#include <../src/vec/is/sf/impls/basic/gatherv/sfgatherv.h>
#include <../src/vec/is/sf/impls/basic/allgather/sfallgather.h>

/* Reuse the type. The difference is some fields (i.e., displs, recvcounts) are not used in Gather, which is not a big deal */
typedef PetscSF_Allgatherv PetscSF_Gather;

PETSC_INTERN PetscErrorCode PetscSFBcastBegin_Gather(PetscSF sf, MPI_Datatype unit, PetscMemType rootmtype, const void *rootdata, PetscMemType leafmtype, void *leafdata, MPI_Op op) {
  PetscSFLink  link;
  PetscMPIInt  sendcount;
  MPI_Comm     comm;
  void        *rootbuf = NULL, *leafbuf = NULL;
  MPI_Request *req;

  PetscFunctionBegin;
  PetscCall(PetscSFLinkCreate(sf, unit, rootmtype, rootdata, leafmtype, leafdata, op, PETSCSF_BCAST, &link));
  PetscCall(PetscSFLinkPackRootData(sf, link, PETSCSF_REMOTE, rootdata));
  PetscCall(PetscSFLinkCopyRootBufferInCaseNotUseGpuAwareMPI(sf, link, PETSC_TRUE /* device2host before sending */));
  PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
  PetscCall(PetscMPIIntCast(sf->nroots, &sendcount));
  PetscCall(PetscSFLinkGetMPIBuffersAndRequests(sf, link, PETSCSF_ROOT2LEAF, &rootbuf, &leafbuf, &req, NULL));
  PetscCall(PetscSFLinkSyncStreamBeforeCallMPI(sf, link, PETSCSF_ROOT2LEAF));
  PetscCallMPI(MPIU_Igather(rootbuf == leafbuf ? MPI_IN_PLACE : rootbuf, sendcount, unit, leafbuf, sendcount, unit, 0 /*rank 0*/, comm, req));
  PetscFunctionReturn(0);
}

static PetscErrorCode PetscSFReduceBegin_Gather(PetscSF sf, MPI_Datatype unit, PetscMemType leafmtype, const void *leafdata, PetscMemType rootmtype, void *rootdata, MPI_Op op) {
  PetscSFLink  link;
  PetscMPIInt  recvcount;
  MPI_Comm     comm;
  void        *rootbuf = NULL, *leafbuf = NULL;
  MPI_Request *req;

  PetscFunctionBegin;
  PetscCall(PetscSFLinkCreate(sf, unit, rootmtype, rootdata, leafmtype, leafdata, op, PETSCSF_REDUCE, &link));
  PetscCall(PetscSFLinkPackLeafData(sf, link, PETSCSF_REMOTE, leafdata));
  PetscCall(PetscSFLinkCopyLeafBufferInCaseNotUseGpuAwareMPI(sf, link, PETSC_TRUE /* device2host before sending */));
  PetscCall(PetscObjectGetComm((PetscObject)sf, &comm));
  PetscCall(PetscMPIIntCast(sf->nroots, &recvcount));
  PetscCall(PetscSFLinkGetMPIBuffersAndRequests(sf, link, PETSCSF_LEAF2ROOT, &rootbuf, &leafbuf, &req, NULL));
  PetscCall(PetscSFLinkSyncStreamBeforeCallMPI(sf, link, PETSCSF_LEAF2ROOT));
  PetscCallMPI(MPIU_Iscatter(leafbuf, recvcount, unit, rootbuf == leafbuf ? MPI_IN_PLACE : rootbuf, recvcount, unit, 0 /*rank 0*/, comm, req));
  PetscFunctionReturn(0);
}

PETSC_INTERN PetscErrorCode PetscSFCreate_Gather(PetscSF sf) {
  PetscSF_Gather *dat = (PetscSF_Gather *)sf->data;

  PetscFunctionBegin;
  sf->ops->BcastEnd  = PetscSFBcastEnd_Basic;
  sf->ops->ReduceEnd = PetscSFReduceEnd_Basic;

  /* Inherit from Allgatherv */
  sf->ops->Reset         = PetscSFReset_Allgatherv;
  sf->ops->Destroy       = PetscSFDestroy_Allgatherv;
  sf->ops->GetGraph      = PetscSFGetGraph_Allgatherv;
  sf->ops->GetRootRanks  = PetscSFGetRootRanks_Allgatherv;
  sf->ops->GetLeafRanks  = PetscSFGetLeafRanks_Allgatherv;
  sf->ops->FetchAndOpEnd = PetscSFFetchAndOpEnd_Allgatherv;
  sf->ops->CreateLocalSF = PetscSFCreateLocalSF_Allgatherv;

  /* Inherit from Allgather */
  sf->ops->SetUp = PetscSFSetUp_Allgather;

  /* Inherit from Gatherv */
  sf->ops->FetchAndOpBegin = PetscSFFetchAndOpBegin_Gatherv;

  /* Gather stuff */
  sf->ops->BcastBegin  = PetscSFBcastBegin_Gather;
  sf->ops->ReduceBegin = PetscSFReduceBegin_Gather;

  PetscCall(PetscNewLog(sf, &dat));
  sf->data = (void *)dat;
  PetscFunctionReturn(0);
}