#include <mbgl/layout/symbol_layout.hpp>
#include <mbgl/layout/merge_lines.hpp>
#include <mbgl/layout/clip_lines.hpp>
#include <mbgl/renderer/bucket_parameters.hpp>
#include <mbgl/renderer/layers/render_symbol_layer.hpp>
#include <mbgl/renderer/image_atlas.hpp>
#include <mbgl/text/get_anchors.hpp>
#include <mbgl/text/shaping.hpp>
#include <mbgl/util/utf.hpp>
#include <mbgl/util/constants.hpp>
#include <mbgl/util/string.hpp>
#include <mbgl/util/i18n.hpp>
#include <mbgl/util/platform.hpp>
#include <mbgl/tile/geometry_tile_data.hpp>
#include <mbgl/tile/tile.hpp>

#include <mapbox/polylabel.hpp>

namespace mbgl {

using namespace style;

template <class Property>
static bool has(const style::SymbolLayoutProperties::PossiblyEvaluated& layout) {
    return layout.get<Property>().match(
        [] (const typename Property::Type& t) { return !t.empty(); },
        [] (const auto&) { return true; }
    );
}

namespace {
expression::Value sectionOptionsToValue(const SectionOptions& options) {
    std::unordered_map<std::string, expression::Value> result;
    // TODO: Data driven properties that can be overridden on per section basis.
    // TextOpacity
    // TextHaloColor
    // TextHaloWidth
    // TextHaloBlur
    if (options.textColor) {
        result.emplace(expression::kFormattedSectionTextColor, *options.textColor);
    }
    return result;
}

inline const SymbolLayerProperties& toSymbolLayerProperties(const Immutable<LayerProperties>& layer) {
    return static_cast<const SymbolLayerProperties&>(*layer);
}

inline Immutable<style::SymbolLayoutProperties::PossiblyEvaluated> createLayout(const SymbolLayoutProperties::Unevaluated& unevaluated, float zoom) {
    auto layout = makeMutable<style::SymbolLayoutProperties::PossiblyEvaluated>(unevaluated.evaluate(PropertyEvaluationParameters(zoom)));

    if (layout->get<IconRotationAlignment>() == AlignmentType::Auto) {
        if (layout->get<SymbolPlacement>() != SymbolPlacementType::Point) {
            layout->get<IconRotationAlignment>() = AlignmentType::Map;
        } else {
            layout->get<IconRotationAlignment>() = AlignmentType::Viewport;
        }
    }

    if (layout->get<TextRotationAlignment>() == AlignmentType::Auto) {
        if (layout->get<SymbolPlacement>() != SymbolPlacementType::Point) {
            layout->get<TextRotationAlignment>() = AlignmentType::Map;
        } else {
            layout->get<TextRotationAlignment>() = AlignmentType::Viewport;
        }
    }

    // If unspecified `*-pitch-alignment` inherits `*-rotation-alignment`
    if (layout->get<TextPitchAlignment>() == AlignmentType::Auto) {
        layout->get<TextPitchAlignment>() = layout->get<TextRotationAlignment>();
    }
    if (layout->get<IconPitchAlignment>() == AlignmentType::Auto) {
        layout->get<IconPitchAlignment>() = layout->get<IconRotationAlignment>();
    }

