//    Copyright (C) 2019 Jakub Melka
//
//    This file is part of PdfForQt.
//
//    PdfForQt is free software: you can redistribute it and/or modify
//    it under the terms of the GNU Lesser General Public License as published by
//    the Free Software Foundation, either version 3 of the License, or
//    (at your option) any later version.
//
//    PdfForQt is distributed in the hope that it will be useful,
//    but WITHOUT ANY WARRANTY; without even the implied warranty of
//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//    GNU Lesser General Public License for more details.
//
//    You should have received a copy of the GNU Lesser General Public License
//    along with PDFForQt.  If not, see <https://www.gnu.org/licenses/>.

#include "pdfpattern.h"
#include "pdfdocument.h"
#include "pdfexception.h"
#include "pdfutils.h"
#include "pdfcolorspaces.h"

#include <QPainter>

#include <execution>

namespace pdf
{

PatternType PDFShadingPattern::getType() const
{
    return PatternType::Shading;
}

ShadingType PDFAxialShading::getShadingType() const
{
    return ShadingType::Axial;
}

PDFPatternPtr PDFPattern::createPattern(const PDFDictionary* colorSpaceDictionary, const PDFDocument* document, const PDFObject& object)
{
    const PDFObject& dereferencedObject = document->getObject(object);
    if (dereferencedObject.isDictionary())
    {
        PDFPatternPtr result;

        const PDFDictionary* patternDictionary = dereferencedObject.getDictionary();
        PDFDocumentDataLoaderDecorator loader(document);

        const PatternType patternType = static_cast<PatternType>(loader.readIntegerFromDictionary(patternDictionary, "PatternType", static_cast<PDFInteger>(PatternType::Invalid)));
        switch (patternType)
        {
            case PatternType::Tiling:
            {
                // TODO: Implement tiling pattern
                throw PDFParserException(PDFTranslationContext::tr("Tiling pattern not implemented."));
                break;
            }

            case PatternType::Shading:
            {
                PDFObject patternGraphicState = document->getObject(patternDictionary->get("ExtGState"));
                QMatrix matrix = loader.readMatrixFromDictionary(patternDictionary, "Matrix", QMatrix());
                return createShadingPattern(colorSpaceDictionary, document, patternDictionary->get("Shading"), matrix, patternGraphicState, false);
            }

            default:
                throw PDFParserException(PDFTranslationContext::tr("Invalid pattern."));
        }

        return result;
    }

    throw PDFParserException(PDFTranslationContext::tr("Invalid pattern."));
    return PDFPatternPtr();
}

PDFPatternPtr PDFPattern::createShadingPattern(const PDFDictionary* colorSpaceDictionary,
                                               const PDFDocument* document,
                                               const PDFObject& shadingObject,
                                               const QMatrix& matrix,
                                               const PDFObject& patternGraphicState,
                                               bool ignoreBackgroundColor)
{
    const PDFObject& dereferencedShadingObject = document->getObject(shadingObject);
    if (!dereferencedShadingObject.isDictionary() && !dereferencedShadingObject.isStream())
    {
        throw PDFParserException(PDFTranslationContext::tr("Invalid shading."));
    }

    PDFDocumentDataLoaderDecorator loader(document);
    const PDFDictionary* shadingDictionary = nullptr;
    const PDFStream* stream = nullptr;

    if (dereferencedShadingObject.isDictionary())
    {
        shadingDictionary = dereferencedShadingObject.getDictionary();
    }
    else if (dereferencedShadingObject.isStream())
    {
        stream = dereferencedShadingObject.getStream();
        shadingDictionary = stream->getDictionary();
    }

    // Parse common data for all shadings
    PDFColorSpacePointer colorSpace = PDFAbstractColorSpace::createColorSpace(colorSpaceDictionary, document, document->getObject(shadingDictionary->get("ColorSpace")));

    if (colorSpace->getPattern())
    {
        throw PDFParserException(PDFTranslationContext::tr("Pattern color space is not valid for shading patterns."));
    }

    QColor backgroundColor;
    if (!ignoreBackgroundColor)
    {
        std::vector<PDFReal> backgroundColorValues = loader.readNumberArrayFromDictionary(shadingDictionary, "Background");
        if (!backgroundColorValues.empty())
        {
            backgroundColor = colorSpace->getCheckedColor(PDFAbstractColorSpace::convertToColor(backgroundColorValues));
        }
    }
    QRectF boundingBox = loader.readRectangle(shadingDictionary->get("BBox"), QRectF());
    bool antialias = loader.readBooleanFromDictionary(shadingDictionary, "AntiAlias", false);
    const PDFObject& extendObject = document->getObject(shadingDictionary->get("Extend"));
    bool extendStart = false;
    bool extendEnd = false;
    if (extendObject.isArray())
    {
        const PDFArray* array = extendObject.getArray();
        if (array->getCount() != 2)
        {
            throw PDFParserException(PDFTranslationContext::tr("Invalid shading pattern extends. Expected 2, but %1 provided.").arg(array->getCount()));
        }

        extendStart = loader.readBoolean(array->getItem(0), false);
        extendEnd = loader.readBoolean(array->getItem(1), false);
    }
    std::vector<PDFFunctionPtr> functions;
    const PDFObject& functionsObject = document->getObject(shadingDictionary->get("Function"));
    if (functionsObject.isArray())
    {
        const PDFArray* functionsArray = functionsObject.getArray();
        functions.reserve(functionsArray->getCount());
        for (size_t i = 0, functionCount = functionsArray->getCount(); i < functionCount; ++i)
        {
            functions.push_back(PDFFunction::createFunction(document, functionsArray->getItem(i)));
        }
    }
    else if (!functionsObject.isNull())
    {
        functions.push_back(PDFFunction::createFunction(document, functionsObject));
    }

    const ShadingType shadingType = static_cast<ShadingType>(loader.readIntegerFromDictionary(shadingDictionary, "ShadingType", static_cast<PDFInteger>(ShadingType::Invalid)));
    switch (shadingType)
    {
        case ShadingType::Function:
        {
            PDFFunctionShading* functionShading = new PDFFunctionShading();
            PDFPatternPtr result(functionShading);

            std::vector<PDFReal> functionDomain = loader.readNumberArrayFromDictionary(shadingDictionary, "Domain", { 0.0, 1.0, 0.0, 1.0 });
            if (functionDomain.size() != 4)
            {
                throw PDFParserException(PDFTranslationContext::tr("Invalid function shading pattern domain. Expected 4 values, but %1 provided.").arg(functionDomain.size()));
            }
            if (functionDomain[1] < functionDomain[0] || functionDomain[3] < functionDomain[2])
            {
                throw PDFParserException(PDFTranslationContext::tr("Invalid function shading pattern domain. Invalid domain ranges."));
            }

