use std::rc::{Rc, Weak};
use std::cell::RefCell;

pub struct ListHead<T> {
    prev: Weak::<RefCell::<ListHead<T>>>,
    next: Weak::<RefCell::<ListHead<T>>>,
    data: Weak::<RefCell::<T>>,
}

impl<T> ListHead<T> {

    pub fn new_head() -> Rc::<RefCell::<ListHead<T>>> {
        let this = Rc::new(RefCell::new(ListHead{
            prev: Weak::<RefCell::<ListHead<T>>>::new(),
            next: Weak::<RefCell::<ListHead<T>>>::new(),
            data: Weak::<RefCell::<T>>::new()
        }));
        this.borrow_mut().init();
        return this;
    }

    pub fn new_node(data: Weak::<RefCell::<T>>) -> Rc::<RefCell::<ListHead<T>>> {
        let this = Rc::new(RefCell::new(ListHead{
            prev: Weak::<RefCell::<ListHead<T>>>::new(),
            next: Weak::<RefCell::<ListHead<T>>>::new(),
            data: data
        }));
        this.borrow_mut().init();
        return this;
    }

    fn get_rc_refcell(&self) -> Rc::<RefCell::<ListHead<T>>> {
        let cell_rc: &Rc<RefCell<ListHead<T>>> = &self.next.upgrade().unwrap();
        let head: &ListHead<T> = &*cell_rc.borrow();
        let cell_start = cell_rc.as_ptr() as *const u8;
        let data_start = head as *const ListHead<T> as *const u8;
        let cell_offset = unsafe { data_start.offset_from(cell_start) };
        unsafe {
            return Rc::from_raw(cell_start as *const RefCell::<ListHead<T>>);
        };
    }

    fn init(&mut self) {
        self.prev = Rc::downgrade(&self.get_rc_refcell());
        self.next = Rc::downgrade(&self.get_rc_refcell());
    }

    pub fn data(&self) -> Weak::<RefCell::<T>> {
        return self.data.clone();
    }

    pub fn del_init(&mut self) {
        self.next.upgrade().unwrap().borrow_mut().prev = self.prev.clone();
        self.prev.upgrade().unwrap().borrow_mut().next = self.next.clone();
        self.init();
    }

    pub fn empty(&self) -> bool {
        return self as *const ListHead<T> == self.next.upgrade().unwrap().as_ptr();
    }

    pub fn add_tail(head: &mut Rc::<RefCell::<ListHead<T>>>,
                    pnew: &mut Rc::<RefCell::<ListHead<T>>>) {
        let prev = &mut head.borrow_mut().prev;
        let next = Rc::downgrade(head);

        next.upgrade().unwrap().borrow_mut().prev = Rc::downgrade(pnew);
        pnew.borrow_mut().next = next;
        pnew.borrow_mut().prev = prev.clone();
        prev.upgrade().unwrap().borrow_mut().next = Rc::downgrade(pnew);
    }

    pub fn first_entry(&self) -> Weak::<RefCell::<T>> {
        if self.empty() {
        }
        return self.next.upgrade().unwrap().borrow().data();
    }

    pub fn replace_init(head: &mut Rc::<RefCell::<ListHead<T>>>,
                        pnew: &mut Rc::<RefCell::<ListHead<T>>>) {
        pnew.borrow_mut().next = head.borrow_mut().next.clone();
        pnew.borrow_mut().next.upgrade().unwrap().borrow_mut().prev = Rc::downgrade(pnew);
        pnew.borrow_mut().prev = head.borrow_mut().prev.clone();
        head.borrow_mut().init();
    }

    pub fn for_each(&self, cb: fn (&Weak::<RefCell::<T>>) -> bool) {
        let mut pos = self.next.clone();
        let self_weak = &Rc::downgrade(&self.get_rc_refcell());
        while !Weak::ptr_eq(&pos, self_weak) {
            if !cb(&pos.upgrade().unwrap().borrow().data()) {
                break;
            }
            pos = pos.upgrade().unwrap().borrow().next.clone();
        }
    }

}