/// This module is intended to be used as a fixed-point physics system.
/// The hope is that this will make deterministic physics easier,
/// and therefore networking a bit less of a pain.
use bevy::{
    app::{Plugin, Update},
    ecs::{component::Component, system::Query},
    math::I64Vec2,
};

const MAX_SPEED: i64 = 400;

#[derive(Default, Debug)]
pub struct Physics2DPlugin {}

impl Plugin for Physics2DPlugin {
    fn build(&self, app: &mut bevy::app::App) {
        app.add_systems(Update, tick_physics);
    }
}

fn tick_physics(mut query: Query<&mut PhysicsBody2D>) {
    query.iter_mut().for_each(|mut pb| {
        pb.tick();
    });
}

#[derive(Default, Debug, Component)]
pub struct PhysicsBody2D {
    pub pos: I64Vec2,
    pub vel: I64Vec2,
}

impl PhysicsBody2D {
    pub fn tick(&mut self) {
        self.pos += self.vel;
    }

    pub fn add_vel(&mut self, force: I64Vec2) {
        let mut vel = self.vel + force;
        if vel.length_squared() >= MAX_SPEED.pow(2) {
            let l = vel.length_squared();
            let x = vel.x * vel.x;
            let y = vel.y * vel.y;

            vel.x = match vel.x {
                ..0 => (x * -MAX_SPEED) / l,
                _ => (x * MAX_SPEED) / l,
            };
            vel.y = match vel.y {
                ..0 => (y * -MAX_SPEED) / l,
                _ => (y * MAX_SPEED) / l,
            };
        }
        self.vel = vel;
    }
}