/*
 * SPDX-FileCopyrightText: 2026 Oak Ridge National Laboratory and Contributors
 *
 * SPDX-License-Identifier: Apache-2.0
 */

#include <cstdint>
#include <cstring>

#include <iostream>
#include <numeric> //std::iota
#include <stdexcept>

#include <adios2.h>

#include <gtest/gtest.h>

#include "../TestHelpers.h"

std::string engineName;       // comes from command line
std::string engineParameters; // comes from command line

class BPWriteReadTestFlatten : public ::testing::Test
{
public:
    BPWriteReadTestFlatten() = default;

    SmallTestData m_TestData;
};

//******************************************************************************
// 1D 1x8 test data
//******************************************************************************

// Flatten BP write and read 1D arrays
TEST_F(BPWriteReadTestFlatten, FlattenBPWriteRead1D8)
{
    // Each process would write a 1x8 array and all processes would
    // form a mpiSize * Nx 1D array

    int mpiRank = 0, mpiSize = 1;
    // Number of rows
    const size_t Nx = 8;

#if ADIOS2_USE_MPI
    MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
    MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
    const std::string fname("FlattenBPWriteRead1D8_MPI.bp");
#else
    const std::string fname("FlattenBPWriteRead1D8.bp");
#endif

    // Write test data using BP

#if ADIOS2_USE_MPI
    adios2::ADIOS adios(MPI_COMM_WORLD);
#else
    adios2::ADIOS adios;
#endif
    {
        adios2::IO io = adios.DeclareIO("TestIO");

        // Declare 1D variables (NumOfProcesses * Nx)
        // The local process' part (start, count) can be defined now or later
        // before Write().
        {
            const adios2::Dims shape{static_cast<size_t>(Nx * mpiSize)};
            const adios2::Dims start{static_cast<size_t>(Nx * mpiRank)};
            const adios2::Dims count{Nx};

            auto var_char = io.DefineVariable<char>("ch", shape, start, count);
            EXPECT_TRUE(var_char);
            auto var_iString = io.DefineVariable<std::string>("iString");
            EXPECT_TRUE(var_iString);
            auto var_i8 = io.DefineVariable<int8_t>("i8", shape, start, count);
            EXPECT_TRUE(var_i8);
            auto var_i16 = io.DefineVariable<int16_t>("i16", shape, start, count);
            EXPECT_TRUE(var_i16);
            auto var_i32 = io.DefineVariable<int32_t>("i32", shape, start, count);
            EXPECT_TRUE(var_i32);
            auto var_i64 = io.DefineVariable<int64_t>("i64", shape, start, count);
            EXPECT_TRUE(var_i64);
            auto var_u8 = io.DefineVariable<uint8_t>("u8", shape, start, count);
            EXPECT_TRUE(var_u8);
            auto var_u16 = io.DefineVariable<uint16_t>("u16", shape, start, count);
            EXPECT_TRUE(var_u16);
            auto var_u32 = io.DefineVariable<uint32_t>("u32", shape, start, count);
            EXPECT_TRUE(var_u32);
            auto var_u64 = io.DefineVariable<uint64_t>("u64", shape, start, count);
            EXPECT_TRUE(var_u64);
            auto var_r32 = io.DefineVariable<float>("r32", shape, start, count);
            EXPECT_TRUE(var_r32);
            auto var_r64 = io.DefineVariable<double>("r64", shape, start, count);
            EXPECT_TRUE(var_r64);
        }

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        else
        {
            // Create the BP Engine
            io.SetEngine("BPFile");
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }

        io.SetParameters("FlattenSteps=on");
        io.AddTransport("file");

        adios2::Engine bpWriter = io.Open(fname, adios2::Mode::Write);

        EXPECT_EQ(bpWriter.OpenMode(), adios2::Mode::Write);

        for (size_t step = 0; step < (size_t)mpiSize; ++step)
        {
            // Generate test data for each process uniquely (all as if for step 0)
            SmallTestData currentTestData =
                generateNewSmallTestData(m_TestData, static_cast<int>(0), mpiRank, mpiSize);

            // Retrieve the variables that previously went out of scope
            auto var_char = io.InquireVariable<char>("ch");
            auto var_iString = io.InquireVariable<std::string>("iString");
            auto var_i8 = io.InquireVariable<int8_t>("i8");
            auto var_i16 = io.InquireVariable<int16_t>("i16");
            auto var_i32 = io.InquireVariable<int32_t>("i32");
            auto var_i64 = io.InquireVariable<int64_t>("i64");
            auto var_u8 = io.InquireVariable<uint8_t>("u8");
            auto var_u16 = io.InquireVariable<uint16_t>("u16");
            auto var_u32 = io.InquireVariable<uint32_t>("u32");
            auto var_u64 = io.InquireVariable<uint64_t>("u64");
            auto var_r32 = io.InquireVariable<float>("r32");
            auto var_r64 = io.InquireVariable<double>("r64");

            // Make a 1D selection to describe the local dimensions of the
            // variable we write and its offsets in the global spaces
            adios2::Box<adios2::Dims> sel({mpiRank * Nx}, {Nx});

            var_char.SetSelection(sel);
            EXPECT_THROW(var_iString.SetSelection(sel), std::invalid_argument);
            var_i8.SetSelection(sel);
            var_i16.SetSelection(sel);
            var_i32.SetSelection(sel);
            var_i64.SetSelection(sel);
            var_u8.SetSelection(sel);
            var_u16.SetSelection(sel);
            var_u32.SetSelection(sel);
            var_u64.SetSelection(sel);
            var_r32.SetSelection(sel);
            var_r64.SetSelection(sel);

            // Write each one
            // fill in the variable with values from starting index to
            // starting index + count
            bpWriter.BeginStep();

            if (step == (size_t)mpiRank)
            {
                bpWriter.Put(var_char, currentTestData.CHAR.data());
                bpWriter.Put(var_iString, currentTestData.S1);
                bpWriter.Put(var_i8, currentTestData.I8.data());
                bpWriter.Put(var_i16, currentTestData.I16.data());
                bpWriter.Put(var_i32, currentTestData.I32.data());
                bpWriter.Put(var_i64, currentTestData.I64.data());
                bpWriter.Put(var_u8, currentTestData.U8.data());
                bpWriter.Put(var_u16, currentTestData.U16.data());
                bpWriter.Put(var_u32, currentTestData.U32.data());
                bpWriter.Put(var_u64, currentTestData.U64.data());
                bpWriter.Put(var_r32, currentTestData.R32.data());
                bpWriter.Put(var_r64, currentTestData.R64.data());
            }
            bpWriter.EndStep();
        }

