/******************************************************************************
 *
 * Project:  GDAL
 * Purpose:  Interpolate in nodata areas.
 * Author:   Frank Warmerdam, warmerdam@pobox.com
 *
 ******************************************************************************
 * Copyright (c) 2008, Frank Warmerdam
 * Copyright (c) 2009-2013, Even Rouault <even dot rouault at spatialys.com>
 * Copyright (c) 2015, Sean Gillies <sean@mapbox.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included
 * in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 * OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
 * DEALINGS IN THE SOFTWARE.
 ***************************************************************************/

#include "cpl_port.h"
#include "gdal_alg.h"

#include <cmath>
#include <cstring>

#include <algorithm>
#include <string>
#include <utility>

#include "cpl_conv.h"
#include "cpl_error.h"
#include "cpl_progress.h"
#include "cpl_string.h"
#include "cpl_vsi.h"
#include "gdal.h"
#include "gdal_priv.h"

/************************************************************************/
/*                           GDALFilterLine()                           */
/*                                                                      */
/*      Apply 3x3 filtering one one scanline with masking for which     */
/*      pixels are to be interpolated (ThisFMask) and which window      */
/*      pixels are valid to include in the interpolation (TMask).       */
/************************************************************************/

static void GDALFilterLine(const float *pafLastLine, const float *pafThisLine,
                           const float *pafNextLine, float *pafOutLine,
                           const GByte *pabyLastTMask,
                           const GByte *pabyThisTMask,
                           const GByte *pabyNextTMask,
                           const GByte *pabyThisFMask, int nXSize)

{
    for (int iX = 0; iX < nXSize; iX++)
    {
        if (!pabyThisFMask[iX])
        {
            pafOutLine[iX] = pafThisLine[iX];
            continue;
        }

        CPLAssert(pabyThisTMask[iX]);

        double dfValSum = 0.0;
        double dfWeightSum = 0.0;

        // Previous line.
        if (pafLastLine != nullptr)
        {
            if (iX > 0 && pabyLastTMask[iX - 1])
            {
                dfValSum += pafLastLine[iX - 1];
                dfWeightSum += 1.0;
            }
            if (pabyLastTMask[iX])
            {
                dfValSum += pafLastLine[iX];
                dfWeightSum += 1.0;
            }
            if (iX < nXSize - 1 && pabyLastTMask[iX + 1])
            {
                dfValSum += pafLastLine[iX + 1];
                dfWeightSum += 1.0;
            }
        }

        // Current Line.
        if (iX > 0 && pabyThisTMask[iX - 1])
        {
            dfValSum += pafThisLine[iX - 1];
            dfWeightSum += 1.0;
        }
        if (pabyThisTMask[iX])
        {
            dfValSum += pafThisLine[iX];
            dfWeightSum += 1.0;
        }
        if (iX < nXSize - 1 && pabyThisTMask[iX + 1])
        {
            dfValSum += pafThisLine[iX + 1];
            dfWeightSum += 1.0;
        }

        // Next line.
        if (pafNextLine != nullptr)
        {
            if (iX > 0 && pabyNextTMask[iX - 1])
            {
                dfValSum += pafNextLine[iX - 1];
                dfWeightSum += 1.0;
            }
            if (pabyNextTMask[iX])
            {
                dfValSum += pafNextLine[iX];
                dfWeightSum += 1.0;
            }
            if (iX < nXSize - 1 && pabyNextTMask[iX + 1])
            {
                dfValSum += pafNextLine[iX + 1];
                dfWeightSum += 1.0;
            }
        }

        pafOutLine[iX] = static_cast<float>(dfValSum / dfWeightSum);
    }
}

/************************************************************************/
/*                          GDALMultiFilter()                           */
/*                                                                      */
/*      Apply multiple iterations of a 3x3 smoothing filter over a      */
/*      band with masking controlling what pixels should be             */
/*      filtered (FiltMaskBand non zero) and which pixels can be        */
/*      considered valid contributors to the filter                     */
/*      (TargetMaskBand non zero).                                      */
/*                                                                      */
/*      This implementation attempts to apply many iterations in        */
/*      one IO pass by managing the filtering over a rolling buffer     */
/*      of nIterations+2 scanlines.  While possibly clever this        */
/*      makes the algorithm implementation largely                      */
/*      incomprehensible.                                               */
/************************************************************************/

static CPLErr GDALMultiFilter(GDALRasterBandH hTargetBand,
                              GDALRasterBandH hTargetMaskBand,
                              GDALRasterBandH hFiltMaskBand, int nIterations,
                              GDALProgressFunc pfnProgress, void *pProgressArg)

