#![warn(missing_docs)]
//! This file implements a labelled graph.  See the
//! [trait][super::LabelGraph] for details.
//!
//! Since the method
//! [`find_children_with_label`][super::LabelGraph::find_children_with_label]
//! needs to be implemented efficiently, we store the mappings between
//! labels and edges in both directions.

#[allow(unused_imports)]
use super::{Graph, GraphLabel, LabelExtGraph, LabelGraph};
#[allow(unused_imports)]
use crate::error::Error;

// We use BTreeMap and BTreeSet here as we need to exclude duplicate
// edge sets, while an ordinary hashmap and hashset do not allow
// hashing.
use std::collections::{
    btree_map::{Iter as MapIter, Keys},
    btree_set::Iter,
    BTreeMap as Map, BTreeSet as Set, HashMap as HMap,
};

#[derive(Debug, Clone, Default)]
struct DLNode<T: GraphLabel> {
    by_target: Map<usize, Set<T>>,
    by_label: Map<T, Set<usize>>,
    flat: Vec<(T, usize)>,
}

impl<T: GraphLabel> DLNode<T> {
    fn new(
        by_target: Map<usize, Set<T>>,
        by_label: Map<T, Set<usize>>,
        flat: Vec<(T, usize)>,
    ) -> Self {
        Self {
            by_target,
            by_label,
            flat,
        }
    }
}

/// Mapping a set of edges to an index of node.
type EdgeMap<T> = HMap<Set<(T, usize)>, usize>;

/// Double direction Labelled Graph.
///
/// Each node is supposed to have a unique edge set.  Constructing
/// methods such as from the trait
/// [`LabelExtGraph`][super::LabelExtGraph] already handles the
/// elimination of duplication.
#[derive(Debug, Clone)]
pub struct DLGraph<T: GraphLabel> {
    nodes: Vec<DLNode<T>>,
    edges_table: EdgeMap<T>,
}

impl<T: GraphLabel> DLGraph<T> {
    #[inline]
    /// Return an empty graph.
    pub fn new() -> Self {
        Self {
            nodes: Vec::new(),
            edges_table: HMap::default(),
        }
    }
}

impl<T: GraphLabel> Default for DLGraph<T> {
    #[inline]
    fn default() -> Self {
        Self::new()
    }
}

impl<T: GraphLabel> Graph for DLGraph<T> {
    // Not using a boxed pointer is supposed to save some allocations.
    type Iter<'a> = std::iter::Copied<Keys<'a, usize, Set<T>>> where T: 'a;

    #[inline]
    fn is_empty(&self) -> bool {
        self.nodes.is_empty()
    }

    #[inline]
    fn nodes_len(&self) -> usize {
        self.nodes.len()
    }

    #[inline]
    fn children_of(&self, node_id: usize) -> Result<Self::Iter<'_>, Error> {
        match self.nodes.get(node_id) {
            Some(node) => Ok(node.by_target.keys().copied()),
            None => Err(Error::IndexOutOfBounds(node_id, self.nodes.len())),
        }
    }

    #[inline]
    /// Return the number of "children" of a node, or an error if the
    /// node is not a member of the graph.
    ///
    /// This counts edges with different labels as different edges.
    fn degree(&self, node_id: usize) -> Result<usize, Error> {
        self.nodes
            .get(node_id)
            .ok_or(Error::IndexOutOfBounds(node_id, self.nodes.len()))
            .map(|node| node.flat.len())
    }

    #[inline]
    fn is_empty_node(&self, node_id: usize) -> Result<bool, Error> {
        self.nodes
            .get(node_id)
            .ok_or(Error::IndexOutOfBounds(node_id, self.nodes.len()))
            .map(|node| node.flat.is_empty())
    }

    fn has_edge(&self, source: usize, target: usize) -> Result<bool, Error> {
        match self.nodes.get(source) {
            Some(source_node) => {
                if self.nodes.get(target).is_none() {
                    return Err(Error::IndexOutOfBounds(target, self.nodes.len()));
                }

                Ok(source_node.by_target.contains_key(&target))
            }
            None => Err(Error::IndexOutOfBounds(source, self.nodes.len())),
        }
    }
}