        // Close the file
        bpWriter.Close();
    }

    {
        adios2::IO io = adios.DeclareIO("ReadIO");

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }

        adios2::Engine bpReader = io.Open(fname, adios2::Mode::ReadRandomAccess);

        EXPECT_EQ(bpReader.Steps(), 1);

        auto var_char = io.InquireVariable<char>("ch");
        EXPECT_TRUE(var_char);
        ASSERT_EQ(var_char.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_char.Steps(), 1);
        ASSERT_EQ(var_char.Shape()[0], mpiSize * Nx);

        auto var_iString = io.InquireVariable<std::string>("iString");
        EXPECT_TRUE(var_iString);
        ASSERT_EQ(var_iString.Shape().size(), 0);
        ASSERT_EQ(var_iString.Steps(), 1);

        auto var_i8 = io.InquireVariable<int8_t>("i8");
        EXPECT_TRUE(var_i8);
        ASSERT_EQ(var_i8.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i8.Steps(), 1);
        ASSERT_EQ(var_i8.Shape()[0], mpiSize * Nx);

        auto var_i16 = io.InquireVariable<int16_t>("i16");
        EXPECT_TRUE(var_i16);
        ASSERT_EQ(var_i16.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i16.Steps(), 1);
        ASSERT_EQ(var_i16.Shape()[0], mpiSize * Nx);

        auto var_i32 = io.InquireVariable<int32_t>("i32");
        EXPECT_TRUE(var_i32);
        ASSERT_EQ(var_i32.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i32.Steps(), 1);
        ASSERT_EQ(var_i32.Shape()[0], mpiSize * Nx);

        auto var_i64 = io.InquireVariable<int64_t>("i64");
        EXPECT_TRUE(var_i64);
        ASSERT_EQ(var_i64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i64.Steps(), 1);
        ASSERT_EQ(var_i64.Shape()[0], mpiSize * Nx);

        auto var_u8 = io.InquireVariable<uint8_t>("u8");
        EXPECT_TRUE(var_u8);
        ASSERT_EQ(var_u8.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u8.Steps(), 1);
        ASSERT_EQ(var_u8.Shape()[0], mpiSize * Nx);

        auto var_u16 = io.InquireVariable<uint16_t>("u16");
        EXPECT_TRUE(var_u16);
        ASSERT_EQ(var_u16.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u16.Steps(), 1);
        ASSERT_EQ(var_u16.Shape()[0], mpiSize * Nx);

        auto var_u32 = io.InquireVariable<uint32_t>("u32");
        EXPECT_TRUE(var_u32);
        ASSERT_EQ(var_u32.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u32.Steps(), 1);
        ASSERT_EQ(var_u32.Shape()[0], mpiSize * Nx);

        auto var_u64 = io.InquireVariable<uint64_t>("u64");
        EXPECT_TRUE(var_u64);
        ASSERT_EQ(var_u64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u64.Steps(), 1);
        ASSERT_EQ(var_u64.Shape()[0], mpiSize * Nx);

        auto var_r32 = io.InquireVariable<float>("r32");
        EXPECT_TRUE(var_r32);
        ASSERT_EQ(var_r32.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_r32.Steps(), 1);
        ASSERT_EQ(var_r32.Shape()[0], mpiSize * Nx);

        auto var_r64 = io.InquireVariable<double>("r64");
        EXPECT_TRUE(var_r64);
        ASSERT_EQ(var_r64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_r64.Steps(), 1);
        ASSERT_EQ(var_r64.Shape()[0], mpiSize * Nx);

        // TODO: other types

        SmallTestData testData;

        std::string IString;
        std::array<int8_t, Nx> I8;
        std::array<int16_t, Nx> I16;
        std::array<int32_t, Nx> I32;
        std::array<int64_t, Nx> I64;
        std::array<uint8_t, Nx> U8;
        std::array<uint16_t, Nx> U16;
        std::array<uint32_t, Nx> U32;
        std::array<uint64_t, Nx> U64;
        std::array<float, Nx> R32;
        std::array<double, Nx> R64;
        std::array<char, Nx> CHAR;

        const adios2::Dims start{mpiRank * Nx};
        const adios2::Dims count{Nx};

        const adios2::Box<adios2::Dims> sel(start, count);

        for (size_t t = 0; t < 1; ++t)
        {
            var_char.SetSelection(sel);

            var_i8.SetSelection(sel);
            var_i16.SetSelection(sel);
            var_i32.SetSelection(sel);
            var_i64.SetSelection(sel);
            var_u8.SetSelection(sel);
            var_u16.SetSelection(sel);
            var_u32.SetSelection(sel);
            var_u64.SetSelection(sel);
            var_r32.SetSelection(sel);
            var_r64.SetSelection(sel);

            // default step selection should be 0, 1, so no need for that

            // Generate test data for each rank uniquely
            SmallTestData currentTestData =
                generateNewSmallTestData(m_TestData, static_cast<int>(0), mpiRank, mpiSize);

            bpReader.Get(var_char, CHAR.data());
            bpReader.Get(var_iString, IString);
            bpReader.Get(var_i8, I8.data());
            bpReader.Get(var_i16, I16.data());
            bpReader.Get(var_i32, I32.data());
            bpReader.Get(var_i64, I64.data());
            bpReader.Get(var_u8, U8.data());
            bpReader.Get(var_u16, U16.data());
            bpReader.Get(var_u32, U32.data());
            bpReader.Get(var_u64, U64.data());
            bpReader.Get(var_r32, R32.data());
            bpReader.Get(var_r64, R64.data());

            bpReader.PerformGets();

            EXPECT_EQ(IString, currentTestData.S1) << "rank=" << mpiRank;

            for (size_t i = 0; i < Nx; ++i)
            {
                std::stringstream ss;
                ss << "t=" << t << " i=" << i << " rank=" << mpiRank;
                std::string msg = ss.str();

