use super::units::*;
use super::orbital::*;
use std::vec::Vec;
use std::rc::Rc;
use std::cell::RefCell;

pub struct System
{
    pub orbitals : Rc<RefCell<Vec<Orbital>>>,
}

pub struct SystemBuilder
{
    orbitals : Rc<RefCell<Vec<Orbital>>>,
}

impl System
{
    fn orbital_set(&self, orbitals : &mut [Orbital], i : usize)
        -> (&mut Orbital, Option<&mut Orbital>)
    {
        //The orbital vector must first be converted to a mutable span, so that I can access the raw data.
        assert!(i < orbitals.len());
        unsafe {
        //From the orbital span, take a raw pointer from the given index, 
        //cast to a pointer to a mutable Orbital, and dereference.
            let orbital = &mut *(orbitals.get_unchecked_mut(i) as *mut Orbital);
            //Assuming the orbital is a valid object, check for the parent orbital.
            match orbital.origin() {
                Some(origin_i) => {
                    //Make sure the origin index does not break rules.
                    assert!(origin_i != i, "Object cannot orbit itself");
                    assert!(origin_i < orbitals.len());
                    let origin = &mut *(orbitals.get_unchecked_mut(origin_i) as *mut Orbital);
                    (orbital, Some(origin))
                },
                None => (orbital, None)
            }
        }
    }

    pub fn tick(&self, t : Second)
    {
        let orbitals = &mut self.orbitals.borrow_mut()[..];
        for i in 0..orbitals.len() {
            let orbital_set = self.orbital_set(orbitals, i);
            match orbital_set.1 {
                Some(origin) => { orbital_set.0.tick(origin, t); },
                None => {}
            }
        }
    }
}

impl SystemBuilder
{
    pub fn new() -> SystemBuilder
    {
        SystemBuilder {
            orbitals : Rc::new(RefCell::new(vec![]))
        }
    }

    pub fn add_body(&self, orbital : Orbital) -> usize
    {
        let mut orbitals = self.orbitals.borrow_mut();
        let new_ind = orbitals.len();
        orbitals.push(orbital);
        new_ind
    }

    pub fn build(self) -> System
    {
        System {
            orbitals : self.orbitals
        }
    }
}