            QMatrix domainToTargetTransform = loader.readMatrixFromDictionary(shadingDictionary, "Matrix", QMatrix());

            size_t colorComponentCount = colorSpace->getColorComponentCount();
            if (functions.size() > 1 && colorComponentCount != functions.size())
            {
                throw PDFParserException(PDFTranslationContext::tr("Invalid axial shading pattern color functions. Expected %1 functions, but %2 provided.").arg(int(colorComponentCount)).arg(int(functions.size())));
            }

            // Load items for function shading
            functionShading->m_antiAlias = antialias;
            functionShading->m_backgroundColor = backgroundColor;
            functionShading->m_colorSpace = colorSpace;
            functionShading->m_boundingBox = boundingBox;
            functionShading->m_domain = QRectF(functionDomain[0], functionDomain[2], functionDomain[1] - functionDomain[0], functionDomain[3] - functionDomain[2]);
            functionShading->m_domainToTargetTransform = domainToTargetTransform;
            functionShading->m_functions = qMove(functions);
            functionShading->m_matrix = matrix;
            functionShading->m_patternGraphicState = patternGraphicState;

            return result;
        }

        case ShadingType::Axial:
        {
            PDFAxialShading* axialShading = new PDFAxialShading();
            PDFPatternPtr result(axialShading);

            std::vector<PDFReal> coordinates = loader.readNumberArrayFromDictionary(shadingDictionary, "Coords");
            if (coordinates.size() != 4)
            {
                throw PDFParserException(PDFTranslationContext::tr("Invalid axial shading pattern coordinates. Expected 4, but %1 provided.").arg(coordinates.size()));
            }

            std::vector<PDFReal> domain = loader.readNumberArrayFromDictionary(shadingDictionary, "Domain");
            if (domain.empty())
            {
                domain = { 0.0, 1.0 };
            }
            if (domain.size() != 2)
            {
                throw PDFParserException(PDFTranslationContext::tr("Invalid axial shading pattern domain. Expected 2, but %1 provided.").arg(domain.size()));
            }

            size_t colorComponentCount = colorSpace->getColorComponentCount();
            if (functions.size() > 1 && colorComponentCount != functions.size())
            {
                throw PDFParserException(PDFTranslationContext::tr("Invalid axial shading pattern color functions. Expected %1 functions, but %2 provided.").arg(int(colorComponentCount)).arg(int(functions.size())));
            }

            // Load items for axial shading
            axialShading->m_antiAlias = antialias;
            axialShading->m_backgroundColor = backgroundColor;
            axialShading->m_colorSpace = colorSpace;
            axialShading->m_boundingBox = boundingBox;
            axialShading->m_domainStart = domain[0];
            axialShading->m_domainEnd = domain[1];
            axialShading->m_startPoint = QPointF(coordinates[0], coordinates[1]);
            axialShading->m_endPoint = QPointF(coordinates[2], coordinates[3]);
            axialShading->m_extendStart = extendStart;
            axialShading->m_extendEnd = extendEnd;
            axialShading->m_functions = qMove(functions);
            axialShading->m_matrix = matrix;
            axialShading->m_patternGraphicState = patternGraphicState;

            return result;
        }

        case ShadingType::Radial:
        {
            PDFRadialShading* radialShading = new PDFRadialShading();
            PDFPatternPtr result(radialShading);

            std::vector<PDFReal> coordinates = loader.readNumberArrayFromDictionary(shadingDictionary, "Coords");
            if (coordinates.size() != 6)
            {
                throw PDFParserException(PDFTranslationContext::tr("Invalid radial shading pattern coordinates. Expected 6, but %1 provided.").arg(coordinates.size()));
            }

            std::vector<PDFReal> domain = loader.readNumberArrayFromDictionary(shadingDictionary, "Domain");
            if (domain.empty())
            {
                domain = { 0.0, 1.0 };
            }
            if (domain.size() != 2)
            {
                throw PDFParserException(PDFTranslationContext::tr("Invalid radial shading pattern domain. Expected 2, but %1 provided.").arg(domain.size()));
            }

            size_t colorComponentCount = colorSpace->getColorComponentCount();
            if (functions.size() > 1 && colorComponentCount != functions.size())
            {
                throw PDFParserException(PDFTranslationContext::tr("Invalid radial shading pattern color functions. Expected %1 functions, but %2 provided.").arg(int(colorComponentCount)).arg(int(functions.size())));
            }

            if (coordinates[2] < 0.0 || coordinates[5] < 0.0)
            {
                throw PDFParserException(PDFTranslationContext::tr("Radial shading cannot have negative circle radius."));
            }

            // Load items for axial shading
            radialShading->m_antiAlias = antialias;
            radialShading->m_backgroundColor = backgroundColor;
            radialShading->m_colorSpace = colorSpace;
            radialShading->m_boundingBox = boundingBox;
            radialShading->m_domainStart = domain[0];
            radialShading->m_domainEnd = domain[1];
            radialShading->m_startPoint = QPointF(coordinates[0], coordinates[1]);
            radialShading->m_r0 = coordinates[2];
            radialShading->m_endPoint = QPointF(coordinates[3], coordinates[4]);
            radialShading->m_r1 = coordinates[5];
            radialShading->m_extendStart = extendStart;
            radialShading->m_extendEnd = extendEnd;
            radialShading->m_functions = qMove(functions);
            radialShading->m_matrix = matrix;
            radialShading->m_patternGraphicState = patternGraphicState;

            return result;
        }

        default:
        {
            throw PDFParserException(PDFTranslationContext::tr("Invalid shading pattern type (%1).").arg(static_cast<PDFInteger>(shadingType)));
        }
    }

    throw PDFParserException(PDFTranslationContext::tr("Invalid shading."));
    return PDFPatternPtr();
}

