hypergraph 1.3.9

use indexmap::IndexSet;

use crate::{errors::HypergraphError, HyperedgeTrait, Hypergraph, VertexIndex, VertexTrait};

impl<V, HE> Hypergraph<V, HE>
where
    V: VertexTrait,
    HE: HyperedgeTrait,
{
    /// Adds a vertex with a custom weight to the hypergraph.
    /// Returns the index of the vertex.
    pub fn add_vertex(&mut self, weight: V) -> Result<VertexIndex, HypergraphError<V, HE>> {
        // Return an error if the weight is already assigned to another vertex.
        if self.vertices.contains_key(&weight) {
            return Err(HypergraphError::VertexWeightAlreadyAssigned(weight));
        }

        self.vertices
            .entry(weight)
            .or_insert(IndexSet::with_capacity(0));

        let internal_index = self
            .vertices
            .get_index_of(&weight)
            // This safe-check should always pass since the weight has been
            // inserted upfront.
            .ok_or(HypergraphError::VertexWeightNotFound(weight))?;

        Ok(self.add_vertex_index(internal_index))
    }
}