{
    const int nXSize = GDALGetRasterBandXSize(hTargetBand);
    const int nYSize = GDALGetRasterBandYSize(hTargetBand);

    /* -------------------------------------------------------------------- */
    /*      Report starting progress value.                                 */
    /* -------------------------------------------------------------------- */
    if (!pfnProgress(0.0, "Smoothing Filter...", pProgressArg))
    {
        CPLError(CE_Failure, CPLE_UserInterrupt, "User terminated");
        return CE_Failure;
    }

    /* -------------------------------------------------------------------- */
    /*      Allocate rotating buffers.                                      */
    /* -------------------------------------------------------------------- */
    const int nBufLines = nIterations + 2;

    GByte *pabyTMaskBuf =
        static_cast<GByte *>(VSI_MALLOC2_VERBOSE(nXSize, nBufLines));
    GByte *pabyFMaskBuf =
        static_cast<GByte *>(VSI_MALLOC2_VERBOSE(nXSize, nBufLines));

    float *paf3PassLineBuf = static_cast<float *>(
        VSI_MALLOC3_VERBOSE(nXSize, nBufLines, 3 * sizeof(float)));
    if (pabyTMaskBuf == nullptr || pabyFMaskBuf == nullptr ||
        paf3PassLineBuf == nullptr)
    {
        CPLFree(pabyTMaskBuf);
        CPLFree(pabyFMaskBuf);
        CPLFree(paf3PassLineBuf);

        return CE_Failure;
    }

    /* -------------------------------------------------------------------- */
    /*      Process rotating buffers.                                       */
    /* -------------------------------------------------------------------- */

    CPLErr eErr = CE_None;

    int iPassCounter = 0;

    for (int nNewLine = 0;  // Line being loaded (zero based scanline).
         eErr == CE_None && nNewLine < nYSize + nIterations; nNewLine++)
    {
        /* --------------------------------------------------------------------
         */
        /*      Rotate pass buffers. */
        /* --------------------------------------------------------------------
         */
        iPassCounter = (iPassCounter + 1) % 3;

        float *const pafSLastPass =
            paf3PassLineBuf + ((iPassCounter + 0) % 3) * nXSize * nBufLines;
        float *const pafLastPass =
            paf3PassLineBuf + ((iPassCounter + 1) % 3) * nXSize * nBufLines;
        float *const pafThisPass =
            paf3PassLineBuf + ((iPassCounter + 2) % 3) * nXSize * nBufLines;

        /* --------------------------------------------------------------------
         */
        /*      Where does the new line go in the rotating buffer? */
        /* --------------------------------------------------------------------
         */
        const int iBufOffset = nNewLine % nBufLines;

        /* --------------------------------------------------------------------
         */
        /*      Read the new data line if it is't off the bottom of the */
        /*      image. */
        /* --------------------------------------------------------------------
         */
        if (nNewLine < nYSize)
        {
            eErr = GDALRasterIO(hTargetMaskBand, GF_Read, 0, nNewLine, nXSize,
                                1, pabyTMaskBuf + nXSize * iBufOffset, nXSize,
                                1, GDT_Byte, 0, 0);

            if (eErr != CE_None)
                break;

            eErr = GDALRasterIO(hFiltMaskBand, GF_Read, 0, nNewLine, nXSize, 1,
                                pabyFMaskBuf + nXSize * iBufOffset, nXSize, 1,
                                GDT_Byte, 0, 0);

            if (eErr != CE_None)
                break;

            eErr = GDALRasterIO(hTargetBand, GF_Read, 0, nNewLine, nXSize, 1,
                                pafThisPass + nXSize * iBufOffset, nXSize, 1,
                                GDT_Float32, 0, 0);

            if (eErr != CE_None)
                break;
        }

        /* --------------------------------------------------------------------
         */
        /*      Loop over the loaded data, applying the filter to all loaded */
        /*      lines with neighbours. */
        /* --------------------------------------------------------------------
         */
        for (int iFLine = nNewLine - 1;
             eErr == CE_None && iFLine >= nNewLine - nIterations; iFLine--)
        {
            const int iLastOffset = (iFLine - 1) % nBufLines;
            const int iThisOffset = (iFLine) % nBufLines;
            const int iNextOffset = (iFLine + 1) % nBufLines;

            // Default to preserving the old value.
            if (iFLine >= 0)
                memcpy(pafThisPass + iThisOffset * nXSize,
                       pafLastPass + iThisOffset * nXSize,
                       sizeof(float) * nXSize);

            // TODO: Enable first and last line.
            // Skip the first and last line.
            if (iFLine < 1 || iFLine >= nYSize - 1)
            {
                continue;
            }

