use crate::connectivity::{
    CellConnectivity, Connectivity, ConnectivityMut, Hex20Connectivity, Hex27Connectivity, Hex8Connectivity,
    Quad4d2Connectivity, Quad9d2Connectivity, Tet10Connectivity, Tet20Connectivity, Tet4Connectivity,
    Tri3d2Connectivity, Tri3d3Connectivity, Tri6d2Connectivity,
};
use crate::geometry::{AxisAlignedBoundingBox, BoundedGeometry, GeometryCollection};
use fenris_nested_vec::NestedVec;
use nalgebra::allocator::Allocator;
use nalgebra::{DefaultAllocator, DimName, OPoint, OVector, RealField, Scalar, U2, U3};
use serde::{Deserialize, Serialize};
use std::collections::{BTreeMap, HashMap};
use std::iter::once;

pub mod procedural;
pub mod reorder;

/// Index-based data structure for conforming meshes (i.e. no hanging nodes).
#[derive(Debug, Clone, PartialEq, Eq, Deserialize, Serialize)]
// TODO: Remove T: De(Serialize) bounds once nalgebra PR #953 has been merged and released
#[serde(bound(serialize = "T: Serialize", deserialize = "T: Deserialize<'de>"))]
pub struct Mesh<T: Scalar, D, Connectivity>
where
    D: DimName,
    DefaultAllocator: Allocator<T, D>,
{
    // serde's not able correctly determine the necessary trait bounds in this case,
    // so write our own
    #[serde(bound(
        serialize = "<DefaultAllocator as Allocator<T, D>>::Buffer: Serialize",
        deserialize = "<DefaultAllocator as Allocator<T, D>>::Buffer: Deserialize<'de>"
    ))]
    vertices: Vec<OPoint<T, D>>,
    #[serde(bound(
        serialize = "Connectivity: Serialize",
        deserialize = "Connectivity: Deserialize<'de>"
    ))]
    connectivity: Vec<Connectivity>,
}

/// Index-based data structure for conforming meshes (i.e. no hanging nodes).
pub type Mesh2d<T, Connectivity> = Mesh<T, U2, Connectivity>;
pub type Mesh3d<T, Connectivity> = Mesh<T, U3, Connectivity>;

pub type TriangleMesh2d<T> = Mesh2d<T, Tri3d2Connectivity>;
pub type Tri6Mesh2d<T> = Mesh2d<T, Tri6d2Connectivity>;
pub type QuadMesh2d<T> = Mesh2d<T, Quad4d2Connectivity>;
pub type Quad9Mesh2d<T> = Mesh2d<T, Quad9d2Connectivity>;
pub type TriangleMesh3d<T> = Mesh3d<T, Tri3d3Connectivity>;
// TODO: Rename to Hex8Mesh
pub type HexMesh<T> = Mesh3d<T, Hex8Connectivity>;
pub type Hex20Mesh<T> = Mesh3d<T, Hex20Connectivity>;
pub type Hex27Mesh<T> = Mesh3d<T, Hex27Connectivity>;
pub type Tet4Mesh<T> = Mesh3d<T, Tet4Connectivity>;
pub type Tet10Mesh<T> = Mesh3d<T, Tet10Connectivity>;
pub type Tet20Mesh<T> = Mesh3d<T, Tet20Connectivity>;

impl<T, D, Connectivity> Mesh<T, D, Connectivity>
where
    T: Scalar,
    D: DimName,
    DefaultAllocator: Allocator<T, D>,
{
    pub fn vertices_mut(&mut self) -> &mut [OPoint<T, D>] {
        &mut self.vertices
    }

    pub fn vertices(&self) -> &[OPoint<T, D>] {
        &self.vertices
    }

    pub fn connectivity(&self) -> &[Connectivity] {
        &self.connectivity
    }

    /// Construct a mesh from vertices and connectivity.
    ///
    /// The provided connectivity is expected only to return valid (i.e. in-bounds) indices,
    /// but this can not be trusted. Users of the mesh are permitted to panic if they encounter
    /// invalid indices, but unchecked indexing may easily lead to undefined behavior.
    ///
    /// In other words, if the connectivity references indices out of bounds, then the code is
    /// incorrect. However, since this can be done exclusively with safe code, unchecked
    /// or unsafe indexing in which the user is *trusted* to provide valid indices may
    /// produce undefined behavior.Therefore, the connectivity must always be checked.
    pub fn from_vertices_and_connectivity(vertices: Vec<OPoint<T, D>>, connectivity: Vec<Connectivity>) -> Self {
        Self { vertices, connectivity }
    }
}

