#include <ATen/ATen.h>

#include <cuda.h>
#include <cuda_runtime.h>

__global__ 
void ChamferDistanceKernel(
	int b,
	int n,
	const float* xyz,
	int m,
	const float* xyz2,
	float* result,
	int* result_i)
{
	const int batch=512;
	__shared__ float buf[batch*3];
	for (int i=blockIdx.x;i<b;i+=gridDim.x){
		for (int k2=0;k2<m;k2+=batch){
			int end_k=min(m,k2+batch)-k2;
			for (int j=threadIdx.x;j<end_k*3;j+=blockDim.x){
				buf[j]=xyz2[(i*m+k2)*3+j];
			}
			__syncthreads();
			for (int j=threadIdx.x+blockIdx.y*blockDim.x;j<n;j+=blockDim.x*gridDim.y){
				float x1=xyz[(i*n+j)*3+0];
				float y1=xyz[(i*n+j)*3+1];
				float z1=xyz[(i*n+j)*3+2];
				int best_i=0;
				float best=0;
				int end_ka=end_k-(end_k&3);
				
				for (int k=0;k<end_ka;k+=1){
					{
						float x2=buf[k*3+0]-x1;
						float y2=buf[k*3+1]-y1;
						float z2=buf[k*3+2]-z1;
						float d=x2*x2+y2*y2+z2*z2;
						if (k==0 || d<best){
							best=d;
							best_i=k+k2;
						}
					}
				}
				
	
				if (k2==0 || result[(i*n+j)]>best){
					result[(i*n+j)]=best;
					result_i[(i*n+j)]=best_i;
				}
			}
			__syncthreads();
		}
	}
}

void ChamferDistanceKernelLauncher(
    const int b, const int n,
    const float* xyz,
    const int m,
    const float* xyz2,
    float* result,
    int* result_i,
    float* result2,
    int* result2_i)
{
	ChamferDistanceKernel<<<dim3(32,16,1),512>>>(b, n, xyz, m, xyz2, result, result_i);
	ChamferDistanceKernel<<<dim3(32,16,1),512>>>(b, m, xyz2, n, xyz, result2, result2_i);

	cudaError_t err = cudaGetLastError();
	if (err != cudaSuccess)
	    printf("error in chamfer distance updateOutput: %s\n", cudaGetErrorString(err));
}