            GDALFilterLine(pafSLastPass + iLastOffset * nXSize,
                           pafLastPass + iThisOffset * nXSize,
                           pafThisPass + iNextOffset * nXSize,
                           pafThisPass + iThisOffset * nXSize,
                           pabyTMaskBuf + iLastOffset * nXSize,
                           pabyTMaskBuf + iThisOffset * nXSize,
                           pabyTMaskBuf + iNextOffset * nXSize,
                           pabyFMaskBuf + iThisOffset * nXSize, nXSize);
        }

        /* --------------------------------------------------------------------
         */
        /*      Write out the top data line that will be rolling out of our */
        /*      buffer. */
        /* --------------------------------------------------------------------
         */
        const int iLineToSave = nNewLine - nIterations;

        if (iLineToSave >= 0 && eErr == CE_None)
        {
            const int iBufOffset2 = iLineToSave % nBufLines;

            eErr = GDALRasterIO(hTargetBand, GF_Write, 0, iLineToSave, nXSize,
                                1, pafThisPass + nXSize * iBufOffset2, nXSize,
                                1, GDT_Float32, 0, 0);
        }

        /* --------------------------------------------------------------------
         */
        /*      Report progress. */
        /* --------------------------------------------------------------------
         */
        if (eErr == CE_None &&
            !pfnProgress((nNewLine + 1) /
                             static_cast<double>(nYSize + nIterations),
                         "Smoothing Filter...", pProgressArg))
        {
            CPLError(CE_Failure, CPLE_UserInterrupt, "User terminated");
            eErr = CE_Failure;
        }
    }

    /* -------------------------------------------------------------------- */
    /*      Cleanup                                                         */
    /* -------------------------------------------------------------------- */
    CPLFree(pabyTMaskBuf);
    CPLFree(pabyFMaskBuf);
    CPLFree(paf3PassLineBuf);

    return eErr;
}

/************************************************************************/
/*                             QUAD_CHECK()                             */
/*                                                                      */
/*      macro for checking whether a point is nearer than the           */
/*      existing closest point.                                         */
/************************************************************************/

inline void QUAD_CHECK(double &dfQuadDist, float &fQuadValue, int target_x,
                       GUInt32 target_y, int origin_x, int origin_y,
                       float fTargetValue, GUInt32 nNoDataVal)
{
    if (target_y != nNoDataVal)
    {
        const double dfDx =
            static_cast<double>(target_x) - static_cast<double>(origin_x);
        const double dfDy =
            static_cast<double>(target_y) - static_cast<double>(origin_y);
        double dfDistSq = dfDx * dfDx + dfDy * dfDy;

        if (dfDistSq < dfQuadDist * dfQuadDist)
        {
            CPLAssert(dfDistSq > 0.0);
            dfQuadDist = sqrt(dfDistSq);
            fQuadValue = fTargetValue;
        }
    }
}

/************************************************************************/
/*                           GDALFillNodata()                           */
/************************************************************************/

/**
 * Fill selected raster regions by interpolation from the edges.
 *
 * This algorithm will interpolate values for all designated
 * nodata pixels (marked by zeros in hMaskBand). For each pixel
 * a four direction conic search is done to find values to interpolate
 * from (using inverse distance weighting by default). Once all values are
 * interpolated, zero or more smoothing iterations (3x3 average
 * filters on interpolated pixels) are applied to smooth out
 * artifacts.
 *
 * This algorithm is generally suitable for interpolating missing
 * regions of fairly continuously varying rasters (such as elevation
 * models for instance). It is also suitable for filling small holes
 * and cracks in more irregularly varying images (like airphotos). It
 * is generally not so great for interpolating a raster from sparse
 * point data - see the algorithms defined in gdal_grid.h for that case.
 *
 * @param hTargetBand the raster band to be modified in place.
 * @param hMaskBand a mask band indicating pixels to be interpolated
 * (zero valued). If hMaskBand is set to NULL, this method will internally use
 * the mask band returned by GDALGetMaskBand(hTargetBand).
 * @param dfMaxSearchDist the maximum number of pixels to search in all
 * directions to find values to interpolate from.
 * @param bDeprecatedOption unused argument, should be zero.
 * @param nSmoothingIterations the number of 3x3 smoothing filter passes to
 * run (0 or more).
 * @param papszOptions additional name=value options in a string list.
 * <ul>
 * <li>TEMP_FILE_DRIVER=gdal_driver_name. For example MEM.</li>
 * <li>NODATA=value (starting with GDAL 2.4).
 * Source pixels at that value will be ignored by the interpolator. Warning:
 * currently this will not be honored by smoothing passes.</li>
 * <li>INTERPOLATION=INV_DIST/NEAREST (GDAL >= 3.9). By default, pixels are
 * interpolated using an inverse distance weighting (INV_DIST). It is also
 * possible to choose a nearest neighbour (NEAREST) strategy.</li>
 * </ul>
 * @param pfnProgress the progress function to report completion.
 * @param pProgressArg callback data for progress function.
 *
 * @return CE_None on success or CE_Failure if something goes wrong.
 */