ShadingType PDFFunctionShading::getShadingType() const
{
    return ShadingType::Function;
}

PDFMesh PDFFunctionShading::createMesh(const PDFMeshQualitySettings& settings) const
{
    PDFMesh mesh;

    QMatrix domainToDeviceSpaceMatrix = m_domainToTargetTransform * settings.userSpaceToDeviceSpaceMatrix;
    QLineF topLine(m_domain.topLeft(), m_domain.topRight());
    QLineF leftLine(m_domain.topLeft(), m_domain.bottomLeft());

    Q_ASSERT(domainToDeviceSpaceMatrix.isInvertible());
    QMatrix deviceSpaceToDomainMatrix = domainToDeviceSpaceMatrix.inverted();

    QLineF topLineDS = domainToDeviceSpaceMatrix.map(topLine);
    QLineF leftLineDS = domainToDeviceSpaceMatrix.map(leftLine);

    const size_t colorComponents = m_colorSpace->getColorComponentCount();
    auto resolutions = { settings.preferredMeshResolution,
                         interpolate(0.25, 0.0, 1.0, settings.preferredMeshResolution, settings.minimalMeshResolution),
                         interpolate(0.50, 0.0, 1.0, settings.preferredMeshResolution, settings.minimalMeshResolution),
                         interpolate(0.75, 0.0, 1.0, settings.preferredMeshResolution, settings.minimalMeshResolution),
                         settings.minimalMeshResolution
                       };

    for (PDFReal resolution : resolutions)
    {
        const PDFReal xSteps = qMax(std::floor(topLineDS.length() / resolution), 2.0);
        const PDFReal ySteps = qMax(std::floor(leftLineDS.length() / resolution), 2.0);
        const PDFReal xStep = 1.0 / xSteps;
        const PDFReal yStep = 1.0 / ySteps;

        // Prepare x/y ordinates array for given resolution
        std::vector<PDFReal> xOrdinates;
        std::vector<PDFReal> yOrdinates;
        xOrdinates.reserve(xSteps + 1);
        yOrdinates.reserve(ySteps + 1);

        for (PDFReal x = 0.0; x <= 1.0; x += xStep)
        {
            xOrdinates.push_back(x);
        }
        if (xOrdinates.back() + PDF_EPSILON >= 1.0)
        {
            xOrdinates.pop_back();
        }
        xOrdinates.push_back(1.0);

        for (PDFReal y = 0.0; y <= 1.0; y += yStep)
        {
            yOrdinates.push_back(y);
        }
        if (yOrdinates.back() + PDF_EPSILON >= 1.0)
        {
            yOrdinates.pop_back();
        }
        yOrdinates.push_back(1.0);

        // We have determined x/y ordinates. Now we must create result array with colors,
        // which for each x/y ordinate tells us, what color in the given position is.
        const size_t rowCount = yOrdinates.size();
        const size_t columnCount = xOrdinates.size();
        const size_t nodesCount = rowCount * columnCount;
        const size_t stride = columnCount * colorComponents;

        std::vector<size_t> indices;
        indices.resize(nodesCount, 0);
        std::iota(indices.begin(), indices.end(), 0);

        auto indexToRowColumn = [columnCount](size_t index) -> std::pair<size_t, size_t>
        {
            return std::make_pair(index / columnCount, index % columnCount);
        };

        auto rowColumnToIndex = [columnCount](size_t row, size_t column) -> size_t
        {
            return row * columnCount + column;
        };

        auto rowColumnToFirstColorComponent = [stride, colorComponents](size_t row, size_t column) -> size_t
        {
            return row * stride + column * colorComponents;
        };

        const bool isSingleFunction = m_functions.size() == 1;
        std::vector<PDFReal> sourceColorBuffer;
        sourceColorBuffer.resize(indices.size() * colorComponents, 0.0);

        std::vector<QPointF> gridPoints;
        gridPoints.resize(nodesCount);

        QMutex functionErrorMutex;
        PDFFunction::FunctionResult functionError(true);

        auto setColor = [&](size_t index)
        {
            auto [row, column] = indexToRowColumn(index);
            QPointF nodeDS = topLineDS.pointAt(xOrdinates[column]) + leftLineDS.pointAt(yOrdinates[row]) - topLineDS.p1();
            QPointF node = deviceSpaceToDomainMatrix.map(nodeDS);
            const size_t colorComponentIndex = rowColumnToFirstColorComponent(row, column);
            Q_ASSERT(colorComponentIndex <= sourceColorBuffer.size());

            gridPoints[index] = nodeDS;

            PDFReal* sourceColorBegin = sourceColorBuffer.data() + colorComponentIndex;
            PDFReal* sourceColorEnd = sourceColorBegin + colorComponents;

            std::array<PDFReal, 2> uv = { node.x(), node.y() };

            if (isSingleFunction)
            {
                PDFFunction::FunctionResult result = m_functions.front()->apply(uv.data(), uv.data() + uv.size(), sourceColorBegin, sourceColorEnd);
                if (!result)
                {
                    QMutexLocker lock(&functionErrorMutex);
                    if (!functionError)
                    {
                        functionError = result;
                    }
                }
            }
            else
            {
                for (size_t i = 0, count = colorComponents; i < count; ++i)
                {
                    PDFFunction::FunctionResult result = m_functions[i]->apply(uv.data(), uv.data() + uv.size(), sourceColorBegin + i, sourceColorBegin + i + 1);
                    if (!result)
                    {
                        QMutexLocker lock(&functionErrorMutex);
                        if (!functionError)
                        {
                            functionError = result;
                        }
                    }
                }
            }
        };

        std::for_each(std::execution::parallel_policy(), indices.cbegin(), indices.cend(), setColor);

        if (!functionError)
        {
            throw PDFRendererException(RenderErrorType::Error, PDFTranslationContext::tr("Error occured during mesh generation of shading: %1").arg(functionError.errorMessage));
        }