    return std::move(layout);
}

} // namespace

SymbolLayout::SymbolLayout(const BucketParameters& parameters,
                           const std::vector<Immutable<style::LayerProperties>>& layers,
                           std::unique_ptr<GeometryTileLayer> sourceLayer_,
                           ImageDependencies& imageDependencies,
                           GlyphDependencies& glyphDependencies)
    : bucketLeaderID(layers.front()->baseImpl->id),
      sourceLayer(std::move(sourceLayer_)),
      overscaling(parameters.tileID.overscaleFactor()),
      zoom(parameters.tileID.overscaledZ),
      mode(parameters.mode),
      pixelRatio(parameters.pixelRatio),
      tileSize(util::tileSize * overscaling),
      tilePixelRatio(float(util::EXTENT) / tileSize),
      textSize(toSymbolLayerProperties(layers.at(0)).layerImpl().layout.get<TextSize>()),
      iconSize(toSymbolLayerProperties(layers.at(0)).layerImpl().layout.get<IconSize>()),
      layout(createLayout(toSymbolLayerProperties(layers.at(0)).layerImpl().layout, zoom)) {
    const SymbolLayer::Impl& leader = toSymbolLayerProperties(layers.at(0)).layerImpl();

    const bool hasText = has<TextField>(*layout) && has<TextFont>(*layout);
    const bool hasIcon = has<IconImage>(*layout);

    if (!hasText && !hasIcon) {
        return;
    }

    const bool hasSymbolSortKey = !leader.layout.get<SymbolSortKey>().isUndefined();
    const auto symbolZOrder = layout->get<SymbolZOrder>();
    const bool sortFeaturesByKey = symbolZOrder != SymbolZOrderType::ViewportY && hasSymbolSortKey;
    const bool zOrderByViewportY = symbolZOrder == SymbolZOrderType::ViewportY || (symbolZOrder == SymbolZOrderType::Auto && !sortFeaturesByKey);
    sortFeaturesByY = zOrderByViewportY && (layout->get<TextAllowOverlap>() || layout->get<IconAllowOverlap>() ||
        layout->get<TextIgnorePlacement>() || layout->get<IconIgnorePlacement>());

    for (const auto& layer : layers) {
        layerPaintProperties.emplace(layer->baseImpl->id, layer);
    }

    // Determine glyph dependencies
    const size_t featureCount = sourceLayer->featureCount();
    for (size_t i = 0; i < featureCount; ++i) {
        auto feature = sourceLayer->getFeature(i);
        if (!leader.filter(expression::EvaluationContext { this->zoom, feature.get() }))
            continue;

        SymbolFeature ft(std::move(feature));

        ft.index = i;

        if (hasText) {
            auto formatted = layout->evaluate<TextField>(zoom, ft);
            auto textTransform = layout->evaluate<TextTransform>(zoom, ft);
            FontStack baseFontStack = layout->evaluate<TextFont>(zoom, ft);

            ft.formattedText = TaggedString();
            for (const auto & section : formatted.sections) {
                std::string u8string = section.text;
                if (textTransform == TextTransformType::Uppercase) {
                    u8string = platform::uppercase(u8string);
                } else if (textTransform == TextTransformType::Lowercase) {
                    u8string = platform::lowercase(u8string);
                }

                ft.formattedText->addSection(applyArabicShaping(util::convertUTF8ToUTF16(u8string)),
                                             section.fontScale ? *section.fontScale : 1.0,
                                             section.fontStack ? *section.fontStack : baseFontStack,
                                             section.textColor);
            }


            const bool canVerticalizeText = layout->get<TextRotationAlignment>() == AlignmentType::Map
                                         && layout->get<SymbolPlacement>() != SymbolPlacementType::Point
                                         && util::i18n::allowsVerticalWritingMode(ft.formattedText->rawText());

            // Loop through all characters of this text and collect unique codepoints.
            for (std::size_t j = 0; j < ft.formattedText->length(); j++) {
                const auto& sectionFontStack = formatted.sections[ft.formattedText->getSectionIndex(j)].fontStack;
                GlyphIDs& dependencies = glyphDependencies[sectionFontStack ? *sectionFontStack : baseFontStack];
                char16_t codePoint = ft.formattedText->getCharCodeAt(j);
                dependencies.insert(codePoint);
                if (canVerticalizeText) {
                    if (char16_t verticalChr = util::i18n::verticalizePunctuation(codePoint)) {
                        dependencies.insert(verticalChr);
                    }
                }
            }
        }