                // EXPECT_EQ(TF[i], currentTestData.TF[i]) << msg;
                EXPECT_EQ(CHAR[i], currentTestData.CHAR[i]) << msg;
                EXPECT_EQ(I8[i], currentTestData.I8[i]) << msg;
                EXPECT_EQ(I16[i], currentTestData.I16[i]) << msg;
                EXPECT_EQ(I32[i], currentTestData.I32[i]) << msg;
                EXPECT_EQ(I64[i], currentTestData.I64[i]) << msg;
                EXPECT_EQ(U8[i], currentTestData.U8[i]) << msg;
                EXPECT_EQ(U16[i], currentTestData.U16[i]) << msg;
                EXPECT_EQ(U32[i], currentTestData.U32[i]) << msg;
                EXPECT_EQ(U64[i], currentTestData.U64[i]) << msg;
                EXPECT_EQ(R32[i], currentTestData.R32[i]) << msg;
                EXPECT_EQ(R64[i], currentTestData.R64[i]) << msg;
            }
        }
        bpReader.Close();
    }

#if ADIOS2_USE_MPI
    CleanupTestFilesMPI(fname, MPI_COMM_WORLD);
#else
    CleanupTestFiles(fname);
#endif
}

//******************************************************************************
// 2D 2x4 test data
//******************************************************************************

// ADIOS2 BP write and read 2D array
TEST_F(BPWriteReadTestFlatten, FlattenBPWriteRead2D2x4)
{
    // Each process would write a 2x4 array and all processes would
    // form a 2D 2 * (numberOfProcess*Nx) matrix where Nx is 4 here

    int mpiRank = 0, mpiSize = 1;
    // Number of rows
    const std::size_t Nx = 4;

    // Number of rows
    const std::size_t Ny = 2;

#if ADIOS2_USE_MPI
    MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
    MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
    const std::string fname("FlattenBPWriteRead2D2x4Test_MPI.bp");
#else
    const std::string fname("FlattenBPWriteRead2D2x4Test.bp");
#endif

    // Write test data using ADIOS2

#if ADIOS2_USE_MPI
    adios2::ADIOS adios(MPI_COMM_WORLD);
#else
    adios2::ADIOS adios;
#endif
    {
        adios2::IO io = adios.DeclareIO("TestIO");

        // Declare 2D variables (Ny * (NumOfProcesses * Nx))
        // The local process' part (start, count) can be defined now or later
        // before Write().
        {
            const adios2::Dims shape{Ny, static_cast<size_t>(Nx * mpiSize)};
            const adios2::Dims start{0, static_cast<size_t>(mpiRank * Nx)};
            const adios2::Dims count{Ny, Nx};

            auto var_iString = io.DefineVariable<std::string>("iString");
            EXPECT_TRUE(var_iString);
            auto var_i8 = io.DefineVariable<int8_t>("i8", shape, start, count);
            EXPECT_TRUE(var_i8);
            auto var_i16 = io.DefineVariable<int16_t>("i16", shape, start, count);
            EXPECT_TRUE(var_i16);
            auto var_i32 = io.DefineVariable<int32_t>("i32", shape, start, count);
            EXPECT_TRUE(var_i32);
            auto var_i64 = io.DefineVariable<int64_t>("i64", shape, start, count);
            EXPECT_TRUE(var_i64);
            auto var_u8 = io.DefineVariable<uint8_t>("u8", shape, start, count);
            EXPECT_TRUE(var_u8);
            auto var_u16 = io.DefineVariable<uint16_t>("u16", shape, start, count);
            EXPECT_TRUE(var_u16);
            auto var_u32 = io.DefineVariable<uint32_t>("u32", shape, start, count);
            EXPECT_TRUE(var_u32);
            auto var_u64 = io.DefineVariable<uint64_t>("u64", shape, start, count);
            EXPECT_TRUE(var_u64);
            auto var_r32 = io.DefineVariable<float>("r32", shape, start, count);
            EXPECT_TRUE(var_r32);
            auto var_r64 = io.DefineVariable<double>("r64", shape, start, count);
            EXPECT_TRUE(var_r64);
        }

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        else
        {
            // Create the BP Engine
            io.SetEngine("BPFile");
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }
        io.AddTransport("file");

        io.SetParameters("FlattenSteps=on");
        adios2::Engine bpWriter = io.Open(fname, adios2::Mode::Write);

        for (size_t step = 0; step < (size_t)mpiSize; ++step)
        {
            // Generate test data for each process uniquely
            SmallTestData currentTestData =
                generateNewSmallTestData(m_TestData, static_cast<int>(0), mpiRank, mpiSize);

            // Retrieve the variables that previously went out of scope
            auto var_iString = io.InquireVariable<std::string>("iString");
            auto var_i8 = io.InquireVariable<int8_t>("i8");
            auto var_i16 = io.InquireVariable<int16_t>("i16");
            auto var_i32 = io.InquireVariable<int32_t>("i32");
            auto var_i64 = io.InquireVariable<int64_t>("i64");
            auto var_u8 = io.InquireVariable<uint8_t>("u8");
            auto var_u16 = io.InquireVariable<uint16_t>("u16");
            auto var_u32 = io.InquireVariable<uint32_t>("u32");
            auto var_u64 = io.InquireVariable<uint64_t>("u64");
            auto var_r32 = io.InquireVariable<float>("r32");
            auto var_r64 = io.InquireVariable<double>("r64");

            // Make a 2D selection to describe the local dimensions of the
            // variable we write and its offsets in the global spaces
            adios2::Box<adios2::Dims> sel({0, static_cast<size_t>(mpiRank * Nx)}, {Ny, Nx});
            var_i8.SetSelection(sel);
            var_i16.SetSelection(sel);
            var_i32.SetSelection(sel);
            var_i64.SetSelection(sel);
            var_u8.SetSelection(sel);
            var_u16.SetSelection(sel);
            var_u32.SetSelection(sel);
            var_u64.SetSelection(sel);
            var_r32.SetSelection(sel);
            var_r64.SetSelection(sel);

            // Write each one
            // fill in the variable with values from starting index to
            // starting index + count
            bpWriter.BeginStep();
            if (step == (size_t)mpiRank)
            {
                bpWriter.Put(var_iString, currentTestData.S1);
                bpWriter.Put(var_i8, currentTestData.I8.data());
                bpWriter.Put(var_i16, currentTestData.I16.data());
                bpWriter.Put(var_i32, currentTestData.I32.data());
                bpWriter.Put(var_i64, currentTestData.I64.data());
                bpWriter.Put(var_u8, currentTestData.U8.data());
                bpWriter.Put(var_u16, currentTestData.U16.data());
                bpWriter.Put(var_u32, currentTestData.U32.data());
                bpWriter.Put(var_u64, currentTestData.U64.data());
                bpWriter.Put(var_r32, currentTestData.R32.data());
                bpWriter.Put(var_r64, currentTestData.R64.data());
            }
            bpWriter.EndStep();
        }

