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use crate::BlenderMesh;
impl BlenderMesh {
    /// When exporting a mesh from Blender, faces will usually have 4 vertices (quad) but some
    /// faces might have 3 (triangle).
    ///
    /// We read `self.num_vertices_in_each_face` to check how
    /// many vertices each face has.
    ///
    /// If a face has 4 vertices we convert it into two triangles, each with 3 vertices.
    ///
    /// # Panics
    ///
    /// Panics if a face has more than 4 vertices. In the future we might support 5+ vertices,
    /// but I haven't run into that yet. Not even sure if Blender can have faces with 5 vertices..
    pub(crate) fn triangulate(&self, indices: &Vec<u16>) -> Vec<u16> {
        let mut triangulated_position_indices = vec![];
        let mut triangulated_face_vertex_counts = vec![];

        let mut face_pointer = 0;

        for num_verts_in_face in self
            .multi_indexed_vertex_attributes
            .vertices_in_each_face
            .iter()
        {
            triangulated_position_indices.push(indices[face_pointer]);
            triangulated_position_indices.push(indices[face_pointer + 1]);
            triangulated_position_indices.push(indices[face_pointer + 2]);

            triangulated_face_vertex_counts.push(3);

            match num_verts_in_face {
                &3 => {}
                &4 => {
                    triangulated_position_indices.push(indices[face_pointer]);
                    triangulated_position_indices.push(indices[face_pointer + 2]);
                    triangulated_position_indices.push(indices[face_pointer + 3]);

                    triangulated_face_vertex_counts.push(3);
                }
                _ => {
                    panic!("blender-mesh currently only supports triangulating faces with 3 or 4 vertices");
                }
            };

            face_pointer += *num_verts_in_face as usize;
        }

        // TODO: ? Set to Uniform(3)
        // multi.vertices_in_each_face = triangulated_face_vertex_counts;

        return triangulated_position_indices;
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::vertex_attributes::{
        IndexedAttribute, MultiIndexedVertexAttributes, VertexAttribute,
    };

    #[test]
    fn triangulate_faces() {
        let start_mesh = BlenderMesh {
            multi_indexed_vertex_attributes: MultiIndexedVertexAttributes {
                positions: IndexedAttribute {
                    indices: vec![0, 1, 2, 3, 4, 5, 6, 7],
                    attribute: VertexAttribute::default(),
                },
                vertices_in_each_face: vec![4, 4],
                ..MultiIndexedVertexAttributes::default()
            }
            .into(),
            ..BlenderMesh::default()
        };

        let triangulated_indices = start_mesh.triangulate(&vec![0, 1, 2, 3, 4, 5, 6, 7]);
        assert_eq!(
            triangulated_indices,
            vec![0, 1, 2, 0, 2, 3, 4, 5, 6, 4, 6, 7]
        );
    }
}