/******************************************************************************
 *
 * Project:  OpenGIS Simple Features Reference Implementation
 * Purpose:  Implements OGRMemLayer class.
 * Author:   Frank Warmerdam, warmerdam@pobox.com
 *
 ******************************************************************************
 * Copyright (c) 2003, Frank Warmerdam <warmerdam@pobox.com>
 * Copyright (c) 2009-2013, Even Rouault <even dot rouault at spatialys.com>
 *
 * SPDX-License-Identifier: MIT
 ****************************************************************************/

#include "cpl_port.h"
#include "memdataset.h"

#include <cstddef>
#include <cstring>
#include <algorithm>
#include <map>
#include <new>
#include <utility>

#include "cpl_conv.h"
#include "cpl_error.h"
#include "cpl_vsi.h"
#include "ogr_api.h"
#include "ogr_core.h"
#include "ogr_feature.h"
#include "ogr_geometry.h"
#include "ogr_p.h"
#include "ogr_spatialref.h"
#include "ogrsf_frmts.h"

/************************************************************************/
/*                      IOGRMemLayerFeatureIterator                     */
/************************************************************************/

class IOGRMemLayerFeatureIterator
{
  public:
    virtual ~IOGRMemLayerFeatureIterator();

    virtual OGRFeature *Next() = 0;
};

IOGRMemLayerFeatureIterator::~IOGRMemLayerFeatureIterator() = default;

/************************************************************************/
/*                            OGRMemLayer()                             */
/************************************************************************/

OGRMemLayer::OGRMemLayer(const char *pszName,
                         const OGRSpatialReference *poSRSIn,
                         OGRwkbGeometryType eReqType)
    : m_poFeatureDefn(new OGRFeatureDefn(pszName))
{
    m_poFeatureDefn->Reference();

    SetDescription(m_poFeatureDefn->GetName());
    m_poFeatureDefn->SetGeomType(eReqType);

    if (eReqType != wkbNone && poSRSIn != nullptr)
    {
        OGRSpatialReference *poSRS = poSRSIn->Clone();
        m_poFeatureDefn->GetGeomFieldDefn(0)->SetSpatialRef(poSRS);
        poSRS->Release();
    }

    m_oMapFeaturesIter = m_oMapFeatures.begin();
    m_poFeatureDefn->Seal(/* bSealFields = */ true);
}

OGRMemLayer::OGRMemLayer(const OGRFeatureDefn &oFeatureDefn)
    : m_poFeatureDefn(oFeatureDefn.Clone())
{
    m_poFeatureDefn->Reference();

    SetDescription(m_poFeatureDefn->GetName());

    m_oMapFeaturesIter = m_oMapFeatures.begin();
    m_poFeatureDefn->Seal(/* bSealFields = */ true);
}

/************************************************************************/
/*                           ~OGRMemLayer()                           */
/************************************************************************/

OGRMemLayer::~OGRMemLayer()

{
    if (m_nFeaturesRead > 0 && m_poFeatureDefn != nullptr)
    {
        CPLDebug("Mem", CPL_FRMT_GIB " features read on layer '%s'.",
                 m_nFeaturesRead, m_poFeatureDefn->GetName());
    }

    if (m_papoFeatures != nullptr)
    {
        for (GIntBig i = 0; i < m_nMaxFeatureCount; i++)
        {
            if (m_papoFeatures[i] != nullptr)
                delete m_papoFeatures[i];
        }
        CPLFree(m_papoFeatures);
    }

    if (m_poFeatureDefn)
        m_poFeatureDefn->Release();
}

/************************************************************************/
/*                            ResetReading()                            */
/************************************************************************/

void OGRMemLayer::ResetReading()

{
    m_iNextReadFID = 0;
    m_oMapFeaturesIter = m_oMapFeatures.begin();
}

/************************************************************************/
/*                           GetNextFeature()                           */
/************************************************************************/

OGRFeature *OGRMemLayer::GetNextFeature()

