/******************************************************************************
 *
 * Project:  Virtual GDAL Datasets
 * Purpose:  Implementation of a sourced raster band that derives its raster
 *           by applying an algorithm (GDALDerivedPixelFunc) to the sources.
 * Author:   Pete Nagy
 *
 ******************************************************************************
 * Copyright (c) 2005 Vexcel Corp.
 * Copyright (c) 2008-2011, Even Rouault <even dot rouault at spatialys.com>
 *
 * SPDX-License-Identifier: MIT
 *****************************************************************************/

#include "cpl_minixml.h"
#include "cpl_string.h"
#include "vrtdataset.h"
#include "cpl_multiproc.h"
#include "gdalpython.h"

#include <algorithm>
#include <map>
#include <vector>
#include <utility>

/*! @cond Doxygen_Suppress */

using namespace GDALPy;

// #define GDAL_VRT_DISABLE_PYTHON

#ifndef GDAL_VRT_ENABLE_PYTHON_DEFAULT
// Can be YES, NO or TRUSTED_MODULES
#define GDAL_VRT_ENABLE_PYTHON_DEFAULT "TRUSTED_MODULES"
#endif

/* Flags for getting buffers */
#define PyBUF_WRITABLE 0x0001
#define PyBUF_FORMAT 0x0004
#define PyBUF_ND 0x0008
#define PyBUF_STRIDES (0x0010 | PyBUF_ND)
#define PyBUF_INDIRECT (0x0100 | PyBUF_STRIDES)
#define PyBUF_FULL (PyBUF_INDIRECT | PyBUF_WRITABLE | PyBUF_FORMAT)

/************************************************************************/
/*                        GDALCreateNumpyArray()                        */
/************************************************************************/

static PyObject *GDALCreateNumpyArray(PyObject *pCreateArray, void *pBuffer,
                                      GDALDataType eType, int nHeight,
                                      int nWidth)
{
    PyObject *poPyBuffer;
    const size_t nSize =
        static_cast<size_t>(nHeight) * nWidth * GDALGetDataTypeSizeBytes(eType);
    Py_buffer pybuffer;
    if (PyBuffer_FillInfo(&pybuffer, nullptr, static_cast<char *>(pBuffer),
                          nSize, 0, PyBUF_FULL) != 0)
    {
        return nullptr;
    }
    poPyBuffer = PyMemoryView_FromBuffer(&pybuffer);
    PyObject *pArgsCreateArray = PyTuple_New(4);
    PyTuple_SetItem(pArgsCreateArray, 0, poPyBuffer);
    const char *pszDataType = nullptr;
    switch (eType)
    {
        case GDT_Byte:
            pszDataType = "uint8";
            break;
        case GDT_Int8:
            pszDataType = "int8";
            break;
        case GDT_UInt16:
            pszDataType = "uint16";
            break;
        case GDT_Int16:
            pszDataType = "int16";
            break;
        case GDT_UInt32:
            pszDataType = "uint32";
            break;
        case GDT_Int32:
            pszDataType = "int32";
            break;
        case GDT_Int64:
            pszDataType = "int64";
            break;
        case GDT_UInt64:
            pszDataType = "uint64";
            break;
        case GDT_Float16:
            pszDataType = "float16";
            break;
        case GDT_Float32:
            pszDataType = "float32";
            break;
        case GDT_Float64:
            pszDataType = "float64";
            break;
        case GDT_CInt16:
        case GDT_CInt32:
            CPLAssert(FALSE);
            break;
        case GDT_CFloat16:
            CPLAssert(FALSE);
            break;
        case GDT_CFloat32:
            pszDataType = "complex64";
            break;
        case GDT_CFloat64:
            pszDataType = "complex128";
            break;
        case GDT_Unknown:
        case GDT_TypeCount:
            CPLAssert(FALSE);
            break;
    }
    PyTuple_SetItem(
        pArgsCreateArray, 1,
        PyBytes_FromStringAndSize(pszDataType, strlen(pszDataType)));
    PyTuple_SetItem(pArgsCreateArray, 2, PyLong_FromLong(nHeight));
    PyTuple_SetItem(pArgsCreateArray, 3, PyLong_FromLong(nWidth));
    PyObject *poNumpyArray =
        PyObject_Call(pCreateArray, pArgsCreateArray, nullptr);
    Py_DecRef(pArgsCreateArray);
    if (PyErr_Occurred())
        PyErr_Print();
    return poNumpyArray;
}

/************************************************************************/
/* ==================================================================== */
/*                     VRTDerivedRasterBandPrivateData                  */
/* ==================================================================== */
/************************************************************************/

class VRTDerivedRasterBandPrivateData
{
    VRTDerivedRasterBandPrivateData(const VRTDerivedRasterBandPrivateData &) =
        delete;
    VRTDerivedRasterBandPrivateData &
    operator=(const VRTDerivedRasterBandPrivateData &) = delete;

  public:
    CPLString m_osCode{};
    CPLString m_osLanguage = "C";
    int m_nBufferRadius = 0;
    PyObject *m_poGDALCreateNumpyArray = nullptr;
    PyObject *m_poUserFunction = nullptr;
    bool m_bPythonInitializationDone = false;
    bool m_bPythonInitializationSuccess = false;
    bool m_bExclusiveLock = false;
    bool m_bFirstTime = true;
    std::vector<std::pair<CPLString, CPLString>> m_oFunctionArgs{};
    bool m_bSkipNonContributingSourcesSpecified = false;
    bool m_bSkipNonContributingSources = false;

    VRTDerivedRasterBandPrivateData() = default;

    virtual ~VRTDerivedRasterBandPrivateData()
    {
        if (m_poGDALCreateNumpyArray)
            Py_DecRef(m_poGDALCreateNumpyArray);
        if (m_poUserFunction)
            Py_DecRef(m_poUserFunction);
    }
};

/************************************************************************/
/* ==================================================================== */
/*                          VRTDerivedRasterBand                        */
/* ==================================================================== */
/************************************************************************/

/************************************************************************/
/*                        VRTDerivedRasterBand()                        */
/************************************************************************/

VRTDerivedRasterBand::VRTDerivedRasterBand(GDALDataset *poDSIn, int nBandIn)
    : VRTSourcedRasterBand(poDSIn, nBandIn), m_poPrivate(nullptr),
      pszFuncName(nullptr), eSourceTransferType(GDT_Unknown)
{
    m_poPrivate = new VRTDerivedRasterBandPrivateData;
}

/************************************************************************/
/*                        VRTDerivedRasterBand()                        */
/************************************************************************/

VRTDerivedRasterBand::VRTDerivedRasterBand(GDALDataset *poDSIn, int nBandIn,
                                           GDALDataType eType, int nXSize,
                                           int nYSize)
    : VRTSourcedRasterBand(poDSIn, nBandIn, eType, nXSize, nYSize),
      m_poPrivate(nullptr), pszFuncName(nullptr),
      eSourceTransferType(GDT_Unknown)
{
    m_poPrivate = new VRTDerivedRasterBandPrivateData;
}

/************************************************************************/
/*                       ~VRTDerivedRasterBand()                        */
/************************************************************************/

VRTDerivedRasterBand::~VRTDerivedRasterBand()

{
    CPLFree(pszFuncName);
    delete m_poPrivate;
}

/************************************************************************/
/*                               Cleanup()                              */
/************************************************************************/

void VRTDerivedRasterBand::Cleanup()
{
}

/************************************************************************/
/*                      GetGlobalMapPixelFunction()                     */
/************************************************************************/

static std::map<std::string,
                std::pair<VRTDerivedRasterBand::PixelFunc, std::string>> &
GetGlobalMapPixelFunction()
{
    static std::map<std::string,
                    std::pair<VRTDerivedRasterBand::PixelFunc, std::string>>
        gosMapPixelFunction;
    return gosMapPixelFunction;
}

