use std::cell::RefCell;
use std::option::Option;
use std::rc::Rc;
#[derive(Debug, Clone)]
struct Double_Node {
    val: i64,
    // use Rc because you want multiple references (multiple mutable reference is impossible)
    // you do want these reference can mutate the data
    // so you need the runtime to check the borrow rule dynamically
    next: Option<Rc<RefCell<Double_Node>>>,
    prev: Option<Rc<RefCell<Double_Node>>>,
}

impl Double_Node {
    fn new(val: i64) -> Rc<RefCell<Double_Node>> {
        return Rc::new(RefCell::new(Double_Node {
            val,
            next: None,
            prev: None,
        }));
    }
}

pub struct Double_LinkedList {
    length: usize,
    head: Option<Rc<RefCell<Double_Node>>>,
    tail: Option<Rc<RefCell<Double_Node>>>,
}

impl Double_LinkedList {
    pub fn new() -> Double_LinkedList {
        return Double_LinkedList {
            length: 0,
            head: None,
            tail: None,
        };
    }

    pub fn append(&mut self, val: i64) {
        let new_node = Double_Node::new(val);
        if self.length == 0 {
            self.head = Some(new_node.clone());
            self.tail = Some(new_node.clone());
        } else {
            let tail = self.tail.take().unwrap(); // take the last node and let the self.tail be None
            tail.borrow_mut().next = Some(new_node.clone()); // clone the Rc type
            new_node.borrow_mut().prev = Some(tail.clone());
            self.tail = Some(new_node.clone());
        }
        self.length += 1;
    }

    pub fn pop(&mut self) -> Option<i64> {
        let tail = self.tail.take();
        let mut result = None;
        match tail{
            Some(node)=>{
                result = Some(node.borrow().val);
                self.tail = node.borrow().prev.clone();
                match self.tail.as_ref(){
                    Some(tail)=>{
                        tail.borrow_mut().next=None;
                    }
                    None=>{
                        self.head = None;    
                    }
                }


            }
            None => {
                return None;
            }
        }
       result
    }

    pub fn iter(&self) -> Double_LinkedList_Iterator {
        return Double_LinkedList_Iterator::new(self.head.clone());
    }
}

pub struct Double_LinkedList_Iterator {
    current: Option<Rc<RefCell<Double_Node>>>,
}

impl Double_LinkedList_Iterator {
    fn new(current: Option<Rc<RefCell<Double_Node>>>) -> Double_LinkedList_Iterator {
        return Double_LinkedList_Iterator { current };
    }
}

impl Iterator for Double_LinkedList_Iterator {
    type Item = i64;

    // get the value and change the current
    fn next(&mut self) -> Option<i64> {
        let mut result = None;
        self.current = match &self.current {
            Some(current) => {
                let current = current.borrow(); // borrowing current Double Node
                result = Some(current.val);
                match current.next.as_ref() {// we don't want move the value in the current.next, we only want a reference to it
                    Some(current) => Some(current.clone()),
                    None => None,
                }
            }
            None => None,
        };
        result
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_double_node_new() {
        let mut test_double_node = Double_Node::new(10);
    }
    #[test]
    fn test_double_linkedlist_iterator() {
        let mut test = Double_LinkedList::new();
        test.append(10);
        test.append(15);
        test.append(19);
        test.append(21);
        //a.append("world".to_string());
        for i in test.iter() {
            print!("{:?}\n", i);
        }
    }

    #[test]
    fn test_double_linkedlist_pop(){
        let mut test = Double_LinkedList::new();
        test.append(10);
        test.append(15);
        test.append(19);
        test.append(21);
        test.pop();
        test.pop();
        test.pop();
        //a.append("world".to_string());
        for i in test.iter() {
            print!("{:?}\n", i);
        }
    }
}