt.0 as f32);
    }
}