// impl<T, D, C> Mesh<T, D, C>
// where
//     T: Scalar,
//     D: DimName,
//     C: ConnectivityMut,
//     DefaultAllocator: Allocator<T, D>,
// {
//     /// Creates a new mesh with each cell disconnected from all its neighbors.
//     ///
//     /// In other words, each vertex is only referenced exactly once, and the result is
//     /// effectively a "soup" of cells.
//     pub fn disconnect_cells(&self) -> Self {
//         let old_vertices = self.vertices();
//         let mut new_vertices = Vec::new();
//         let mut new_connectivity = Vec::new();
//
//         for conn in self.connectivity() {
//             let mut new_conn = conn.clone();
//
//             for v_idx in new_conn.vertex_indices_mut() {
//                 let new_vertex_idx = new_vertices.len();
//                 new_vertices.push(old_vertices[*v_idx].clone());
//                 *v_idx = new_vertex_idx;
//             }
//             new_connectivity.push(new_conn);
//         }
//
//         Self::from_vertices_and_connectivity(new_vertices, new_connectivity)
//     }
// }

impl<T, D, Connectivity> Mesh<T, D, Connectivity>
where
    T: Scalar,
    D: DimName,
    DefaultAllocator: Allocator<T, D>,
    Connectivity: CellConnectivity<T, D>,
{
    pub fn get_cell(&self, index: usize) -> Option<Connectivity::Cell> {
        self.connectivity()
            .get(index)
            .and_then(|conn| conn.cell(self.vertices()))
    }

    pub fn cell_iter<'a>(&'a self) -> impl 'a + Iterator<Item = Connectivity::Cell> {
        self.connectivity().iter().map(move |connectivity| {
            connectivity
                .cell(&self.vertices)
                .expect("Mesh2d is not allowed to contain cells with indices out of bounds.")
        })
    }
}

impl<T, D, C> Mesh<T, D, C>
where
    T: Scalar,
    D: DimName,
    C: Connectivity,
    C::FaceConnectivity: Connectivity,
    DefaultAllocator: Allocator<T, D>,
{
    /// Finds cells that have at least one boundary face.
    pub fn find_boundary_cells(&self) -> Vec<usize> {
        let mut cells: Vec<_> = self
            .find_boundary_faces()
            .into_iter()
            .map(|(_, cell_index, _)| cell_index)
            .collect();
        cells.sort_unstable();
        cells.dedup();
        cells
    }

    /// Finds faces which are only connected to exactly one cell, along with the connected cell
    /// index and the local index of the face within that cell.
    pub fn find_boundary_faces(&self) -> Vec<(C::FaceConnectivity, usize, usize)> {
        let mut sorted_slices = NestedVec::new();
        let mut face_info = Vec::new();

        // We want to use (sorted) slices as keys in a hash map, so we need to store
        // and sort the slices first
        for (conn_idx, cell_conn) in self.connectivity.iter().enumerate() {
            let num_faces = cell_conn.num_faces();
            for local_idx in 0..num_faces {
                let face_conn = cell_conn.get_face_connectivity(local_idx).unwrap();
                sorted_slices.push(face_conn.vertex_indices());
                let indices = sorted_slices.last_mut().unwrap();
                indices.sort_unstable();
                face_info.push((face_conn, conn_idx, local_idx));
            }
        }

        // Count the number of occurrences of "equivalent" faces (in the sense that they refer
        // to the same vertex indices). Use a BTreeMap to avoid non-determinism due to
        // HashMap's internal randomization.
        let mut slice_counts = BTreeMap::new();
        let num_slices = sorted_slices.len();
        for i in 0..num_slices {
            slice_counts
                .entry(sorted_slices.get(i).unwrap())
                .and_modify(|(_, count)| *count += 1)
                .or_insert((i, 1));
        }

