#include <petsc/private/deviceimpl.h>
#include <petsc/private/randomimpl.h>
#include <curand.h>

typedef struct {
  curandGenerator_t gen;
} PetscRandom_CURAND;

PetscErrorCode PetscRandomSeed_CURAND(PetscRandom r)
{
  PetscRandom_CURAND *curand = (PetscRandom_CURAND*)r->data;

  PetscFunctionBegin;
  PetscCallCURAND(curandSetPseudoRandomGeneratorSeed(curand->gen,r->seed));
  PetscFunctionReturn(0);
}

PETSC_INTERN PetscErrorCode PetscRandomCurandScale_Private(PetscRandom,size_t,PetscReal*,PetscBool);

PetscErrorCode  PetscRandomGetValuesReal_CURAND(PetscRandom r, PetscInt n, PetscReal *val)
{
  PetscRandom_CURAND *curand = (PetscRandom_CURAND*)r->data;
  size_t             nn = n < 0 ? (size_t)(-2*n) : n; /* handle complex case */

  PetscFunctionBegin;
#if defined(PETSC_USE_REAL_SINGLE)
  PetscCallCURAND(curandGenerateUniform(curand->gen,val,nn));
#else
  PetscCallCURAND(curandGenerateUniformDouble(curand->gen,val,nn));
#endif
  if (r->iset) {
    PetscCall(PetscRandomCurandScale_Private(r,nn,val,(PetscBool)(n<0)));
  }
  PetscFunctionReturn(0);
}

PetscErrorCode PetscRandomGetValues_CURAND(PetscRandom r, PetscInt n, PetscScalar *val)
{
  PetscFunctionBegin;
#if defined(PETSC_USE_COMPLEX)
  /* pass negative size to flag complex scaling (if needed) */
  PetscCall(PetscRandomGetValuesReal_CURAND(r,-n,(PetscReal*)val));
#else
  PetscCall(PetscRandomGetValuesReal_CURAND(r,n,val));
#endif
  PetscFunctionReturn(0);
}

PetscErrorCode PetscRandomDestroy_CURAND(PetscRandom r)
{
  PetscRandom_CURAND *curand = (PetscRandom_CURAND*)r->data;

  PetscFunctionBegin;
  PetscCallCURAND(curandDestroyGenerator(curand->gen));
  PetscCall(PetscFree(r->data));
  PetscFunctionReturn(0);
}

static struct _PetscRandomOps PetscRandomOps_Values = {
  PetscDesignatedInitializer(seed,PetscRandomSeed_CURAND),
  PetscDesignatedInitializer(getvalue,NULL),
  PetscDesignatedInitializer(getvaluereal,NULL),
  PetscDesignatedInitializer(getvalues,PetscRandomGetValues_CURAND),
  PetscDesignatedInitializer(getvaluesreal,PetscRandomGetValuesReal_CURAND),
  PetscDesignatedInitializer(destroy,PetscRandomDestroy_CURAND),
};

/*MC
   PETSCCURAND - access to the CUDA random number generator

  PETSc must be ./configure with the option --with-cuda to use this random number generator.

  Level: beginner

.seealso: `PetscRandomCreate()`, `PetscRandomSetType()`
M*/

PETSC_EXTERN PetscErrorCode PetscRandomCreate_CURAND(PetscRandom r)
{
  PetscRandom_CURAND *curand;

  PetscFunctionBegin;
  PetscCall(PetscDeviceInitialize(PETSC_DEVICE_CUDA));
  PetscCall(PetscNewLog(r,&curand));
  PetscCallCURAND(curandCreateGenerator(&curand->gen,CURAND_RNG_PSEUDO_DEFAULT));
  /* https://docs.nvidia.com/cuda/curand/host-api-overview.html#performance-notes2 */
  PetscCallCURAND(curandSetGeneratorOrdering(curand->gen,CURAND_ORDERING_PSEUDO_SEEDED));
  PetscCall(PetscMemcpy(r->ops,&PetscRandomOps_Values,sizeof(PetscRandomOps_Values)));
  PetscCall(PetscObjectChangeTypeName((PetscObject)r,PETSCCURAND));
  r->data = curand;
  r->seed = 1234ULL; /* taken from example */
  PetscCall(PetscRandomSeed_CURAND(r));
  PetscFunctionReturn(0);
}