{
    if (m_iNextReadFID < 0)
        return nullptr;

    while (true)
    {
        OGRFeature *poFeature = nullptr;
        if (m_papoFeatures)
        {
            if (m_iNextReadFID >= m_nMaxFeatureCount)
                return nullptr;
            poFeature = m_papoFeatures[m_iNextReadFID++];
            if (poFeature == nullptr)
                continue;
        }
        else if (m_oMapFeaturesIter != m_oMapFeatures.end())
        {
            poFeature = m_oMapFeaturesIter->second.get();
            ++m_oMapFeaturesIter;
        }
        else
        {
            break;
        }

        if ((m_poFilterGeom == nullptr ||
             FilterGeometry(poFeature->GetGeomFieldRef(m_iGeomFieldFilter))) &&
            (m_poAttrQuery == nullptr || m_poAttrQuery->Evaluate(poFeature)))
        {
            m_nFeaturesRead++;
            return poFeature->Clone();
        }
    }

    return nullptr;
}

/************************************************************************/
/*                           SetNextByIndex()                           */
/************************************************************************/

OGRErr OGRMemLayer::SetNextByIndex(GIntBig nIndex)

{
    if (m_poFilterGeom != nullptr || m_poAttrQuery != nullptr ||
        m_papoFeatures == nullptr || m_bHasHoles)
        return OGRLayer::SetNextByIndex(nIndex);

    if (nIndex < 0 || nIndex >= m_nMaxFeatureCount)
    {
        m_iNextReadFID = -1;
        return OGRERR_NON_EXISTING_FEATURE;
    }

    m_iNextReadFID = nIndex;

    return OGRERR_NONE;
}

/************************************************************************/
/*                         GetFeatureRef()                              */
/************************************************************************/

OGRFeature *OGRMemLayer::GetFeatureRef(GIntBig nFeatureId)

{
    if (nFeatureId < 0)
        return nullptr;

    OGRFeature *poFeature = nullptr;
    if (m_papoFeatures != nullptr)
    {
        if (nFeatureId >= m_nMaxFeatureCount)
            return nullptr;
        poFeature = m_papoFeatures[nFeatureId];
    }
    else
    {
        FeatureIterator oIter = m_oMapFeatures.find(nFeatureId);
        if (oIter != m_oMapFeatures.end())
            poFeature = oIter->second.get();
    }

    return poFeature;
}

/************************************************************************/
/*                             GetFeature()                             */
/************************************************************************/

OGRFeature *OGRMemLayer::GetFeature(GIntBig nFeatureId)

{
    const OGRFeature *poFeature = GetFeatureRef(nFeatureId);
    return poFeature ? poFeature->Clone() : nullptr;
}

/************************************************************************/
/*                             ISetFeature()                             */
/************************************************************************/

OGRErr OGRMemLayer::ISetFeature(OGRFeature *poFeature)

{
    if (!m_bUpdatable)
        return OGRERR_FAILURE;

    if (poFeature == nullptr)
        return OGRERR_FAILURE;

    // If we don't have a FID, find one available
    GIntBig nFID = poFeature->GetFID();
    if (nFID == OGRNullFID)
    {
        if (m_papoFeatures != nullptr)
        {
            while (m_iNextCreateFID < m_nMaxFeatureCount &&
                   m_papoFeatures[m_iNextCreateFID] != nullptr)
            {
                m_iNextCreateFID++;
            }
        }
        else
        {
            FeatureIterator oIter;
            while ((oIter = m_oMapFeatures.find(m_iNextCreateFID)) !=
                   m_oMapFeatures.end())
                ++m_iNextCreateFID;
        }
        nFID = m_iNextCreateFID++;
        poFeature->SetFID(nFID);
    }
    else if (nFID < OGRNullFID)
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "negative FID are not supported");
        return OGRERR_FAILURE;
    }
    else
    {
        if (!m_bHasHoles)
        {
            // If the feature does not exist, set m_bHasHoles
            if (m_papoFeatures != nullptr)
            {
                if (nFID >= m_nMaxFeatureCount ||
                    m_papoFeatures[nFID] == nullptr)
                {
                    m_bHasHoles = true;
                }
            }
            else
            {
                FeatureIterator oIter = m_oMapFeatures.find(nFID);
                if (oIter == m_oMapFeatures.end())
                    m_bHasHoles = true;
            }
        }
    }

    auto poFeatureCloned = std::unique_ptr<OGRFeature>(poFeature->Clone());
    if (poFeatureCloned == nullptr)
        return OGRERR_FAILURE;