        // Take only the faces which have a count of 1, which correspond to boundary faces
        slice_counts
            .into_iter()
            .map(|(_key, value)| value)
            .filter(|&(_, count)| count == 1)
            .map(move |(i, _)| face_info[i].clone())
            .collect()
    }

    /// Returns a sorted list of vertices that are determined to be on the boundary.
    ///
    /// A vertex is considered to be a part of the boundary if it belongs to a boundary face.
    pub fn find_boundary_vertices(&self) -> Vec<usize> {
        let mut indices = Vec::new();
        for (connectivity, _, _) in self.find_boundary_faces() {
            indices.extend(connectivity.vertex_indices());
        }
        indices.sort_unstable();
        indices.dedup();
        indices
    }
}

impl<T, D, Connectivity> BoundedGeometry<T> for Mesh<T, D, Connectivity>
where
    T: RealField,
    D: DimName,
    DefaultAllocator: Allocator<T, D>,
    Connectivity: CellConnectivity<T, D>,
    Connectivity::Cell: BoundedGeometry<T, Dimension = D>,
{
    type Dimension = D;

    fn bounding_box(&self) -> AxisAlignedBoundingBox<T, D> {
        let mut bbs = self.cell_iter().map(|cell| cell.bounding_box());
        bbs.next()
            .map(|first_bb| bbs.fold(first_bb, |bb1, bb2| bb1.enclose(&bb2)))
            .unwrap_or_else(|| AxisAlignedBoundingBox::new(OVector::zeros(), OVector::zeros()))
    }
}

impl<T, D, C> Mesh<T, D, C>
where
    T: RealField,
    D: DimName,
    DefaultAllocator: Allocator<T, D>,
{
    /// Translates all vertices of the mesh by the given translation vector.
    pub fn translate(&mut self, translation: &OVector<T, D>) {
        self.transform_vertices(|p| *p += translation);
    }

    /// Transform all vertices of the mesh by the given transformation function.
    pub fn transform_vertices<F>(&mut self, mut transformation: F)
    where
        F: FnMut(&mut OPoint<T, D>),
    {
        for p in &mut self.vertices {
            transformation(p);
        }
    }

    pub fn transform_all_vertices<F>(&mut self, mut transformation: F)
    where
        F: FnMut(&mut [OPoint<T, D>]),
    {
        transformation(&mut self.vertices);
    }
}

impl<T> QuadMesh2d<T>
where
    T: RealField,
{
    pub fn split_into_triangles(self) -> TriangleMesh2d<T> {
        let triangles = self
            .connectivity()
            .iter()
            .flat_map(|connectivity| {
                let Quad4d2Connectivity(c) = connectivity;
                let quad = connectivity
                    .cell(self.vertices())
                    .expect("Indices must be in bounds");
                let (tri1, tri2) = quad.split_into_triangle_connectivities();
                let tri1_global = Tri3d2Connectivity([c[tri1[0]], c[tri1[1]], c[tri1[2]]]);
                let tri2_global = Tri3d2Connectivity([c[tri2[0]], c[tri2[1]], c[tri2[2]]]);
                once(tri1_global).chain(once(tri2_global))
            })
            .collect();

        TriangleMesh2d::from_vertices_and_connectivity(self.vertices, triangles)
    }
}

impl<T, D, C> Mesh<T, D, C>
where
    T: Scalar,
    D: DimName,
    C: ConnectivityMut,
    DefaultAllocator: Allocator<T, D>,
{
    /// Returns a new mesh in which only the desired cells are kept. The vertices are removed or
    /// relabeled as necessary.
    pub fn keep_cells(&self, cell_indices: &[usize]) -> Self {
        // TODO: Return Result instead of panicking if indices are out of bounds

