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//! Submodule declaring outerplanarity detection for simple undirected graphs.
//!
//! Outerplanarity is implemented as a mode of the same simple-undirected
//! edge-addition embedding engine used for planarity, plus the final
//! external-face coverage check required by the outerplanar contract.
use num_traits::AsPrimitive;
use super::topology_wrapper_macros::define_planarity_derived_error;
use crate::traits::{PlanarityDetection, UndirectedMonopartiteMonoplexGraph};
define_planarity_derived_error!(
/// Error type for outerplanarity detection.
pub enum OuterplanarityError => OuterplanarityError,
mapper = map_planarity_error_to_outerplanarity_error,
self_loop = "The outerplanarity algorithm currently supports only simple undirected graphs and does not accept self-loops.",
parallel = "The outerplanarity algorithm currently supports only simple undirected graphs and does not accept parallel edges."
);
/// Trait providing outerplanarity detection for simple undirected graphs.
pub trait OuterplanarityDetection: UndirectedMonopartiteMonoplexGraph + PlanarityDetection {
/// Returns whether the graph is outerplanar.
///
/// The implementation reuses the crate's internal simple-undirected
/// edge-addition embedding engine in outerplanar mode and then checks that
/// every primary vertex lies on the external face of the resulting
/// embedding.
///
/// # Errors
///
/// Returns an error when the graph violates the simple-undirected contract,
/// such as by containing self-loops, parallel edges, or malformed edge
/// endpoints from a custom graph implementation.
///
/// # Examples
///
/// ```rust
/// use geometric_traits::{
/// impls::{CSR2D, SortedVec, SymmetricCSR2D},
/// prelude::*,
/// traits::{EdgesBuilder, OuterplanarityDetection, VocabularyBuilder},
/// };
///
/// fn build_undigraph(node_count: usize, edges: &[(usize, usize)]) -> UndiGraph<usize> {
/// let nodes: SortedVec<usize> = GenericVocabularyBuilder::default()
/// .expected_number_of_symbols(node_count)
/// .symbols((0..node_count).enumerate())
/// .build()
/// .unwrap();
///
/// let mut normalized_edges = edges.to_vec();
/// for (left, right) in &mut normalized_edges {
/// if *left > *right {
/// core::mem::swap(left, right);
/// }
/// }
/// normalized_edges.sort_unstable();
///
/// let matrix: SymmetricCSR2D<CSR2D<usize, usize, usize>> = UndiEdgesBuilder::default()
/// .expected_number_of_edges(normalized_edges.len())
/// .expected_shape(node_count)
/// .edges(normalized_edges.into_iter())
/// .build()
/// .unwrap();
///
/// UndiGraph::from((nodes, matrix))
/// }
///
/// let outerplanar = build_undigraph(4, &[(0, 1), (1, 2), (2, 3), (0, 2), (1, 3)]);
/// let planar_but_not_outerplanar =
/// build_undigraph(4, &[(0, 1), (0, 2), (0, 3), (1, 2), (1, 3), (2, 3)]);
///
/// assert!(outerplanar.is_outerplanar()?);
/// assert!(!planar_but_not_outerplanar.is_outerplanar()?);
/// # Ok::<(), geometric_traits::errors::MonopartiteError<UndiGraph<usize>>>(())
/// ```
#[inline]
fn is_outerplanar(&self) -> Result<bool, crate::errors::MonopartiteError<Self>>
where
Self: Sized,
Self::NodeId: AsPrimitive<usize>,
{
crate::traits::algorithms::planarity_detection::is_outerplanar_simple_undirected_graph(self)
.map_err(map_planarity_error_to_outerplanarity_error::<Self>)
}
}
impl<G> OuterplanarityDetection for G where
G: ?Sized + UndirectedMonopartiteMonoplexGraph + PlanarityDetection
{
}
#[cfg(test)]
mod tests {
use super::{OuterplanarityError, map_planarity_error_to_outerplanarity_error};
use crate::{
errors::{
MonopartiteError, monopartite_graph_error::algorithms::MonopartiteAlgorithmError,
},
prelude::UndiGraph,
traits::algorithms::PlanarityError,
};
#[test]
fn test_map_planarity_self_loop_error_to_outerplanarity_error() {
let error: MonopartiteError<UndiGraph<usize>> =
map_planarity_error_to_outerplanarity_error(PlanarityError::SelfLoopsUnsupported);
assert!(matches!(
error,
MonopartiteError::AlgorithmError(MonopartiteAlgorithmError::OuterplanarityError(
OuterplanarityError::SelfLoopsUnsupported
))
));
}
#[test]
fn test_map_planarity_parallel_edge_error_to_outerplanarity_error() {
let error: MonopartiteError<UndiGraph<usize>> =
map_planarity_error_to_outerplanarity_error(PlanarityError::ParallelEdgesUnsupported);
assert!(matches!(
error,
MonopartiteError::AlgorithmError(MonopartiteAlgorithmError::OuterplanarityError(
OuterplanarityError::ParallelEdgesUnsupported
))
));
}
#[test]
fn test_map_planarity_invalid_endpoint_error_to_outerplanarity_error() {
let error: MonopartiteError<UndiGraph<usize>> =
map_planarity_error_to_outerplanarity_error(PlanarityError::InvalidEdgeEndpoint {
endpoint: 9,
node_count: 4,
});
assert!(matches!(
error,
MonopartiteError::AlgorithmError(MonopartiteAlgorithmError::OuterplanarityError(
OuterplanarityError::InvalidEdgeEndpoint { endpoint: 9, node_count: 4 }
))
));
}
}