    if (m_papoFeatures != nullptr && nFID > 100000 &&
        nFID > m_nMaxFeatureCount + 1000)
    {
        // Convert to map if gap from current max size is too big.
        auto poIter =
            std::unique_ptr<IOGRMemLayerFeatureIterator>(GetIterator());
        try
        {
            OGRFeature *poFeatureIter = nullptr;
            while ((poFeatureIter = poIter->Next()) != nullptr)
            {
                m_oMapFeatures[poFeatureIter->GetFID()] =
                    std::unique_ptr<OGRFeature>(poFeatureIter);
            }
            CPLFree(m_papoFeatures);
            m_papoFeatures = nullptr;
            m_nMaxFeatureCount = 0;
        }
        catch (const std::bad_alloc &)
        {
            m_oMapFeatures.clear();
            m_oMapFeaturesIter = m_oMapFeatures.end();
            CPLError(CE_Failure, CPLE_OutOfMemory, "Cannot allocate memory");
            return OGRERR_FAILURE;
        }
    }

    for (int i = 0; i < m_poFeatureDefn->GetGeomFieldCount(); ++i)
    {
        OGRGeometry *poGeom = poFeatureCloned->GetGeomFieldRef(i);
        if (poGeom != nullptr && poGeom->getSpatialReference() == nullptr)
        {
            poGeom->assignSpatialReference(
                m_poFeatureDefn->GetGeomFieldDefn(i)->GetSpatialRef());
        }
    }

    if (m_papoFeatures != nullptr || (m_oMapFeatures.empty() && nFID <= 100000))
    {
        if (nFID >= m_nMaxFeatureCount)
        {
            const GIntBig nNewCount = std::max(
                m_nMaxFeatureCount + m_nMaxFeatureCount / 3 + 10, nFID + 1);
            if (static_cast<GIntBig>(static_cast<size_t>(sizeof(OGRFeature *)) *
                                     nNewCount) !=
                static_cast<GIntBig>(sizeof(OGRFeature *)) * nNewCount)
            {
                CPLError(CE_Failure, CPLE_OutOfMemory,
                         "Cannot allocate array of " CPL_FRMT_GIB " elements",
                         nNewCount);
                return OGRERR_FAILURE;
            }

            OGRFeature **papoNewFeatures =
                static_cast<OGRFeature **>(VSI_REALLOC_VERBOSE(
                    m_papoFeatures,
                    static_cast<size_t>(sizeof(OGRFeature *) * nNewCount)));
            if (papoNewFeatures == nullptr)
            {
                return OGRERR_FAILURE;
            }
            m_papoFeatures = papoNewFeatures;
            memset(m_papoFeatures + m_nMaxFeatureCount, 0,
                   sizeof(OGRFeature *) *
                       static_cast<size_t>(nNewCount - m_nMaxFeatureCount));
            m_nMaxFeatureCount = nNewCount;
        }
#ifdef DEBUG
        // Just to please Coverity. Cannot happen.
        if (m_papoFeatures == nullptr)
        {
            return OGRERR_FAILURE;
        }
#endif

        if (m_papoFeatures[nFID] != nullptr)
        {
            delete m_papoFeatures[nFID];
            m_papoFeatures[nFID] = nullptr;
        }
        else
        {
            ++m_nFeatureCount;
        }

        m_papoFeatures[nFID] = poFeatureCloned.release();
    }
    else
    {
        FeatureIterator oIter = m_oMapFeatures.find(nFID);
        if (oIter != m_oMapFeatures.end())
        {
            oIter->second = std::move(poFeatureCloned);
        }
        else
        {
            try
            {
                m_oMapFeatures[nFID] = std::move(poFeatureCloned);
                m_oMapFeaturesIter = m_oMapFeatures.end();
                m_nFeatureCount++;
            }
            catch (const std::bad_alloc &)
            {
                CPLError(CE_Failure, CPLE_OutOfMemory,
                         "Cannot allocate memory");
                return OGRERR_FAILURE;
            }
        }
    }

    m_bUpdated = true;

    return OGRERR_NONE;
}

/************************************************************************/
/*                           ICreateFeature()                            */
/************************************************************************/

OGRErr OGRMemLayer::ICreateFeature(OGRFeature *poFeature)

{
    if (!m_bUpdatable)
        return OGRERR_FAILURE;

    if (poFeature->GetFID() != OGRNullFID &&
        poFeature->GetFID() != m_iNextCreateFID)
        m_bHasHoles = true;

    // If the feature has already a FID and that a feature with the same
    // FID is already registered in the layer, then unset our FID.
    if (poFeature->GetFID() >= 0)
    {
        if (m_papoFeatures != nullptr)
        {
            if (poFeature->GetFID() < m_nMaxFeatureCount &&
                m_papoFeatures[poFeature->GetFID()] != nullptr)
            {
                poFeature->SetFID(OGRNullFID);
            }
        }
        else
        {
            FeatureIterator oIter = m_oMapFeatures.find(poFeature->GetFID());
            if (oIter != m_oMapFeatures.end())
                poFeature->SetFID(OGRNullFID);
        }
    }

