// Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.

#pragma once
#include <torch/extension.h>
#include "pytorch3d_cutils.h"

// Compute indices of nearest neighbors in pointcloud p2 to points
// in pointcloud p1.
//
// Args:
//    p1: FloatTensor of shape (N, P1, D) giving a batch of pointclouds each
//        containing P1 points of dimension D.
//    p2: FloatTensor of shape (N, P2, D) giving a batch of pointclouds each
//        containing P2 points of dimension D.
//
// Returns:
//    p1_neighbor_idx: LongTensor of shape (N, P1), where
//                     p1_neighbor_idx[n, i] = j means that the nearest neighbor
//                     to p1[n, i] in the cloud p2[n] is p2[n, j].
//

// CPU implementation.
at::Tensor NearestNeighborIdxCpu(at::Tensor p1, at::Tensor p2);

#ifdef WITH_CUDA
// Cuda implementation.
at::Tensor NearestNeighborIdxCuda(at::Tensor p1, at::Tensor p2);
#endif

// Implementation which is exposed.
at::Tensor NearestNeighborIdx(at::Tensor p1, at::Tensor p2) {
  if (p1.is_cuda() && p2.is_cuda()) {
#ifdef WITH_CUDA
    CHECK_CONTIGUOUS_CUDA(p1);
    CHECK_CONTIGUOUS_CUDA(p2);
    return NearestNeighborIdxCuda(p1, p2);
#else
    AT_ERROR("Not compiled with GPU support.");
#endif
  }
  return NearestNeighborIdxCpu(p1, p2);
}
