futures-dagtask 0.2.0

use std::mem;
use std::hash::{ Hash, BuildHasher };
use std::vec::IntoIter;
use std::collections::HashMap;
use std::collections::hash_map::RandomState;
use num_traits::{ CheckedAdd, One };


pub struct Graph<N, I=u32, S=RandomState> {
    map: HashMap<Index<I>, (N, Vec<Index<I>>), S>,
    pub(crate) last: Index<I>
}

impl<N, I, S> Default for Graph<N, I, S>
where
    I: Default + Hash + PartialEq + Eq,
    S: Default + BuildHasher
{
    fn default() -> Graph<N, I, S> {
        Graph { map: HashMap::default(), last: Index(Default::default()) }
    }
}

impl<N, I, S> Graph<N, I, S>
where
    I: CheckedAdd + One + Hash + PartialEq + Eq + Clone,
    S: BuildHasher
{
    pub fn add_node(&mut self, node: N) -> Result<Index<I>, N> {
        match self.last.next() {
            Some(index) => {
                self.map.insert(index.clone(), (node, Vec::new()));
                Ok(index)
            },
            None => Err(node)
        }
    }

    pub fn contains(&self, index: &Index<I>) -> bool {
        self.map.contains_key(index)
    }

    pub fn add_edge(&mut self, parent: &Index<I>, next: Index<I>) -> Option<()> {
        self.map.get_mut(parent)
            .map(|(_, sum)| sum.push(next))
    }

    pub fn remove_node(&mut self, index: &Index<I>) -> Option<N> {
        self.map.remove(index)
            .map(|(n, _)| n)
    }

    pub fn get_node_mut(&mut self, index: &Index<I>) -> Option<&mut N> {
        self.map.get_mut(index)
            .map(|(n, _)| n)
    }

    pub fn walk(&mut self, index: &Index<I>) -> IntoIter<Index<I>> {
        self.map.get_mut(index)
            .map(|(_, arr)| mem::replace(arr, Vec::new()))
            .unwrap_or_else(Vec::new)
            .into_iter()
    }
}

#[derive(Hash, PartialEq, Eq, PartialOrd, Ord, Copy, Clone, Debug)]
pub struct Index<I=u32>(I);

impl<I> Index<I>
where I: CheckedAdd + One
{
    fn next(&mut self) -> Option<Index<I>> {
        Some(mem::replace(self, Index(self.0.checked_add(&I::one())?)))
    }
}