    // Prevent calling ISetFeature() from derived classes
    return OGRMemLayer::ISetFeature(poFeature);
}

/************************************************************************/
/*                           UpsertFeature()                            */
/************************************************************************/

OGRErr OGRMemLayer::IUpsertFeature(OGRFeature *poFeature)

{
    if (!TestCapability(OLCUpsertFeature))
        return OGRERR_FAILURE;

    if (GetFeatureRef(poFeature->GetFID()))
    {
        return ISetFeature(poFeature);
    }
    else
    {
        return ICreateFeature(poFeature);
    }
}

/************************************************************************/
/*                           UpdateFeature()                            */
/************************************************************************/

OGRErr OGRMemLayer::IUpdateFeature(OGRFeature *poFeature,
                                   int nUpdatedFieldsCount,
                                   const int *panUpdatedFieldsIdx,
                                   int nUpdatedGeomFieldsCount,
                                   const int *panUpdatedGeomFieldsIdx,
                                   bool bUpdateStyleString)

{
    if (!TestCapability(OLCUpdateFeature))
        return OGRERR_FAILURE;

    auto poFeatureRef = GetFeatureRef(poFeature->GetFID());
    if (!poFeatureRef)
        return OGRERR_NON_EXISTING_FEATURE;

    for (int i = 0; i < nUpdatedFieldsCount; ++i)
    {
        poFeatureRef->SetField(
            panUpdatedFieldsIdx[i],
            poFeature->GetRawFieldRef(panUpdatedFieldsIdx[i]));
    }
    for (int i = 0; i < nUpdatedGeomFieldsCount; ++i)
    {
        poFeatureRef->SetGeomFieldDirectly(
            panUpdatedGeomFieldsIdx[i],
            poFeature->StealGeometry(panUpdatedGeomFieldsIdx[i]));
    }
    if (bUpdateStyleString)
    {
        poFeatureRef->SetStyleString(poFeature->GetStyleString());
    }

    m_bUpdated = true;

    return OGRERR_NONE;
}

/************************************************************************/
/*                           DeleteFeature()                            */
/************************************************************************/

OGRErr OGRMemLayer::DeleteFeature(GIntBig nFID)

{
    if (!m_bUpdatable)
        return OGRERR_FAILURE;

    if (nFID < 0)
    {
        return OGRERR_FAILURE;
    }

    if (m_papoFeatures != nullptr)
    {
        if (nFID >= m_nMaxFeatureCount || m_papoFeatures[nFID] == nullptr)
        {
            return OGRERR_FAILURE;
        }
        delete m_papoFeatures[nFID];
        m_papoFeatures[nFID] = nullptr;
    }
    else
    {
        FeatureIterator oIter = m_oMapFeatures.find(nFID);
        if (oIter == m_oMapFeatures.end())
        {
            return OGRERR_FAILURE;
        }
        m_oMapFeatures.erase(oIter);
    }

    m_bHasHoles = true;
    --m_nFeatureCount;

    m_bUpdated = true;

    return OGRERR_NONE;
}

/************************************************************************/
/*                          GetFeatureCount()                           */
/*                                                                      */
/*      If a spatial filter is in effect, we turn control over to       */
/*      the generic counter.  Otherwise we return the total count.      */
/*      Eventually we should consider implementing a more efficient     */
/*      way of counting features matching a spatial query.              */
/************************************************************************/

GIntBig OGRMemLayer::GetFeatureCount(int bForce)

{
    if (m_poFilterGeom != nullptr || m_poAttrQuery != nullptr)
        return OGRLayer::GetFeatureCount(bForce);

    return m_nFeatureCount;
}

/************************************************************************/
/*                           TestCapability()                           */
/************************************************************************/

int OGRMemLayer::TestCapability(const char *pszCap) const

{
    if (EQUAL(pszCap, OLCRandomRead))
        return TRUE;

    else if (EQUAL(pszCap, OLCSequentialWrite) || EQUAL(pszCap, OLCRandomWrite))
        return m_bUpdatable;

    else if (EQUAL(pszCap, OLCFastFeatureCount))
        return m_poFilterGeom == nullptr && m_poAttrQuery == nullptr;