/************************************************************************/
/*                           AddPixelFunction()                         */
/************************************************************************/

/*! @endcond */

/**
 * This adds a pixel function to the global list of available pixel
 * functions for derived bands.  Pixel functions must be registered
 * in this way before a derived band tries to access data.
 *
 * Derived bands are stored with only the name of the pixel function
 * that it will apply, and if a pixel function matching the name is not
 * found the IRasterIO() call will do nothing.
 *
 * @param pszName Name used to access pixel function
 * @param pfnNewFunction Pixel function associated with name.  An
 *  existing pixel function registered with the same name will be
 *  replaced with the new one.
 *
 * @return CE_None, invalid (NULL) parameters are currently ignored.
 */
CPLErr CPL_STDCALL GDALAddDerivedBandPixelFunc(
    const char *pszName, GDALDerivedPixelFunc pfnNewFunction)
{
    if (pszName == nullptr || pszName[0] == '\0' || pfnNewFunction == nullptr)
    {
        return CE_None;
    }

    GetGlobalMapPixelFunction()[pszName] = {
        [pfnNewFunction](void **papoSources, int nSources, void *pData,
                         int nBufXSize, int nBufYSize, GDALDataType eSrcType,
                         GDALDataType eBufType, int nPixelSpace, int nLineSpace,
                         CSLConstList papszFunctionArgs)
        {
            (void)papszFunctionArgs;
            return pfnNewFunction(papoSources, nSources, pData, nBufXSize,
                                  nBufYSize, eSrcType, eBufType, nPixelSpace,
                                  nLineSpace);
        },
        ""};

    return CE_None;
}

/**
 * This adds a pixel function to the global list of available pixel
 * functions for derived bands.  Pixel functions must be registered
 * in this way before a derived band tries to access data.
 *
 * Derived bands are stored with only the name of the pixel function
 * that it will apply, and if a pixel function matching the name is not
 * found the IRasterIO() call will do nothing.
 *
 * @param pszName Name used to access pixel function
 * @param pfnNewFunction Pixel function associated with name.  An
 *  existing pixel function registered with the same name will be
 *  replaced with the new one.
 * @param pszMetadata Pixel function metadata (not currently implemented)
 *
 * @return CE_None, invalid (NULL) parameters are currently ignored.
 * @since GDAL 3.4
 */
CPLErr CPL_STDCALL GDALAddDerivedBandPixelFuncWithArgs(
    const char *pszName, GDALDerivedPixelFuncWithArgs pfnNewFunction,
    const char *pszMetadata)
{
    if (!pszName || pszName[0] == '\0' || !pfnNewFunction)
    {
        return CE_None;
    }

    GetGlobalMapPixelFunction()[pszName] = {pfnNewFunction,
                                            pszMetadata ? pszMetadata : ""};

    return CE_None;
}

/*! @cond Doxygen_Suppress */

/**
 * This adds a pixel function to the global list of available pixel
 * functions for derived bands.
 *
 * This is the same as the C function GDALAddDerivedBandPixelFunc()
 *
 * @param pszFuncNameIn Name used to access pixel function
 * @param pfnNewFunction Pixel function associated with name.  An
 *  existing pixel function registered with the same name will be
 *  replaced with the new one.
 *
 * @return CE_None, invalid (NULL) parameters are currently ignored.
 */
CPLErr
VRTDerivedRasterBand::AddPixelFunction(const char *pszFuncNameIn,
                                       GDALDerivedPixelFunc pfnNewFunction)
{
    return GDALAddDerivedBandPixelFunc(pszFuncNameIn, pfnNewFunction);
}

CPLErr VRTDerivedRasterBand::AddPixelFunction(
    const char *pszFuncNameIn, GDALDerivedPixelFuncWithArgs pfnNewFunction,
    const char *pszMetadata)
{
    return GDALAddDerivedBandPixelFuncWithArgs(pszFuncNameIn, pfnNewFunction,
                                               pszMetadata);
}

/************************************************************************/
/*                           GetPixelFunction()                         */
/************************************************************************/

/**
 * Get a pixel function previously registered using the global
 * AddPixelFunction.
 *
 * @param pszFuncNameIn The name associated with the pixel function.
 *
 * @return A derived band pixel function, or NULL if none have been
 * registered for pszFuncName.
 */
const std::pair<VRTDerivedRasterBand::PixelFunc, std::string> *
VRTDerivedRasterBand::GetPixelFunction(const char *pszFuncNameIn)
{
    if (pszFuncNameIn == nullptr || pszFuncNameIn[0] == '\0')
    {
        return nullptr;
    }

    const auto &oMapPixelFunction = GetGlobalMapPixelFunction();
    const auto oIter = oMapPixelFunction.find(pszFuncNameIn);

    if (oIter == oMapPixelFunction.end())
        return nullptr;

    return &(oIter->second);
}

/************************************************************************/
/*                         SetPixelFunctionName()                       */
/************************************************************************/

/**
 * Set the pixel function name to be applied to this derived band.  The
 * name should match a pixel function registered using AddPixelFunction.
 *
 * @param pszFuncNameIn Name of pixel function to be applied to this derived
 * band.
 */
void VRTDerivedRasterBand::SetPixelFunctionName(const char *pszFuncNameIn)
{
    CPLFree(pszFuncName);
    pszFuncName = CPLStrdup(pszFuncNameIn);
}

/************************************************************************/
/*                         SetPixelFunctionLanguage()                   */
/************************************************************************/

/**
 * Set the language of the pixel function.
 *
 * @param pszLanguage Language of the pixel function (only "C" and "Python"
 * are supported currently)
 * @since GDAL 2.3
 */
void VRTDerivedRasterBand::SetPixelFunctionLanguage(const char *pszLanguage)
{
    m_poPrivate->m_osLanguage = pszLanguage;
}

/************************************************************************/
/*                         SetSourceTransferType()                      */
/************************************************************************/

/**
 * Set the transfer type to be used to obtain pixel information from
 * all of the sources.  If unset, the transfer type used will be the
 * same as the derived band data type.  This makes it possible, for
 * example, to pass CFloat32 source pixels to the pixel function, even
 * if the pixel function generates a raster for a derived band that
 * is of type Byte.
 *
 * @param eDataTypeIn Data type to use to obtain pixel information from
 * the sources to be passed to the derived band pixel function.
 */
void VRTDerivedRasterBand::SetSourceTransferType(GDALDataType eDataTypeIn)
{
    eSourceTransferType = eDataTypeIn;
}

/************************************************************************/
/*                           InitializePython()                         */
/************************************************************************/

bool VRTDerivedRasterBand::InitializePython()
{
    if (m_poPrivate->m_bPythonInitializationDone)
        return m_poPrivate->m_bPythonInitializationSuccess;

    m_poPrivate->m_bPythonInitializationDone = true;
    m_poPrivate->m_bPythonInitializationSuccess = false;

    const CPLString osPythonFullname(pszFuncName ? pszFuncName : "");
    const size_t nIdxDot = osPythonFullname.rfind(".");
    CPLString osPythonModule;
    CPLString osPythonFunction;
    if (nIdxDot != std::string::npos)
    {
        osPythonModule = osPythonFullname.substr(0, nIdxDot);
        osPythonFunction = osPythonFullname.substr(nIdxDot + 1);
    }
    else
    {
        osPythonFunction = osPythonFullname;
    }

