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pub struct Node<K, V> {
    key: K,
    value: V,
    children: Vec<Box<Node<K, V>>>,
}

pub enum Error {
    ParentNotFound,
}

impl<K, V> Node<K, V>
where
    K: PartialEq,
{
    pub fn new(key: K, value: V) -> Self {
        Self {
            key,
            value,
            children: Vec::new(),
        }
    }

    pub fn add_child(&mut self, child: Node<K, V>) -> Option<Box<Node<K, V>>> {
        let child = Box::new(child);

        let mut old_value = None;
        for i in 0..self.children.len() {
            if self.children[i] == child {
                old_value = Some(self.children.remove(i));
                break;
            }
        }

        self.children.push(child);

        old_value
    }

    pub fn add_child_at_path(
        &mut self,
        path: &[&K],
        child: Node<K, V>,
    ) -> Result<Option<Box<Node<K, V>>>, Error> {
        match self.get_mut_child(path) {
            Some(parent) => Ok(parent.add_child(child)),
            None => Err(Error::ParentNotFound),
        }
    }

    /// Get a child node based on a list of keys.
    ///
    /// # Examples
    ///
    /// ```
    /// use generic_tree::Node;
    ///
    /// # let mut grandparent = Node::new("grandparent".to_owned(), 1);
    /// # let mut parent = Node::new("parent".to_owned(), 2);
    /// # let child = Node::new("child".to_owned(), 3);
    ///
    /// # assert!(parent.add_child(child).is_none());
    /// # assert!(grandparent.add_child(parent).is_none());
    ///
    /// // Tree structure:
    /// // grandparent -> parent -> child
    /// assert!(grandparent.get_child(&["parent", "child"]).is_some());
    /// ```
    pub fn get_child<Q>(&self, path: &[Q]) -> Option<&Node<K, V>>
    where
        Q: PartialEq<K>,
    {
        if path.is_empty() {
            return Some(self);
        }

        let child = &path[0];
        let path = &path[1..];

        for entry in &self.children {
            if child == entry.key() {
                return entry.get_child(path);
            }
        }

        None
    }

    pub fn get_mut_child(&mut self, path: &[&K]) -> Option<&mut Node<K, V>> {
        if path.is_empty() {
            return Some(self);
        }

        let child = path[0];
        let path = &path[1..];

        for entry in &mut self.children {
            if entry.key() == child {
                return entry.get_mut_child(path);
            }
        }

        None
    }

    pub fn take_child(&mut self, path: &[&K]) -> Option<Node<K, V>> {
        if path.is_empty() {
            return None;
        }

        let child = path[0];
        let path = &path[1..];

        for entry in &mut self.children {
            if entry.key() == child {
                return entry.take_child(path);
            }
        }

        None
    }

    pub fn value(&self) -> &V {
        &self.value
    }

    pub fn mut_value(&mut self) -> &mut V {
        &mut self.value
    }

    pub fn key(&self) -> &K {
        &self.key
    }
}

impl<K, V> PartialEq for Node<K, V>
where
    K: PartialEq,
{
    fn eq(&self, other: &Self) -> bool {
        self.key == other.key
    }
}

impl<K, V> PartialEq<K> for Node<K, V>
where
    K: PartialEq,
{
    fn eq(&self, other: &K) -> bool {
        &self.key == other
    }
}