        // Close the file
        bpWriter.Close();
    }

    {
        adios2::IO io = adios.DeclareIO("ReadIO");

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }

        adios2::Engine bpReader = io.Open(fname, adios2::Mode::ReadRandomAccess);

        EXPECT_EQ(bpReader.Steps(), 1);
        auto var_iString = io.InquireVariable<std::string>("iString");
        EXPECT_TRUE(var_iString);
        ASSERT_EQ(var_iString.Shape().size(), 0);
        ASSERT_EQ(var_iString.Steps(), 1);

        auto var_i8 = io.InquireVariable<int8_t>("i8");
        EXPECT_TRUE(var_i8);
        ASSERT_EQ(var_i8.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i8.Steps(), 1);
        ASSERT_EQ(var_i8.Shape()[0], Ny);
        ASSERT_EQ(var_i8.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_i16 = io.InquireVariable<int16_t>("i16");
        EXPECT_TRUE(var_i16);
        ASSERT_EQ(var_i16.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i16.Steps(), 1);
        ASSERT_EQ(var_i16.Shape()[0], Ny);
        ASSERT_EQ(var_i16.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_i32 = io.InquireVariable<int32_t>("i32");
        EXPECT_TRUE(var_i32);
        ASSERT_EQ(var_i32.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i32.Steps(), 1);
        ASSERT_EQ(var_i32.Shape()[0], Ny);
        ASSERT_EQ(var_i32.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_i64 = io.InquireVariable<int64_t>("i64");
        EXPECT_TRUE(var_i64);
        ASSERT_EQ(var_i64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i64.Steps(), 1);
        ASSERT_EQ(var_i64.Shape()[0], Ny);
        ASSERT_EQ(var_i64.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_u8 = io.InquireVariable<uint8_t>("u8");
        EXPECT_TRUE(var_u8);
        ASSERT_EQ(var_u8.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u8.Steps(), 1);
        ASSERT_EQ(var_u8.Shape()[0], Ny);
        ASSERT_EQ(var_u8.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_u16 = io.InquireVariable<uint16_t>("u16");
        EXPECT_TRUE(var_u16);
        ASSERT_EQ(var_u16.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u16.Steps(), 1);
        ASSERT_EQ(var_u16.Shape()[0], Ny);
        ASSERT_EQ(var_u16.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_u32 = io.InquireVariable<uint32_t>("u32");
        EXPECT_TRUE(var_u32);
        ASSERT_EQ(var_u32.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u32.Steps(), 1);
        ASSERT_EQ(var_u32.Shape()[0], Ny);
        ASSERT_EQ(var_u32.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_u64 = io.InquireVariable<uint64_t>("u64");
        EXPECT_TRUE(var_u64);
        ASSERT_EQ(var_u64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u64.Steps(), 1);
        ASSERT_EQ(var_u64.Shape()[0], Ny);
        ASSERT_EQ(var_u64.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_r32 = io.InquireVariable<float>("r32");
        EXPECT_TRUE(var_r32);
        ASSERT_EQ(var_r32.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_r32.Steps(), 1);
        ASSERT_EQ(var_r32.Shape()[0], Ny);
        ASSERT_EQ(var_r32.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_r64 = io.InquireVariable<double>("r64");
        EXPECT_TRUE(var_r64);
        ASSERT_EQ(var_r64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_r64.Steps(), 1);
        ASSERT_EQ(var_r64.Shape()[0], Ny);
        ASSERT_EQ(var_r64.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        std::string IString;
        std::array<int8_t, Nx * Ny> I8;
        std::array<int16_t, Nx * Ny> I16;
        std::array<int32_t, Nx * Ny> I32;
        std::array<int64_t, Nx * Ny> I64;
        std::array<uint8_t, Nx * Ny> U8;
        std::array<uint16_t, Nx * Ny> U16;
        std::array<uint32_t, Nx * Ny> U32;
        std::array<uint64_t, Nx * Ny> U64;
        std::array<float, Nx * Ny> R32;
        std::array<double, Nx * Ny> R64;

        const adios2::Dims start{0, static_cast<size_t>(mpiRank * Nx)};
        const adios2::Dims count{Ny, Nx};

        const adios2::Box<adios2::Dims> sel(start, count);

        var_i8.SetSelection(sel);
        var_i16.SetSelection(sel);
        var_i32.SetSelection(sel);
        var_i64.SetSelection(sel);

        var_u8.SetSelection(sel);
        var_u16.SetSelection(sel);
        var_u32.SetSelection(sel);
        var_u64.SetSelection(sel);

        var_r32.SetSelection(sel);
        var_r64.SetSelection(sel);

        for (size_t t = 0; t < 1; ++t)
        {
            var_i8.SetStepSelection({t, 1});
            var_i16.SetStepSelection({t, 1});
            var_i32.SetStepSelection({t, 1});
            var_i64.SetStepSelection({t, 1});

            var_u8.SetStepSelection({t, 1});
            var_u16.SetStepSelection({t, 1});
            var_u32.SetStepSelection({t, 1});
            var_u64.SetStepSelection({t, 1});

            var_r32.SetStepSelection({t, 1});
            var_r64.SetStepSelection({t, 1});

            bpReader.Get(var_iString, IString);

            bpReader.Get(var_i8, I8.data());
            bpReader.Get(var_i16, I16.data());
            bpReader.Get(var_i32, I32.data());
            bpReader.Get(var_i64, I64.data());

            bpReader.Get(var_u8, U8.data());
            bpReader.Get(var_u16, U16.data());
            bpReader.Get(var_u32, U32.data());
            bpReader.Get(var_u64, U64.data());

            bpReader.Get(var_r32, R32.data());
            bpReader.Get(var_r64, R64.data());

            bpReader.PerformGets();
            // Generate test data for each rank uniquely
            SmallTestData currentTestData =
                generateNewSmallTestData(m_TestData, static_cast<int>(0), mpiRank, mpiSize);

            EXPECT_EQ(IString, currentTestData.S1);

            for (size_t i = 0; i < Nx * Ny; ++i)
            {
                std::stringstream ss;
                ss << "t=" << t << " i=" << i << " rank=" << mpiRank;
                std::string msg = ss.str();

