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/*
 * Copyright (c) 2018 Frank Fischer <frank-fischer@shadow-soft.de>
 *
 * This program is free software: you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see  <http://www.gnu.org/licenses/>
 */

//! Abstraction of neighboring edges.
//!
//! This module implements the arguably simplest representation of a graph: for
//! each node the list of adjacent edges and nodes. No further information like
//! the number of nodes or edges in a graph is available.
//!
//! The purpose of the trait `Adjacencies` is therefore to abstract over the concept
//! if adjacent edges and nodes. Standard examples are "all edges" (in the
//! undirected sense), "incoming edges" and "outgoing edges" represented by the structs
//! `Neighbors`, `InEdges` and `OutEdges`.
//!
//! Some algorithms (e.g. breadth-first search or depth-first search) can be
//! described in terms of adjacencies only.
//!
//! # Example
//!
//! ```
//! use rs_graph::classes;
//! use rs_graph::Net;
//! use rs_graph::traits::*;
//! use rs_graph::adjacencies::*;
//!
//! let g = classes::peterson::<Net>();
//!
//! let neighs = Neighbors(&g);
//! let neighs = neighs.filter(|&(e, _)| {
//!   let (u,v) = g.enodes(e);
//!   (g.node_id(u) < 5) == (g.node_id(v) < 5)
//! });
//! for u in g.nodes() {
//!     assert_eq!(neighs.neighs(u).count(), 2);
//! }
//! ```

use crate::traits::{Directed, GraphType, Undirected};

use std::iter::Filter;

pub trait Adjacencies<'a>: GraphType<'a> {
    type Iter: 'a + Iterator<Item = (Self::Edge, Self::Node)>;

    fn neighs(&self, u: Self::Node) -> Self::Iter;

    fn filter<P>(self, predicate: P) -> FilterAdjacencies<Self, P>
    where
        Self: Sized,
        P: for<'r> Fn(&'r (Self::Edge, Self::Node)) -> bool,
    {
        FilterAdjacencies(self, predicate)
    }
}

pub struct FilterAdjacencies<A, P>(A, P);

impl<'a, A, P> GraphType<'a> for FilterAdjacencies<A, P>
where
    A: Adjacencies<'a>,
{
    type Node = A::Node;
    type Edge = A::Edge;
}

impl<'a, A, P> Adjacencies<'a> for FilterAdjacencies<A, P>
where
    A: Adjacencies<'a>,
    P: 'a + Clone + for<'r> Fn(&'r (A::Edge, A::Node)) -> bool,
{
    type Iter = Filter<A::Iter, P>;

    fn neighs(&self, u: Self::Node) -> Self::Iter {
        self.0.neighs(u).filter(self.1.clone())
    }
}

/// Neighbor access over all adjacent (undirected) edges.
pub struct Neighbors<'g, G>(pub &'g G);

impl<'a, 'g: 'a, G> GraphType<'a> for Neighbors<'g, G>
where
    G: GraphType<'g>,
{
    type Node = G::Node;
    type Edge = G::Edge;
}

impl<'a, 'g: 'a, G> Adjacencies<'a> for Neighbors<'g, G>
where
    G: Undirected<'g>,
{
    type Iter = G::NeighIter;

    fn neighs(&self, u: G::Node) -> Self::Iter {
        self.0.neighs(u)
    }
}

/// Neighbor access over all outgoing edges of a `Digraph`.
pub struct OutEdges<'g, G>(pub &'g G);

impl<'a, 'g: 'a, G> GraphType<'a> for OutEdges<'g, G>
where
    G: Directed<'g>,
{
    type Node = G::Node;
    type Edge = G::Edge;
}

impl<'a, 'g: 'a, G> Adjacencies<'a> for OutEdges<'g, G>
where
    G: Directed<'g>,
{
    type Iter = G::OutEdgeIter;

    fn neighs(&self, u: G::Node) -> Self::Iter {
        self.0.outedges(u)
    }
}

/// Neighbor access over all outgoing edges of a `Digraph`.
pub struct InEdges<'g, G>(pub &'g G);

impl<'a, 'g: 'a, G> GraphType<'a> for InEdges<'g, G>
where
    G: Directed<'g>,
{
    type Node = G::Node;
    type Edge = G::Edge;
}

impl<'a, 'g: 'a, G> Adjacencies<'a> for InEdges<'g, G>
where
    G: Directed<'g>,
{
    type Iter = G::InEdgeIter;

    fn neighs(&self, u: G::Node) -> Self::Iter {
        self.0.inedges(u)
    }
}

/// Implement Adjacencies for references.
impl<'a, A> Adjacencies<'a> for &'a A
where
    A: Adjacencies<'a>,
{
    type Iter = A::Iter;

    fn neighs(&self, u: Self::Node) -> Self::Iter {
        (*self).neighs(u)
    }
}