brepkit-operations 3.2.10

//! Shape query utilities.

use std::collections::{HashMap, HashSet};

use brepkit_topology::Topology;
use brepkit_topology::edge::EdgeId;
use brepkit_topology::face::{FaceId, FaceSurface};
use brepkit_topology::solid::SolidId;

use crate::OperationsError;

/// Filter edges to only those shared by two planar faces in a solid.
///
/// Given a solid and a set of edge IDs, returns only the edges
/// where both adjacent faces have a planar surface.
///
/// # Errors
///
/// Returns `OperationsError::Topology` if any entity ID is invalid.
pub fn filter_planar_edges(
    topo: &Topology,
    solid_id: SolidId,
    edge_ids: &[EdgeId],
) -> Result<Vec<EdgeId>, OperationsError> {
    let solid_data = topo.solid(solid_id)?;
    let shell = topo.shell(solid_data.outer_shell())?;

    let mut edge_faces: HashMap<usize, Vec<FaceId>> = HashMap::new();
    for &fid in shell.faces() {
        let face = topo.face(fid)?;
        let wire = topo.wire(face.outer_wire())?;
        for oe in wire.edges() {
            edge_faces.entry(oe.edge().index()).or_default().push(fid);
        }
    }

    let mut result = Vec::new();
    for &eid in edge_ids {
        if let Some(adj_faces) = edge_faces.get(&eid.index()) {
            let all_planar = adj_faces.iter().all(|&fid| {
                topo.face(fid)
                    .map(|f| matches!(f.surface(), FaceSurface::Plane { .. }))
                    .unwrap_or(false)
            });
            if all_planar {
                result.push(eid);
            }
        }
    }
    Ok(result)
}

/// Filter edges to only those the blend engine can fillet: manifold edges
/// (shared by exactly two distinct faces) that meet at a real (non-tangent)
/// angle.
///
/// Edges bordering a curved neighbour — including a previous fillet's NURBS
/// blend face — ARE filletable: the rolling-ball engine solves the true
/// ball-tangent contacts against any surface. The cases that genuinely have no
/// fillet are **tangent / G1** edges (the two faces meet smoothly, e.g. a
/// fillet face's contact line with its planar neighbour) and degenerate folds;
/// those are excluded here so callers never feed them to the engine.
///
/// `try_fillet` additionally guards each result with a manifold check, so a
/// permissive filter here cannot let a malformed solid through.
///
/// # Errors
///
/// Returns `OperationsError::Topology` if any entity ID is invalid.
pub fn filter_filletable_edges(
    topo: &Topology,
    solid_id: SolidId,
    edge_ids: &[EdgeId],
) -> Result<Vec<EdgeId>, OperationsError> {
    let solid_data = topo.solid(solid_id)?;
    let shell = topo.shell(solid_data.outer_shell())?;

    // Map each edge to its set of *distinct* adjacent faces, walking both outer
    // and inner (hole-boundary) wires — the same adjacency the fillet engine
    // sees. The set dedups a seam edge that a single face's wire lists twice.
    let mut edge_faces: HashMap<usize, HashSet<FaceId>> = HashMap::new();
    for &fid in shell.faces() {
        let face = topo.face(fid)?;
        let mut wires = vec![face.outer_wire()];
        wires.extend(face.inner_wires().iter().copied());
        for wid in wires {
            for oe in topo.wire(wid)?.edges() {
                edge_faces.entry(oe.edge().index()).or_default().insert(fid);
            }
        }
    }

    let mut result = Vec::new();
    for &eid in edge_ids {
        let Some(adj_faces) = edge_faces.get(&eid.index()) else {
            continue;
        };
        if adj_faces.len() != 2 {
            continue;
        }
        if edge_is_tangent(topo, eid, adj_faces)? {
            continue;
        }
        result.push(eid);
    }
    Ok(result)
}