        // Check the colors, if mesh is bad, then refine it
        std::atomic_bool isMeshOK = true;
        auto validateMesh = [&](size_t index)
        {
            if (!isMeshOK.load(std::memory_order_relaxed))
            {
                return;
            }

            auto [row, column] = indexToRowColumn(index);
            const size_t colorComponentIndex = rowColumnToFirstColorComponent(row, column);

            // Check, if color left doesn't differ too much
            if (column > 0)
            {
                const size_t colorOtherComponentIndex = rowColumnToFirstColorComponent(row, column - 1);
                for (size_t i = 0; i < colorComponents; ++i)
                {
                    if (std::fabs(sourceColorBuffer[colorComponentIndex + i] - sourceColorBuffer[colorOtherComponentIndex + i]) > settings.tolerance)
                    {
                        isMeshOK.store(std::memory_order_relaxed);
                        return;
                    }
                }
            }

            if (row > 0)
            {
                const size_t colorOtherComponentIndex = rowColumnToFirstColorComponent(row - 1, column);
                for (size_t i = 0; i < colorComponents; ++i)
                {
                    if (std::fabs(sourceColorBuffer[colorComponentIndex + i] - sourceColorBuffer[colorOtherComponentIndex + i]) > settings.tolerance)
                    {
                        isMeshOK.store(std::memory_order_relaxed);
                        return;
                    }
                }
            }
        };
        std::for_each(std::execution::parallel_policy(), indices.cbegin(), indices.cend(), validateMesh);
        if (!isMeshOK && resolution != settings.minimalMeshResolution)
        {
            continue;
        }

        // Now, we are ready to generate the mesh
        std::vector<QRgb> colors;
        colors.resize(rowCount * columnCount, QRgb());

        mesh.setVertices(qMove(gridPoints));
        std::vector<PDFMesh::Triangle> triangles;
        triangles.resize((rowCount - 1) * (columnCount - 1) * 2);

        auto generateTriangle = [&](size_t index)
        {
            auto [row, column] = indexToRowColumn(index);
                    if (row == 0 || column == 0)
            {
                return;
            }

            Q_ASSERT(index == rowColumnToIndex(row, column));

            const size_t triangleIndex1 = ((row - 1) * (columnCount - 1) + column - 1) * 2;
            const size_t triangleIndex2 = triangleIndex1 + 1;
            const size_t v1 = rowColumnToIndex(row - 1, column - 1);
            const size_t v2 = rowColumnToIndex(row - 1, column);
            const size_t v3 = index;
            const size_t v4 = rowColumnToIndex(row, column - 1);
            std::vector<PDFReal> colorBuffer;
            colorBuffer.resize(colorComponents, 0.0);

            auto calculateColor = [&](const PDFMesh::Triangle& triangle)
            {
                QPointF centerDS = mesh.getTriangleCenter(triangle);
                QPointF center = deviceSpaceToDomainMatrix.map(centerDS);

                std::array<PDFReal, 2> uv = { center.x(), center.y() };

                if (isSingleFunction)
                {
                    PDFFunction::FunctionResult result = m_functions.front()->apply(uv.data(), uv.data() + uv.size(), colorBuffer.data(), colorBuffer.data() + colorBuffer.size());
                    if (!result)
                    {
                        QMutexLocker lock(&functionErrorMutex);
                        if (!functionError)
                        {
                            functionError = result;
                        }
                    }
                }
                else
                {
                    for (size_t i = 0, count = colorComponents; i < count; ++i)
                    {
                        PDFFunction::FunctionResult result = m_functions[i]->apply(uv.data(), uv.data() + uv.size(), colorBuffer.data() + i, colorBuffer.data() + i + 1);
                        if (!result)
                        {
                            QMutexLocker lock(&functionErrorMutex);
                            if (!functionError)
                            {
                                functionError = result;
                            }
                        }
                    }
                }

                return m_colorSpace->getColor(PDFAbstractColorSpace::convertToColor(colorBuffer));
            };

            PDFMesh::Triangle triangle1;
            triangle1.v1 = static_cast<uint32_t>(v1);
            triangle1.v2 = static_cast<uint32_t>(v2);
            triangle1.v3 = static_cast<uint32_t>(v3);
            triangle1.color = calculateColor(triangle1).rgb();

            PDFMesh::Triangle triangle2;
            triangle2.v1 = static_cast<uint32_t>(v3);
            triangle2.v2 = static_cast<uint32_t>(v4);
            triangle2.v3 = static_cast<uint32_t>(v1);
            triangle2.color = calculateColor(triangle2).rgb();

            triangles[triangleIndex1] = triangle1;
            triangles[triangleIndex2] = triangle2;
        };
        std::for_each(std::execution::parallel_policy(), indices.cbegin(), indices.cend(), generateTriangle);
        mesh.setTriangles(qMove(triangles));

        if (!functionError)
        {
            throw PDFRendererException(RenderErrorType::Error, PDFTranslationContext::tr("Error occured during mesh generation of shading: %1").arg(functionError.errorMessage));
        }

        break;
    }

    if (m_backgroundColor.isValid())
    {
        QPainterPath backgroundPath;
        backgroundPath.addRect(settings.deviceSpaceMeshingArea);

        QPainterPath paintedPath;
        paintedPath.addPolygon(domainToDeviceSpaceMatrix.map(m_domain));

        backgroundPath = backgroundPath.subtracted(paintedPath);
        mesh.setBackgroundPath(backgroundPath);
        mesh.setBackgroundColor(m_backgroundColor);
    }