    else if (EQUAL(pszCap, OLCFastSpatialFilter))
        return FALSE;

    else if (EQUAL(pszCap, OLCDeleteFeature) ||
             EQUAL(pszCap, OLCUpsertFeature) || EQUAL(pszCap, OLCUpdateFeature))
        return m_bUpdatable;

    else if (EQUAL(pszCap, OLCCreateField) ||
             EQUAL(pszCap, OLCCreateGeomField) ||
             EQUAL(pszCap, OLCDeleteField) || EQUAL(pszCap, OLCReorderFields) ||
             EQUAL(pszCap, OLCAlterFieldDefn) ||
             EQUAL(pszCap, OLCAlterGeomFieldDefn))
        return m_bUpdatable;

    else if (EQUAL(pszCap, OLCFastSetNextByIndex))
        return m_poFilterGeom == nullptr && m_poAttrQuery == nullptr &&
               ((m_papoFeatures != nullptr && !m_bHasHoles) ||
                m_oMapFeatures.empty());

    else if (EQUAL(pszCap, OLCStringsAsUTF8))
        return m_bAdvertizeUTF8;

    else if (EQUAL(pszCap, OLCCurveGeometries))
        return TRUE;

    else if (EQUAL(pszCap, OLCMeasuredGeometries))
        return TRUE;

    else if (EQUAL(pszCap, OLCZGeometries))
        return TRUE;

    return FALSE;
}

/************************************************************************/
/*                            CreateField()                             */
/************************************************************************/

OGRErr OGRMemLayer::CreateField(const OGRFieldDefn *poField,
                                int /* bApproxOK */)
{
    if (!m_bUpdatable)
        return OGRERR_FAILURE;

    // Simple case, no features exist yet.
    if (m_nFeatureCount == 0)
    {
        whileUnsealing(m_poFeatureDefn)->AddFieldDefn(poField);
        return OGRERR_NONE;
    }

    // Add field definition and setup remap definition.
    {
        whileUnsealing(m_poFeatureDefn)->AddFieldDefn(poField);
    }

    // Remap all the internal features.  Hopefully there aren't any
    // external features referring to our OGRFeatureDefn!
    auto poIter = std::unique_ptr<IOGRMemLayerFeatureIterator>(GetIterator());
    OGRFeature *poFeature = nullptr;
    while ((poFeature = poIter->Next()) != nullptr)
    {
        poFeature->AppendField();
    }

    m_bUpdated = true;

    return OGRERR_NONE;
}

/************************************************************************/
/*                            DeleteField()                             */
/************************************************************************/

OGRErr OGRMemLayer::DeleteField(int iField)
{
    if (!m_bUpdatable)
        return OGRERR_FAILURE;

    if (iField < 0 || iField >= m_poFeatureDefn->GetFieldCount())
    {
        CPLError(CE_Failure, CPLE_NotSupported, "Invalid field index");
        return OGRERR_FAILURE;
    }

    // Update all the internal features.  Hopefully there aren't any
    // external features referring to our OGRFeatureDefn!
    auto poIter = std::unique_ptr<IOGRMemLayerFeatureIterator>(GetIterator());
    while (OGRFeature *poFeature = poIter->Next())
    {
        OGRField *poFieldRaw = poFeature->GetRawFieldRef(iField);
        if (poFeature->IsFieldSetAndNotNull(iField) &&
            !poFeature->IsFieldNull(iField))
        {
            // Little trick to unallocate the field.
            OGRField sField;
            OGR_RawField_SetUnset(&sField);
            poFeature->SetField(iField, &sField);
        }

        if (iField < m_poFeatureDefn->GetFieldCount() - 1)
        {
            memmove(poFieldRaw, poFieldRaw + 1,
                    sizeof(OGRField) *
                        (m_poFeatureDefn->GetFieldCount() - 1 - iField));
        }
    }

    m_bUpdated = true;

    return whileUnsealing(m_poFeatureDefn)->DeleteFieldDefn(iField);
}

/************************************************************************/
/*                           ReorderFields()                            */
/************************************************************************/

OGRErr OGRMemLayer::ReorderFields(int *panMap)
{
    if (!m_bUpdatable)
        return OGRERR_FAILURE;

    if (m_poFeatureDefn->GetFieldCount() == 0)
        return OGRERR_NONE;

    const OGRErr eErr =
        OGRCheckPermutation(panMap, m_poFeatureDefn->GetFieldCount());
    if (eErr != OGRERR_NONE)
        return eErr;

