extern crate sdl2;

use sdl2::pixels::Color;
use sdl2::event::Event;
use sdl2::keyboard::Keycode;
use sdl2::rect::{Rect};
use sdl2::render::WindowCanvas;
use std::time::Duration;

use rand::Rng;

fn magnitude(x: f64,y: f64) -> f64 {
    ((x).powi(2) + (y).powi(2)).sqrt()
}

fn set_mag(x: &f64,y: &f64, mag: &f64) -> Vec<f64>{
        let getmag: f64 = magnitude(*x, *y);
        let rx = (*x / getmag) * mag;
        let ry = (*y / getmag) * mag;

        return vec![rx,ry]
}

//i know i can use sdl points but i wanna make my own thing.
//plus this is more independant.
struct Point{
    x: f64,
    y: f64,
}
impl Point{
    fn add(&mut self, addvec: &Point){
        self.x = self.x + addvec.x;
        self.y = self.y + addvec.y;
    }

    fn sub(&mut self, subvec: &Point){
        self.x = self.x - subvec.x;
        self.y = self.y - subvec.y;
    }

    fn set_mag(&mut self, mag: &f64) {
       let smag = set_mag(&self.x, &self.y, &mag);
       self.x = smag[0];
       self.y = smag[1];
    }
}

struct ObjectG{
    pos: Point,
    vel: Point,
    acc: Point,
    size: i32,
    mass: f64,
}

impl ObjectG{
    fn apply_force(&mut self, force: &Point){
        let force = Point { x: force.x / self.mass, y: force.y / self.mass };

        self.acc.add(&force);
    }

    fn walk(&mut self) {
        self.vel.add(&self.acc);

        self.pos.add(&self.vel);

        self.acc=Point{x:0.0, y:0.0}
    }
}

struct Attractor{
    pos: Point,
    size: i32,
    mass: f64,
}

impl Attractor{
    fn attract(&mut self, obj: &mut ObjectG){
        let mut force = Point{x: self.pos.x, y: self.pos.y};
        force.sub(&obj.pos);

        let dist = magnitude(force.x, force.y);
        let mut dist = dist * dist;

        if dist < 100.0 { dist = 100.0 }
        if dist > 1000.0 { dist = 1000.0 }

        let g = 5.0;

        let strength = g * (self.mass * obj.mass) / dist;

        force.set_mag(&strength);

        obj.apply_force(&force);
    }
}

fn draw(canvas: &mut WindowCanvas, obj_arr: &mut Vec<ObjectG>, atr: &mut Attractor){
    canvas.set_draw_color(Color::RGBA(0,0,0,50));
    canvas.fill_rect(Rect::new(0,0,600,600)).err();
    //canvas.clear();

    for obj in obj_arr{
        obj.walk();
        canvas.set_draw_color(Color::RGBA(150,50,255,150));
        canvas.fill_rect(Rect::new(obj.pos.x as i32 - obj.size, obj.pos.y as i32 - obj.size, (obj.size * 2) as u32, (obj.size * 2) as u32)).err();

        canvas.set_draw_color(Color::RGB(150,50,255));
        canvas.draw_rect(Rect::new(obj.pos.x as i32 - obj.size, obj.pos.y as i32 - obj.size, (obj.size * 2) as u32, (obj.size * 2) as u32)).err();

        atr.attract(obj);
    }

    canvas.set_draw_color(Color::RGB(255,50,150));
    canvas.fill_rect(Rect::new(atr.pos.x as i32 - atr.size, atr.pos.y as i32 - atr.size, (atr.size * 2) as u32, (atr.size * 2) as u32)).err();

    canvas.present();
}



fn main() {
    let sdl2_context = sdl2::init().unwrap();
    let video_subsystem = sdl2_context.video().unwrap();


    let width: u32=600;
    let height: u32=600;

    let window = video_subsystem.window("grav-attraction-point", width, height)
        .position_centered()
        .build()
        .unwrap();

    let mut canvas = window.into_canvas().build().unwrap();
    canvas.default_pixel_format();
    canvas.set_blend_mode(sdl2::render::BlendMode::Blend);

    let mut obj_arr: Vec<ObjectG> = Vec::new();

    for _ in 0..10{
        let mut rng = rand::rng();
        let mut obj = ObjectG{
            pos: Point { x: rng.random_range(6.0..width as f64 -1.0), y: rng.random_range(6.0..width as f64 -1.0)},
            vel: Point { x: rng.random_range(-11.0..10.0), y: rng.random_range(-11.0..10.0)},
            acc: Point { x: 0.0, y: 0.0 },
            size: 0,
            mass: rng.random_range(50.0..150.0),
        };
        obj.size = (obj.mass.sqrt() * 2.0) as i32;
        obj_arr.push(obj);
    }

    let mut atr = Attractor{
        pos: Point{x: width as f64 /2.0, y: height as f64 /2.0},
        size: 0,
        mass: 100.0,
    };

    atr.size = (atr.mass.sqrt() * 2.0) as i32;

    canvas.set_draw_color(Color::RGB(0,0,0));
    canvas.clear();

    let mut event_pump = sdl2_context.event_pump().unwrap();
    draw(&mut canvas, &mut obj_arr, &mut atr);
    'running: loop {
        draw(&mut canvas, &mut obj_arr, &mut atr);
        for event in event_pump.poll_iter() {
            match event {
                Event::Quit {..} |
                Event::KeyDown { keycode: Some(Keycode::Escape), .. } => {
                    break 'running
                },
                _ => {}
            }
        }

        ::std::thread::sleep(Duration::new(0, 1_000_000_000u32 / 60));
    }
}