        // Each entry is true if this vertex should be kept, false otherwise
        let vertex_keep_table = {
            let mut table = vec![false; self.vertices.len()];
            for cell_index in cell_indices {
                let cell_connectivity = &self.connectivity[*cell_index];

                for vertex_index in cell_connectivity.vertex_indices() {
                    table[*vertex_index] = true;
                }
            }
            table
        };

        let old_to_new_label_map = {
            let mut label_map = HashMap::new();
            let mut next_label = 0;
            for (i, keep) in vertex_keep_table.iter().enumerate() {
                if *keep {
                    label_map.insert(i, next_label);
                    next_label += 1;
                }
            }
            label_map
        };

        let relabeled_cells: Vec<_> = cell_indices
            .iter()
            .map(|i| self.connectivity()[*i].clone())
            .map(|mut cell| {
                for index in cell.vertex_indices_mut() {
                    *index = *old_to_new_label_map
                        .get(index)
                        .expect("Index must be in map");
                }
                cell
            })
            .collect();

        let relabeled_vertices: Vec<_> = vertex_keep_table
            .iter()
            .enumerate()
            .filter_map(|(i, should_keep)| if *should_keep { Some(i) } else { None })
            .map(|index| self.vertices[index].clone())
            .collect();

        Mesh::from_vertices_and_connectivity(relabeled_vertices, relabeled_cells)
    }
}

// impl<T, Cell> Mesh2d<T, Cell>
// where
//     T: RealField,
//     Cell: Connectivity<FaceConnectivity = Segment2d2Connectivity>,
// {
//     pub fn extract_contour(&self) -> Result<GeneralPolygon<T>, Box<dyn Error>> {
//         let boundary_edges = self
//             .find_boundary_faces()
//             .into_iter()
//             .map(|(edge, _, _)| edge);
//
//         // For a "proper" mesh, any vertex may be connected to exactly two other vertices.
//         // We build a "path" of vertices by associating each vertex with its neighbor
//         // whose index is the smallest, and visiting each vertex once.
//         let mut neighbors = HashMap::new();
//         let mut smallest_index = std::usize::MAX;
//
//         let mut insert_neighbor = |vertex_index, neighbor_index| {
//             if vertex_index == neighbor_index {
//                 Err(format!(
//                     "Cannot extract contour: vertex {} has edge to itself.",
//                     vertex_index
//                 ))
//             } else {
//                 neighbors
//                     .entry(vertex_index)
//                     .or_insert_with(|| ArrayVec::<[_; 2]>::new())
//                     .try_push(neighbor_index)
//                     .map_err(|_| {
//                         format!(
//                             "Cannot extract contour: vertex {} has more than two neighbors.",
//                             vertex_index
//                         )
//                     })
//             }
//         };
//
//         for edge in boundary_edges {
//             let Segment2d2Connectivity([a, b]) = edge;
//             insert_neighbor(a, b)?;
//             insert_neighbor(b, a)?;
//             smallest_index = min(smallest_index, a);
//             smallest_index = min(smallest_index, b);
//         }
//
//         let num_vertices = neighbors.len();
//         let mut take_next = |vertex_index, prev_index| {
//             debug_assert_ne!(vertex_index, prev_index);
//             let vertex_neighbors = neighbors
//                 .get_mut(&vertex_index)
//                 .expect("All vertices have neighbors");
//
//             const ERROR_MSG: &str =
//                 "Cannot extract contour: There is no closed path connecting vertices.";
//
//             if vertex_neighbors.is_empty() {
//                 Err(ERROR_MSG)
//             } else {
//                 let neighbor_idx = vertex_neighbors
//                     .iter()
//                     .cloned()
//                     .enumerate()
//                     .filter(|(_, vertex_idx)| *vertex_idx != prev_index)
//                     .map(|(i, _)| i)
//                     .next();
//
//                 if let Some(neighbor_idx) = neighbor_idx {
//                     let neighbor = vertex_neighbors[neighbor_idx];
//                     vertex_neighbors.remove(neighbor_idx);
//                     Ok(neighbor)
//                 } else {
//                     Err(ERROR_MSG)
//                 }
//             }
//         };
//
//         // Given a current vertex and the previous vertex, we find the next vertex by
//         // picking the neighbor of "current" which is not equal to the previous.
//         // In order to start this sequence, we must first choose an arbitrary "next" vertex
//         // out of the two neighbors of "prev"
//         let mut vertices = Vec::with_capacity(num_vertices);
//         let mut prev_vertex_index = smallest_index;
//         let mut current_vertex_index = take_next(prev_vertex_index, std::usize::MAX)?;
//         vertices.push(self.vertices()[prev_vertex_index]);
//
//         while current_vertex_index != smallest_index {
//             let next_vertex_index = take_next(current_vertex_index, prev_vertex_index)?;
//             prev_vertex_index = current_vertex_index;
//             current_vertex_index = next_vertex_index;
//             vertices.push(self.vertices()[prev_vertex_index]);
//         }
//
//         // TODO: What if we have a hole in the polygon? Should eventually also support this,
//         // but for the moment we are limited to simple polygons.
//         let mut polygon = GeneralPolygon::from_vertices(vertices);
//         polygon.orient(Counterclockwise);
//
//         Ok(polygon)
//     }
// }