#ifndef GDAL_VRT_DISABLE_PYTHON
    const char *pszPythonEnabled =
        CPLGetConfigOption("GDAL_VRT_ENABLE_PYTHON", nullptr);
#else
    const char *pszPythonEnabled = "NO";
#endif
    const CPLString osPythonEnabled(
        pszPythonEnabled ? pszPythonEnabled : GDAL_VRT_ENABLE_PYTHON_DEFAULT);

    if (EQUAL(osPythonEnabled, "TRUSTED_MODULES"))
    {
        bool bIsTrustedModule = false;
        const CPLString osVRTTrustedModules(
            CPLGetConfigOption("GDAL_VRT_PYTHON_TRUSTED_MODULES", ""));
        if (!osPythonModule.empty())
        {
            char **papszTrustedModules =
                CSLTokenizeString2(osVRTTrustedModules, ",", 0);
            for (char **papszIter = papszTrustedModules;
                 !bIsTrustedModule && papszIter && *papszIter; ++papszIter)
            {
                const char *pszIterModule = *papszIter;
                size_t nIterModuleLen = strlen(pszIterModule);
                if (nIterModuleLen > 2 &&
                    strncmp(pszIterModule + nIterModuleLen - 2, ".*", 2) == 0)
                {
                    bIsTrustedModule =
                        (strncmp(osPythonModule, pszIterModule,
                                 nIterModuleLen - 2) == 0) &&
                        (osPythonModule.size() == nIterModuleLen - 2 ||
                         (osPythonModule.size() >= nIterModuleLen &&
                          osPythonModule[nIterModuleLen - 1] == '.'));
                }
                else if (nIterModuleLen >= 1 &&
                         pszIterModule[nIterModuleLen - 1] == '*')
                {
                    bIsTrustedModule = (strncmp(osPythonModule, pszIterModule,
                                                nIterModuleLen - 1) == 0);
                }
                else
                {
                    bIsTrustedModule =
                        (strcmp(osPythonModule, pszIterModule) == 0);
                }
            }
            CSLDestroy(papszTrustedModules);
        }

        if (!bIsTrustedModule)
        {
            if (osPythonModule.empty())
            {
                CPLError(
                    CE_Failure, CPLE_AppDefined,
                    "Python code needs to be executed, but it uses inline code "
                    "in the VRT whereas the current policy is to trust only "
                    "code from external trusted modules (defined in the "
                    "GDAL_VRT_PYTHON_TRUSTED_MODULES configuration option). "
                    "If you trust the code in %s, you can set the "
                    "GDAL_VRT_ENABLE_PYTHON configuration option to YES.",
                    GetDataset() ? GetDataset()->GetDescription()
                                 : "(unknown VRT)");
            }
            else if (osVRTTrustedModules.empty())
            {
                CPLError(
                    CE_Failure, CPLE_AppDefined,
                    "Python code needs to be executed, but it uses code "
                    "from module '%s', whereas the current policy is to "
                    "trust only code from modules defined in the "
                    "GDAL_VRT_PYTHON_TRUSTED_MODULES configuration option, "
                    "which is currently unset. "
                    "If you trust the code in '%s', you can add module '%s' "
                    "to GDAL_VRT_PYTHON_TRUSTED_MODULES (or set the "
                    "GDAL_VRT_ENABLE_PYTHON configuration option to YES).",
                    osPythonModule.c_str(),
                    GetDataset() ? GetDataset()->GetDescription()
                                 : "(unknown VRT)",
                    osPythonModule.c_str());
            }
            else
            {
                CPLError(
                    CE_Failure, CPLE_AppDefined,
                    "Python code needs to be executed, but it uses code "
                    "from module '%s', whereas the current policy is to "
                    "trust only code from modules '%s' (defined in the "
                    "GDAL_VRT_PYTHON_TRUSTED_MODULES configuration option). "
                    "If you trust the code in '%s', you can add module '%s' "
                    "to GDAL_VRT_PYTHON_TRUSTED_MODULES (or set the "
                    "GDAL_VRT_ENABLE_PYTHON configuration option to YES).",
                    osPythonModule.c_str(), osVRTTrustedModules.c_str(),
                    GetDataset() ? GetDataset()->GetDescription()
                                 : "(unknown VRT)",
                    osPythonModule.c_str());
            }
            return false;
        }
    }

#ifdef disabled_because_this_is_probably_broken_by_design
    // See https://lwn.net/Articles/574215/
    // and http://nedbatchelder.com/blog/201206/eval_really_is_dangerous.html
    else if (EQUAL(osPythonEnabled, "IF_SAFE"))
    {
        bool bSafe = true;
        // If the function comes from another module, then we don't know
        if (!osPythonModule.empty())
        {
            CPLDebug("VRT", "Python function is from another module");
            bSafe = false;
        }

        CPLString osCode(m_poPrivate->m_osCode);

        // Reject all imports except a few trusted modules
        const char *const apszTrustedImports[] = {
            "import math",
            "from math import",
            "import numpy",  // caution: numpy has lots of I/O functions !
            "from numpy import",
            // TODO: not sure if importing arbitrary stuff from numba is OK
            // so let's just restrict to jit.
            "from numba import jit",

            // Not imports but still whitelisted, whereas other __ is banned
            "__init__",
            "__call__",
        };
        for (size_t i = 0; i < CPL_ARRAYSIZE(apszTrustedImports); ++i)
        {
            osCode.replaceAll(CPLString(apszTrustedImports[i]), "");
        }

        // Some dangerous built-in functions or numpy functions
        const char *const apszUntrusted[] = {
            "import",  // and __import__
            "eval",       "compile", "open",
            "load",        // reload, numpy.load
            "file",        // and exec_file, numpy.fromfile, numpy.tofile
            "input",       // and raw_input
            "save",        // numpy.save
            "memmap",      // numpy.memmap
            "DataSource",  // numpy.DataSource
            "genfromtxt",  // numpy.genfromtxt
            "getattr",
            "ctypeslib",  // numpy.ctypeslib
            "testing",    // numpy.testing
            "dump",       // numpy.ndarray.dump
            "fromregex",  // numpy.fromregex
            "__"};
        for (size_t i = 0; i < CPL_ARRAYSIZE(apszUntrusted); ++i)
        {
            if (osCode.find(apszUntrusted[i]) != std::string::npos)
            {
                CPLDebug("VRT", "Found '%s' word in Python code",
                         apszUntrusted[i]);
                bSafe = false;
            }
        }

        if (!bSafe)
        {
            CPLError(CE_Failure, CPLE_AppDefined,
                     "Python code needs to be executed, but we cannot verify "
                     "if it is safe, so this is disabled by default. "
                     "If you trust the code in %s, you can set the "
                     "GDAL_VRT_ENABLE_PYTHON configuration option to YES.",
                     GetDataset() ? GetDataset()->GetDescription()
                                  : "(unknown VRT)");
            return false;
        }
    }
#endif  // disabled_because_this_is_probably_broken_by_design

    else if (!EQUAL(osPythonEnabled, "YES") && !EQUAL(osPythonEnabled, "ON") &&
             !EQUAL(osPythonEnabled, "TRUE"))
    {
        if (pszPythonEnabled == nullptr)
        {
            // Note: this is dead code with our current default policy
            // GDAL_VRT_ENABLE_PYTHON == "TRUSTED_MODULES"
            CPLError(CE_Failure, CPLE_AppDefined,
                     "Python code needs to be executed, but this is "
                     "disabled by default. If you trust the code in %s, "
                     "you can set the GDAL_VRT_ENABLE_PYTHON configuration "
                     "option to YES.",
                     GetDataset() ? GetDataset()->GetDescription()
                                  : "(unknown VRT)");
        }
        else
        {
            CPLError(
                CE_Failure, CPLE_AppDefined,
                "Python code in %s needs to be executed, but this has been "
                "explicitly disabled.",
                GetDataset() ? GetDataset()->GetDescription()
                             : "(unknown VRT)");
        }
        return false;
    }

    if (!GDALPythonInitialize())
        return false;

    // Whether we should just use our own global mutex, in addition to Python
    // GIL locking.
    m_poPrivate->m_bExclusiveLock =
        CPLTestBool(CPLGetConfigOption("GDAL_VRT_PYTHON_EXCLUSIVE_LOCK", "NO"));

    // numba jit'ification doesn't seem to be thread-safe, so force use of
    // lock now and at first execution of function. Later executions seem to
    // be thread-safe. This problem doesn't seem to appear for code in
    // regular files
    const bool bUseExclusiveLock =
        m_poPrivate->m_bExclusiveLock ||
        m_poPrivate->m_osCode.find("@jit") != std::string::npos;
    GIL_Holder oHolder(bUseExclusiveLock);

    // As we don't want to depend on numpy C API/ABI, we use a trick to build
    // a numpy array object. We define a Python function to which we pass a
    // Python buffer object.

