//! Graph Edge related constructs.

use self::Direction::{Incoming, Outgoing};
use crate::graph::{Directed, Graph, Undirected};
use crate::node::NodeTrait;
use crate::traverse::Neighbors;
use indexmap::map::Iter as IndexMapIter;
use indexmap::IndexMap;
use std::marker::PhantomData;

/// A graph's edge type determines whether is has directed edges or not.
pub trait EdgeType {
    fn is_directed() -> bool;
}

impl EdgeType for Directed {
    #[inline]
    fn is_directed() -> bool {
        true
    }
}

impl EdgeType for Undirected {
    #[inline]
    fn is_directed() -> bool {
        false
    }
}

pub struct Edges<'a, N, E: 'a, Ty>
where
    N: 'a + NodeTrait,
    Ty: EdgeType,
{
    from: N,
    edges: &'a IndexMap<(N, N), E>,
    iter: Neighbors<'a, N, Ty>,
}

impl<'a, N, E, Ty> Edges<'a, N, E, Ty>
where
    N: 'a + NodeTrait,
    Ty: EdgeType,
{
    pub fn new(from: N, edges: &'a IndexMap<(N, N), E>, iter: Neighbors<'a, N, Ty>) -> Self {
        Self { from, edges, iter }
    }
}

impl<'a, N, E, Ty> Iterator for Edges<'a, N, E, Ty>
where
    N: 'a + NodeTrait,
    E: 'a,
    Ty: EdgeType,
{
    type Item = (N, N, &'a E);
    fn next(&mut self) -> Option<Self::Item> {
        match self.iter.next() {
            None => None,
            Some(b) => {
                let a = self.from;
                match self.edges.get(&Graph::<N, E, Ty>::edge_key(a, b)) {
                    None => unreachable!(),
                    Some(edge) => Some((a, b, edge)),
                }
            }
        }
    }
}

pub struct AllEdges<'a, N, E: 'a, Ty> {
    inner: IndexMapIter<'a, (N, N), E>,
    ty: PhantomData<Ty>,
}

impl<'a, N, E, Ty> AllEdges<'a, N, E, Ty>
where
    N: 'a + NodeTrait,
{
    pub fn new(inner: IndexMapIter<'a, (N, N), E>, ty: PhantomData<Ty>) -> Self {
        Self { inner, ty }
    }
}

impl<'a, N, E, Ty> Iterator for AllEdges<'a, N, E, Ty>
where
    N: 'a + NodeTrait,
    E: 'a,
    Ty: EdgeType,
{
    type Item = (N, N, &'a E);

    /// Advances the iterator and returns the next value.
    fn next(&mut self) -> Option<Self::Item> {
        match self.inner.next() {
            None => None,
            Some((&(a, b), v)) => Some((a, b, v)),
        }
    }

    /// Returns the bounds on the remaining length of the iterator.
    ///
    /// Specifically, `size_hint()` returns a tuple where the first element
    /// is the lower bound, and the second element is the upper bound.
    ///
    /// The second half of the tuple that is returned is an [`Option`]`<`[`usize`]`>`.
    /// A [`None`] here means that either there is no known upper bound, or the
    /// upper bound is larger than [`usize`].
    ///
    /// # Examples
    ///
    /// Basic usage:
    ///
    /// ```
    /// use indexmap::IndexMap;
    /// use safe_graph::edge::AllEdges;
    /// use safe_graph::graph::Directed;
    /// use std::marker::PhantomData;
    ///
    /// let edges = IndexMap::new();
    /// let all_edges: AllEdges<u32, f32, Directed> = AllEdges::new(edges.iter(), PhantomData);
    ///
    /// assert_eq!(all_edges.size_hint(), (0, Some(0)));
    /// ```
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }

    /// Consumes the iterator, counting the number of iterations and returning it.
    fn count(self) -> usize {
        self.inner.count()
    }

    /// Returns the `n`th element of the iterator.
    ///
    /// Like most indexing operations, the count starts from zero, so `nth(0)`
    /// returns the first value, `nth(1)` the second, and so on.
    ///
    /// Note that all preceding elements, as well as the returned element, will be
    /// consumed from the iterator. That means that the preceding elements will be
    /// discarded, and also that calling `nth(0)` multiple times on the same iterator
    /// will return different elements.
    ///
    /// `nth()` will return [`None`] if `n` is greater than or equal to the length of the
    /// iterator.
    fn nth(&mut self, n: usize) -> Option<Self::Item> {
        self.inner
            .nth(n)
            .map(|(&(n1, n2), weight)| (n1, n2, weight))
    }

