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// this module is transparently re-exported by its parent `graph::inmem`

use std::collections::HashSet;
use std::hash::Hash;

use crate::error::*;
use crate::graph::indexed::IndexedGraph;
use crate::graph::*;
use crate::term::factory::TermFactory;
use crate::term::index_map::TermIndexMap;
use crate::term::{RefTerm, Term, TermData};

/// A generic implementation of [`Graph`] and [`MutableGraph`],
/// storing its terms in a [`TermIndexMap`],
/// and its triples in a [`HashSet`].
///
/// [`Graph`]: ../trait.Graph.html
/// [`MutableGraph`]: ../trait.MutableGraph.html
/// [`TermIndexMap`]: ../../term/index_map/trait.TermIndexMap.html
/// [`HashSet`]: https://doc.rust-lang.org/std/collections/struct.HashSet.html
#[derive(Default)]
pub struct HashGraph<I>
where
    I: TermIndexMap,
    I::Index: Hash,
    <I::Factory as TermFactory>::TermData: 'static,
{
    terms: I,
    triples: HashSet<[I::Index; 3]>,
}

impl<I> HashGraph<I>
where
    I: TermIndexMap,
    I::Index: Hash,
{
    pub fn new() -> HashGraph<I> {
        HashGraph {
            terms: I::default(),
            triples: HashSet::new(),
        }
    }

    pub fn len(&self) -> usize {
        self.triples.len()
    }

    pub fn is_empty(&self) -> bool {
        self.triples.is_empty()
    }
}

impl<I> IndexedGraph for HashGraph<I>
where
    I: TermIndexMap,
    I::Index: Hash,
    <I::Factory as TermFactory>::TermData: 'static,
{
    type Index = I::Index;
    type TermData = <I::Factory as TermFactory>::TermData;

    #[inline]
    fn get_index<T>(&self, t: &Term<T>) -> Option<Self::Index>
    where
        T: TermData,
    {
        self.terms.get_index(&RefTerm::from(t))
    }

    #[inline]
    fn get_term(&'_ self, i: Self::Index) -> Option<&Term<Self::TermData>> {
        self.terms.get_term(i)
    }

    fn insert_indexed<T, U, V>(
        &mut self,
        s: &Term<T>,
        p: &Term<U>,
        o: &Term<V>,
    ) -> Option<[I::Index; 3]>
    where
        T: TermData,
        U: TermData,
        V: TermData,
    {
        let si = self.terms.make_index(&RefTerm::from(s));
        let pi = self.terms.make_index(&RefTerm::from(p));
        let oi = self.terms.make_index(&RefTerm::from(o));
        let modified = self.triples.insert([si, pi, oi]);
        if modified {
            Some([si, pi, oi])
        } else {
            self.terms.dec_ref(si);
            self.terms.dec_ref(pi);
            self.terms.dec_ref(oi);
            None
        }
    }

    fn remove_indexed<T, U, V>(
        &mut self,
        s: &Term<T>,
        p: &Term<U>,
        o: &Term<V>,
    ) -> Option<[I::Index; 3]>
    where
        T: TermData,
        U: TermData,
        V: TermData,
    {
        let si = self.terms.get_index(&RefTerm::from(s));
        let pi = self.terms.get_index(&RefTerm::from(p));
        let oi = self.terms.get_index(&RefTerm::from(o));
        if let (Some(si), Some(pi), Some(oi)) = (si, pi, oi) {
            let modified = self.triples.remove(&[si, pi, oi]);
            if modified {
                self.terms.dec_ref(si);
                self.terms.dec_ref(pi);
                self.terms.dec_ref(oi);
                return Some([si, pi, oi]);
            }
        }
        None
    }

    fn shrink_to_fit(&mut self) {
        self.terms.shrink_to_fit();
        self.triples.shrink_to_fit();
    }
}

impl<'a, I> Graph<'a> for HashGraph<I>
where
    I: TermIndexMap,
    I::Index: Hash,
    <I::Factory as TermFactory>::TermData: 'static,
{
    type Triple = [&'a Term<<Self as IndexedGraph>::TermData>; 3];
    type Error = Never;

    fn triples(&'a self) -> GTripleSource<'a, Self> {
        Box::from(self.triples.iter().map(move |[si, pi, oi]| {
            Ok([
                self.terms.get_term(*si).unwrap(),
                self.terms.get_term(*pi).unwrap(),
                self.terms.get_term(*oi).unwrap(),
            ])
        }))
    }
}

impl<I> MutableGraph for HashGraph<I>
where
    I: TermIndexMap,
    I::Index: Hash,
    <I::Factory as TermFactory>::TermData: 'static,
{
    impl_mutable_graph_for_indexed_graph!();
}

impl<I> SetGraph for HashGraph<I>
where
    I: TermIndexMap,
    I::Index: Hash,
{
}

#[cfg(test)]
mod test {
    // The code from this module is tested through its use in other modules
    // (especially in ./inmem.rs).
}