use std::fmt::Debug;

#[derive(Debug, Clone)]
pub struct List<'parent, T> {
    data: T,
    parent: Link<'parent, T>,
}

type Link<'parent, T> = Option<&'parent List<'parent, T>>;

impl<'parent, T> List<'parent, T> {
    pub fn new(first_item: T) -> Self {
        Self {
            data: first_item,
            parent: None,
        }
    }

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

    pub fn get_parent(&'parent self) -> Link<'parent, T> {
        self.parent
    }

    pub fn iter(&self) -> Iter<'_, T> {
        Iter { next: Some(self) }
    }
}

pub trait ListType<'parent, T> {
    fn push(&'parent self, item: T) -> List<'parent, T>;
}

impl<'parent, T> ListType<'parent, T> for List<'parent, T> {
    fn push(&'parent self, item: T) -> Self {
        Self {
            data: item,
            parent: Some(self),
        }
    }
}

impl<'parent, T> ListType<'parent, T> for Link<'parent, T> {
    fn push(&'parent self, item: T) -> List<'parent, T> {
        List {
            data: item,
            parent: *self,
        }
    }
}

pub struct Iter<'a, T> {
    next: Link<'a, T>,
}

impl<'a, T> Iterator for Iter<'a, T> {
    type Item = &'a T;

    fn next(&mut self) -> Option<Self::Item> {
        let ret = self.next.map(|link| link.get_data());
        self.next = self.next.map(|link| link.get_parent()).flatten();
        ret
    }
}