/// A delegation of iterators.
///
/// This is used to avoid a boxed pointer to an iterator.
#[derive(Default, Debug)]
pub struct LabelIndexIter<'a> {
    iter: Option<std::iter::Copied<Iter<'a, usize>>>,
}

impl<'a> Iterator for LabelIndexIter<'a> {
    type Item = usize;

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        self.iter.as_mut().and_then(|iterator| iterator.next())
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        match &self.iter {
            Some(iter) => iter.size_hint(),
            None => (0, Some(0)),
        }
    }
}

impl<'a> ExactSizeIterator for LabelIndexIter<'a> {
    #[inline]
    fn len(&self) -> usize {
        match &self.iter {
            Some(iter) => iter.len(),
            None => 0,
        }
    }
}

impl<'a> LabelIndexIter<'a> {
    fn new(iter: std::iter::Copied<Iter<'a, usize>>) -> Self {
        let iter = Some(iter);
        Self { iter }
    }
}

// A convenience method
impl<'a> From<&'a Set<usize>> for LabelIndexIter<'a> {
    fn from(set: &'a Set<usize>) -> Self {
        Self::new(set.iter().copied())
    }
}

#[derive(Debug)]
/// A delegation of iterators.
///
/// This is used to avoid a boxed pointer to an iterator.
pub struct LabelIter<'a, T> {
    iter: MapIter<'a, T, Set<usize>>,
}

impl<'a, T> ExactSizeIterator for LabelIter<'a, T> {
    #[inline]
    fn len(&self) -> usize {
        self.iter.len()
    }
}

impl<'a, T> LabelIter<'a, T> {
    fn new(iter: MapIter<'a, T, Set<usize>>) -> Self {
        Self { iter }
    }
}

impl<'a, T> Iterator for LabelIter<'a, T> {
    type Item = (&'a T, LabelIndexIter<'a>);

    #[inline]
    fn next(&mut self) -> Option<Self::Item> {
        self.iter.next().map(|(label, set)| (label, set.into()))
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.iter.size_hint()
    }
}

impl<T: GraphLabel> LabelGraph<T> for DLGraph<T> {
    type Iter<'a> = LabelIndexIter<'a> where T: 'a;

    type LabelIter<'a> = LabelIter<'a,T> where T: 'a;

    fn edge_label(&self, source: usize, target: usize) -> Result<Vec<T>, Error> {
        if self.has_edge(source, target)? {
            Ok(self
                .nodes
                .get(source)
                .unwrap()
                .by_target
                .get(&target)
                .unwrap()
                .iter()
                .copied()
                .collect())
        } else {
            Ok(Vec::new())
        }
    }

    fn find_children_with_label(
        &self,
        node_id: usize,
        label: &T,
    ) -> Result<<Self as LabelGraph<T>>::Iter<'_>, Error> {
        match self
            .nodes
            .get(node_id)
            .ok_or(Error::IndexOutOfBounds(node_id, self.nodes.len()))?
            .by_label
            .get(label)
        {
            Some(set) => Ok(set.into()),
            None => Ok(Default::default()),
        }
    }

    #[inline]
    fn labels_of(&self, node_id: usize) -> Result<Self::LabelIter<'_>, Error> {
        match self.nodes.get(node_id) {
            Some(node) => Ok(Self::LabelIter::new(node.by_label.iter())),
            None => Err(Error::IndexOutOfBounds(node_id, self.nodes.len())),
        }
    }
}

impl<T: GraphLabel> LabelExtGraph<T> for DLGraph<T> {
    fn extend(&mut self, edges: impl IntoIterator<Item = (T, usize)>) -> Result<usize, Error> {
        let mut by_target: Map<usize, Set<T>> = Map::default();
        let mut by_label: Map<T, Set<usize>> = Map::default();
        let mut flat = Vec::new();
        let mut edges_set = Set::new();

        for (label, to) in edges {
            if !self.has_node(to) {
                return Err(Error::IndexOutOfBounds(to, self.nodes.len()));
            }

            edges_set.insert((label, to));