    /// Consumes the iterator, returning the last element.
    fn last(self) -> Option<Self::Item> {
        self.inner
            .last()
            .map(|(&(n1, n2), weight)| (n1, n2, weight))
    }
}

impl<'a, N, E, Ty> DoubleEndedIterator for AllEdges<'a, N, E, Ty>
where
    N: 'a + NodeTrait,
    E: 'a,
    Ty: EdgeType,
{
    /// Removes and returns an element from the end of the iterator.
    ///
    /// Returns `None` when there are no more elements.
    fn next_back(&mut self) -> Option<Self::Item> {
        self.inner
            .next_back()
            .map(|(&(n1, n2), weight)| (n1, n2, weight))
    }
}

/// Convert an element like `(i, j)` or `(i, j, w)` into a triple of source, target, edge weight.
///
/// For `Graph::from_edges`.
pub trait IntoWeightedEdge<E> {
    type NodeId;
    fn into_weighted_edge(self) -> (Self::NodeId, Self::NodeId, E);
}

/// Convert an element like `(i, j)` into a triple of source, target, edge weight.
impl<Ix, E> IntoWeightedEdge<E> for (Ix, Ix)
where
    E: Default,
{
    type NodeId = Ix;

    fn into_weighted_edge(self) -> (Ix, Ix, E) {
        let (s, t) = self;
        (s, t, E::default())
    }
}

/// Convert an element like `(i, j, w)` into a triple of source, target, edge weight.
///
/// Meaning do no change, just return.
impl<Ix, E> IntoWeightedEdge<E> for (Ix, Ix, E) {
    type NodeId = Ix;

    fn into_weighted_edge(self) -> (Ix, Ix, E) {
        self
    }
}

/// Convert an element like `(i, j, w)` into a triple of source, target, edge weight.
///
/// Clone the edge weight from the reference.
impl<'a, Ix, E> IntoWeightedEdge<E> for (Ix, Ix, &'a E)
where
    E: Clone,
{
    type NodeId = Ix;

    fn into_weighted_edge(self) -> (Ix, Ix, E) {
        let (a, b, c) = self;
        (a, b, c.clone())
    }
}

/// Convert an element like `&(i, j)` into a triple of source, target, edge weight.
///
/// See that the element `&(i, j)` is a reference.
impl<'a, Ix, E> IntoWeightedEdge<E> for &'a (Ix, Ix)
where
    Ix: Copy,
    E: Default,
{
    type NodeId = Ix;

    fn into_weighted_edge(self) -> (Ix, Ix, E) {
        let (s, t) = *self;
        (s, t, E::default())
    }
}

/// Convert an element like `&(i, j, w)` into a triple of source, target, edge weight.
///
/// Clone the edge weight from the reference.
/// See that the element `&(i, j, w)` is a reference.
impl<'a, Ix, E> IntoWeightedEdge<E> for &'a (Ix, Ix, E)
where
    Ix: Copy,
    E: Clone,
{
    type NodeId = Ix;
    fn into_weighted_edge(self) -> (Ix, Ix, E) {
        self.clone()
    }
}

/// Edge direction.
#[derive(Copy, Debug, PartialEq, PartialOrd, Ord, Eq, Hash)]
#[repr(usize)]
pub enum Direction {
    /// An `Outgoing` edge is an outward edge *from* the current node.
    Outgoing = 0,
    /// An `Incoming` edge is an inbound edge *to* the current node.
    Incoming = 1,
}

copyclone!(Direction);

impl Direction {
    /// Return the opposite `Direction`.
    #[inline]
    pub fn opposite(self) -> Direction {
        match self {
            Outgoing => Incoming,
            Incoming => Outgoing,
        }
    }

    /// Return `0` for `Outgoing` and `1` for `Incoming`.
    #[inline]
    pub fn index(self) -> usize {
        (self as usize) & 0x1
    }
}

/// Non-repr(usize) version of `Direction`.
#[derive(Copy, Clone, Debug, PartialEq)]
pub enum CompactDirection {
    Outgoing,
    Incoming,
}

impl From<Direction> for CompactDirection {
    fn from(d: Direction) -> Self {
        match d {
            Outgoing => CompactDirection::Outgoing,
            Incoming => CompactDirection::Incoming,
        }
    }
}

impl PartialEq<Direction> for CompactDirection {
    fn eq(&self, rhs: &Direction) -> bool {
        (*self as usize) == (*rhs as usize)
    }
}