    // Create bounding path
    if (m_boundingBox.isValid())
    {
        QPainterPath boundingPath;
        boundingPath.addPolygon(settings.userSpaceToDeviceSpaceMatrix.map(m_boundingBox));
        mesh.setBoundingPath(boundingPath);
    }

    return mesh;
}

PDFMesh PDFAxialShading::createMesh(const PDFMeshQualitySettings& settings) const
{
    PDFMesh mesh;

    QPointF p1 = settings.userSpaceToDeviceSpaceMatrix.map(m_startPoint);
    QPointF p2 = settings.userSpaceToDeviceSpaceMatrix.map(m_endPoint);

    // Strategy: for simplification, we rotate the line clockwise so we will
    // get the shading axis equal to the x-axis. Then we will determine the shading
    // area and create mesh according the settings.
    QLineF line(p1, p2);
    const double angle = line.angleTo(QLineF(0, 0, 1, 0));

    // Matrix p1p2LCS is local coordinate system of line p1-p2. It transforms
    // points on the line to the global coordinate system. So, point (0, 0) will
    // map onto p1 and point (length(p1-p2), 0) will map onto p2.
    QMatrix p1p2LCS;
    p1p2LCS.translate(p1.x(), p1.y());
    p1p2LCS.rotate(angle);
    QMatrix p1p2GCS = p1p2LCS.inverted();

    QPointF p1m = p1p2GCS.map(p1);
    QPointF p2m = p1p2GCS.map(p2);

    Q_ASSERT(isZero(p1m.y()));
    Q_ASSERT(isZero(p2m.y()));
    Q_ASSERT(p1m.x() <= p2m.x());

    QPainterPath meshingArea;
    meshingArea.addPolygon(p1p2GCS.map(settings.deviceSpaceMeshingArea));
    meshingArea.addRect(p1m.x(), p1m.y() - settings.preferredMeshResolution * 0.5, p2m.x() - p1m.x(), settings.preferredMeshResolution);
    QRectF meshingRectangle = meshingArea.boundingRect();

    PDFReal xl = meshingRectangle.left();
    PDFReal xr = meshingRectangle.right();
    PDFReal yt = meshingRectangle.top();
    PDFReal yb = meshingRectangle.bottom();

    // Create coordinate array filled with stops, where we will determine the color
    std::vector<PDFReal> xCoords;
    xCoords.reserve((xr - xl) / settings.minimalMeshResolution + 3);
    xCoords.push_back(xl);
    for (PDFReal x = p1m.x(); x <= p2m.x(); x += settings.minimalMeshResolution)
    {
        if (!qFuzzyCompare(xCoords.back(), x))
        {
            xCoords.push_back(x);
        }
    }

    if (xCoords.back() + PDF_EPSILON < p2m.x())
    {
        xCoords.push_back(p2m.x());
    }

    if (!qFuzzyCompare(xCoords.back(), xr))
    {
        xCoords.push_back(xr);
    }

    const PDFReal tAtStart = m_domainStart;
    const PDFReal tAtEnd = m_domainEnd;
    const PDFReal tMin = qMin(tAtStart, tAtEnd);
    const PDFReal tMax = qMax(tAtStart, tAtEnd);

    const bool isSingleFunction = m_functions.size() == 1;
    std::vector<PDFReal> colorBuffer(m_colorSpace->getColorComponentCount(), 0.0);
    auto getColor = [this, isSingleFunction, &colorBuffer](PDFReal t) -> PDFColor
    {
        if (isSingleFunction)
        {
            PDFFunction::FunctionResult result = m_functions.front()->apply(&t, &t + 1, colorBuffer.data(), colorBuffer.data() + colorBuffer.size());
            if (!result)
            {
                throw PDFRendererException(RenderErrorType::Error, PDFTranslationContext::tr("Error occured during mesh creation of shading: %1").arg(result.errorMessage));
            }
        }
        else
        {
            for (size_t i = 0, count = colorBuffer.size(); i < count; ++i)
            {
                PDFFunction::FunctionResult result = m_functions[i]->apply(&t, &t + 1, colorBuffer.data() + i, colorBuffer.data() + i + 1);
                if (!result)
                {
                    throw PDFRendererException(RenderErrorType::Error, PDFTranslationContext::tr("Error occured during mesh creation of shading: %1").arg(result.errorMessage));
                }
            }
        }

        return PDFAbstractColorSpace::convertToColor(colorBuffer);
    };

    // Determine color of each coordinate
    std::vector<std::pair<PDFReal, PDFColor>> coloredCoordinates;
    coloredCoordinates.reserve(xCoords.size());

    for (PDFReal x : xCoords)
    {
        if (x < p1m.x() - PDF_EPSILON && !m_extendStart)
        {
            // Move to the next coordinate, this is skipped
            continue;
        }

        if (x > p2m.x() + PDF_EPSILON && !m_extendEnd)
        {
            // We are finished no more triangles will occur
            break;
        }

        // Determine current parameter t
        const PDFReal t = interpolate(x, p1m.x(), p2m.x(), tAtStart, tAtEnd);
        const PDFReal tBounded = qBound(tMin, t, tMax);
        const PDFColor color = getColor(tBounded);
        coloredCoordinates.emplace_back(x, color);
    }

