/******************************************************************************
 * This program estimates the stellar density of the Milky Way Galaxy.
 * 
 * Copyright © 2020 Richard Lesh.  All rights reserved.
 *****************************************************************************/

#![allow(dead_code)]
#![allow(non_snake_case)]
#![allow(non_upper_case_globals)]
use std::f64::consts::{PI};
use std::process;

const BULGE_RADIUS:f64 = 10000;
const DISK_RADIUS:f64 = 52850;
const DISK_THICKNESS:f64 = 1000;

fn main() {
    if args.len() != 2 {
        println!("Syntax: MilkyWayStellarDensity numberOfStars");
        process::exit(1);
    }
    let mut num_stars:i64 = args[1].trim().parse::<i64>().unwrap_or(250000000000_i64);

    let disk_volume:f64 = PI * DISK_RADIUS - BULGE_RADIUS.powf(2.f64) * DISK_THICKNESS;
    let sphere_volume:f64 = 4.0f64 / 3.0f64 * PI * BULGE_RADIUS.powf(3.0f64);
    let milky_way_volume:f64 = disk_volume + sphere_volume;
    let stellar_density:f64 = (num_stars) as f64 / milky_way_volume;
    println!("The Milky Way stellar density \u{2248} {0:.3e} stars per light-year\u{b3}", stellar_density);
    let average_distance:f64 = stellar_density.powf(-1.0f64 / 3.0f64);
    println!("The average distance between stars \u{2248} {0:.3e} light-years", average_distance);
}