CPLErr CPL_STDCALL GDALFillNodata(GDALRasterBandH hTargetBand,
                                  GDALRasterBandH hMaskBand,
                                  double dfMaxSearchDist,
                                  CPL_UNUSED int bDeprecatedOption,
                                  int nSmoothingIterations, char **papszOptions,
                                  GDALProgressFunc pfnProgress,
                                  void *pProgressArg)

{
    VALIDATE_POINTER1(hTargetBand, "GDALFillNodata", CE_Failure);

    const int nXSize = GDALGetRasterBandXSize(hTargetBand);
    const int nYSize = GDALGetRasterBandYSize(hTargetBand);

    if (dfMaxSearchDist == 0.0)
        dfMaxSearchDist = std::max(nXSize, nYSize) + 1;

    const int nMaxSearchDist = static_cast<int>(floor(dfMaxSearchDist));

    const char *pszInterpolation =
        CSLFetchNameValueDef(papszOptions, "INTERPOLATION", "INV_DIST");
    const bool bNearest = EQUAL(pszInterpolation, "NEAREST");
    if (!EQUAL(pszInterpolation, "INV_DIST") &&
        !EQUAL(pszInterpolation, "NEAREST"))
    {
        CPLError(CE_Failure, CPLE_NotSupported,
                 "Unsupported interpolation method: %s", pszInterpolation);
        return CE_Failure;
    }

    // Special "x" pixel values identifying pixels as special.
    GDALDataType eType = GDT_UInt16;
    GUInt32 nNoDataVal = 65535;

    if (nXSize > 65533 || nYSize > 65533)
    {
        eType = GDT_UInt32;
        nNoDataVal = 4000002;
    }

    /* -------------------------------------------------------------------- */
    /*      Determine format driver for temp work files.                    */
    /* -------------------------------------------------------------------- */
    CPLString osTmpFileDriver =
        CSLFetchNameValueDef(papszOptions, "TEMP_FILE_DRIVER", "GTiff");
    GDALDriverH hDriver = GDALGetDriverByName(osTmpFileDriver.c_str());

    if (hDriver == nullptr)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "TEMP_FILE_DRIVER=%s driver is not registered",
                 osTmpFileDriver.c_str());
        return CE_Failure;
    }

    if (GDALGetMetadataItem(hDriver, GDAL_DCAP_CREATE, nullptr) == nullptr)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "TEMP_FILE_DRIVER=%s driver is incapable of creating "
                 "temp work files",
                 osTmpFileDriver.c_str());
        return CE_Failure;
    }

    CPLStringList aosWorkFileOptions;
    if (osTmpFileDriver == "GTiff")
    {
        aosWorkFileOptions.SetNameValue("COMPRESS", "LZW");
        aosWorkFileOptions.SetNameValue("BIGTIFF", "IF_SAFER");
    }

    const CPLString osTmpFile = CPLGenerateTempFilename("");

    std::unique_ptr<GDALDataset> poTmpMaskDS;
    if (hMaskBand == nullptr)
    {
        hMaskBand = GDALGetMaskBand(hTargetBand);
    }
    else if (nSmoothingIterations > 0 &&
             hMaskBand != GDALGetMaskBand(hTargetBand))
    {
        // If doing smoothing operations and the user provided its own
        // mask band, we must make a copy of it to be able to update it
        // when we fill pixels during the initial pass.
        const CPLString osMaskTmpFile = osTmpFile + "fill_mask_work.tif";
        poTmpMaskDS.reset(GDALDataset::FromHandle(
            GDALCreate(hDriver, osMaskTmpFile, nXSize, nYSize, 1, GDT_Byte,
                       aosWorkFileOptions.List())));
        if (poTmpMaskDS == nullptr)
        {
            CPLError(CE_Failure, CPLE_AppDefined,
                     "Could not create poTmpMaskDS work file. Check driver "
                     "capabilities.");
            return CE_Failure;
        }
        poTmpMaskDS->MarkSuppressOnClose();
        auto hTmpMaskBand =
            GDALRasterBand::ToHandle(poTmpMaskDS->GetRasterBand(1));
        if (GDALRasterBandCopyWholeRaster(hMaskBand, hTmpMaskBand, nullptr,
                                          nullptr, nullptr) != CE_None)
        {
            return CE_Failure;
        }
        hMaskBand = hTmpMaskBand;
    }