        if (hasIcon) {
            ft.icon = layout->evaluate<IconImage>(zoom, ft);
            imageDependencies.emplace(*ft.icon, ImageType::Icon);
        }

        if (ft.formattedText || ft.icon) {
            if (sortFeaturesByKey) {
                ft.sortKey = layout->evaluate<SymbolSortKey>(zoom, ft);
                const auto lowerBound = std::lower_bound(features.begin(), features.end(), ft);
                features.insert(lowerBound, std::move(ft));
            } else {
                features.push_back(std::move(ft));
            }
        }
    }

    if (layout->get<SymbolPlacement>() == SymbolPlacementType::Line) {
        util::mergeLines(features);
    }
}

bool SymbolLayout::hasDependencies() const {
    return features.size() != 0;
}

bool SymbolLayout::hasSymbolInstances() const {
    return !symbolInstances.empty();
}

namespace {

// The radial offset is to the edge of the text box
// In the horizontal direction, the edge of the text box is where glyphs start
// But in the vertical direction, the glyphs appear to "start" at the baseline
// We don't actually load baseline data, but we assume an offset of ONE_EM - 17
// (see "yOffset" in shaping.js)
const float baselineOffset = 7.0f;

// We don't care which shaping we get because this is used for collision purposes
// and all the justifications have the same collision box.
const Shaping& getDefaultHorizontalShaping(const ShapedTextOrientations& shapedTextOrientations) {
    if (shapedTextOrientations.right) return shapedTextOrientations.right;
    if (shapedTextOrientations.center) return shapedTextOrientations.center;
    if (shapedTextOrientations.left) return shapedTextOrientations.left;
    return shapedTextOrientations.horizontal;
}

Shaping& shapingForTextJustifyType(ShapedTextOrientations& shapedTextOrientations, style::TextJustifyType type) {
    switch(type) {
    case style::TextJustifyType::Right: return shapedTextOrientations.right;
    case style::TextJustifyType::Left: return shapedTextOrientations.left;
    case style::TextJustifyType::Center: return shapedTextOrientations.center;
    default:
        assert(false);
        return shapedTextOrientations.horizontal;
    }
}

}  // namespace

// static
Point<float> SymbolLayout::evaluateRadialOffset(SymbolAnchorType anchor, Point<float> radialOffset) {
    Point<float> result{};
    // solve for r where r^2 + r^2 = radialOffset^2
    const float sqrt2 = 1.41421356237f;
    const float hypotenuseX = radialOffset.x / sqrt2;
    const float hypotenuseY = radialOffset.y / sqrt2;

    switch (anchor) {
    case SymbolAnchorType::TopRight:
    case SymbolAnchorType::TopLeft:
        result.y = hypotenuseY - baselineOffset;
        break;
    case SymbolAnchorType::BottomRight:
    case SymbolAnchorType::BottomLeft:
        result.y = -hypotenuseY + baselineOffset;
        break;
    case SymbolAnchorType::Bottom:
        result.y = -radialOffset.y + baselineOffset;
        break;
    case SymbolAnchorType::Top:
        result.y = radialOffset.y - baselineOffset;
        break;
    default:
        break;
    }

    switch (anchor) {
    case SymbolAnchorType::TopRight:
    case SymbolAnchorType::BottomRight:
        result.x = -hypotenuseX;
        break;
    case SymbolAnchorType::TopLeft:
    case SymbolAnchorType::BottomLeft:
        result.x = hypotenuseX;
        break;
    case SymbolAnchorType::Left:
        result.x = radialOffset.x;
        break;
    case SymbolAnchorType::Right:
        result.x = -radialOffset.x;
        break;
    default:
        break;
    }

    return result;
}

namespace {

Point<float> handleRadialTextOffset(const std::vector<float>& value) {
    switch (value.size())
    {
    case 0:
        return { 0.0f, 0.0f };
    case 1:
        return { value[0] * util::ONE_EM, value[0] * util::ONE_EM };
    default:
        return { value[0] * util::ONE_EM, value[1] * util::ONE_EM };
    };
}