                EXPECT_EQ(I8[i], currentTestData.I8[i]) << msg;
                EXPECT_EQ(I16[i], currentTestData.I16[i]) << msg;
                EXPECT_EQ(I32[i], currentTestData.I32[i]) << msg;
                EXPECT_EQ(I64[i], currentTestData.I64[i]) << msg;
                EXPECT_EQ(U8[i], currentTestData.U8[i]) << msg;
                EXPECT_EQ(U16[i], currentTestData.U16[i]) << msg;
                EXPECT_EQ(U32[i], currentTestData.U32[i]) << msg;
                EXPECT_EQ(U64[i], currentTestData.U64[i]) << msg;
                EXPECT_EQ(R32[i], currentTestData.R32[i]) << msg;
                EXPECT_EQ(R64[i], currentTestData.R64[i]) << msg;
            }
        }
        bpReader.Close();
    }

#if ADIOS2_USE_MPI
    CleanupTestFilesMPI(fname, MPI_COMM_WORLD);
#else
    CleanupTestFiles(fname);
#endif
}

//******************************************************************************
// 2D 4x2 test data
//******************************************************************************

TEST_F(BPWriteReadTestFlatten, FlattenBPWriteRead2D4x2)
{
    // Each process would write a 4x2 array and all processes would
    // form a 2D 4 * (NumberOfProcess * Nx) matrix where Nx is 2 here

    int mpiRank = 0, mpiSize = 1;
    // Number of rows
    const std::size_t Nx = 2;
    // Number of cols
    const std::size_t Ny = 4;

#if ADIOS2_USE_MPI
    MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
    MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
    const std::string fname("FlattenBPWriteRead2D4x2Test_MPI.bp");
#else
    const std::string fname("FlattenBPWriteRead2D4x2Test.bp");
#endif

    // Write test data using ADIOS2

#if ADIOS2_USE_MPI
    adios2::ADIOS adios(MPI_COMM_WORLD);
#else
    adios2::ADIOS adios;
#endif
    {
        adios2::IO io = adios.DeclareIO("TestIO");

        // Declare 2D variables (4 * (NumberOfProcess * Nx))
        // The local process' part (start, count) can be defined now or later
        // before Write().
        {
            adios2::Dims shape{static_cast<unsigned int>(Ny),
                               static_cast<unsigned int>(mpiSize * Nx)};
            adios2::Dims start{static_cast<unsigned int>(0),
                               static_cast<unsigned int>(mpiRank * Nx)};
            adios2::Dims count{static_cast<unsigned int>(Ny), static_cast<unsigned int>(Nx)};
            auto var_i8 = io.DefineVariable<int8_t>("i8", shape, start, count);
            EXPECT_TRUE(var_i8);
            auto var_i16 = io.DefineVariable<int16_t>("i16", shape, start, count);
            EXPECT_TRUE(var_i16);
            auto var_i32 = io.DefineVariable<int32_t>("i32", shape, start, count);
            EXPECT_TRUE(var_i32);
            auto var_i64 = io.DefineVariable<int64_t>("i64", shape, start, count);
            EXPECT_TRUE(var_i64);
            auto var_u8 = io.DefineVariable<uint8_t>("u8", shape, start, count);
            EXPECT_TRUE(var_u8);
            auto var_u16 = io.DefineVariable<uint16_t>("u16", shape, start, count);
            EXPECT_TRUE(var_u16);
            auto var_u32 = io.DefineVariable<uint32_t>("u32", shape, start, count);
            EXPECT_TRUE(var_u32);
            auto var_u64 = io.DefineVariable<uint64_t>("u64", shape, start, count);
            EXPECT_TRUE(var_u64);
            auto var_r32 = io.DefineVariable<float>("r32", shape, start, count);
            EXPECT_TRUE(var_r32);
            auto var_r64 = io.DefineVariable<double>("r64", shape, start, count);
            EXPECT_TRUE(var_r64);
        }

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        else
        {
            // Create the BP Engine
            io.SetEngine("BPFile");
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }

        io.AddTransport("file");

        io.SetParameters("FlattenSteps=on");
        adios2::Engine bpWriter = io.Open(fname, adios2::Mode::Write);

        for (size_t step = 0; step < (size_t)mpiSize; ++step)
        {
            // Generate test data for each process uniquely
            SmallTestData currentTestData =
                generateNewSmallTestData(m_TestData, static_cast<int>(0), mpiRank, mpiSize);

            // Retrieve the variables that previously went out of scope
            auto var_i8 = io.InquireVariable<int8_t>("i8");
            auto var_i16 = io.InquireVariable<int16_t>("i16");
            auto var_i32 = io.InquireVariable<int32_t>("i32");
            auto var_i64 = io.InquireVariable<int64_t>("i64");
            auto var_u8 = io.InquireVariable<uint8_t>("u8");
            auto var_u16 = io.InquireVariable<uint16_t>("u16");
            auto var_u32 = io.InquireVariable<uint32_t>("u32");
            auto var_u64 = io.InquireVariable<uint64_t>("u64");
            auto var_r32 = io.InquireVariable<float>("r32");
            auto var_r64 = io.InquireVariable<double>("r64");

            // Make a 2D selection to describe the local dimensions of the
            // variable we write and its offsets in the global spaces
            adios2::Box<adios2::Dims> sel({0, static_cast<unsigned int>(mpiRank * Nx)}, {Ny, Nx});
            var_i8.SetSelection(sel);
            var_i16.SetSelection(sel);
            var_i32.SetSelection(sel);
            var_i64.SetSelection(sel);
            var_u8.SetSelection(sel);
            var_u16.SetSelection(sel);
            var_u32.SetSelection(sel);
            var_u64.SetSelection(sel);
            var_r32.SetSelection(sel);
            var_r64.SetSelection(sel);

            // Write each one
            // fill in the variable with values from starting index to
            // starting index + count
            bpWriter.BeginStep();
            if (step == (size_t)mpiRank)
            {
                bpWriter.Put(var_i8, currentTestData.I8.data());
                bpWriter.Put(var_i16, currentTestData.I16.data());
                bpWriter.Put(var_i32, currentTestData.I32.data());
                bpWriter.Put(var_i64, currentTestData.I64.data());
                bpWriter.Put(var_u8, currentTestData.U8.data());
                bpWriter.Put(var_u16, currentTestData.U16.data());
                bpWriter.Put(var_u32, currentTestData.U32.data());
                bpWriter.Put(var_u64, currentTestData.U64.data());
                bpWriter.Put(var_r32, currentTestData.R32.data());
                bpWriter.Put(var_r64, currentTestData.R64.data());
            }
            bpWriter.EndStep();
        }