    // Remap all the internal features.  Hopefully there aren't any
    // external features referring to our OGRFeatureDefn!
    auto poIter = std::unique_ptr<IOGRMemLayerFeatureIterator>(GetIterator());
    while (OGRFeature *poFeature = poIter->Next())
    {
        poFeature->RemapFields(nullptr, panMap);
    }

    m_bUpdated = true;

    return whileUnsealing(m_poFeatureDefn)->ReorderFieldDefns(panMap);
}

/************************************************************************/
/*                           AlterFieldDefn()                           */
/************************************************************************/

OGRErr OGRMemLayer::AlterFieldDefn(int iField, OGRFieldDefn *poNewFieldDefn,
                                   int nFlagsIn)
{
    if (!m_bUpdatable)
        return OGRERR_FAILURE;

    if (iField < 0 || iField >= m_poFeatureDefn->GetFieldCount())
    {
        CPLError(CE_Failure, CPLE_NotSupported, "Invalid field index");
        return OGRERR_FAILURE;
    }

    OGRFieldDefn *poFieldDefn = m_poFeatureDefn->GetFieldDefn(iField);
    auto oTemporaryUnsealer(poFieldDefn->GetTemporaryUnsealer());

    if ((nFlagsIn & ALTER_TYPE_FLAG) &&
        (poFieldDefn->GetType() != poNewFieldDefn->GetType() ||
         poFieldDefn->GetSubType() != poNewFieldDefn->GetSubType()))
    {
        if ((poNewFieldDefn->GetType() == OFTDate ||
             poNewFieldDefn->GetType() == OFTTime ||
             poNewFieldDefn->GetType() == OFTDateTime) &&
            (poFieldDefn->GetType() == OFTDate ||
             poFieldDefn->GetType() == OFTTime ||
             poFieldDefn->GetType() == OFTDateTime))
        {
            // Do nothing on features.
        }
        else if (poNewFieldDefn->GetType() == OFTInteger64 &&
                 poFieldDefn->GetType() == OFTInteger)
        {
            // Update all the internal features.  Hopefully there aren't any
            // external features referring to our OGRFeatureDefn!
            IOGRMemLayerFeatureIterator *poIter = GetIterator();
            OGRFeature *poFeature = nullptr;
            while ((poFeature = poIter->Next()) != nullptr)
            {
                OGRField *poFieldRaw = poFeature->GetRawFieldRef(iField);
                if (poFeature->IsFieldSetAndNotNull(iField) &&
                    !poFeature->IsFieldNull(iField))
                {
                    const GIntBig nVal = poFieldRaw->Integer;
                    poFieldRaw->Integer64 = nVal;
                }
            }
            delete poIter;
        }
        else if (poNewFieldDefn->GetType() == OFTReal &&
                 poFieldDefn->GetType() == OFTInteger)
        {
            // Update all the internal features.  Hopefully there aren't any
            // external features referring to our OGRFeatureDefn!
            IOGRMemLayerFeatureIterator *poIter = GetIterator();
            OGRFeature *poFeature = nullptr;
            while ((poFeature = poIter->Next()) != nullptr)
            {
                OGRField *poFieldRaw = poFeature->GetRawFieldRef(iField);
                if (poFeature->IsFieldSetAndNotNull(iField) &&
                    !poFeature->IsFieldNull(iField))
                {
                    const double dfVal = poFieldRaw->Integer;
                    poFieldRaw->Real = dfVal;
                }
            }
            delete poIter;
        }
        else if (poNewFieldDefn->GetType() == OFTReal &&
                 poFieldDefn->GetType() == OFTInteger64)
        {
            // Update all the internal features.  Hopefully there aren't any
            // external features referring to our OGRFeatureDefn!
            IOGRMemLayerFeatureIterator *poIter = GetIterator();
            OGRFeature *poFeature = nullptr;
            while ((poFeature = poIter->Next()) != nullptr)
            {
                OGRField *poFieldRaw = poFeature->GetRawFieldRef(iField);
                if (poFeature->IsFieldSetAndNotNull(iField) &&
                    !poFeature->IsFieldNull(iField))
                {
                    const double dfVal =
                        static_cast<double>(poFieldRaw->Integer64);
                    poFieldRaw->Real = dfVal;
                }
            }
            delete poIter;
        }
        else
        {
            if (poFieldDefn->GetType() != OGRUnknownType)
            {
                if (poNewFieldDefn->GetType() != OFTString)
                {
                    CPLError(CE_Failure, CPLE_NotSupported,
                             "Can only convert from OFTInteger to OFTReal, "
                             "or from anything to OFTString");
                    return OGRERR_FAILURE;
                }
            }