} // namespace

void SymbolLayout::prepareSymbols(const GlyphMap& glyphMap, const GlyphPositions& glyphPositions,
                           const ImageMap& imageMap, const ImagePositions& imagePositions) {
    const bool isPointPlacement = layout->get<SymbolPlacement>() == SymbolPlacementType::Point;
    const bool textAlongLine = layout->get<TextRotationAlignment>() == AlignmentType::Map && !isPointPlacement;

    for (auto it = features.begin(); it != features.end(); ++it) {
        auto& feature = *it;
        if (feature.geometry.empty()) continue;

        ShapedTextOrientations shapedTextOrientations;
        optional<PositionedIcon> shapedIcon;
        Point<float> textOffset;

        // if feature has text, shape the text
        if (feature.formattedText) {
            const float lineHeight = layout->get<TextLineHeight>() * util::ONE_EM;
            const float spacing = util::i18n::allowsLetterSpacing(feature.formattedText->rawText()) ? layout->evaluate<TextLetterSpacing>(zoom, feature) * util::ONE_EM : 0.0f;

            auto applyShaping = [&] (const TaggedString& formattedText, WritingModeType writingMode, SymbolAnchorType textAnchor, TextJustifyType textJustify) {
                const Shaping result = getShaping(
                    /* string */ formattedText,
                    /* maxWidth: ems */ isPointPlacement ? layout->evaluate<TextMaxWidth>(zoom, feature) * util::ONE_EM : 0.0f,
                    /* ems */ lineHeight,
                    textAnchor,
                    textJustify,
                    /* ems */ spacing,
                    /* translate */ textOffset,
                    /* writingMode */ writingMode,
                    /* bidirectional algorithm object */ bidi,
                    /* glyphs */ glyphMap);

                return result;
            };
            const std::vector<style::TextVariableAnchorType> variableTextAnchor = layout->evaluate<TextVariableAnchor>(zoom, feature);
            const Point<float> radialOffset = handleRadialTextOffset(layout->evaluate<TextRadialOffset>(zoom, feature));
            const SymbolAnchorType textAnchor = layout->evaluate<TextAnchor>(zoom, feature); 
            if (variableTextAnchor.empty()) {
                // Layers with variable anchors use the `text-radial-offset` property and the [x, y] offset vector
                // is calculated at placement time instead of layout time
                if (radialOffset.x > 0.0f && radialOffset.y > 0.0f) {
                    // The style spec says don't use `text-offset` and `text-radial-offset` together
                    // but doesn't actually specify what happens if you use both. We go with the radial offset.
                    textOffset = evaluateRadialOffset(textAnchor, radialOffset);
                } else {
                    textOffset = { layout->evaluate<TextOffset>(zoom, feature)[0] * util::ONE_EM,
                                   layout->evaluate<TextOffset>(zoom, feature)[1] * util::ONE_EM};
                }
            }
            TextJustifyType textJustify = textAlongLine ? TextJustifyType::Center : layout->evaluate<TextJustify>(zoom, feature);
             // If this layer uses text-variable-anchor, generate shapings for all justification possibilities.
            if (!textAlongLine && !variableTextAnchor.empty()) {
                std::vector<TextJustifyType> justifications;
                if (textJustify != TextJustifyType::Auto) {
                    justifications.push_back(textJustify);
                } else {
                    for (auto anchor : variableTextAnchor) {
                        justifications.push_back(getAnchorJustification(anchor));
                    }
                }
                for (TextJustifyType justification: justifications) {
                    Shaping& shapingForJustification = shapingForTextJustifyType(shapedTextOrientations, justification);
                    if (shapingForJustification) {
                        continue;
                    }
                    // If using text-variable-anchor for the layer, we use a center anchor for all shapings and apply
                    // the offsets for the anchor in the placement step.
                    Shaping shaping = applyShaping(*feature.formattedText, WritingModeType::Horizontal, SymbolAnchorType::Center, justification);
                    if (shaping) {
                        shapingForJustification = std::move(shaping);
                        if (shaping.lineCount == 1u) {
                            shapedTextOrientations.singleLine = true;
                            break;
                        }
                    }
                }
            } else {
                if (textJustify == TextJustifyType::Auto) {
                    textJustify = getAnchorJustification(textAnchor);
                }
                Shaping shaping = applyShaping(*feature.formattedText, WritingModeType::Horizontal, textAnchor, textJustify);
                if (shaping) {
                    shapedTextOrientations.horizontal = std::move(shaping);
                }