        // Close the file
        bpWriter.Close();
    }

    {
        adios2::IO io = adios.DeclareIO("ReadIO");

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }

        adios2::Engine bpReader = io.Open(fname, adios2::Mode::ReadRandomAccess);

        EXPECT_EQ(bpReader.Steps(), 1);

        auto var_i8 = io.InquireVariable<int8_t>("i8");
        EXPECT_TRUE(var_i8);
        ASSERT_EQ(var_i8.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i8.Steps(), 1);
        ASSERT_EQ(var_i8.Shape()[0], Ny);
        ASSERT_EQ(var_i8.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_i16 = io.InquireVariable<int16_t>("i16");
        EXPECT_TRUE(var_i16);
        ASSERT_EQ(var_i16.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i16.Steps(), 1);
        ASSERT_EQ(var_i16.Shape()[0], Ny);
        ASSERT_EQ(var_i16.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_i32 = io.InquireVariable<int32_t>("i32");
        EXPECT_TRUE(var_i32);
        ASSERT_EQ(var_i32.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i32.Steps(), 1);
        ASSERT_EQ(var_i32.Shape()[0], Ny);
        ASSERT_EQ(var_i32.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_i64 = io.InquireVariable<int64_t>("i64");
        EXPECT_TRUE(var_i64);
        ASSERT_EQ(var_i64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_i64.Steps(), 1);
        ASSERT_EQ(var_i64.Shape()[0], Ny);
        ASSERT_EQ(var_i64.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_u8 = io.InquireVariable<uint8_t>("u8");
        EXPECT_TRUE(var_u8);
        ASSERT_EQ(var_u8.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u8.Steps(), 1);
        ASSERT_EQ(var_u8.Shape()[0], Ny);
        ASSERT_EQ(var_u8.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_u16 = io.InquireVariable<uint16_t>("u16");
        EXPECT_TRUE(var_u16);
        ASSERT_EQ(var_u16.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u16.Steps(), 1);
        ASSERT_EQ(var_u16.Shape()[0], Ny);
        ASSERT_EQ(var_u16.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_u32 = io.InquireVariable<uint32_t>("u32");
        EXPECT_TRUE(var_u32);
        ASSERT_EQ(var_u32.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u32.Steps(), 1);
        ASSERT_EQ(var_u32.Shape()[0], Ny);
        ASSERT_EQ(var_u32.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_u64 = io.InquireVariable<uint64_t>("u64");
        EXPECT_TRUE(var_u64);
        ASSERT_EQ(var_u64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_u64.Steps(), 1);
        ASSERT_EQ(var_u64.Shape()[0], Ny);
        ASSERT_EQ(var_u64.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_r32 = io.InquireVariable<float>("r32");
        EXPECT_TRUE(var_r32);
        ASSERT_EQ(var_r32.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_r32.Steps(), 1);
        ASSERT_EQ(var_r32.Shape()[0], Ny);
        ASSERT_EQ(var_r32.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        auto var_r64 = io.InquireVariable<double>("r64");
        EXPECT_TRUE(var_r64);
        ASSERT_EQ(var_r64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_r64.Steps(), 1);
        ASSERT_EQ(var_r64.Shape()[0], Ny);
        ASSERT_EQ(var_r64.Shape()[1], static_cast<size_t>(mpiSize * Nx));

        // If the size of the array is smaller than the data
        // the result is weird... double and uint64_t would get
        // completely garbage data
        std::array<int8_t, Nx * Ny> I8;
        std::array<int16_t, Nx * Ny> I16;
        std::array<int32_t, Nx * Ny> I32;
        std::array<int64_t, Nx * Ny> I64;
        std::array<uint8_t, Nx * Ny> U8;
        std::array<uint16_t, Nx * Ny> U16;
        std::array<uint32_t, Nx * Ny> U32;
        std::array<uint64_t, Nx * Ny> U64;
        std::array<float, Nx * Ny> R32;
        std::array<double, Nx * Ny> R64;

        const adios2::Dims start{0, static_cast<size_t>(mpiRank * Nx)};
        const adios2::Dims count{Ny, Nx};

        const adios2::Box<adios2::Dims> sel(start, count);

        var_i8.SetSelection(sel);
        var_i16.SetSelection(sel);
        var_i32.SetSelection(sel);
        var_i64.SetSelection(sel);

        var_u8.SetSelection(sel);
        var_u16.SetSelection(sel);
        var_u32.SetSelection(sel);
        var_u64.SetSelection(sel);

        var_r32.SetSelection(sel);
        var_r64.SetSelection(sel);

        for (size_t t = 0; t < 1; ++t)
        {
            var_i8.SetStepSelection({t, 1});
            var_i16.SetStepSelection({t, 1});
            var_i32.SetStepSelection({t, 1});
            var_i64.SetStepSelection({t, 1});

            var_u8.SetStepSelection({t, 1});
            var_u16.SetStepSelection({t, 1});
            var_u32.SetStepSelection({t, 1});
            var_u64.SetStepSelection({t, 1});

            var_r32.SetStepSelection({t, 1});
            var_r64.SetStepSelection({t, 1});

            bpReader.Get(var_i8, I8.data());
            bpReader.Get(var_i16, I16.data());
            bpReader.Get(var_i32, I32.data());
            bpReader.Get(var_i64, I64.data());

            bpReader.Get(var_u8, U8.data());
            bpReader.Get(var_u16, U16.data());
            bpReader.Get(var_u32, U32.data());
            bpReader.Get(var_u64, U64.data());

            bpReader.Get(var_r32, R32.data());
            bpReader.Get(var_r64, R64.data());

            bpReader.PerformGets();

            // Generate test data for each rank uniquely
            SmallTestData currentTestData =
                generateNewSmallTestData(m_TestData, static_cast<int>(t), mpiRank, mpiSize);

            for (size_t i = 0; i < Nx * Ny; ++i)
            {
                std::stringstream ss;
                ss << "t=" << t << " i=" << i << " rank=" << mpiRank;
                std::string msg = ss.str();