/// Whether the two faces of `eid` meet tangentially (G1) — their effective
/// outward normals are (anti)parallel at the edge midpoint, so there is no
/// real dihedral to round. Returns `true` for the degenerate cases the fillet
/// engine cannot blend.
fn edge_is_tangent(
    topo: &Topology,
    eid: EdgeId,
    faces: &HashSet<FaceId>,
) -> Result<bool, OperationsError> {
    let mut it = faces.iter().copied();
    let (Some(f1), Some(f2)) = (it.next(), it.next()) else {
        return Ok(true);
    };
    let edge = topo.edge(eid)?;
    let a = topo.vertex(edge.start())?.point();
    let b = topo.vertex(edge.end())?.point();
    let mid = a + (b - a) * 0.5;

    let normal = |fid: FaceId| -> Option<brepkit_math::vec::Vec3> {
        let face = topo.face(fid).ok()?;
        let n = match face.surface() {
            FaceSurface::Plane { normal, .. } => *normal,
            other => {
                let (u, v) = other.project_point(mid)?;
                other.normal(u, v)
            }
        };
        let n = if face.is_reversed() { -n } else { n };
        n.normalize().ok()
    };

    match (normal(f1), normal(f2)) {
        (Some(n1), Some(n2)) => {
            let cos = n1.dot(n2).clamp(-1.0, 1.0);
            // Tangent within ~5°: |angle| < 5° (cos > 0.9962) or > 175°.
            Ok(cos.abs() > 0.9962)
        }
        // Can't determine a normal — don't exclude; the engine + manifold guard
        // will decide.
        _ => Ok(false),
    }
}

#[cfg(test)]
mod tests {
    #![allow(clippy::unwrap_used, clippy::expect_used, deprecated)]

    use brepkit_topology::explorer::solid_edges;

    use super::*;

    #[test]
    fn filletable_edges_all_planar_box() {
        let mut topo = Topology::new();
        let cube = crate::primitives::make_box(&mut topo, 10.0, 10.0, 10.0).unwrap();
        let edges = solid_edges(&topo, cube).unwrap();
        let filletable = filter_filletable_edges(&topo, cube, &edges).unwrap();
        assert_eq!(
            filletable.len(),
            edges.len(),
            "every box edge is plane↔plane and filletable"
        );
        assert_eq!(edges.len(), 12);
    }

    #[test]
    fn filletable_edges_keep_nontangent_blend_edges_drop_tangent() {
        // A single rolling-ball fillet makes a watertight solid with a NURBS
        // blend face. Its NURBS-blend-border edges split into tangent/G1 contact
        // lines (degenerate → excluded) and real-angle end-caps (→ kept).
        let mut topo = Topology::new();
        let cube = crate::primitives::make_box(&mut topo, 10.0, 10.0, 10.0).unwrap();
        let edges = solid_edges(&topo, cube).unwrap();
        let filleted =
            crate::fillet::fillet_rolling_ball(&mut topo, cube, &[edges[0]], 1.0).unwrap();
        let r_edges = solid_edges(&topo, filleted).unwrap();
        let filletable: HashSet<usize> = filter_filletable_edges(&topo, filleted, &r_edges)
            .unwrap()
            .iter()
            .map(|e| e.index())
            .collect();

        let sh = topo
            .shell(topo.solid(filleted).unwrap().outer_shell())
            .unwrap();
        // The blend face, whatever surface type it carries. A straight box
        // edge blends to an exact cylinder; only curved neighbours give NURBS.
        let blend_faces: HashSet<usize> = sh
            .faces()
            .iter()
            .filter(|&&f| !topo.face(f).unwrap().surface().is_planar())
            .map(|f| f.index())
            .collect();
        assert!(
            !blend_faces.is_empty(),
            "first fillet must create a blend face"
        );

        let mut ef: HashMap<usize, HashSet<FaceId>> = HashMap::new();
        for &fid in sh.faces() {
            for oe in topo
                .wire(topo.face(fid).unwrap().outer_wire())
                .unwrap()
                .edges()
            {
                ef.entry(oe.edge().index()).or_default().insert(fid);
            }
        }

        let (mut saw_kept, mut saw_dropped_tangent) = (false, false);
        for &e in &r_edges {
            let Some(fs) = ef.get(&e.index()) else {
                continue;
            };
            if fs.len() != 2 || !fs.iter().any(|f| blend_faces.contains(&f.index())) {
                continue;
            }
            if edge_is_tangent(&topo, e, fs).unwrap() {
                assert!(
                    !filletable.contains(&e.index()),
                    "tangent blend-contact edge {} must be excluded",
                    e.index()
                );
                saw_dropped_tangent = true;
            } else {
                assert!(
                    filletable.contains(&e.index()),
                    "non-tangent blend-adjacent edge {} must stay filletable",
                    e.index()
                );
                saw_kept = true;
            }
        }
        assert!(saw_kept, "expected a kept non-tangent NURBS-blend edge");
        assert!(
            saw_dropped_tangent,
            "expected an excluded tangent contact edge"
        );
    }
}