    // If there are smoothing iterations, reserve 10% of the progress for them.
    const double dfProgressRatio = nSmoothingIterations > 0 ? 0.9 : 1.0;

    const char *pszNoData = CSLFetchNameValue(papszOptions, "NODATA");
    bool bHasNoData = false;
    float fNoData = 0.0f;
    if (pszNoData)
    {
        bHasNoData = true;
        fNoData = static_cast<float>(CPLAtof(pszNoData));
    }

    /* -------------------------------------------------------------------- */
    /*      Initialize progress counter.                                    */
    /* -------------------------------------------------------------------- */
    if (pfnProgress == nullptr)
        pfnProgress = GDALDummyProgress;

    if (!pfnProgress(0.0, "Filling...", pProgressArg))
    {
        CPLError(CE_Failure, CPLE_UserInterrupt, "User terminated");
        return CE_Failure;
    }

    /* -------------------------------------------------------------------- */
    /*      Create a work file to hold the Y "last value" indices.          */
    /* -------------------------------------------------------------------- */
    const CPLString osYTmpFile = osTmpFile + "fill_y_work.tif";

    auto poYDS = std::unique_ptr<GDALDataset>(GDALDataset::FromHandle(
        GDALCreate(hDriver, osYTmpFile, nXSize, nYSize, 1, eType,
                   aosWorkFileOptions.List())));

    if (poYDS == nullptr)
    {
        CPLError(
            CE_Failure, CPLE_AppDefined,
            "Could not create Y index work file. Check driver capabilities.");
        return CE_Failure;
    }
    poYDS->MarkSuppressOnClose();

    GDALRasterBandH hYBand =
        GDALRasterBand::FromHandle(poYDS->GetRasterBand(1));

    /* -------------------------------------------------------------------- */
    /*      Create a work file to hold the pixel value associated with      */
    /*      the "last xy value" pixel.                                      */
    /* -------------------------------------------------------------------- */
    const CPLString osValTmpFile = osTmpFile + "fill_val_work.tif";

    auto poValDS =
        std::unique_ptr<GDALDataset>(GDALDataset::FromHandle(GDALCreate(
            hDriver, osValTmpFile, nXSize, nYSize, 1,
            GDALGetRasterDataType(hTargetBand), aosWorkFileOptions.List())));

    if (poValDS == nullptr)
    {
        CPLError(
            CE_Failure, CPLE_AppDefined,
            "Could not create XY value work file. Check driver capabilities.");
        return CE_Failure;
    }
    poValDS->MarkSuppressOnClose();

    GDALRasterBandH hValBand =
        GDALRasterBand::FromHandle(poValDS->GetRasterBand(1));

    /* -------------------------------------------------------------------- */
    /*      Create a mask file to make it clear what pixels can be filtered */
    /*      on the filtering pass.                                          */
    /* -------------------------------------------------------------------- */
    const CPLString osFiltMaskTmpFile = osTmpFile + "fill_filtmask_work.tif";

    auto poFiltMaskDS = std::unique_ptr<GDALDataset>(GDALDataset::FromHandle(
        GDALCreate(hDriver, osFiltMaskTmpFile, nXSize, nYSize, 1, GDT_Byte,
                   aosWorkFileOptions.List())));

    if (poFiltMaskDS == nullptr)
    {
        CPLError(CE_Failure, CPLE_AppDefined,
                 "Could not create mask work file. Check driver capabilities.");
        return CE_Failure;
    }
    poFiltMaskDS->MarkSuppressOnClose();

    GDALRasterBandH hFiltMaskBand =
        GDALRasterBand::FromHandle(poFiltMaskDS->GetRasterBand(1));

    /* -------------------------------------------------------------------- */
    /*      Allocate buffers for last scanline and this scanline.           */
    /* -------------------------------------------------------------------- */

    GUInt32 *panLastY =
        static_cast<GUInt32 *>(VSI_CALLOC_VERBOSE(nXSize, sizeof(GUInt32)));
    GUInt32 *panThisY =
        static_cast<GUInt32 *>(VSI_CALLOC_VERBOSE(nXSize, sizeof(GUInt32)));
    GUInt32 *panTopDownY =
        static_cast<GUInt32 *>(VSI_CALLOC_VERBOSE(nXSize, sizeof(GUInt32)));
    float *pafLastValue =
        static_cast<float *>(VSI_CALLOC_VERBOSE(nXSize, sizeof(float)));
    float *pafThisValue =
        static_cast<float *>(VSI_CALLOC_VERBOSE(nXSize, sizeof(float)));
    float *pafTopDownValue =
        static_cast<float *>(VSI_CALLOC_VERBOSE(nXSize, sizeof(float)));
    float *pafScanline =
        static_cast<float *>(VSI_CALLOC_VERBOSE(nXSize, sizeof(float)));
    GByte *pabyMask = static_cast<GByte *>(VSI_CALLOC_VERBOSE(nXSize, 1));
    GByte *pabyFiltMask = static_cast<GByte *>(VSI_CALLOC_VERBOSE(nXSize, 1));