                if (util::i18n::allowsVerticalWritingMode(feature.formattedText->rawText()) && textAlongLine) {
                    feature.formattedText->verticalizePunctuation();
                    shapedTextOrientations.vertical = applyShaping(*feature.formattedText, WritingModeType::Vertical, textAnchor, textJustify);
                }
            }
        }

        // if feature has icon, get sprite atlas position
        if (feature.icon) {
            auto image = imageMap.find(*feature.icon);
            if (image != imageMap.end()) {
                shapedIcon = PositionedIcon::shapeIcon(
                    imagePositions.at(*feature.icon),
                    layout->evaluate<IconOffset>(zoom, feature),
                    layout->evaluate<IconAnchor>(zoom, feature),
                    layout->evaluate<IconRotate>(zoom, feature) * util::DEG2RAD);
                if (image->second->sdf) {
                    sdfIcons = true;
                }
                if (image->second->pixelRatio != pixelRatio) {
                    iconsNeedLinear = true;
                } else if (layout->get<IconRotate>().constantOr(1) != 0) {
                    iconsNeedLinear = true;
                }
            }
        }

        // if either shapedText or icon position is present, add the feature
        if (getDefaultHorizontalShaping(shapedTextOrientations) || shapedIcon) {
            addFeature(std::distance(features.begin(), it), feature, shapedTextOrientations, shapedIcon, glyphPositions, textOffset);
        }

        feature.geometry.clear();
    }

    compareText.clear();
}

void SymbolLayout::addFeature(const std::size_t layoutFeatureIndex,
                              const SymbolFeature& feature,
                              const ShapedTextOrientations& shapedTextOrientations,
                              const optional<PositionedIcon>& shapedIcon,
                              const GlyphPositions& glyphPositions,
                              Point<float> offset) {
    const float minScale = 0.5f;
    const float glyphSize = 24.0f;

    const float layoutTextSize = layout->evaluate<TextSize>(zoom + 1, feature);
    const float layoutIconSize = layout->evaluate<IconSize>(zoom + 1, feature);
    const std::array<float, 2> textOffset = {{ offset.x, offset.y }};

    const std::array<float, 2> iconOffset = layout->evaluate<IconOffset>(zoom, feature);

    // To reduce the number of labels that jump around when zooming we need
    // to use a text-size value that is the same for all zoom levels.
    // This calculates text-size at a high zoom level so that all tiles can
    // use the same value when calculating anchor positions.
    const float textMaxSize = layout->evaluate<TextSize>(18, feature);

    const float fontScale = layoutTextSize / glyphSize;
    const float textBoxScale = tilePixelRatio * fontScale;
    const float textMaxBoxScale = tilePixelRatio * textMaxSize / glyphSize;
    const float iconBoxScale = tilePixelRatio * layoutIconSize;
    const float symbolSpacing = tilePixelRatio * layout->get<SymbolSpacing>();
    const float textPadding = layout->get<TextPadding>() * tilePixelRatio;
    const float iconPadding = layout->get<IconPadding>() * tilePixelRatio;
    const float textMaxAngle = layout->get<TextMaxAngle>() * util::DEG2RAD;
    const float rotation = layout->evaluate<IconRotate>(zoom, feature);
    const Point<float> radialTextOffset = handleRadialTextOffset(layout->evaluate<TextRadialOffset>(zoom, feature));
    const SymbolPlacementType textPlacement = layout->get<TextRotationAlignment>() != AlignmentType::Map
                                                  ? SymbolPlacementType::Point
                                                  : layout->get<SymbolPlacement>();

