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use crate::core::state::accumulator_id::accumulators;
use crate::core::state::compute_state::ComputeStateVec;
use crate::db::task::context::Context;
use crate::db::task::task::{ATask, Job, Step};
use crate::db::task::task_runner::TaskRunner;
use crate::db::view_api::*;
use rustc_hash::FxHashSet;

/// Computes the number of triangles in a graph using a fast algorithm
///
/// # Arguments
///
/// * `g` - A reference to the graph
/// * `window` - A range indicating the temporal window to consider
///
/// # Returns
///
/// An optional integer containing the number of triangles in the graph. If the computation failed,
/// the function returns `None`.
///
/// # Example
/// ```rust
/// use std::{cmp::Reverse, iter::once};
/// use raphtory::db::graph::Graph;
/// use raphtory::algorithms::triangle_count::triangle_count;
///
/// let graph = Graph::new(2);
///
/// let edges = vec![
///     // triangle 1
///     (1, 2, 1),
///     (2, 3, 1),
///     (3, 1, 1),
///     //triangle 2
///     (4, 5, 1),
///     (5, 6, 1),
///     (6, 4, 1),
///     // triangle 4 and 5
///     (7, 8, 2),
///     (8, 9, 3),
///     (9, 7, 4),
///     (8, 10, 5),
///     (10, 9, 6),
/// ];
///
/// for (src, dst, ts) in edges {
///     graph.add_edge(ts, src, dst, &vec![], None);
/// }
///
/// let actual_tri_count = triangle_count(&graph, None);
/// ```
///
pub fn triangle_count<G: GraphViewOps>(g: &G, threads: Option<usize>) -> usize {
    let mut ctx: Context<G, ComputeStateVec> = g.into();

    let neighbours_set = accumulators::hash_set::<u64>(0);
    let count = accumulators::sum::<usize>(1);

    ctx.agg(neighbours_set);
    ctx.global_agg(count);

    let step1 = ATask::new(move |s| {
        for t in s.neighbours() {
            if s.id() > t.id() {
                t.update(&neighbours_set, s.id());
            }
        }
        Step::Continue
    });

    let step2 = ATask::new(move |s| {
        for t in s.neighbours() {
            if s.id() > t.id() {
                let intersection_count = {
                    // when using entry() we need to make sure the reference is released before we can update the state, otherwise we break the Rc<RefCell<_>> invariant
                    // where there can either be one mutable or many immutable references

                    match (
                        s.entry(&neighbours_set)
                            .read_ref()
                            .unwrap_or(&FxHashSet::default()),
                        t.entry(&neighbours_set)
                            .read_ref()
                            .unwrap_or(&FxHashSet::default()),
                    ) {
                        (s_set, t_set) => {
                            let intersection = s_set.intersection(t_set);
                            intersection.count()
                        }
                    }
                };
                s.global_update(&count, intersection_count);
            }
        }
        Step::Continue
    });

    let init_tasks = vec![Job::new(step1)];
    let tasks = vec![Job::new(step2)];

    let mut runner: TaskRunner<G, _> = TaskRunner::new(ctx);

    runner.run(
        init_tasks,
        tasks,
        (),
        |egs, _, _, _| egs.finalize(&count),
        threads,
        1,
        None,
        None,
    )
}

#[cfg(test)]
mod triangle_count_tests {
    use super::*;
    use crate::db::graph::Graph;

    #[test]
    fn triangle_count_1() {
        let graph = Graph::new(2);

        let edges = vec![
            // triangle 1
            (1, 2, 1),
            (2, 3, 1),
            (3, 1, 1),
            //triangle 2
            (4, 5, 1),
            (5, 6, 1),
            (6, 4, 1),
            // triangle 4 and 5
            (7, 8, 2),
            (8, 9, 3),
            (9, 7, 4),
            (8, 10, 5),
            (10, 9, 6),
        ];

        for (src, dst, ts) in edges {
            graph.add_edge(ts, src, dst, &vec![], None).unwrap();
        }

        let actual_tri_count = triangle_count(&graph, Some(2));

        assert_eq!(actual_tri_count, 4)
    }

    #[test]
    fn triangle_count_3() {
        let graph = Graph::new(2);

        let edges = vec![
            (1, 2, 1),
            (1, 3, 2),
            (1, 4, 3),
            (3, 1, 4),
            (3, 4, 5),
            (3, 5, 6),
            (4, 5, 7),
            (5, 6, 8),
            (5, 8, 9),
            (7, 5, 10),
            (8, 5, 11),
            (1, 9, 12),
            (9, 1, 13),
            (6, 3, 14),
            (4, 8, 15),
            (8, 3, 16),
            (5, 10, 17),
            (10, 5, 18),
            (10, 8, 19),
            (1, 11, 20),
            (11, 1, 21),
            (9, 11, 22),
            (11, 9, 23),
        ];

        for (src, dst, ts) in edges {
            graph.add_edge(ts, src, dst, &vec![], None).unwrap();
        }

        let actual_tri_count = triangle_count(&graph, None);

        assert_eq!(actual_tri_count, 8)
    }
}