            // Update all the internal features.  Hopefully there aren't any
            // external features referring to our OGRFeatureDefn!
            IOGRMemLayerFeatureIterator *poIter = GetIterator();
            OGRFeature *poFeature = nullptr;
            while ((poFeature = poIter->Next()) != nullptr)
            {
                OGRField *poFieldRaw = poFeature->GetRawFieldRef(iField);
                if (poFeature->IsFieldSetAndNotNull(iField) &&
                    !poFeature->IsFieldNull(iField))
                {
                    char *pszVal =
                        CPLStrdup(poFeature->GetFieldAsString(iField));

                    // Little trick to unallocate the field.
                    OGRField sField;
                    OGR_RawField_SetUnset(&sField);
                    poFeature->SetField(iField, &sField);

                    poFieldRaw->String = pszVal;
                }
            }
            delete poIter;
        }

        poFieldDefn->SetSubType(OFSTNone);
        poFieldDefn->SetType(poNewFieldDefn->GetType());
        poFieldDefn->SetSubType(poNewFieldDefn->GetSubType());
    }

    if (nFlagsIn & ALTER_NAME_FLAG)
        poFieldDefn->SetName(poNewFieldDefn->GetNameRef());
    if (nFlagsIn & ALTER_WIDTH_PRECISION_FLAG)
    {
        poFieldDefn->SetWidth(poNewFieldDefn->GetWidth());
        poFieldDefn->SetPrecision(poNewFieldDefn->GetPrecision());
    }

    m_bUpdated = true;

    return OGRERR_NONE;
}

/************************************************************************/
/*                         AlterGeomFieldDefn()                         */
/************************************************************************/

OGRErr OGRMemLayer::AlterGeomFieldDefn(
    int iGeomField, const OGRGeomFieldDefn *poNewGeomFieldDefn, int nFlagsIn)
{
    if (!m_bUpdatable)
        return OGRERR_FAILURE;

    if (iGeomField < 0 || iGeomField >= m_poFeatureDefn->GetGeomFieldCount())
    {
        CPLError(CE_Failure, CPLE_NotSupported, "Invalid field index");
        return OGRERR_FAILURE;
    }

    auto poFieldDefn = m_poFeatureDefn->GetGeomFieldDefn(iGeomField);
    auto oTemporaryUnsealer(poFieldDefn->GetTemporaryUnsealer());

    if (nFlagsIn & ALTER_GEOM_FIELD_DEFN_NAME_FLAG)
        poFieldDefn->SetName(poNewGeomFieldDefn->GetNameRef());
    if (nFlagsIn & ALTER_GEOM_FIELD_DEFN_TYPE_FLAG)
    {
        if (poNewGeomFieldDefn->GetType() == wkbNone)
            return OGRERR_FAILURE;
        poFieldDefn->SetType(poNewGeomFieldDefn->GetType());
    }
    if (nFlagsIn & ALTER_GEOM_FIELD_DEFN_NULLABLE_FLAG)
        poFieldDefn->SetNullable(poNewGeomFieldDefn->IsNullable());

    if (nFlagsIn & ALTER_GEOM_FIELD_DEFN_SRS_FLAG)
    {
        OGRSpatialReference *poSRSNew = nullptr;
        const auto poSRSNewRef = poNewGeomFieldDefn->GetSpatialRef();
        if (poSRSNewRef)
        {
            poSRSNew = poSRSNewRef->Clone();
            if ((nFlagsIn & ALTER_GEOM_FIELD_DEFN_SRS_COORD_EPOCH_FLAG) == 0)
            {
                const auto poSRSOld = poFieldDefn->GetSpatialRef();
                if (poSRSOld)
                    poSRSNew->SetCoordinateEpoch(
                        poSRSOld->GetCoordinateEpoch());
                else
                    poSRSNew->SetCoordinateEpoch(0);
            }
        }
        poFieldDefn->SetSpatialRef(poSRSNew);
        if (poSRSNew)
            poSRSNew->Release();
    }
    else if (nFlagsIn & ALTER_GEOM_FIELD_DEFN_SRS_COORD_EPOCH_FLAG)
    {
        const auto poSRSOld = poFieldDefn->GetSpatialRef();
        const auto poSRSNewRef = poNewGeomFieldDefn->GetSpatialRef();
        if (poSRSOld && poSRSNewRef)
        {
            auto poSRSNew = poSRSOld->Clone();
            poSRSNew->SetCoordinateEpoch(poSRSNewRef->GetCoordinateEpoch());
            poFieldDefn->SetSpatialRef(poSRSNew);
            poSRSNew->Release();
        }
    }

    m_bUpdated = true;

    return OGRERR_NONE;
}

/************************************************************************/
/*                          CreateGeomField()                           */
/************************************************************************/