    CPLErr eErr = CE_None;

    if (panLastY == nullptr || panThisY == nullptr || panTopDownY == nullptr ||
        pafLastValue == nullptr || pafThisValue == nullptr ||
        pafTopDownValue == nullptr || pafScanline == nullptr ||
        pabyMask == nullptr || pabyFiltMask == nullptr)
    {
        eErr = CE_Failure;
        goto end;
    }

    for (int iX = 0; iX < nXSize; iX++)
    {
        panLastY[iX] = nNoDataVal;
    }

    /* ==================================================================== */
    /*      Make first pass from top to bottom collecting the "last         */
    /*      known value" for each column and writing it out to the work     */
    /*      files.                                                          */
    /* ==================================================================== */

    for (int iY = 0; iY < nYSize && eErr == CE_None; iY++)
    {
        /* --------------------------------------------------------------------
         */
        /*      Read data and mask for this line. */
        /* --------------------------------------------------------------------
         */
        eErr = GDALRasterIO(hMaskBand, GF_Read, 0, iY, nXSize, 1, pabyMask,
                            nXSize, 1, GDT_Byte, 0, 0);

        if (eErr != CE_None)
            break;

        eErr = GDALRasterIO(hTargetBand, GF_Read, 0, iY, nXSize, 1, pafScanline,
                            nXSize, 1, GDT_Float32, 0, 0);

        if (eErr != CE_None)
            break;

        /* --------------------------------------------------------------------
         */
        /*      Figure out the most recent pixel for each column. */
        /* --------------------------------------------------------------------
         */

        for (int iX = 0; iX < nXSize; iX++)
        {
            if (pabyMask[iX])
            {
                pafThisValue[iX] = pafScanline[iX];
                panThisY[iX] = iY;
            }
            else if (iY <= dfMaxSearchDist + panLastY[iX])
            {
                pafThisValue[iX] = pafLastValue[iX];
                panThisY[iX] = panLastY[iX];
            }
            else
            {
                panThisY[iX] = nNoDataVal;
            }
        }

        /* --------------------------------------------------------------------
         */
        /*      Write out best index/value to working files. */
        /* --------------------------------------------------------------------
         */
        eErr = GDALRasterIO(hYBand, GF_Write, 0, iY, nXSize, 1, panThisY,
                            nXSize, 1, GDT_UInt32, 0, 0);
        if (eErr != CE_None)
            break;

        eErr = GDALRasterIO(hValBand, GF_Write, 0, iY, nXSize, 1, pafThisValue,
                            nXSize, 1, GDT_Float32, 0, 0);
        if (eErr != CE_None)
            break;

        /* --------------------------------------------------------------------
         */
        /*      Flip this/last buffers. */
        /* --------------------------------------------------------------------
         */
        std::swap(pafThisValue, pafLastValue);
        std::swap(panThisY, panLastY);

        /* --------------------------------------------------------------------
         */
        /*      report progress. */
        /* --------------------------------------------------------------------
         */
        if (!pfnProgress(dfProgressRatio *
                             (0.5 * (iY + 1) / static_cast<double>(nYSize)),
                         "Filling...", pProgressArg))
        {
            CPLError(CE_Failure, CPLE_UserInterrupt, "User terminated");
            eErr = CE_Failure;
        }
    }

    for (int iX = 0; iX < nXSize; iX++)
    {
        panLastY[iX] = nNoDataVal;
    }

    /* ==================================================================== */
    /*      Now we will do collect similar this/last information from       */
    /*      bottom to top and use it in combination with the top to         */
    /*      bottom search info to interpolate.                              */
    /* ==================================================================== */
    for (int iY = nYSize - 1; iY >= 0 && eErr == CE_None; iY--)
    {
        eErr = GDALRasterIO(hMaskBand, GF_Read, 0, iY, nXSize, 1, pabyMask,
                            nXSize, 1, GDT_Byte, 0, 0);

        if (eErr != CE_None)
            break;

        eErr = GDALRasterIO(hTargetBand, GF_Read, 0, iY, nXSize, 1, pafScanline,
                            nXSize, 1, GDT_Float32, 0, 0);

        if (eErr != CE_None)
            break;