    // We need to build a unique module name, otherwise this will crash in
    // multithreaded use cases.
    CPLString osModuleName(CPLSPrintf("gdal_vrt_module_%p", this));
    PyObject *poCompiledString = Py_CompileString(
        ("import numpy\n"
         "def GDALCreateNumpyArray(buffer, dtype, height, width):\n"
         "    return numpy.frombuffer(buffer, str(dtype.decode('ascii')))."
         "reshape([height, width])\n"
         "\n" +
         m_poPrivate->m_osCode)
            .c_str(),
        osModuleName, Py_file_input);
    if (poCompiledString == nullptr || PyErr_Occurred())
    {
        CPLError(CE_Failure, CPLE_AppDefined, "Couldn't compile code:\n%s",
                 GetPyExceptionString().c_str());
        return false;
    }
    PyObject *poModule =
        PyImport_ExecCodeModule(osModuleName, poCompiledString);
    Py_DecRef(poCompiledString);

    if (poModule == nullptr || PyErr_Occurred())
    {
        CPLError(CE_Failure, CPLE_AppDefined, "%s",
                 GetPyExceptionString().c_str());
        return false;
    }

    // Fetch user computation function
    if (!osPythonModule.empty())
    {
        PyObject *poUserModule = PyImport_ImportModule(osPythonModule);
        if (poUserModule == nullptr || PyErr_Occurred())
        {
            CPLString osException = GetPyExceptionString();
            if (!osException.empty() && osException.back() == '\n')
            {
                osException.pop_back();
            }
            if (osException.find("ModuleNotFoundError") == 0)
            {
                osException += ". You may need to define PYTHONPATH";
            }
            CPLError(CE_Failure, CPLE_AppDefined, "%s", osException.c_str());
            Py_DecRef(poModule);
            return false;
        }
        m_poPrivate->m_poUserFunction =
            PyObject_GetAttrString(poUserModule, osPythonFunction);
        Py_DecRef(poUserModule);
    }
    else
    {
        m_poPrivate->m_poUserFunction =
            PyObject_GetAttrString(poModule, osPythonFunction);
    }
    if (m_poPrivate->m_poUserFunction == nullptr || PyErr_Occurred())
    {
        CPLError(CE_Failure, CPLE_AppDefined, "%s",
                 GetPyExceptionString().c_str());
        Py_DecRef(poModule);
        return false;
    }
    if (!PyCallable_Check(m_poPrivate->m_poUserFunction))
    {
        CPLError(CE_Failure, CPLE_AppDefined, "Object '%s' is not callable",
                 osPythonFunction.c_str());
        Py_DecRef(poModule);
        return false;
    }

    // Fetch our GDALCreateNumpyArray python function
    m_poPrivate->m_poGDALCreateNumpyArray =
        PyObject_GetAttrString(poModule, "GDALCreateNumpyArray");
    if (m_poPrivate->m_poGDALCreateNumpyArray == nullptr || PyErr_Occurred())
    {
        // Shouldn't happen normally...
        CPLError(CE_Failure, CPLE_AppDefined, "%s",
                 GetPyExceptionString().c_str());
        Py_DecRef(poModule);
        return false;
    }
    Py_DecRef(poModule);

    m_poPrivate->m_bPythonInitializationSuccess = true;
    return true;
}

CPLErr VRTDerivedRasterBand::GetPixelFunctionArguments(
    const CPLString &osMetadata,
    std::vector<std::pair<CPLString, CPLString>> &oAdditionalArgs)
{

    auto poArgs = CPLXMLTreeCloser(CPLParseXMLString(osMetadata));
    if (poArgs != nullptr && poArgs->eType == CXT_Element &&
        !strcmp(poArgs->pszValue, "PixelFunctionArgumentsList"))
    {
        for (CPLXMLNode *psIter = poArgs->psChild; psIter != nullptr;
             psIter = psIter->psNext)
        {
            if (psIter->eType == CXT_Element &&
                !strcmp(psIter->pszValue, "Argument"))
            {
                CPLString osName, osType, osValue;
                auto pszName = CPLGetXMLValue(psIter, "name", nullptr);
                if (pszName != nullptr)
                    osName = pszName;
                auto pszType = CPLGetXMLValue(psIter, "type", nullptr);
                if (pszType != nullptr)
                    osType = pszType;
                auto pszValue = CPLGetXMLValue(psIter, "value", nullptr);
                if (pszValue != nullptr)
                    osValue = pszValue;
                if (osType == "constant" && osValue != "" && osName != "")
                    oAdditionalArgs.push_back(
                        std::pair<CPLString, CPLString>(osName, osValue));
                if (osType == "builtin")
                {
                    double dfVal;
                    int success;
                    if (osValue == "NoData")
                        dfVal = this->GetNoDataValue(&success);
                    else if (osValue == "scale")
                        dfVal = this->GetScale(&success);
                    else if (osValue == "offset")
                        dfVal = this->GetOffset(&success);
                    else
                    {
                        CPLError(CE_Failure, CPLE_NotSupported,
                                 "PixelFunction builtin %s not supported",
                                 osValue.c_str());
                        return CE_Failure;
                    }
                    if (!success)
                    {
                        if (CPLTestBool(
                                CPLGetXMLValue(psIter, "optional", "false")))
                            continue;

                        CPLError(CE_Failure, CPLE_AppDefined,
                                 "Raster has no %s", osValue.c_str());
                        return CE_Failure;
                    }

                    oAdditionalArgs.push_back(std::pair<CPLString, CPLString>(
                        osValue, CPLSPrintf("%.17g", dfVal)));
                    CPLDebug("VRT",
                             "Added builtin pixel function argument %s = %s",
                             osValue.c_str(), CPLSPrintf("%.17g", dfVal));
                }
            }
        }
    }

    return CE_None;
}

/************************************************************************/
/*                             IRasterIO()                              */
/************************************************************************/

/**
 * Read/write a region of image data for this band.
 *
 * Each of the sources for this derived band will be read and passed to
 * the derived band pixel function.  The pixel function is responsible
 * for applying whatever algorithm is necessary to generate this band's
 * pixels from the sources.
 *
 * The sources will be read using the transfer type specified for sources
 * using SetSourceTransferType().  If no transfer type has been set for
 * this derived band, the band's data type will be used as the transfer type.
 *
 * @see gdalrasterband
 *
 * @param eRWFlag Either GF_Read to read a region of data, or GT_Write to
 * write a region of data.
 *
 * @param nXOff The pixel offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the left side.
 *
 * @param nYOff The line offset to the top left corner of the region
 * of the band to be accessed.  This would be zero to start from the top.
 *
 * @param nXSize The width of the region of the band to be accessed in pixels.
 *
 * @param nYSize The height of the region of the band to be accessed in lines.
 *
 * @param pData The buffer into which the data should be read, or from which
 * it should be written.  This buffer must contain at least nBufXSize *
 * nBufYSize words of type eBufType.  It is organized in left to right,
 * top to bottom pixel order.  Spacing is controlled by the nPixelSpace,
 * and nLineSpace parameters.
 *
 * @param nBufXSize The width of the buffer image into which the desired
 * region is to be read, or from which it is to be written.
 *
 * @param nBufYSize The height of the buffer image into which the desired
 * region is to be read, or from which it is to be written.
 *
 * @param eBufType The type of the pixel values in the pData data buffer.  The
 * pixel values will automatically be translated to/from the GDALRasterBand
 * data type as needed.
 *
 * @param nPixelSpace The byte offset from the start of one pixel value in
 * pData to the start of the next pixel value within a scanline.  If defaulted
 * (0) the size of the datatype eBufType is used.
 *
 * @param nLineSpace The byte offset from the start of one scanline in
 * pData to the start of the next.  If defaulted the size of the datatype
 * eBufType * nBufXSize is used.
 *
 * @return CE_Failure if the access fails, otherwise CE_None.
 */
CPLErr VRTDerivedRasterBand::IRasterIO(
    GDALRWFlag eRWFlag, int nXOff, int nYOff, int nXSize, int nYSize,
    void *pData, int nBufXSize, int nBufYSize, GDALDataType eBufType,
    GSpacing nPixelSpace, GSpacing nLineSpace, GDALRasterIOExtraArg *psExtraArg)
{
    if (eRWFlag == GF_Write)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "Writing through VRTSourcedRasterBand is not supported.");
        return CE_Failure;
    }