    // Filter coordinates according the meshing criteria
    std::vector<std::pair<PDFReal, PDFColor>> filteredCoordinates;
    filteredCoordinates.reserve(coloredCoordinates.size());

    for (auto it = coloredCoordinates.cbegin(); it != coloredCoordinates.cend(); ++it)
    {
        // We will skip this coordinate, if both of meshing criteria have been met:
        //  1) Color difference is small (lesser than tolerance)
        //  2) Distance from previous and next point is less than preffered meshing resolution OR colors are equal

        if (it != coloredCoordinates.cbegin() && std::next(it) != coloredCoordinates.cend())
        {
            auto itNext = std::next(it);

            const std::pair<PDFReal, PDFColor>& prevItem = filteredCoordinates.back();
            const std::pair<PDFReal, PDFColor>& currentItem = *it;
            const std::pair<PDFReal, PDFColor>& nextItem = *itNext;

            if (currentItem.first != p1m.x() && currentItem.first != p2m.x())
            {
                if (prevItem.second == currentItem.second && currentItem.second == nextItem.second)
                {
                    // Colors are same, skip the test
                    continue;
                }

                if (PDFAbstractColorSpace::isColorEqual(prevItem.second, currentItem.second, settings.tolerance) &&
                        PDFAbstractColorSpace::isColorEqual(currentItem.second, nextItem.second, settings.tolerance) &&
                        PDFAbstractColorSpace::isColorEqual(prevItem.second, nextItem.second, settings.tolerance) &&
                        (nextItem.first - prevItem.first < settings.preferredMeshResolution))
                {
                    continue;
                }
            }
        }

        filteredCoordinates.push_back(*it);
    }

    if (!filteredCoordinates.empty())
    {
        size_t vertexCount = filteredCoordinates.size() * 2;
        size_t triangleCount = filteredCoordinates.size() * 2 - 2;

        if (m_backgroundColor.isValid())
        {
            vertexCount += 8;
            triangleCount += 4;
        }
        mesh.reserve(vertexCount, triangleCount);

        PDFColor previousColor = filteredCoordinates.front().second;
        uint32_t topLeft = mesh.addVertex(QPointF(filteredCoordinates.front().first, yt));
        uint32_t bottomLeft = mesh.addVertex(QPointF(filteredCoordinates.front().first, yb));
        for (auto it = std::next(filteredCoordinates.cbegin()); it != filteredCoordinates.cend(); ++it)
        {
            const std::pair<PDFReal, PDFColor>& item = *it;

            uint32_t topRight = mesh.addVertex(QPointF(item.first, yt));
            uint32_t bottomRight = mesh.addVertex(QPointF(item.first, yb));

            PDFColor mixedColor = PDFAbstractColorSpace::mixColors(previousColor, item.second, 0.5);
            QColor color = m_colorSpace->getColor(mixedColor);
            mesh.addQuad(topLeft, topRight, bottomRight, bottomLeft, color.rgb());

            topLeft = topRight;
            bottomLeft = bottomRight;
            previousColor = item.second;
        }
    }

    // Create background color triangles
    if (m_backgroundColor.isValid() && (!m_extendStart || !m_extendEnd))
    {
        if (!m_extendStart && xl + PDF_EPSILON < p1m.x())
        {
            uint32_t topLeft = mesh.addVertex(QPointF(xl, yt));
            uint32_t topRight = mesh.addVertex(QPointF(p1m.x(), yt));
            uint32_t bottomLeft = mesh.addVertex(QPointF(xl, yb));
            uint32_t bottomRight = mesh.addVertex(QPointF(p1m.x(), yb));
            mesh.addQuad(topLeft, topRight, bottomRight, bottomLeft, m_backgroundColor.rgb());
        }

        if (!m_extendEnd && p2m.x() + PDF_EPSILON < xr)
        {
            uint32_t topRight = mesh.addVertex(QPointF(xr, yt));
            uint32_t topLeft = mesh.addVertex(QPointF(p2m.x(), yt));
            uint32_t bottomRight = mesh.addVertex(QPointF(xr, yb));
            uint32_t bottomLeft = mesh.addVertex(QPointF(p2m.x(), yb));
            mesh.addQuad(topLeft, topRight, bottomRight, bottomLeft, m_backgroundColor.rgb());
        }
    }

    // Transform mesh to the device space coordinates
    mesh.transform(p1p2LCS);

    // Create bounding path
    if (m_boundingBox.isValid())
    {
        QPainterPath boundingPath;
        boundingPath.addPolygon(settings.userSpaceToDeviceSpaceMatrix.map(m_boundingBox));
        mesh.setBoundingPath(boundingPath);
    }

    return mesh;
}

void PDFMesh::paint(QPainter* painter) const
{
    if (m_triangles.empty())
    {
        return;
    }

    painter->save();
    painter->setPen(Qt::NoPen);
    painter->setRenderHint(QPainter::Antialiasing, true);

    // Set the clipping area, if we have it
    if (!m_boundingPath.isEmpty())
    {
        painter->setClipPath(m_boundingPath, Qt::IntersectClip);
    }

    if (!m_backgroundPath.isEmpty() && m_backgroundColor.isValid())
    {
        painter->setBrush(QBrush(m_backgroundColor, Qt::SolidPattern));
        painter->drawPath(m_backgroundPath);
    }

    QColor color;

    // Draw all triangles
    for (const Triangle& triangle : m_triangles)
    {
        if (color != triangle.color)
        {
            painter->setPen(QColor(triangle.color));
            painter->setBrush(QBrush(triangle.color, Qt::SolidPattern));
            color = triangle.color;
        }

        std::array<QPointF, 3> triangleCorners = { m_vertices[triangle.v1], m_vertices[triangle.v2], m_vertices[triangle.v3] };
        painter->drawConvexPolygon(triangleCorners.data(), static_cast<int>(triangleCorners.size()));
    }

    painter->restore();
}

void PDFMesh::transform(const QMatrix& matrix)
{
    for (QPointF& vertex : m_vertices)
    {
        vertex = matrix.map(vertex);
    }

    m_boundingPath = matrix.map(m_boundingPath);
    m_backgroundPath = matrix.map(m_backgroundPath);
}

QPointF PDFMesh::getTriangleCenter(const PDFMesh::Triangle& triangle) const
{
    return (m_vertices[triangle.v1] + m_vertices[triangle.v2] + m_vertices[triangle.v3]) / 3.0;
}

void PDFMeshQualitySettings::initDefaultResolution()
{
    // We will take 0.5% percent of device space meshing area as minimal resolution (it is ~1.5 mm for
    // A4 page) and default resolution 4x number of that.

