use std::fmt::Debug;
use std::rc::Rc;

#[derive(Debug)]
pub struct List<T> {
    head: Option<Rc<Node<T>>>,
}

impl<T> Clone for List<T> {
    fn clone(&self) -> Self {
        List {
            head: self.head.clone(),
        }
    }
}

#[derive(Debug, Clone)]
pub struct Node<T> {
    data: T,
    parent: Option<Rc<Node<T>>>,
}

impl<T> Node<T> {
    pub fn get_data(&self) -> &T {
        &self.data
    }
}

// TODO: This Debug is only needed because of the try_unwrap+expect
impl<T: Debug> List<T> {
    pub fn new() -> Self {
        List { head: None }
    }

    pub fn push_front(&self, data: T) -> List<T> {
        List {
            head: Some(Rc::new(Node {
                data: data,
                parent: self.head.clone(),
            })),
        }
    }

    pub fn pop_front(&mut self) -> (Option<T>, List<T>) {
        match self.head.take() {
            None => (None, List::new()),
            Some(popped_node) => {
                let extracted_node =
                    Rc::try_unwrap(popped_node).expect("TODO I should handle this better");
                (
                    Some(extracted_node.data),
                    List {
                        head: extracted_node.parent,
                    },
                )
            }
        }
    }

    pub fn without_front(&self) -> List<T> {
        List {
            head: self.head.as_ref().map(|node| node.parent.clone()).flatten(),
        }
    }

    pub fn get_data(&self) -> Option<&T> {
        self.head.as_ref().map(|rc_node| &rc_node.data)
    }

    pub fn is_empty(&self) -> bool {
        self.head.is_none()
    }

    pub fn ptr_eq(&self, other: &List<T>) -> bool {
        match (self.head.as_ref(), other.head.as_ref()) {
            (None, None) => true,
            (None, Some(_)) | (Some(_), None) => false,
            (Some(me), Some(them)) => Rc::ptr_eq(me, them),
        }
    }

    pub fn iter(&self) -> impl Iterator<Item = &Rc<Node<T>>> {
        NodeIter {
            position: &self.head,
        }
    }

    pub fn iter_until<'a>(&'a self, other: &'a List<T>) -> impl Iterator<Item = &Rc<Node<T>>> {
        NodeIterUntil {
            position: &self.head,
            stop: &other.head,
        }
    }
}

pub struct NodeIter<'a, T> {
    position: &'a Option<Rc<Node<T>>>,
}

impl<'a, T> Iterator for NodeIter<'a, T> {
    type Item = &'a Rc<Node<T>>;

    fn next(&mut self) -> Option<Self::Item> {
        let (return_value, next_position) = match &self.position {
            None => return None,
            Some(rc_node) => {
                let next_position = &rc_node.parent;
                let return_value = rc_node;
                (return_value, next_position)
            }
        };
        self.position = next_position;
        Some(return_value)
    }
}

pub struct NodeIterUntil<'a, T> {
    position: &'a Option<Rc<Node<T>>>,
    stop: &'a Option<Rc<Node<T>>>,
}

impl<'a, T> Iterator for NodeIterUntil<'a, T> {
    type Item = &'a Rc<Node<T>>;

    fn next(&mut self) -> Option<Self::Item> {
        match (self.position, self.stop) {
            (_, None) => {}
            (None, _) => {}
            (Some(this_rc), Some(stop_rc)) => {
                if Rc::ptr_eq(this_rc, stop_rc) {
                    return None;
                }
            }
        };
        let (return_value, next_position) = match &self.position {
            None => return None,
            Some(rc_node) => {
                let next_position = &rc_node.parent;
                let return_value = rc_node;
                (return_value, next_position)
            }
        };
        self.position = next_position;
        Some(return_value)
    }
}