    const int nBufTypeSize = GDALGetDataTypeSizeBytes(eBufType);
    GDALDataType eSrcType = eSourceTransferType;
    if (eSrcType == GDT_Unknown || eSrcType >= GDT_TypeCount)
    {
        eSrcType = eBufType;
    }
    const int nSrcTypeSize = GDALGetDataTypeSizeBytes(eSrcType);

    /* -------------------------------------------------------------------- */
    /*      Initialize the buffer to some background value. Use the         */
    /*      nodata value if available.                                      */
    /* -------------------------------------------------------------------- */
    if (SkipBufferInitialization())
    {
        // Do nothing
    }
    else if (nPixelSpace == nBufTypeSize &&
             (!m_bNoDataValueSet || m_dfNoDataValue == 0))
    {
        memset(pData, 0,
               static_cast<size_t>(nBufXSize) * nBufYSize * nBufTypeSize);
    }
    else if (m_bNoDataValueSet)
    {
        double dfWriteValue = m_dfNoDataValue;

        for (int iLine = 0; iLine < nBufYSize; iLine++)
        {
            GDALCopyWords(&dfWriteValue, GDT_Float64, 0,
                          static_cast<GByte *>(pData) + nLineSpace * iLine,
                          eBufType, static_cast<int>(nPixelSpace), nBufXSize);
        }
    }

    /* -------------------------------------------------------------------- */
    /*      Do we have overviews that would be appropriate to satisfy       */
    /*      this request?                                                   */
    /* -------------------------------------------------------------------- */
    if ((nBufXSize < nXSize || nBufYSize < nYSize) && GetOverviewCount() > 0)
    {
        if (OverviewRasterIO(eRWFlag, nXOff, nYOff, nXSize, nYSize, pData,
                             nBufXSize, nBufYSize, eBufType, nPixelSpace,
                             nLineSpace, psExtraArg) == CE_None)
            return CE_None;
    }

    /* ---- Get pixel function for band ---- */
    const std::pair<PixelFunc, std::string> *poPixelFunc = nullptr;
    std::vector<std::pair<CPLString, CPLString>> oAdditionalArgs;

    if (EQUAL(m_poPrivate->m_osLanguage, "C"))
    {
        poPixelFunc = VRTDerivedRasterBand::GetPixelFunction(pszFuncName);
        if (poPixelFunc == nullptr)
        {
            CPLError(CE_Failure, CPLE_IllegalArg,
                     "VRTDerivedRasterBand::IRasterIO:"
                     "Derived band pixel function '%s' not registered.",
                     this->pszFuncName);
            return CE_Failure;
        }

        if (poPixelFunc->second != "")
        {
            if (GetPixelFunctionArguments(poPixelFunc->second,
                                          oAdditionalArgs) != CE_None)
            {
                return CE_Failure;
            }
        }
    }

    /* TODO: It would be nice to use a MallocBlock function for each
       individual buffer that would recycle blocks of memory from a
       cache by reassigning blocks that are nearly the same size.
       A corresponding FreeBlock might only truly free if the total size
       of freed blocks gets to be too great of a percentage of the size
       of the allocated blocks. */

    // Get buffers for each source.
    const int nBufferRadius = m_poPrivate->m_nBufferRadius;
    if (nBufferRadius > (INT_MAX - nBufXSize) / 2 ||
        nBufferRadius > (INT_MAX - nBufYSize) / 2)
    {
        return CE_Failure;
    }
    const int nExtBufXSize = nBufXSize + 2 * nBufferRadius;
    const int nExtBufYSize = nBufYSize + 2 * nBufferRadius;
    int nBufferCount = 0;
    void **pBuffers =
        static_cast<void **>(CPLMalloc(sizeof(void *) * nSources));
    std::vector<int> anMapBufferIdxToSourceIdx(nSources);
    for (int iSource = 0; iSource < nSources; iSource++)
    {
        if (m_poPrivate->m_bSkipNonContributingSources &&
            papoSources[iSource]->IsSimpleSource())
        {
            bool bError = false;
            double dfReqXOff, dfReqYOff, dfReqXSize, dfReqYSize;
            int nReqXOff, nReqYOff, nReqXSize, nReqYSize;
            int nOutXOff, nOutYOff, nOutXSize, nOutYSize;
            auto poSource =
                static_cast<VRTSimpleSource *>(papoSources[iSource]);
            if (!poSource->GetSrcDstWindow(
                    nXOff, nYOff, nXSize, nYSize, nBufXSize, nBufYSize,
                    &dfReqXOff, &dfReqYOff, &dfReqXSize, &dfReqYSize, &nReqXOff,
                    &nReqYOff, &nReqXSize, &nReqYSize, &nOutXOff, &nOutYOff,
                    &nOutXSize, &nOutYSize, bError))
            {
                if (bError)
                {
                    for (int i = 0; i < nBufferCount; i++)
                    {
                        VSIFree(pBuffers[i]);
                    }
                    CPLFree(pBuffers);
                    return CE_Failure;
                }

                // Skip non contributing source
                continue;
            }
        }

        anMapBufferIdxToSourceIdx[nBufferCount] = iSource;
        pBuffers[nBufferCount] =
            VSI_MALLOC3_VERBOSE(nSrcTypeSize, nExtBufXSize, nExtBufYSize);
        if (pBuffers[nBufferCount] == nullptr)
        {
            for (int i = 0; i < nBufferCount; i++)
            {
                VSIFree(pBuffers[i]);
            }
            CPLFree(pBuffers);
            return CE_Failure;
        }

        /* ------------------------------------------------------------ */
        /* #4045: Initialize the newly allocated buffers before handing */
        /* them off to the sources. These buffers are packed, so we     */
        /* don't need any special line-by-line handling when a nonzero  */
        /* nodata value is set.                                         */
        /* ------------------------------------------------------------ */
        if (!m_bNoDataValueSet || m_dfNoDataValue == 0)
        {
            memset(pBuffers[nBufferCount], 0,
                   static_cast<size_t>(nSrcTypeSize) * nExtBufXSize *
                       nExtBufYSize);
        }
        else
        {
            GDALCopyWords(&m_dfNoDataValue, GDT_Float64, 0,
                          static_cast<GByte *>(pBuffers[nBufferCount]),
                          eSrcType, nSrcTypeSize, nExtBufXSize * nExtBufYSize);
        }

        ++nBufferCount;
    }

    // No contributing sources and SkipNonContributingSources mode ?
    // Do not call the pixel function and just return the 0/nodata initialized
    // output buffer.
    if (nBufferCount == 0 && m_poPrivate->m_bSkipNonContributingSources)
    {
        CPLFree(pBuffers);
        return CE_None;
    }