    Q_ASSERT(deviceSpaceMeshingArea.isValid());
    PDFReal size = qMax(deviceSpaceMeshingArea.width(), deviceSpaceMeshingArea.height());
    minimalMeshResolution = size * 0.005;
    preferredMeshResolution = minimalMeshResolution * 4;
}

ShadingType PDFRadialShading::getShadingType() const
{
    return ShadingType::Radial;
}

PDFMesh PDFRadialShading::createMesh(const PDFMeshQualitySettings& settings) const
{
    PDFMesh mesh;

    QPointF p1 = settings.userSpaceToDeviceSpaceMatrix.map(m_startPoint);
    QPointF p2 = settings.userSpaceToDeviceSpaceMatrix.map(m_endPoint);

    QPointF r1TestPoint = settings.userSpaceToDeviceSpaceMatrix.map(QPointF(m_startPoint.x(), m_startPoint.y() + m_r0));
    QPointF r2TestPoint = settings.userSpaceToDeviceSpaceMatrix.map(QPointF(m_endPoint.x(), m_endPoint.y() + m_r1));

    const PDFReal r1 = QLineF(p1, r1TestPoint).length();
    const PDFReal r2 = QLineF(p2, r2TestPoint).length();

    // Strategy: for simplification, we rotate the line clockwise so we will
    // get the shading axis equal to the x-axis. Then we will determine the shading
    // area and create mesh according the settings.
    QLineF line(p1, p2);
    const double angle = line.angleTo(QLineF(0, 0, 1, 0));

    // Matrix p1p2LCS is local coordinate system of line p1-p2. It transforms
    // points on the line to the global coordinate system. So, point (0, 0) will
    // map onto p1 and point (length(p1-p2), 0) will map onto p2.
    QMatrix p1p2LCS;
    p1p2LCS.translate(p1.x(), p1.y());
    p1p2LCS.rotate(angle);
    QMatrix p1p2GCS = p1p2LCS.inverted();

    QPointF p1m = p1p2GCS.map(p1);
    QPointF p2m = p1p2GCS.map(p2);

    Q_ASSERT(isZero(p1m.y()));
    Q_ASSERT(isZero(p2m.y()));
    Q_ASSERT(p1m.x() <= p2m.x());

    QPainterPath meshingArea;
    meshingArea.addPolygon(p1p2GCS.map(settings.deviceSpaceMeshingArea));
    QRectF meshingRectangle = meshingArea.boundingRect();

    PDFReal xl = p1m.x();
    PDFReal xr = p2m.x();

    if (m_extendStart)
    {
        // Well, we must calculate the "zero" point, i.e. when starting radius become zero.
        // It will happen, when r1 < r2, if r1 >= r2, then radius never become zero. We also
        // bound the start by target draw area. We have line between points:
        //
        //  Line: (x1, r1) to (x2, r2)
        // and we will calculate intersection with x axis. If we found intersection points, which
        // is on the left side, then we

        if (r1 > r2)
        {
            xl = meshingRectangle.left() - 2 * r1;
        }
        else
        {
            QLineF radiusInterpolationLine(p1m.x(), r1, p2m.x(), r2);
            QLineF xAxisLine(p1m.x(), 0, p2m.x(), 0);

            QPointF intersectionPoint;
            if (radiusInterpolationLine.intersect(xAxisLine, &intersectionPoint) != QLineF::NoIntersection)
            {
                xl = qBound(meshingRectangle.left() - r1, intersectionPoint.x(), xl);
            }
            else
            {
                xl = meshingRectangle.left() - 2 * r1;
            }
        }
    }

    if (m_extendEnd)
    {
        // Similar as in previous case, find the "zero" point, i.e. when ending radius become zero.

        if (r1 < r2)
        {
            xr = meshingRectangle.right() + 2 * r2;
        }
        else
        {
            QLineF radiusInterpolationLine(p1m.x(), r1, p2m.x(), r2);
            QLineF xAxisLine(p1m.x(), 0, p2m.x(), 0);

            QPointF intersectionPoint;
            if (radiusInterpolationLine.intersect(xAxisLine, &intersectionPoint) != QLineF::NoIntersection)
            {
                xr = qBound(xr, intersectionPoint.x(), meshingRectangle.right() + r2);
            }
            else
            {
                xr = meshingRectangle.right() + 2 * r2;
            }
        }
    }

    // Create coordinate array filled with stops, where we will determine the color
    std::vector<PDFReal> xCoords;
    xCoords.reserve((xr - xl) / settings.minimalMeshResolution + 3);
    xCoords.push_back(xl);
    for (PDFReal x = p1m.x(); x <= p2m.x(); x += settings.minimalMeshResolution)
    {
        if (!qFuzzyCompare(xCoords.back(), x))
        {
            xCoords.push_back(x);
        }
    }

    if (xCoords.back() + PDF_EPSILON < p2m.x())
    {
        xCoords.push_back(p2m.x());
    }

    if (!qFuzzyCompare(xCoords.back(), xr))
    {
        xCoords.push_back(xr);
    }

    const PDFReal tAtStart = m_domainStart;
    const PDFReal tAtEnd = m_domainEnd;
    const PDFReal tMin = qMin(tAtStart, tAtEnd);
    const PDFReal tMax = qMax(tAtStart, tAtEnd);

    const bool isSingleFunction = m_functions.size() == 1;
    std::vector<PDFReal> colorBuffer(m_colorSpace->getColorComponentCount(), 0.0);
    auto getColor = [this, isSingleFunction, &colorBuffer](PDFReal t) -> PDFColor
    {
        if (isSingleFunction)
        {
            PDFFunction::FunctionResult result = m_functions.front()->apply(&t, &t + 1, colorBuffer.data(), colorBuffer.data() + colorBuffer.size());
            if (!result)
            {
                throw PDFRendererException(RenderErrorType::Error, PDFTranslationContext::tr("Error occured during mesh creation of shading: %1").arg(result.errorMessage));
            }
        }
        else
        {
            for (size_t i = 0, count = colorBuffer.size(); i < count; ++i)
            {
                PDFFunction::FunctionResult result = m_functions[i]->apply(&t, &t + 1, colorBuffer.data() + i, colorBuffer.data() + i + 1);
                if (!result)
                {
                    throw PDFRendererException(RenderErrorType::Error, PDFTranslationContext::tr("Error occured during mesh creation of shading: %1").arg(result.errorMessage));
                }
            }
        }

        return PDFAbstractColorSpace::convertToColor(colorBuffer);
    };