    const float textRepeatDistance = symbolSpacing / 2;
    const auto evaluatedLayoutProperties = layout->evaluate(zoom, feature);
    IndexedSubfeature indexedFeature(feature.index, sourceLayer->getName(), bucketLeaderID, symbolInstances.size());

    auto addSymbolInstance = [&] (Anchor& anchor, std::shared_ptr<SymbolInstanceSharedData> sharedData) {
        assert(sharedData);
        const bool anchorInsideTile = anchor.point.x >= 0 && anchor.point.x < util::EXTENT && anchor.point.y >= 0 && anchor.point.y < util::EXTENT;

        if (mode == MapMode::Tile || anchorInsideTile) {
            // For static/continuous rendering, only add symbols anchored within this tile:
            //  neighboring symbols will be added as part of the neighboring tiles.
            // In tiled rendering mode, add all symbols in the buffers so that we can:
            //  (1) render symbols that overlap into this tile
            //  (2) approximate collision detection effects from neighboring symbols
            symbolInstances.emplace_back(anchor, std::move(sharedData), shapedTextOrientations, shapedIcon,
                    textBoxScale, textPadding, textPlacement, textOffset,
                    iconBoxScale, iconPadding, iconOffset, indexedFeature,
                    layoutFeatureIndex, feature.index,
                    feature.formattedText ? feature.formattedText->rawText() : std::u16string(),
                    overscaling, rotation, radialTextOffset);
        }
    };

    const auto createSymbolInstanceSharedData = [&] (GeometryCoordinates line) {
        return std::make_shared<SymbolInstanceSharedData>(std::move(line),
            shapedTextOrientations, shapedIcon, evaluatedLayoutProperties, layoutTextSize,
            textPlacement, textOffset, glyphPositions);
    };

    const auto& type = feature.getType();

    if (layout->get<SymbolPlacement>() == SymbolPlacementType::Line) {
        auto clippedLines = util::clipLines(feature.geometry, 0, 0, util::EXTENT, util::EXTENT);
        for (auto& line : clippedLines) {
            Anchors anchors = getAnchors(line,
                                         symbolSpacing,
                                         textMaxAngle,
                                         (shapedTextOrientations.vertical ?: getDefaultHorizontalShaping(shapedTextOrientations)).left,
                                         (shapedTextOrientations.vertical ?: getDefaultHorizontalShaping(shapedTextOrientations)).right,
                                         (shapedIcon ? shapedIcon->left() : 0),
                                         (shapedIcon ? shapedIcon->right() : 0),
                                         glyphSize,
                                         textMaxBoxScale,
                                         overscaling);
            auto sharedData = createSymbolInstanceSharedData(std::move(line));
            for (auto& anchor : anchors) {
                if (!feature.formattedText || !anchorIsTooClose(feature.formattedText->rawText(), textRepeatDistance, anchor)) {
                    addSymbolInstance(anchor, sharedData);
                }
            }
        }
    } else if (layout->get<SymbolPlacement>() == SymbolPlacementType::LineCenter) {
        // No clipping, multiple lines per feature are allowed
        // "lines" with only one point are ignored as in clipLines
        for (const auto& line : feature.geometry) {
            if (line.size() > 1) {
                optional<Anchor> anchor = getCenterAnchor(line,
                                                          textMaxAngle,
                                                          (shapedTextOrientations.vertical ?: getDefaultHorizontalShaping(shapedTextOrientations)).left,
                                                          (shapedTextOrientations.vertical ?: getDefaultHorizontalShaping(shapedTextOrientations)).right,
                                                          (shapedIcon ? shapedIcon->left() : 0),
                                                          (shapedIcon ? shapedIcon->right() : 0),
                                                          glyphSize,
                                                          textMaxBoxScale);
                if (anchor) {
                    addSymbolInstance(*anchor, createSymbolInstanceSharedData(line));
                }
            }
        }
    } else if (type == FeatureType::Polygon) {
        for (const auto& polygon : classifyRings(feature.geometry)) {
            Polygon<double> poly;
            for (const auto& ring : polygon) {
                LinearRing<double> r;
                for (const auto& p : ring) {
                    r.push_back(convertPoint<double>(p));
                }
                poly.push_back(r);
            }