#[cfg(test)]
mod tests {
    use crate::edge::{AllEdges, CompactDirection, Direction, EdgeType, Edges, IntoWeightedEdge};
    use crate::graph::{Directed, Undirected};
    use crate::traverse::Neighbors;
    use indexmap::IndexMap;
    use std::cmp::PartialEq;
    use std::marker::PhantomData;

    #[test]
    fn edge_type_is_directed() {
        assert_eq!(Directed::is_directed(), true);
        assert_eq!(Undirected::is_directed(), false);
    }

    #[test]
    fn edges_new() {
        // Prepare arguments.
        let from: u32 = 1;
        let edges: IndexMap<(u32, u32), f32> = IndexMap::new();
        let node_neighbors: Vec<(u32, CompactDirection)> = vec![];
        let iter = node_neighbors.iter();
        let neighbors: Neighbors<u32, Directed> = Neighbors::new(iter, PhantomData);

        // Test `Edges` struct creation.
        Edges::new(from, &edges, neighbors);
    }

    #[test]
    fn edges_next() {
        // Prepare arguments.
        let from: u32 = 1;
        let mut edges: IndexMap<(u32, u32), f32> = IndexMap::with_capacity(3);
        edges.insert((2, 1), 2.0);
        edges.insert((1, 3), 3.0);
        edges.insert((1, 4), 4.0);
        let node_neighbors: Vec<(u32, CompactDirection)> = vec![
            (2, CompactDirection::Incoming),
            (3, CompactDirection::Outgoing),
            (4, CompactDirection::Outgoing),
        ];
        let neighbors: Neighbors<u32, Directed> =
            Neighbors::new(node_neighbors.iter(), PhantomData);

        // Construct edges from `1`.
        // The edge (2, 1) is being filtered out as the edges are directed.
        let mut edges = Edges::new(from, &edges, neighbors);

        // Test all existing edges from `1`.
        assert_eq!(edges.next(), Some((1, 3, &3.0)));
        assert_eq!(edges.next(), Some((1, 4, &4.0)));

        // Test the end of iteration.
        assert_eq!(edges.next(), None);
    }

    #[test]
    #[should_panic]
    fn edges_next_unreachable() {
        // Prepare arguments.
        let from: u32 = 1;
        let edges: IndexMap<(u32, u32), f32> = IndexMap::new();
        let node_neighbors: Vec<(u32, CompactDirection)> = vec![(2, CompactDirection::Incoming)];
        let neighbors: Neighbors<u32, Directed> =
            Neighbors::new(node_neighbors.iter(), PhantomData);

        // Construct edges.
        let mut edges = Edges::new(from, &edges, neighbors);

        assert_eq!(edges.next(), Some((1, 2, &0.0)));
    }

    #[test]
    fn all_edges_new() {
        let _all_edges: AllEdges<u32, f32, Directed> =
            AllEdges::new(IndexMap::new().iter(), PhantomData);
    }

    #[test]
    fn all_edges_next() {
        let mut edges: IndexMap<(u32, u32), f32> = IndexMap::with_capacity(3);
        edges.insert((2, 1), 2.0);
        edges.insert((1, 3), 3.0);
        edges.insert((1, 4), 4.0);

        let mut all_edges: AllEdges<u32, f32, Directed> = AllEdges::new(edges.iter(), PhantomData);

        assert_eq!(all_edges.next(), Some((2, 1, &2.0)));
        assert_eq!(all_edges.next(), Some((1, 3, &3.0)));
        assert_eq!(all_edges.next(), Some((1, 4, &4.0)));
        assert_eq!(all_edges.next(), None);
    }

    #[test]
    fn all_edges_size_hint() {
        let mut edges: IndexMap<(u32, u32), f32> = IndexMap::with_capacity(3);
        edges.insert((2, 1), 2.0);
        edges.insert((1, 3), 3.0);
        edges.insert((1, 4), 4.0);
        let mut all_edges: AllEdges<u32, f32, Directed> = AllEdges::new(edges.iter(), PhantomData);

        assert_eq!(all_edges.size_hint(), (3, Some(3)));

        // Lower the length of the iterator.
        all_edges.next();

        assert_eq!(all_edges.size_hint(), (2, Some(2)));

        // Lower the length of the iterator.
        all_edges.next();

        assert_eq!(all_edges.size_hint(), (1, Some(1)));