// impl<T, D, C> Mesh<T, D, C>
// where
//     T: Scalar,
//     D: DimName,
//     C: Connectivity,
//     C::FaceConnectivity: Connectivity + ConnectivityMut,
//     DefaultAllocator: Allocator<T, D>,
// {
//     /// Creates a mesh that consists of all unique faces of this mesh.
//     /// Face normals are only preserved for boundary faces.
//     pub fn extract_face_soup(&self) -> Mesh<T, D, C::FaceConnectivity> {
//         let mut unique_connectivity = HashMap::new();
//         let mut faces = Vec::new();
//
//         for cell_conn in self.connectivity.iter() {
//             let num_faces = cell_conn.num_faces();
//             for i in 0..num_faces {
//                 let face_conn = cell_conn.get_face_connectivity(i).unwrap();
//
//                 let mut vertex_indices = face_conn.vertex_indices().to_vec();
//                 vertex_indices.sort_unstable();
//
//                 if let HashMapEntry::Vacant(entry) = unique_connectivity.entry(vertex_indices) {
//                     entry.insert(faces.len());
//                     faces.push(face_conn);
//                 }
//             }
//         }
//
//         let new_mesh = Mesh::from_vertices_and_connectivity(self.vertices.clone(), faces);
//         let cells_to_keep: Vec<_> = (0..new_mesh.connectivity().len()).collect();
//         // Remove unconnected vertices
//         new_mesh.keep_cells(&cells_to_keep)
//     }
// }

impl<T, D, C> Mesh<T, D, C>
where
    T: Scalar,
    D: DimName,
    C: Connectivity,
    C::FaceConnectivity: ConnectivityMut,
    DefaultAllocator: Allocator<T, D>,
{
    /// Constructs a new mesh from the surface cells of the mesh.
    ///
    /// The orientation of the faces are preserved.
    pub fn extract_surface_mesh(&self) -> Mesh<T, D, C::FaceConnectivity> {
        let connectivity = self
            .find_boundary_faces()
            .into_iter()
            .map(|(face, _, _)| face)
            .collect();

        // TODO: This is rather inefficient
        let new_mesh = Mesh::from_vertices_and_connectivity(self.vertices.clone(), connectivity);
        let cells_to_keep: Vec<_> = (0..new_mesh.connectivity().len()).collect();
        new_mesh.keep_cells(&cells_to_keep)
    }
}

impl<'a, T, D, C> GeometryCollection<'a> for Mesh<T, D, C>
where
    T: Scalar,
    D: DimName,
    C: CellConnectivity<T, D>,
    DefaultAllocator: Allocator<T, D>,
{
    type Geometry = C::Cell;

    fn num_geometries(&self) -> usize {
        self.connectivity.len()
    }

    fn get_geometry(&'a self, index: usize) -> Option<Self::Geometry> {
        self.connectivity()
            .get(index)
            .map(|conn| conn.cell(self.vertices()).unwrap())
    }
}