    GDALRasterIOExtraArg sExtraArg;
    GDALCopyRasterIOExtraArg(&sExtraArg, psExtraArg);

    int nXShiftInBuffer = 0;
    int nYShiftInBuffer = 0;
    int nExtBufXSizeReq = nExtBufXSize;
    int nExtBufYSizeReq = nExtBufYSize;

    int nXOffExt = nXOff;
    int nYOffExt = nYOff;
    int nXSizeExt = nXSize;
    int nYSizeExt = nYSize;

    if (nBufferRadius)
    {
        double dfXRatio = static_cast<double>(nXSize) / nBufXSize;
        double dfYRatio = static_cast<double>(nYSize) / nBufYSize;

        if (!sExtraArg.bFloatingPointWindowValidity)
        {
            sExtraArg.dfXOff = nXOff;
            sExtraArg.dfYOff = nYOff;
            sExtraArg.dfXSize = nXSize;
            sExtraArg.dfYSize = nYSize;
        }

        sExtraArg.dfXOff -= dfXRatio * nBufferRadius;
        sExtraArg.dfYOff -= dfYRatio * nBufferRadius;
        sExtraArg.dfXSize += 2 * dfXRatio * nBufferRadius;
        sExtraArg.dfYSize += 2 * dfYRatio * nBufferRadius;
        if (sExtraArg.dfXOff < 0)
        {
            nXShiftInBuffer = -static_cast<int>(sExtraArg.dfXOff / dfXRatio);
            nExtBufXSizeReq -= nXShiftInBuffer;
            sExtraArg.dfXSize += sExtraArg.dfXOff;
            sExtraArg.dfXOff = 0;
        }
        if (sExtraArg.dfYOff < 0)
        {
            nYShiftInBuffer = -static_cast<int>(sExtraArg.dfYOff / dfYRatio);
            nExtBufYSizeReq -= nYShiftInBuffer;
            sExtraArg.dfYSize += sExtraArg.dfYOff;
            sExtraArg.dfYOff = 0;
        }
        if (sExtraArg.dfXOff + sExtraArg.dfXSize > nRasterXSize)
        {
            nExtBufXSizeReq -= static_cast<int>(
                (sExtraArg.dfXOff + sExtraArg.dfXSize - nRasterXSize) /
                dfXRatio);
            sExtraArg.dfXSize = nRasterXSize - sExtraArg.dfXOff;
        }
        if (sExtraArg.dfYOff + sExtraArg.dfYSize > nRasterYSize)
        {
            nExtBufYSizeReq -= static_cast<int>(
                (sExtraArg.dfYOff + sExtraArg.dfYSize - nRasterYSize) /
                dfYRatio);
            sExtraArg.dfYSize = nRasterYSize - sExtraArg.dfYOff;
        }

        nXOffExt = static_cast<int>(sExtraArg.dfXOff);
        nYOffExt = static_cast<int>(sExtraArg.dfYOff);
        nXSizeExt = std::min(static_cast<int>(sExtraArg.dfXSize + 0.5),
                             nRasterXSize - nXOffExt);
        nYSizeExt = std::min(static_cast<int>(sExtraArg.dfYSize + 0.5),
                             nRasterYSize - nYOffExt);
    }

    // Load values for sources into packed buffers.
    CPLErr eErr = CE_None;
    VRTSource::WorkingState oWorkingState;
    for (int iBuffer = 0; iBuffer < nBufferCount && eErr == CE_None; iBuffer++)
    {
        const int iSource = anMapBufferIdxToSourceIdx[iBuffer];
        GByte *pabyBuffer = static_cast<GByte *>(pBuffers[iBuffer]);
        eErr = static_cast<VRTSource *>(papoSources[iSource])
                   ->RasterIO(
                       eSrcType, nXOffExt, nYOffExt, nXSizeExt, nYSizeExt,
                       pabyBuffer +
                           (nYShiftInBuffer * nExtBufXSize + nXShiftInBuffer) *
                               nSrcTypeSize,
                       nExtBufXSizeReq, nExtBufYSizeReq, eSrcType, nSrcTypeSize,
                       static_cast<GSpacing>(nSrcTypeSize) * nExtBufXSize,
                       &sExtraArg, oWorkingState);

        // Extend first lines
        for (int iY = 0; iY < nYShiftInBuffer; iY++)
        {
            memcpy(pabyBuffer +
                       static_cast<size_t>(iY) * nExtBufXSize * nSrcTypeSize,
                   pabyBuffer + static_cast<size_t>(nYShiftInBuffer) *
                                    nExtBufXSize * nSrcTypeSize,
                   static_cast<size_t>(nExtBufXSize) * nSrcTypeSize);
        }
        // Extend last lines
        for (int iY = nYShiftInBuffer + nExtBufYSizeReq; iY < nExtBufYSize;
             iY++)
        {
            memcpy(pabyBuffer +
                       static_cast<size_t>(iY) * nExtBufXSize * nSrcTypeSize,
                   pabyBuffer + static_cast<size_t>(nYShiftInBuffer +
                                                    nExtBufYSizeReq - 1) *
                                    nExtBufXSize * nSrcTypeSize,
                   static_cast<size_t>(nExtBufXSize) * nSrcTypeSize);
        }
        // Extend first cols
        if (nXShiftInBuffer)
        {
            for (int iY = 0; iY < nExtBufYSize; iY++)
            {
                for (int iX = 0; iX < nXShiftInBuffer; iX++)
                {
                    memcpy(pabyBuffer +
                               static_cast<size_t>(iY * nExtBufXSize + iX) *
                                   nSrcTypeSize,
                           pabyBuffer +
                               (static_cast<size_t>(iY) * nExtBufXSize +
                                nXShiftInBuffer) *
                                   nSrcTypeSize,
                           nSrcTypeSize);
                }
            }
        }
        // Extent last cols
        if (nXShiftInBuffer + nExtBufXSizeReq < nExtBufXSize)
        {
            for (int iY = 0; iY < nExtBufYSize; iY++)
            {
                for (int iX = nXShiftInBuffer + nExtBufXSizeReq;
                     iX < nExtBufXSize; iX++)
                {
                    memcpy(pabyBuffer +
                               (static_cast<size_t>(iY) * nExtBufXSize + iX) *
                                   nSrcTypeSize,
                           pabyBuffer +
                               (static_cast<size_t>(iY) * nExtBufXSize +
                                nXShiftInBuffer + nExtBufXSizeReq - 1) *
                                   nSrcTypeSize,
                           nSrcTypeSize);
                }
            }
        }
    }

    // Apply pixel function.
    if (eErr == CE_None && EQUAL(m_poPrivate->m_osLanguage, "Python"))
    {
        eErr = CE_Failure;

        // numpy doesn't have native cint16/cint32/cfloat16
        if (eSrcType == GDT_CInt16 || eSrcType == GDT_CInt32 ||
            eSrcType == GDT_CFloat16)
        {
            CPLError(CE_Failure, CPLE_AppDefined,
                     "CInt16/CInt32/CFloat16 data type not supported for "
                     "SourceTransferType");
            goto end;
        }
        if (eDataType == GDT_CInt16 || eDataType == GDT_CInt32 ||
            eDataType == GDT_CFloat16)
        {
            CPLError(
                CE_Failure, CPLE_AppDefined,
                "CInt16/CInt32/CFloat16 data type not supported for data type");
            goto end;
        }

        if (!InitializePython())
            goto end;

        GByte *pabyTmpBuffer = nullptr;
        // Do we need a temporary buffer or can we use directly the output
        // buffer ?
        if (nBufferRadius != 0 || eDataType != eBufType ||
            nPixelSpace != nBufTypeSize ||
            nLineSpace != static_cast<GSpacing>(nBufTypeSize) * nBufXSize)
        {
            pabyTmpBuffer = static_cast<GByte *>(VSI_CALLOC_VERBOSE(
                static_cast<size_t>(nExtBufXSize) * nExtBufYSize,
                GDALGetDataTypeSizeBytes(eDataType)));
            if (!pabyTmpBuffer)
                goto end;
        }