        /* --------------------------------------------------------------------
         */
        /*      Figure out the most recent pixel for each column. */
        /* --------------------------------------------------------------------
         */

        for (int iX = 0; iX < nXSize; iX++)
        {
            if (pabyMask[iX])
            {
                pafThisValue[iX] = pafScanline[iX];
                panThisY[iX] = iY;
            }
            else if (panLastY[iX] - iY <= dfMaxSearchDist)
            {
                pafThisValue[iX] = pafLastValue[iX];
                panThisY[iX] = panLastY[iX];
            }
            else
            {
                panThisY[iX] = nNoDataVal;
            }
        }

        /* --------------------------------------------------------------------
         */
        /*      Load the last y and corresponding value from the top down pass.
         */
        /* --------------------------------------------------------------------
         */
        eErr = GDALRasterIO(hYBand, GF_Read, 0, iY, nXSize, 1, panTopDownY,
                            nXSize, 1, GDT_UInt32, 0, 0);

        if (eErr != CE_None)
            break;

        eErr = GDALRasterIO(hValBand, GF_Read, 0, iY, nXSize, 1,
                            pafTopDownValue, nXSize, 1, GDT_Float32, 0, 0);

        if (eErr != CE_None)
            break;

        /* --------------------------------------------------------------------
         */
        /*      Attempt to interpolate any pixels that are nodata. */
        /* --------------------------------------------------------------------
         */
        memset(pabyFiltMask, 0, nXSize);
        for (int iX = 0; iX < nXSize; iX++)
        {
            int nThisMaxSearchDist = nMaxSearchDist;

            // If this was a valid target - no change.
            if (pabyMask[iX])
                continue;

            enum Quadrants
            {
                QUAD_TOP_LEFT = 0,
                QUAD_BOTTOM_LEFT = 1,
                QUAD_TOP_RIGHT = 2,
                QUAD_BOTTOM_RIGHT = 3,
            };

            constexpr int QUAD_COUNT = 4;
            double adfQuadDist[QUAD_COUNT] = {};
            float afQuadValue[QUAD_COUNT] = {};

            for (int iQuad = 0; iQuad < QUAD_COUNT; iQuad++)
            {
                adfQuadDist[iQuad] = dfMaxSearchDist + 1.0;
                afQuadValue[iQuad] = 0.0;
            }

            // Step left and right by one pixel searching for the closest
            // target value for each quadrant.
            for (int iStep = 0; iStep <= nThisMaxSearchDist; iStep++)
            {
                const int iLeftX = std::max(0, iX - iStep);
                const int iRightX = std::min(nXSize - 1, iX + iStep);

                // Top left includes current line.
                QUAD_CHECK(adfQuadDist[QUAD_TOP_LEFT],
                           afQuadValue[QUAD_TOP_LEFT], iLeftX,
                           panTopDownY[iLeftX], iX, iY, pafTopDownValue[iLeftX],
                           nNoDataVal);

                // Bottom left.
                QUAD_CHECK(adfQuadDist[QUAD_BOTTOM_LEFT],
                           afQuadValue[QUAD_BOTTOM_LEFT], iLeftX,
                           panLastY[iLeftX], iX, iY, pafLastValue[iLeftX],
                           nNoDataVal);

                // Top right and bottom right do no include center pixel.
                if (iStep == 0)
                    continue;

                // Top right includes current line.
                QUAD_CHECK(adfQuadDist[QUAD_TOP_RIGHT],
                           afQuadValue[QUAD_TOP_RIGHT], iRightX,
                           panTopDownY[iRightX], iX, iY,
                           pafTopDownValue[iRightX], nNoDataVal);

                // Bottom right.
                QUAD_CHECK(adfQuadDist[QUAD_BOTTOM_RIGHT],
                           afQuadValue[QUAD_BOTTOM_RIGHT], iRightX,
                           panLastY[iRightX], iX, iY, pafLastValue[iRightX],
                           nNoDataVal);

                // Every four steps, recompute maximum distance.
                if ((iStep & 0x3) == 0)
                    nThisMaxSearchDist = static_cast<int>(floor(
                        std::max(std::max(adfQuadDist[0], adfQuadDist[1]),
                                 std::max(adfQuadDist[2], adfQuadDist[3]))));
            }

            bool bHasSrcValues = false;
            if (bNearest)
            {
                double dfNearestDist = dfMaxSearchDist + 1;
                float fNearestValue = 0.0f;