// impl<'a, T, D, C, QueryGeometry> DistanceQuery<'a, QueryGeometry> for Mesh<T, D, C>
// where
//     T: RealField,
//     D: DimName,
//     C: CellConnectivity<T, D>,
//     C::Cell: Distance<T, QueryGeometry>,
//     DefaultAllocator: Allocator<T, D>,
// {
//     fn nearest(&'a self, query_geometry: &'a QueryGeometry) -> Option<usize> {
//         let (_, min_index) = (0..self.num_geometries())
//             .map(|idx| {
//                 let geometry = self.get_geometry(idx).expect(
//                     "num_geometries must report the correct number of available geometries",
//                 );
//                 (idx, geometry)
//             })
//             .fold(
//                 (T::max_value(), None),
//                 |(mut min_dist, mut min_index), (idx, geometry)| {
//                     let dist = geometry.distance(query_geometry);
//                     // TODO: Square distance?
//                     if dist < min_dist {
//                         min_index = Some(idx);
//                         min_dist = dist;
//                     }
//                     (min_dist, min_index)
//                 },
//             );
//         min_index
//     }
// }

// pub trait PlanarFace<T>
// where
//     T: Scalar,
//     DefaultAllocator: Allocator<T, Self::Dimension>,
// {
//     type Dimension: DimName;
//
//     fn normal(&self) -> OVector<T, Self::Dimension>;
// }
//
// impl<T> PlanarFace<T> for LineSegment2d<T>
// where
//     T: RealField,
// {
//     type Dimension = U2;
//
//     fn normal(&self) -> Vector2<T> {
//         self.normal_dir().normalize()
//     }
// }

// /// Creates a poly mesh by joining the face connectivity of each cell to a polygon
// /// (only works if the cells are topologically 2D)
// pub fn poly_mesh_from_surface_mesh<T, C, D>(mesh: &Mesh<T, D, C>) -> PolyMesh<T, D>
// where
//     T: Scalar,
//     C: Connectivity,
//     D: DimName,
//     DefaultAllocator: Allocator<T, D>,
// {
//     // TODO: Implement using the From trait?
//
//     let mut old_to_new_vertex_indices: HashMap<usize, usize> =
//         HashMap::with_capacity(mesh.vertices().len());
//     let mut faces = NestedVec::new();
//
//     // Convert cells to polygonal faces by extracting the cells face connectivity
//     for cell in mesh.connectivity() {
//         let num_faces = cell.num_faces();
//         let mut polygon = Vec::new();
//         for i in 0..num_faces {
//             let face_connectivity = cell.get_face_connectivity(i).unwrap();
//             let new_vertices: Vec<_> = face_connectivity
//                 .vertex_indices()
//                 .iter()
//                 .copied()
//                 .map(|v_old| {
//                     let v_new = old_to_new_vertex_indices.len();
//                     *old_to_new_vertex_indices.entry(v_old).or_insert(v_new)
//                 })
//                 .collect();
//             polygon.extend(new_vertices);
//         }
//         // Remove the last vertex if it is the same as the first
//         if let (Some(first), Some(last)) = (polygon.first(), polygon.last()) {
//             if *first == *last {
//                 polygon.pop();
//             }
//         }
//         // Remove repeating vertices (because of the concatenation of faces)
//         polygon.dedup();
//
//         faces.push(polygon.as_slice());
//     }
//
//     // Reorder the old vertex indices into the order used by the extracted faces
//     let old_vertex_indices = {
//         let mut old_to_new_vertex_indices: Vec<(_, _)> =
//             old_to_new_vertex_indices.into_iter().collect();
//         old_to_new_vertex_indices
//             .sort_unstable_by(|(_, v_new_a), (_, v_new_b)| v_new_a.cmp(v_new_b));
//         let old_vertex_indices: Vec<_> = old_to_new_vertex_indices
//             .into_iter()
//             .map(|(v_old, _)| v_old)
//             .collect();
//         old_vertex_indices
//     };
//
//     // Extract the subset of vertices required by the faces
//     let mut vertices = Vec::with_capacity(old_vertex_indices.len());
//     for v_old in old_vertex_indices {
//         vertices.push(
//             mesh.vertices()
//                 .get(v_old)
//                 .expect("missing vertex of cell face")
//                 .clone(),
//         )
//     }
//
//     let cells = NestedVec::new();
//     PolyMesh::from_poly_data(vertices, faces, cells)
// }