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//! Floyd-Warshall result.

use safe_graph::{Graph, NodeTrait};

/// Floyd-Warshall algorithm Result structure.
///
/// # 'FloydWarshallResult' struct is parametrized over:
///
/// - Node index/label `N`.
/// - Number type `E` giving a weight to edges.
pub struct FloydWarshallResult<N, E> {
    pub path: Graph<N, E>,
    pub next: Graph<N, N>,
}

impl<N, E> FloydWarshallResult<N, E>
where
    N: NodeTrait,
{
    /// Create a new instance of FloydWarshallResult structure.
    pub(super) fn new(path: Graph<N, E>, next: Graph<N, N>) -> Self {
        Self { path, next }
    }

    /// Get path rate.
    ///
    /// The path is specified by starting node `a` and end node `b`.
    ///
    /// This is just a wrapper around `Graph::edge_weight()` method.
    pub fn get_path_rate(&self, a: N, b: N) -> Option<&E> {
        self.path.edge_weight(a, b)
    }

    /// Collect path nodes.
    ///
    /// The collected nodes list starts with `a`, ends with `b` and contains all the intermediate
    /// steps on the best rated (shortest) path from `a` to `b`.
    pub fn collect_path_nodes(&self, a: N, b: N) -> Vec<N> {
        // if self.next.contains_edge(a, b);

        // Get the first path step.
        let next = self.next.edge_weight(a, b);

        match next {
            Some(&n) => {
                // Initiate with `a`.
                let mut nodes = vec![a];
                // Collect the middle.
                self.collect_path_middle(n, b, &mut nodes);
                // Close with `b`.
                nodes.push(b);

                nodes
            }
            // Return empty vector if there is no path between `a` and `b`.
            None => return vec![],
        }
    }

    /// Collect path intermediate steps on the best rated (shortest) path from `a` to `b`.
    fn collect_path_middle(&self, mut next: N, end: N, nodes: &mut Vec<N>) {
        // Continue till the end node is reached.
        while next != end {
            nodes.push(next);

            // Loop detection.
            if nodes.len() > self.path.node_count() {
                // Break out of the loop otherwise it would loop here infinitely.
                break;
            }

            // Find out a possible next step.
            let new_next = self.next.edge_weight(next, end);

            match new_next {
                Some(&n) => next = n,
                None => break,
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use crate::result::FloydWarshallResult;
    use safe_graph::Graph;

    #[test]
    fn new() {
        let path: Graph<&str, f32> = Graph::new();
        let rate: Graph<&str, &str> = Graph::new();

        let _result: FloydWarshallResult<&str, f32> = FloydWarshallResult::new(path, rate);
    }

    #[test]
    fn get_path_rate() {
        let mut path: Graph<&str, f32> = Graph::new();
        let rate: Graph<&str, &str> = Graph::new();

        let a = "a";
        let b = "b";
        let weight = 12.4;

        path.add_edge(a, b, weight);

        let result: FloydWarshallResult<&str, f32> = FloydWarshallResult::new(path, rate);

        assert_eq!(result.get_path_rate(a, b), Some(&weight));
    }

    #[test]
    fn collect_path_nodes() {
        let mut path: Graph<&str, f32> = Graph::new();
        let mut rate: Graph<&str, &str> = Graph::new();

        let w_a_b = 1.2;
        let w_a_c = 4.2;
        let w_b_d = 0.2;
        let w_c_d = 3.3;

        path.add_edge("a", "b", w_a_b);
        path.add_edge("a", "c", w_a_c);
        path.add_edge("b", "d", w_b_d);
        path.add_edge("c", "d", w_c_d);
        path.add_edge("a", "d", w_a_b + w_b_d);

        rate.add_edge("a", "b", "b");
        rate.add_edge("a", "c", "c");
        rate.add_edge("b", "d", "d");
        rate.add_edge("c", "d", "d");
        rate.add_edge("a", "d", "d");

        rate.add_edge("a", "d", "b");
        rate.add_edge("b", "d", "d");

        let result: FloydWarshallResult<&str, f32> = FloydWarshallResult::new(path, rate);

        // Test that path rate and nodes are returned right for the path `(a, b)`.
        assert_eq!(result.get_path_rate("a", "b"), Some(&w_a_b));
        assert_eq!(result.collect_path_nodes("a", "b"), vec!["a", "b"]);

        // Test that path rate and nodes are returned right for the path `(a, d)`.
        assert_eq!(result.get_path_rate("a", "d"), Some(&(w_a_b + w_b_d)));
        assert_eq!(result.collect_path_nodes("a", "d"), vec!["a", "b", "d"]);
    }
}