                for (int iQuad = 0; iQuad < QUAD_COUNT; iQuad++)
                {
                    if (adfQuadDist[iQuad] < dfNearestDist)
                    {
                        bHasSrcValues = true;
                        if (!bHasNoData || afQuadValue[iQuad] != fNoData)
                        {
                            fNearestValue = afQuadValue[iQuad];
                            dfNearestDist = adfQuadDist[iQuad];
                        }
                    }
                }

                if (bHasSrcValues)
                {
                    pabyFiltMask[iX] = 255;
                    if (dfNearestDist <= dfMaxSearchDist)
                    {
                        pabyMask[iX] = 255;
                        pafScanline[iX] = fNearestValue;
                    }
                    else
                        pafScanline[iX] = fNoData;
                }
            }
            else
            {
                double dfWeightSum = 0.0;
                double dfValueSum = 0.0;

                for (int iQuad = 0; iQuad < QUAD_COUNT; iQuad++)
                {
                    if (adfQuadDist[iQuad] <= dfMaxSearchDist)
                    {
                        bHasSrcValues = true;
                        if (!bHasNoData || afQuadValue[iQuad] != fNoData)
                        {
                            const double dfWeight = 1.0 / adfQuadDist[iQuad];
                            dfWeightSum += dfWeight;
                            dfValueSum += afQuadValue[iQuad] * dfWeight;
                        }
                    }
                }

                if (bHasSrcValues)
                {
                    pabyFiltMask[iX] = 255;
                    if (dfWeightSum > 0.0)
                    {
                        pabyMask[iX] = 255;
                        pafScanline[iX] =
                            static_cast<float>(dfValueSum / dfWeightSum);
                    }
                    else
                        pafScanline[iX] = fNoData;
                }
            }
        }

        /* --------------------------------------------------------------------
         */
        /*      Write out the updated data and mask information. */
        /* --------------------------------------------------------------------
         */
        eErr = GDALRasterIO(hTargetBand, GF_Write, 0, iY, nXSize, 1,
                            pafScanline, nXSize, 1, GDT_Float32, 0, 0);

        if (eErr != CE_None)
            break;

        if (poTmpMaskDS != nullptr)
        {
            // Update (copy of) mask band when it has been provided by the
            // user
            eErr = GDALRasterIO(hMaskBand, GF_Write, 0, iY, nXSize, 1, pabyMask,
                                nXSize, 1, GDT_Byte, 0, 0);

            if (eErr != CE_None)
                break;
        }

        eErr = GDALRasterIO(hFiltMaskBand, GF_Write, 0, iY, nXSize, 1,
                            pabyFiltMask, nXSize, 1, GDT_Byte, 0, 0);

        if (eErr != CE_None)
            break;

        /* --------------------------------------------------------------------
         */
        /*      Flip this/last buffers. */
        /* --------------------------------------------------------------------
         */
        std::swap(pafThisValue, pafLastValue);
        std::swap(panThisY, panLastY);

        /* --------------------------------------------------------------------
         */
        /*      report progress. */
        /* --------------------------------------------------------------------
         */
        if (!pfnProgress(
                dfProgressRatio *
                    (0.5 + 0.5 * (nYSize - iY) / static_cast<double>(nYSize)),
                "Filling...", pProgressArg))
        {
            CPLError(CE_Failure, CPLE_UserInterrupt, "User terminated");
            eErr = CE_Failure;
        }
    }

    /* ==================================================================== */
    /*      Now we will do iterative average filters over the               */
    /*      interpolated values to smooth things out and make linear        */
    /*      artifacts less obvious.                                         */
    /* ==================================================================== */
    if (eErr == CE_None && nSmoothingIterations > 0)
    {
        if (poTmpMaskDS == nullptr)
        {
            // Force masks to be to flushed and recomputed when the user
            // didn't pass a user-provided hMaskBand, and we assigned it
            // to be the mask band of hTargetBand.
            GDALFlushRasterCache(hMaskBand);
        }

        void *pScaledProgress = GDALCreateScaledProgress(
            dfProgressRatio, 1.0, pfnProgress, pProgressArg);

        eErr = GDALMultiFilter(hTargetBand, hMaskBand, hFiltMaskBand,
                               nSmoothingIterations, GDALScaledProgress,
                               pScaledProgress);

        GDALDestroyScaledProgress(pScaledProgress);
    }

/* -------------------------------------------------------------------- */
/*      Close and clean up temporary files. Free working buffers        */
/* -------------------------------------------------------------------- */
end:
    CPLFree(panLastY);
    CPLFree(panThisY);
    CPLFree(panTopDownY);
    CPLFree(pafLastValue);
    CPLFree(pafThisValue);
    CPLFree(pafTopDownValue);
    CPLFree(pafScanline);
    CPLFree(pabyMask);
    CPLFree(pabyFiltMask);

    return eErr;
}