    // Determine color of each coordinate
    std::vector<std::pair<PDFReal, PDFColor>> coloredCoordinates;
    coloredCoordinates.reserve(xCoords.size());

    for (PDFReal x : xCoords)
    {
        // Determine current parameter t
        const PDFReal t = interpolate(x, p1m.x(), p2m.x(), tAtStart, tAtEnd);
        const PDFReal tBounded = qBound(tMin, t, tMax);
        const PDFColor color = getColor(tBounded);
        coloredCoordinates.emplace_back(x, color);
    }

    // Filter coordinates according the meshing criteria
    std::vector<std::pair<PDFReal, PDFColor>> filteredCoordinates;
    filteredCoordinates.reserve(coloredCoordinates.size());

    for (auto it = coloredCoordinates.cbegin(); it != coloredCoordinates.cend(); ++it)
    {
        // We will skip this coordinate, if both of meshing criteria have been met:
        //  1) Color difference is small (lesser than tolerance)
        //  2) Distance from previous and next point is less than preffered meshing resolution OR colors are equal

        if (it != coloredCoordinates.cbegin() && std::next(it) != coloredCoordinates.cend())
        {
            auto itNext = std::next(it);

            const std::pair<PDFReal, PDFColor>& prevItem = filteredCoordinates.back();
            const std::pair<PDFReal, PDFColor>& currentItem = *it;
            const std::pair<PDFReal, PDFColor>& nextItem = *itNext;

            if (currentItem.first != p1m.x() && currentItem.first != p2m.x())
            {
                if (prevItem.second == currentItem.second && currentItem.second == nextItem.second)
                {
                    // Colors are same, skip the test
                    continue;
                }

                if (PDFAbstractColorSpace::isColorEqual(prevItem.second, currentItem.second, settings.tolerance) &&
                        PDFAbstractColorSpace::isColorEqual(currentItem.second, nextItem.second, settings.tolerance) &&
                        PDFAbstractColorSpace::isColorEqual(prevItem.second, nextItem.second, settings.tolerance) &&
                        (nextItem.first - prevItem.first < settings.preferredMeshResolution))
                {
                    continue;
                }
            }
        }

        filteredCoordinates.push_back(*it);
    }

    if (!filteredCoordinates.empty())
    {
        constexpr const int SLICES = 120;

        size_t vertexCount = filteredCoordinates.size() * SLICES * 4;
        size_t triangleCount = filteredCoordinates.size() * SLICES * 2;

        if (m_backgroundColor.isValid())
        {
            vertexCount += 4;
            triangleCount += 2;
        }
        mesh.reserve(vertexCount, triangleCount);

        // Create background color triangles
        if (m_backgroundColor.isValid())
        {
            uint32_t topLeft = mesh.addVertex(meshingRectangle.topLeft());
            uint32_t topRight = mesh.addVertex(meshingRectangle.topRight());
            uint32_t bottomLeft = mesh.addVertex(meshingRectangle.bottomRight());
            uint32_t bottomRight = mesh.addVertex(meshingRectangle.bottomLeft());
            mesh.addQuad(topLeft, topRight, bottomRight, bottomLeft, m_backgroundColor.rgb());
        }

        // Create radial shading triangles
        QLineF rLine(QPointF(p1m.x(), r1), QPointF(p2m.x(), r2));
        const PDFReal rlength = rLine.length();

        for (auto it = std::next(filteredCoordinates.cbegin()); it != filteredCoordinates.cend(); ++it)
        {
            const std::pair<PDFReal, PDFColor>& leftItem = *std::prev(it);
            const std::pair<PDFReal, PDFColor>& rightItem = *it;

            const PDFReal x0 = leftItem.first;
            const PDFReal x1 = rightItem.first;
            const PDFColor mixedColor = PDFAbstractColorSpace::mixColors(leftItem.second, rightItem.second, 0.5);
            const PDFReal angleStep = 2 * M_PI / SLICES;
            const PDFReal r0 = rLine.pointAt((x0 - p1m.x()) / rlength).y();
            const PDFReal r1 = rLine.pointAt((x1 - p1m.x()) / rlength).y();

            PDFReal angle0 = 0;
            for (int i = 0; i < SLICES; ++i)
            {
                const PDFReal angle1 = angle0 + angleStep;
                const PDFReal cos0 = std::cos(angle0);
                const PDFReal sin0 = std::sin(angle0);
                const PDFReal cos1 = std::cos(angle1);
                const PDFReal sin1 = std::sin(angle1);

                QPointF p1(x0 + cos0 * r0, sin0 * r0);
                QPointF p2(x1 + cos0 * r1, sin0 * r1);
                QPointF p3(x1 + cos1 * r1, sin1 * r1);
                QPointF p4(x0 + cos1 * r0, sin1 * r0);

                uint32_t v1 = mesh.addVertex(p1);
                uint32_t v2 = mesh.addVertex(p2);
                uint32_t v3 = mesh.addVertex(p3);
                uint32_t v4 = mesh.addVertex(p4);

                QColor color = m_colorSpace->getColor(mixedColor);
                mesh.addQuad(v1, v2, v3, v4, color.rgb());

                angle0 = angle1;
            }
        }
    }

    // Transform mesh to the device space coordinates
    mesh.transform(p1p2LCS);

    // Create bounding path
    if (m_boundingBox.isValid())
    {
        QPainterPath boundingPath;
        boundingPath.addPolygon(settings.userSpaceToDeviceSpaceMatrix.map(m_boundingBox));
        mesh.setBoundingPath(boundingPath);
    }

    return mesh;
}

// TODO: Apply graphic state of the pattern
// TODO: Implement settings of meshing in the settings dialog

}   // namespace pdf