        {
            const bool bUseExclusiveLock =
                m_poPrivate->m_bExclusiveLock ||
                (m_poPrivate->m_bFirstTime &&
                 m_poPrivate->m_osCode.find("@jit") != std::string::npos);
            m_poPrivate->m_bFirstTime = false;
            GIL_Holder oHolder(bUseExclusiveLock);

            // Prepare target numpy array
            PyObject *poPyDstArray =
                GDALCreateNumpyArray(m_poPrivate->m_poGDALCreateNumpyArray,
                                     pabyTmpBuffer ? pabyTmpBuffer : pData,
                                     eDataType, nExtBufYSize, nExtBufXSize);
            if (!poPyDstArray)
            {
                VSIFree(pabyTmpBuffer);
                goto end;
            }

            // Wrap source buffers as input numpy arrays
            PyObject *pyArgInputArray = PyTuple_New(nBufferCount);
            for (int i = 0; i < nBufferCount; i++)
            {
                GByte *pabyBuffer = static_cast<GByte *>(pBuffers[i]);
                PyObject *poPySrcArray = GDALCreateNumpyArray(
                    m_poPrivate->m_poGDALCreateNumpyArray, pabyBuffer, eSrcType,
                    nExtBufYSize, nExtBufXSize);
                CPLAssert(poPySrcArray);
                PyTuple_SetItem(pyArgInputArray, i, poPySrcArray);
            }

            // Create arguments
            PyObject *pyArgs = PyTuple_New(10);
            PyTuple_SetItem(pyArgs, 0, pyArgInputArray);
            PyTuple_SetItem(pyArgs, 1, poPyDstArray);
            PyTuple_SetItem(pyArgs, 2, PyLong_FromLong(nXOff));
            PyTuple_SetItem(pyArgs, 3, PyLong_FromLong(nYOff));
            PyTuple_SetItem(pyArgs, 4, PyLong_FromLong(nXSize));
            PyTuple_SetItem(pyArgs, 5, PyLong_FromLong(nYSize));
            PyTuple_SetItem(pyArgs, 6, PyLong_FromLong(nRasterXSize));
            PyTuple_SetItem(pyArgs, 7, PyLong_FromLong(nRasterYSize));
            PyTuple_SetItem(pyArgs, 8, PyLong_FromLong(nBufferRadius));

            double adfGeoTransform[6];
            adfGeoTransform[0] = 0;
            adfGeoTransform[1] = 1;
            adfGeoTransform[2] = 0;
            adfGeoTransform[3] = 0;
            adfGeoTransform[4] = 0;
            adfGeoTransform[5] = 1;
            if (GetDataset())
                GetDataset()->GetGeoTransform(adfGeoTransform);
            PyObject *pyGT = PyTuple_New(6);
            for (int i = 0; i < 6; i++)
                PyTuple_SetItem(pyGT, i,
                                PyFloat_FromDouble(adfGeoTransform[i]));
            PyTuple_SetItem(pyArgs, 9, pyGT);

            // Prepare kwargs
            PyObject *pyKwargs = PyDict_New();
            for (size_t i = 0; i < m_poPrivate->m_oFunctionArgs.size(); ++i)
            {
                const char *pszKey =
                    m_poPrivate->m_oFunctionArgs[i].first.c_str();
                const char *pszValue =
                    m_poPrivate->m_oFunctionArgs[i].second.c_str();
                PyDict_SetItemString(
                    pyKwargs, pszKey,
                    PyBytes_FromStringAndSize(pszValue, strlen(pszValue)));
            }

            // Call user function
            PyObject *pRetValue =
                PyObject_Call(m_poPrivate->m_poUserFunction, pyArgs, pyKwargs);

            Py_DecRef(pyArgs);
            Py_DecRef(pyKwargs);

            if (ErrOccurredEmitCPLError())
            {
                // do nothing
            }
            else
            {
                eErr = CE_None;
            }
            if (pRetValue)
                Py_DecRef(pRetValue);
        }  // End of GIL section

        if (pabyTmpBuffer)
        {
            // Copy numpy destination array to user buffer
            for (int iY = 0; iY < nBufYSize; iY++)
            {
                size_t nSrcOffset =
                    (static_cast<size_t>(iY + nBufferRadius) * nExtBufXSize +
                     nBufferRadius) *
                    GDALGetDataTypeSizeBytes(eDataType);
                GDALCopyWords(pabyTmpBuffer + nSrcOffset, eDataType,
                              GDALGetDataTypeSizeBytes(eDataType),
                              static_cast<GByte *>(pData) + iY * nLineSpace,
                              eBufType, static_cast<int>(nPixelSpace),
                              nBufXSize);
            }

            VSIFree(pabyTmpBuffer);
        }
    }
    else if (eErr == CE_None && poPixelFunc != nullptr)
    {
        char **papszArgs = nullptr;

        oAdditionalArgs.insert(oAdditionalArgs.end(),
                               m_poPrivate->m_oFunctionArgs.begin(),
                               m_poPrivate->m_oFunctionArgs.end());
        for (const auto &oArg : oAdditionalArgs)
        {
            const char *pszKey = oArg.first.c_str();
            const char *pszValue = oArg.second.c_str();
            papszArgs = CSLSetNameValue(papszArgs, pszKey, pszValue);
        }

        CPLString osSourceNames;
        for (int iBuffer = 0; iBuffer < nBufferCount; iBuffer++)
        {
            int iSource = anMapBufferIdxToSourceIdx[iBuffer];
            const VRTSource *poSource = papoSources[iSource];

            if (iBuffer > 0)
            {
                osSourceNames += "|";
            }

            const auto &osName = poSource->GetName();
            if (osName.empty())
            {
                osSourceNames += "B" + std::to_string(iBuffer + 1);
            }
            else
            {
                osSourceNames += osName;
            }
        }

        papszArgs =
            CSLSetNameValue(papszArgs, "SOURCE_NAMES", osSourceNames.c_str());

        eErr = (poPixelFunc->first)(
            static_cast<void **>(pBuffers), nBufferCount, pData, nBufXSize,
            nBufYSize, eSrcType, eBufType, static_cast<int>(nPixelSpace),
            static_cast<int>(nLineSpace), papszArgs);

        CSLDestroy(papszArgs);
    }
end:
    // Release buffers.
    for (int iBuffer = 0; iBuffer < nBufferCount; iBuffer++)
    {
        VSIFree(pBuffers[iBuffer]);
    }
    CPLFree(pBuffers);

    return eErr;
}

/************************************************************************/
/*                         IGetDataCoverageStatus()                     */
/************************************************************************/

int VRTDerivedRasterBand::IGetDataCoverageStatus(
    int /* nXOff */, int /* nYOff */, int /* nXSize */, int /* nYSize */,
    int /* nMaskFlagStop */, double *pdfDataPct)
{
    if (pdfDataPct != nullptr)
        *pdfDataPct = -1.0;
    return GDAL_DATA_COVERAGE_STATUS_UNIMPLEMENTED |
           GDAL_DATA_COVERAGE_STATUS_DATA;
}

/************************************************************************/
/*                              XMLInit()                               */
/************************************************************************/

CPLErr VRTDerivedRasterBand::XMLInit(const CPLXMLNode *psTree,
                                     const char *pszVRTPath,
                                     VRTMapSharedResources &oMapSharedSources)

{
    const CPLErr eErr =
        VRTSourcedRasterBand::XMLInit(psTree, pszVRTPath, oMapSharedSources);
    if (eErr != CE_None)
        return eErr;