                EXPECT_EQ(I8[i], currentTestData.I8[i]) << msg;
                EXPECT_EQ(I16[i], currentTestData.I16[i]) << msg;
                EXPECT_EQ(I32[i], currentTestData.I32[i]) << msg;
                EXPECT_EQ(I64[i], currentTestData.I64[i]) << msg;
                EXPECT_EQ(U8[i], currentTestData.U8[i]) << msg;
                EXPECT_EQ(U16[i], currentTestData.U16[i]) << msg;
                EXPECT_EQ(U32[i], currentTestData.U32[i]) << msg;
                EXPECT_EQ(U64[i], currentTestData.U64[i]) << msg;
                EXPECT_EQ(R32[i], currentTestData.R32[i]) << msg;
                EXPECT_EQ(R64[i], currentTestData.R64[i]) << msg;
            }
        }
        bpReader.Close();
    }

#if ADIOS2_USE_MPI
    CleanupTestFilesMPI(fname, MPI_COMM_WORLD);
#else
    CleanupTestFiles(fname);
#endif
}

TEST_F(BPWriteReadTestFlatten, FlattenBPWriteRead10D2x2)
{
    // Each process would write a 2x2x...x2 9D array and all processes would
    // form a 10D NumberOfProcess x 2 x ... x 2) array

    int mpiRank = 0, mpiSize = 1;

#if ADIOS2_USE_MPI
    MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
    MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);
    const std::string fname("FlattenBPWriteRead10D2x2Test_MPI.bp");
#else
    const std::string fname("FlattenBPWriteRead10D2x2Test.bp");
#endif

    size_t NX = static_cast<unsigned int>(mpiSize);
    size_t OX = static_cast<unsigned int>(mpiRank);
    const adios2::Dims shape{NX, 2, 2, 2, 2, 2, 2, 2, 2, 2};
    const adios2::Dims start{OX, 0, 0, 0, 0, 0, 0, 0, 0, 0};
    const adios2::Dims count{1, 2, 2, 2, 2, 2, 2, 2, 2, 2};

    std::array<double, 512> R64w, R64r;
    std::array<std::complex<double>, 512> CR64w, CR64r;

    // Write test data using ADIOS2

#if ADIOS2_USE_MPI
    adios2::ADIOS adios(MPI_COMM_WORLD);
#else
    adios2::ADIOS adios;
#endif
    {
        adios2::IO io = adios.DeclareIO("TestIO");

        // Declare 10D variables
        {
            auto var_r64 = io.DefineVariable<double>("r64", shape, start, count);
            EXPECT_TRUE(var_r64);
            auto var_c64 = io.DefineVariable<std::complex<double>>("cr64", shape, start, count);
            EXPECT_TRUE(var_c64);
        }

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        else
        {
            // Create the BP Engine
            io.SetEngine("BPFile");
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }

        io.AddTransport("file");

        io.SetParameters("FlattenSteps=on");
        adios2::Engine bpWriter = io.Open(fname, adios2::Mode::Write);

        for (size_t step = 0; step < (size_t)mpiSize; ++step)
        {
            // double d = mpiRank + 1 + step / 10.0;
            double d = mpiRank + 1 / 10.0; // every step is the same
            // Generate test data for each process uniquely
            std::for_each(R64w.begin(), R64w.end(), [&](double &v) {
                v = d;
                d += 0.0001;
            });
            std::for_each(CR64w.begin(), CR64w.end(), [&](std::complex<double> &v) {
                v.real(d);
                v.imag(d);
            });

            // Retrieve the variables that previously went out of scope
            auto var_r64 = io.InquireVariable<double>("r64");
            auto var_cr64 = io.InquireVariable<std::complex<double>>("cr64");

            // Make a 2D selection to describe the local dimensions of the
            // variable we write and its offsets in the global spaces
            adios2::Box<adios2::Dims> sel({start, count});
            var_r64.SetSelection(sel);
            var_cr64.SetSelection(sel);

            // Write each one
            // fill in the variable with values from starting index to
            // starting index + count
            bpWriter.BeginStep();
            // write ranks in reverse, end down
            if (step == (size_t)(mpiSize - mpiRank - 1))
            {
                bpWriter.Put(var_r64, R64w.data());
                bpWriter.Put(var_cr64, CR64w.data());
            }
            bpWriter.EndStep();
        }

        // Close the file
        bpWriter.Close();
    }

    {
        adios2::IO io = adios.DeclareIO("ReadIO");

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }

        adios2::Engine bpReader = io.Open(fname, adios2::Mode::ReadRandomAccess);

        EXPECT_EQ(bpReader.Steps(), 1);

        auto var_r64 = io.InquireVariable<double>("r64");
        EXPECT_TRUE(var_r64);
        ASSERT_EQ(var_r64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_r64.Steps(), 1);
        ASSERT_EQ(var_r64.Shape().size(), 10);
        ASSERT_EQ(var_r64.Shape()[0], NX);
        ASSERT_EQ(var_r64.Shape()[1], 2);
        ASSERT_EQ(var_r64.Shape()[2], 2);
        ASSERT_EQ(var_r64.Shape()[3], 2);
        ASSERT_EQ(var_r64.Shape()[4], 2);
        ASSERT_EQ(var_r64.Shape()[5], 2);
        ASSERT_EQ(var_r64.Shape()[6], 2);
        ASSERT_EQ(var_r64.Shape()[7], 2);
        ASSERT_EQ(var_r64.Shape()[8], 2);
        ASSERT_EQ(var_r64.Shape()[9], 2);

        auto var_cr64 = io.InquireVariable<std::complex<double>>("cr64");
        EXPECT_TRUE(var_cr64);
        ASSERT_EQ(var_cr64.ShapeID(), adios2::ShapeID::GlobalArray);
        ASSERT_EQ(var_cr64.Steps(), 1);
        ASSERT_EQ(var_cr64.Shape().size(), 10);
        ASSERT_EQ(var_cr64.Shape()[0], NX);
        ASSERT_EQ(var_cr64.Shape()[1], 2);
        ASSERT_EQ(var_cr64.Shape()[2], 2);
        ASSERT_EQ(var_cr64.Shape()[3], 2);
        ASSERT_EQ(var_cr64.Shape()[4], 2);
        ASSERT_EQ(var_cr64.Shape()[5], 2);
        ASSERT_EQ(var_cr64.Shape()[6], 2);
        ASSERT_EQ(var_cr64.Shape()[7], 2);
        ASSERT_EQ(var_cr64.Shape()[8], 2);
        ASSERT_EQ(var_cr64.Shape()[9], 2);

        const adios2::Box<adios2::Dims> sel(start, count);

        var_r64.SetSelection(sel);
        var_cr64.SetSelection(sel);

        for (size_t step = 0; step < 1; ++step)
        {
            var_r64.SetStepSelection({step, 1});
            var_cr64.SetStepSelection({step, 1});
            bpReader.Get(var_r64, R64r.data());
            bpReader.Get(var_cr64, CR64r.data());
            bpReader.PerformGets();