OGRErr OGRMemLayer::CreateGeomField(const OGRGeomFieldDefn *poGeomField,
                                    int /* bApproxOK */)
{
    if (!m_bUpdatable)
        return OGRERR_FAILURE;

    // Simple case, no features exist yet.
    if (m_nFeatureCount == 0)
    {
        whileUnsealing(m_poFeatureDefn)->AddGeomFieldDefn(poGeomField);
        return OGRERR_NONE;
    }

    // Add field definition and setup remap definition.
    whileUnsealing(m_poFeatureDefn)->AddGeomFieldDefn(poGeomField);

    const int nGeomFieldCount = m_poFeatureDefn->GetGeomFieldCount();
    std::vector<int> anRemap(nGeomFieldCount);
    for (int i = 0; i < nGeomFieldCount; ++i)
    {
        if (i < nGeomFieldCount - 1)
            anRemap[i] = i;
        else
            anRemap[i] = -1;
    }

    // Remap all the internal features.  Hopefully there aren't any
    // external features referring to our OGRFeatureDefn!
    auto poIter = std::unique_ptr<IOGRMemLayerFeatureIterator>(GetIterator());
    while (OGRFeature *poFeature = poIter->Next())
    {
        poFeature->RemapGeomFields(nullptr, anRemap.data());
    }

    m_bUpdated = true;

    return OGRERR_NONE;
}

/************************************************************************/
/*                        OGRMemLayerIteratorArray                      */
/************************************************************************/

class OGRMemLayerIteratorArray final : public IOGRMemLayerFeatureIterator
{
    GIntBig m_iCurIdx = 0;
    const GIntBig m_nMaxFeatureCount;
    OGRFeature **const m_papoFeatures;

    CPL_DISALLOW_COPY_ASSIGN(OGRMemLayerIteratorArray)

  public:
    OGRMemLayerIteratorArray(GIntBig nMaxFeatureCount,
                             OGRFeature **papoFeatures)
        : m_nMaxFeatureCount(nMaxFeatureCount), m_papoFeatures(papoFeatures)
    {
    }

    OGRFeature *Next() override;
};

OGRFeature *OGRMemLayerIteratorArray::Next()
{
    while (m_iCurIdx < m_nMaxFeatureCount)
    {
        OGRFeature *poFeature = m_papoFeatures[m_iCurIdx];
        ++m_iCurIdx;
        if (poFeature != nullptr)
            return poFeature;
    }
    return nullptr;
}

/************************************************************************/
/*                         OGRMemLayerIteratorMap                       */
/************************************************************************/

class OGRMemLayerIteratorMap final : public IOGRMemLayerFeatureIterator
{
    typedef std::map<GIntBig, std::unique_ptr<OGRFeature>> FeatureMap;
    typedef FeatureMap::iterator FeatureIterator;

    const FeatureMap &m_oMapFeatures;
    FeatureIterator m_oIter;

  public:
    explicit OGRMemLayerIteratorMap(FeatureMap &oMapFeatures)
        : m_oMapFeatures(oMapFeatures), m_oIter(oMapFeatures.begin())
    {
    }

    OGRFeature *Next() override;

  private:
    CPL_DISALLOW_COPY_ASSIGN(OGRMemLayerIteratorMap)
};

OGRFeature *OGRMemLayerIteratorMap::Next()
{
    if (m_oIter != m_oMapFeatures.end())
    {
        OGRFeature *poFeature = m_oIter->second.get();
        ++m_oIter;
        return poFeature;
    }
    return nullptr;
}

/************************************************************************/
/*                            GetIterator()                             */
/************************************************************************/

IOGRMemLayerFeatureIterator *OGRMemLayer::GetIterator()
{
    if (m_oMapFeatures.empty())
        return new OGRMemLayerIteratorArray(m_nMaxFeatureCount, m_papoFeatures);

    return new OGRMemLayerIteratorMap(m_oMapFeatures);
}