    // Read derived pixel function type.
    SetPixelFunctionName(CPLGetXMLValue(psTree, "PixelFunctionType", nullptr));
    if (pszFuncName == nullptr || EQUAL(pszFuncName, ""))
    {
        CPLError(CE_Failure, CPLE_AppDefined, "PixelFunctionType missing");
        return CE_Failure;
    }

    m_poPrivate->m_osLanguage =
        CPLGetXMLValue(psTree, "PixelFunctionLanguage", "C");
    if (!EQUAL(m_poPrivate->m_osLanguage, "C") &&
        !EQUAL(m_poPrivate->m_osLanguage, "Python"))
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "Unsupported PixelFunctionLanguage");
        return CE_Failure;
    }

    m_poPrivate->m_osCode = CPLGetXMLValue(psTree, "PixelFunctionCode", "");
    if (!m_poPrivate->m_osCode.empty() &&
        !EQUAL(m_poPrivate->m_osLanguage, "Python"))
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "PixelFunctionCode can only be used with Python");
        return CE_Failure;
    }

    m_poPrivate->m_nBufferRadius =
        atoi(CPLGetXMLValue(psTree, "BufferRadius", "0"));
    if (m_poPrivate->m_nBufferRadius < 0 || m_poPrivate->m_nBufferRadius > 1024)
    {
        CPLError(CE_Failure, CPLE_AppDefined, "Invalid value for BufferRadius");
        return CE_Failure;
    }
    if (m_poPrivate->m_nBufferRadius != 0 &&
        !EQUAL(m_poPrivate->m_osLanguage, "Python"))
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "BufferRadius can only be used with Python");
        return CE_Failure;
    }

    const CPLXMLNode *const psArgs =
        CPLGetXMLNode(psTree, "PixelFunctionArguments");
    if (psArgs != nullptr)
    {
        for (const CPLXMLNode *psIter = psArgs->psChild; psIter;
             psIter = psIter->psNext)
        {
            if (psIter->eType == CXT_Attribute)
            {
                m_poPrivate->m_oFunctionArgs.push_back(
                    std::pair<CPLString, CPLString>(psIter->pszValue,
                                                    psIter->psChild->pszValue));
            }
        }
    }

    // Read optional source transfer data type.
    const char *pszTypeName =
        CPLGetXMLValue(psTree, "SourceTransferType", nullptr);
    if (pszTypeName != nullptr)
    {
        eSourceTransferType = GDALGetDataTypeByName(pszTypeName);
    }

    // Whether to skip non contributing sources
    const char *pszSkipNonContributiongSources =
        CPLGetXMLValue(psTree, "SkipNonContributingSources", nullptr);
    if (pszSkipNonContributiongSources)
    {
        m_poPrivate->m_bSkipNonContributingSourcesSpecified = true;
        m_poPrivate->m_bSkipNonContributingSources =
            CPLTestBool(pszSkipNonContributiongSources);
    }

    return CE_None;
}

/************************************************************************/
/*                           SerializeToXML()                           */
/************************************************************************/

CPLXMLNode *VRTDerivedRasterBand::SerializeToXML(const char *pszVRTPath,
                                                 bool &bHasWarnedAboutRAMUsage,
                                                 size_t &nAccRAMUsage)
{
    CPLXMLNode *psTree = VRTSourcedRasterBand::SerializeToXML(
        pszVRTPath, bHasWarnedAboutRAMUsage, nAccRAMUsage);

    /* -------------------------------------------------------------------- */
    /*      Set subclass.                                                   */
    /* -------------------------------------------------------------------- */
    CPLCreateXMLNode(CPLCreateXMLNode(psTree, CXT_Attribute, "subClass"),
                     CXT_Text, "VRTDerivedRasterBand");

    /* ---- Encode DerivedBand-specific fields ---- */
    if (!EQUAL(m_poPrivate->m_osLanguage, "C"))
    {
        CPLSetXMLValue(psTree, "PixelFunctionLanguage",
                       m_poPrivate->m_osLanguage);
    }
    if (pszFuncName != nullptr && strlen(pszFuncName) > 0)
        CPLSetXMLValue(psTree, "PixelFunctionType", pszFuncName);
    if (!m_poPrivate->m_oFunctionArgs.empty())
    {
        CPLXMLNode *psArgs =
            CPLCreateXMLNode(psTree, CXT_Element, "PixelFunctionArguments");
        for (size_t i = 0; i < m_poPrivate->m_oFunctionArgs.size(); ++i)
        {
            const char *pszKey = m_poPrivate->m_oFunctionArgs[i].first.c_str();
            const char *pszValue =
                m_poPrivate->m_oFunctionArgs[i].second.c_str();
            CPLCreateXMLNode(CPLCreateXMLNode(psArgs, CXT_Attribute, pszKey),
                             CXT_Text, pszValue);
        }
    }
    if (!m_poPrivate->m_osCode.empty())
    {
        if (m_poPrivate->m_osCode.find("<![CDATA[") == std::string::npos)
        {
            CPLCreateXMLNode(
                CPLCreateXMLNode(psTree, CXT_Element, "PixelFunctionCode"),
                CXT_Literal,
                ("<![CDATA[" + m_poPrivate->m_osCode + "]]>").c_str());
        }
        else
        {
            CPLSetXMLValue(psTree, "PixelFunctionCode", m_poPrivate->m_osCode);
        }
    }
    if (m_poPrivate->m_nBufferRadius != 0)
        CPLSetXMLValue(psTree, "BufferRadius",
                       CPLSPrintf("%d", m_poPrivate->m_nBufferRadius));
    if (this->eSourceTransferType != GDT_Unknown)
        CPLSetXMLValue(psTree, "SourceTransferType",
                       GDALGetDataTypeName(eSourceTransferType));

    if (m_poPrivate->m_bSkipNonContributingSourcesSpecified)
    {
        CPLSetXMLValue(psTree, "SkipNonContributingSources",
                       m_poPrivate->m_bSkipNonContributingSources ? "true"
                                                                  : "false");
    }

    return psTree;
}

/************************************************************************/
/*                             GetMinimum()                             */
/************************************************************************/

double VRTDerivedRasterBand::GetMinimum(int *pbSuccess)
{
    return GDALRasterBand::GetMinimum(pbSuccess);
}

/************************************************************************/
/*                             GetMaximum()                             */
/************************************************************************/

double VRTDerivedRasterBand::GetMaximum(int *pbSuccess)
{
    return GDALRasterBand::GetMaximum(pbSuccess);
}

/************************************************************************/
/*                       ComputeRasterMinMax()                          */
/************************************************************************/

CPLErr VRTDerivedRasterBand::ComputeRasterMinMax(int bApproxOK,
                                                 double *adfMinMax)
{
    return GDALRasterBand::ComputeRasterMinMax(bApproxOK, adfMinMax);
}

/************************************************************************/
/*                         ComputeStatistics()                          */
/************************************************************************/

CPLErr VRTDerivedRasterBand::ComputeStatistics(int bApproxOK, double *pdfMin,
                                               double *pdfMax, double *pdfMean,
                                               double *pdfStdDev,
                                               GDALProgressFunc pfnProgress,
                                               void *pProgressData)

{
    return GDALRasterBand::ComputeStatistics(bApproxOK, pdfMin, pdfMax, pdfMean,
                                             pdfStdDev, pfnProgress,
                                             pProgressData);
}

/************************************************************************/
/*                            GetHistogram()                            */
/************************************************************************/

CPLErr VRTDerivedRasterBand::GetHistogram(double dfMin, double dfMax,
                                          int nBuckets, GUIntBig *panHistogram,
                                          int bIncludeOutOfRange, int bApproxOK,
                                          GDALProgressFunc pfnProgress,
                                          void *pProgressData)

{
    return VRTRasterBand::GetHistogram(dfMin, dfMax, nBuckets, panHistogram,
                                       bIncludeOutOfRange, bApproxOK,
                                       pfnProgress, pProgressData);
}

/*! @endcond */