            // double d = mpiRank + 1 + step / 10.0;
            double d = mpiRank + 1 / 10.0;
            // Re-generate test data for each process uniquely that was written
            std::for_each(R64w.begin(), R64w.end(), [&](double &v) {
                v = d;
                d += 0.0001;
            });
            std::for_each(CR64w.begin(), CR64w.end(), [&](std::complex<double> &v) {
                v.real(d);
                v.imag(d);
            });

            for (size_t i = 0; i < 512; ++i)
            {
                std::stringstream ss;
                ss << "t=" << step << " i=" << i << " rank=" << mpiRank;
                std::string msg = ss.str();

                EXPECT_EQ(R64r[i], R64w[i]) << msg;
                EXPECT_EQ(CR64r[i], CR64w[i]) << msg;
            }
        }
        bpReader.Close();
    }

#if ADIOS2_USE_MPI
    CleanupTestFilesMPI(fname, MPI_COMM_WORLD);
#else
    CleanupTestFiles(fname);
#endif
}

// ADIOS2 BP write and read 1D arrays
TEST_F(BPWriteReadTestFlatten, FlattenBPWriteReadEmptyProcess)
{
#if ADIOS2_USE_MPI
    // Each process, except rank 0 would write a 1x8 array and all
    // processes would form a (mpiSize-1) * Nx 1D array
    const std::string fname("FlattenBPWriteReadEmptyProces.bp");

    int mpiRank = 0, mpiSize = 1;
    // Number of rows
    const size_t Nx = 8;

    MPI_Comm_rank(MPI_COMM_WORLD, &mpiRank);
    MPI_Comm_size(MPI_COMM_WORLD, &mpiSize);

    // Number of steps
    const size_t NSteps = mpiSize;

    /* This is a parallel test, do not run in serial */
    adios2::ADIOS adios(MPI_COMM_WORLD);
    {
        adios2::IO io = adios.DeclareIO("TestIO");
        // Declare 1D variables (NumOfProcesses * Nx)
        // The local process' part (start, count) can be defined now or later
        // before Write().

        adios2::Dims shape{static_cast<size_t>(Nx * (mpiSize - 1))};
        adios2::Dims start{static_cast<size_t>(Nx * (mpiRank - 1))};
        adios2::Dims count{Nx};
        if (!mpiRank)
        {
            count[0] = 0;
            start[0] = 0;
        }

        auto var_r32 = io.DefineVariable<float>("r32", shape, start, count);
        EXPECT_TRUE(var_r32);

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        else
        {
            // Create the BP Engine
            io.SetEngine("BPFile");
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }

        io.SetParameters("FlattenSteps=on");
        adios2::Engine bpWriter = io.Open(fname, adios2::Mode::Write);

        for (size_t step = 0; step < NSteps; ++step)
        {
            // Generate test data for each process uniquely
            SmallTestData currentTestData =
                generateNewSmallTestData(m_TestData, static_cast<int>(0), mpiRank, mpiSize);

            bpWriter.BeginStep();
            if (step == (size_t)mpiRank)
            {
                if (mpiRank != 0)
                {
                    bpWriter.Put(var_r32, currentTestData.R32.data());
                }
            }
            bpWriter.EndStep();
        }

        // Close the file
        bpWriter.Close();
    }

    {
        adios2::IO io = adios.DeclareIO("ReadIO");

        if (!engineName.empty())
        {
            io.SetEngine(engineName);
        }
        if (!engineParameters.empty())
        {
            io.SetParameters(engineParameters);
        }

        adios2::Engine bpReader = io.Open(fname, adios2::Mode::ReadRandomAccess);

        for (size_t step = 0; step < 1; ++step)
        {
            // Generate test data for each process uniquely
            SmallTestData currentTestData =
                generateNewSmallTestData(m_TestData, static_cast<int>(0), mpiRank + 1, mpiSize);

            auto var_r32 = io.InquireVariable<float>("r32");
            EXPECT_TRUE(var_r32);
            ASSERT_EQ(var_r32.ShapeID(), adios2::ShapeID::GlobalArray);
            ASSERT_EQ(var_r32.Shape()[0], (mpiSize - 1) * Nx);

            SmallTestData testData;
            std::array<float, Nx> R32;

            // last process does not read
            // readers 0..N-2, while data was produced by 1..N-1
            adios2::Dims start{mpiRank * Nx};
            adios2::Dims count{Nx};

            if (mpiRank == mpiSize - 1)
            {
                count[0] = 0;
                start[0] = 0;
            }

            const adios2::Box<adios2::Dims> sel(start, count);
            var_r32.SetSelection(sel);

            if (mpiRank < mpiSize - 1)
            {
                bpReader.Get(var_r32, R32.data(), adios2::Mode::Sync);
                for (size_t i = 0; i < Nx; ++i)
                {
                    std::stringstream ss;
                    ss << "t=" << step << " i=" << i << " rank=" << mpiRank;
                    std::string msg = ss.str();
                    EXPECT_EQ(R32[i], currentTestData.R32[i]) << msg;
                }
            }
        }
        bpReader.Close();
    }

#if ADIOS2_USE_MPI
    CleanupTestFilesMPI(fname, MPI_COMM_WORLD);
#else
    CleanupTestFiles(fname);
#endif
#else
    return;
#endif
}

//******************************************************************************
// main
//******************************************************************************

int main(int argc, char **argv)
{
#if ADIOS2_USE_MPI
    int provided;

    // MPI_THREAD_MULTIPLE is only required if you enable the SST MPI_DP
    MPI_Init_thread(nullptr, nullptr, MPI_THREAD_MULTIPLE, &provided);
#endif

    int result;
    ::testing::InitGoogleTest(&argc, argv);

    if (argc > 1)
    {
        engineName = std::string(argv[1]);
    }
    if (argc > 2)
    {
        engineParameters = std::string(argv[2]);
    }
    result = RUN_ALL_TESTS();

#if ADIOS2_USE_MPI
    MPI_Finalize();
#endif

    return result;
}