            if let Some(set) = by_target.get(&to) {
                if !set.contains(&label) {
                    flat.push((label, to));
                    by_target.get_mut(&to).unwrap().insert(label);
                    by_label
                        .entry(label)
                        .or_insert_with(Default::default)
                        .insert(to);
                }
            } else {
                flat.push((label, to));
                by_target
                    .entry(to)
                    .or_insert_with(Default::default)
                    .insert(label);
                by_label
                    .entry(label)
                    .or_insert_with(Default::default)
                    .insert(to);
            }
        }

        match self.edges_table.get(&edges_set) {
            Some(old_index) => Ok(*old_index),
            None => {
                let new_node = DLNode::new(by_target, by_label, flat);
                let new_index = self.nodes_len();

                self.edges_table.insert(edges_set, new_index);

                self.nodes.push(new_node);

                Ok(new_index)
            }
        }
    }
}

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

    macro_rules! set {
        () => { Set::<usize>::default() };
        ($($num:literal),*) => {
            {
                let mut set: Set<usize> = Set::default();
                $(set.insert($num);)*
                set
            }
        };
    }

    macro_rules! map {
        () => { Map::<usize, Set<usize>>::default() };
        ($(($key:literal, $value:expr)),*) => {
            {
                let mut map: Map<usize, Set<usize>> = Map::default();
                $(map.insert($key, $value);)*
                map
            }
        };
    }

    #[test]
    fn test_graph_apis() -> Result<(), Error> {
        let mut graph: DLGraph<usize> = Default::default();

        // testing empty graph
        assert!(graph.is_empty());

        // testing adding an empty node
        assert_eq!(graph.extend(std::iter::empty())?, 0);

        // testing nodes_len
        assert_eq!(graph.nodes_len(), 1);

        // testing extension

        assert_eq!(graph.extend([(0, 0)].iter().copied())?, 1);
        assert_eq!(graph.extend([(1, 0), (1, 1)].iter().copied())?, 2);
        assert_eq!(graph.extend([(3, 0), (3, 2)].iter().copied())?, 3);
        assert_eq!(graph.extend([(1, 1), (1, 2)].iter().copied())?, 4);
        assert_eq!(graph.extend([(2, 1), (3, 2), (2, 3)].iter().copied())?, 5);

        // testing adding a duplicated edge set
        assert_eq!(graph.extend([(2, 1), (2, 3), (3, 2)].iter().copied())?, 5);
        assert_eq!(graph.extend([(3, 2), (3, 0)].iter().copied())?, 3);

        let graph = graph;

        // ensuring the correct length
        assert_eq!(graph.nodes_len(), 6);

        // testing children_of
        assert_eq!(graph.children_of(5)?.collect::<Set<_>>(), set!(1, 3, 2));

        // testing find_children_with_label
        assert_eq!(
            graph.find_children_with_label(5, &2)?.collect::<Set<_>>(),
            set!(1, 3)
        );

        // testing edge_label
        assert_eq!(
            graph.edge_label(5, 2)?.into_iter().collect::<Set<_>>(),
            set!(3)
        );
        assert!(matches!(
            graph.edge_label(6, 2),
            Err(Error::IndexOutOfBounds(6, 6))
        ));

        // testing degree
        assert_eq!(graph.degree(4)?, 2);

        // testing is_empty_node
        assert!(graph.is_empty_node(0)?);
        assert!(!graph.is_empty_node(1)?);

        // testing has_edge
        assert!(graph.has_edge(3, 2)?);
        assert!(!graph.has_edge(3, 1)?);
        assert!(matches!(
            graph.has_edge(3, 6),
            Err(Error::IndexOutOfBounds(6, 6))
        ));

        // testing labels_of
        let mut label_map: Map<usize, Set<usize>> = Map::default();

        for (label, children) in graph.labels_of(5)? {
            label_map.insert(*label, children.collect());
        }

        let compare_map = map!((2, set!(1, 3)), (3, set!(2)));

        assert_eq!(label_map, compare_map);

        assert!(matches!(
            graph.labels_of(6),
            Err(Error::IndexOutOfBounds(6, 6))
        ));

        Ok(())
    }
}