        // Lower the length of the iterator.
        all_edges.next();

        assert_eq!(all_edges.size_hint(), (0, Some(0)));
    }

    #[test]
    fn all_edges_count() {
        let mut edges: IndexMap<(u32, u32), f32> = IndexMap::with_capacity(3);
        edges.insert((2, 1), 2.0);
        edges.insert((1, 3), 3.0);
        edges.insert((1, 4), 4.0);
        let all_edges: AllEdges<u32, f32, Directed> = AllEdges::new(edges.iter(), PhantomData);

        assert_eq!(all_edges.count(), 3);
    }

    #[test]
    fn all_edges_nth() {
        let mut edges: IndexMap<(u32, u32), f32> = IndexMap::with_capacity(3);
        edges.insert((2, 1), 2.0);
        edges.insert((1, 3), 3.0);
        edges.insert((1, 4), 4.0);
        let mut all_edges: AllEdges<u32, f32, Directed> = AllEdges::new(edges.iter(), PhantomData);

        assert_eq!(all_edges.nth(2), Some((1, 4, &4.0)));
        assert_eq!(all_edges.nth(0), None);
    }

    #[test]
    fn all_edges_last() {
        let mut edges: IndexMap<(u32, u32), f32> = IndexMap::with_capacity(3);
        edges.insert((2, 1), 2.0);
        edges.insert((1, 3), 3.0);
        edges.insert((1, 4), 4.0);
        let all_edges: AllEdges<u32, f32, Directed> = AllEdges::new(edges.iter(), PhantomData);

        assert_eq!(all_edges.last(), Some((1, 4, &4.0)));
    }

    #[test]
    fn all_edges_next_back() {
        let mut edges: IndexMap<(u32, u32), f32> = IndexMap::with_capacity(3);
        edges.insert((2, 1), 2.0);
        edges.insert((1, 3), 3.0);
        edges.insert((1, 4), 4.0);

        let mut all_edges: AllEdges<u32, f32, Directed> = AllEdges::new(edges.iter(), PhantomData);

        // Iterate backwards.
        assert_eq!(all_edges.next_back(), Some((1, 4, &4.0)));
        assert_eq!(all_edges.next_back(), Some((1, 3, &3.0)));
        assert_eq!(all_edges.next_back(), Some((2, 1, &2.0)));
        assert_eq!(all_edges.next_back(), None);
    }

    #[test]
    fn into_weighted_edge() {
        // Test with tuple.
        assert_eq!((1, 2).into_weighted_edge(), (1, 2, f32::default()));

        // Test with triple.
        assert_eq!((1, 2, 3).into_weighted_edge(), (1, 2, 3));

        // Test with triple having edge weight as reference.
        assert_eq!((1, 2, &3).into_weighted_edge(), (1, 2, 3));

        // Test with tuple as reference.
        assert_eq!((&(1, 2)).into_weighted_edge(), (1, 2, f32::default()));

        // Test with triple as reference.
        assert_eq!((&(1, 2, 3)).into_weighted_edge(), (1, 2, 3));
    }

    #[test]
    fn direction_opposite() {
        assert_eq!(Direction::Incoming.opposite(), Direction::Outgoing);
        assert_eq!(Direction::Outgoing.opposite(), Direction::Incoming);
    }

    #[test]
    fn direction_index() {
        assert_eq!(Direction::Incoming.index(), Direction::Incoming as usize);
        assert_eq!(Direction::Outgoing.index(), Direction::Outgoing as usize);
    }

    #[test]
    fn direction_clone() {
        assert_eq!(Direction::Incoming.clone(), Direction::Incoming);
        assert_eq!(Direction::Outgoing.clone(), Direction::Outgoing);
    }

    #[test]
    fn compact_direction_from() {
        assert_eq!(
            CompactDirection::from(Direction::Incoming),
            CompactDirection::Incoming
        );
        assert_eq!(
            CompactDirection::from(Direction::Outgoing),
            CompactDirection::Outgoing
        );
    }

    #[test]
    fn compact_direction_partial_equal_with_direction() {
        assert_eq!(CompactDirection::Incoming.eq(&Direction::Incoming), true);
        assert_eq!(CompactDirection::Incoming.eq(&Direction::Outgoing), false);

        assert_eq!(CompactDirection::Outgoing.eq(&Direction::Outgoing), true);
        assert_eq!(CompactDirection::Outgoing.eq(&Direction::Incoming), false);
    }
}