            // 1 pixel worth of precision, in tile coordinates
            auto poi = mapbox::polylabel(poly, double(util::EXTENT / util::tileSize));
            Anchor anchor(poi.x, poi.y, 0, minScale);
            addSymbolInstance(anchor, createSymbolInstanceSharedData(polygon[0]));
        }
    } else if (type == FeatureType::LineString) {
        for (const auto& line : feature.geometry) {
            Anchor anchor(line[0].x, line[0].y, 0, minScale);
            addSymbolInstance(anchor, createSymbolInstanceSharedData(line));
        }
    } else if (type == FeatureType::Point) {
        for (const auto& points : feature.geometry) {
            for (const auto& point : points) {
                Anchor anchor(point.x, point.y, 0, minScale);
                addSymbolInstance(anchor, createSymbolInstanceSharedData({point}));
            }
        }
    }
}

bool SymbolLayout::anchorIsTooClose(const std::u16string& text, const float repeatDistance, const Anchor& anchor) {
    if (compareText.find(text) == compareText.end()) {
        compareText.emplace(text, Anchors());
    } else {
        auto otherAnchors = compareText.find(text)->second;
        for (const Anchor& otherAnchor : otherAnchors) {
            if (util::dist<float>(anchor.point, otherAnchor.point) < repeatDistance) {
                return true;
            }
        }
    }
    compareText[text].push_back(anchor);
    return false;
}

// Analog of `addToLineVertexArray` in JS. This version doesn't need to build up a line array like the
// JS version does, but it uses the same logic to calculate tile distances.
std::vector<float> CalculateTileDistances(const GeometryCoordinates& line, const Anchor& anchor) {
    std::vector<float> tileDistances(line.size());
    if (anchor.segment != -1) {
        auto sumForwardLength = util::dist<float>(anchor.point, line[anchor.segment + 1]);
        auto sumBackwardLength = util::dist<float>(anchor.point, line[anchor.segment]);
        for (size_t i = anchor.segment + 1; i < line.size(); i++) {
            tileDistances[i] = sumForwardLength;
            if (i < line.size() - 1) {
                sumForwardLength += util::dist<float>(line[i + 1], line[i]);
            }
        }
        for (auto i = anchor.segment; i >= 0; i--) {
            tileDistances[i] = sumBackwardLength;
            if (i > 0) {
                sumBackwardLength += util::dist<float>(line[i - 1], line[i]);
            }
        }
    }
    return tileDistances;
}

void SymbolLayout::createBucket(const ImagePositions&, std::unique_ptr<FeatureIndex>&, std::unordered_map<std::string, LayerRenderData>& renderData, const bool firstLoad, const bool showCollisionBoxes) {
    auto bucket = std::make_shared<SymbolBucket>(layout, layerPaintProperties, textSize, iconSize, zoom, sdfIcons, iconsNeedLinear, sortFeaturesByY, bucketLeaderID, std::move(symbolInstances), tilePixelRatio);

    for (SymbolInstance &symbolInstance : bucket->symbolInstances) {
        const bool hasText = symbolInstance.hasText;
        const bool hasIcon = symbolInstance.hasIcon;
        const bool singleLine = symbolInstance.singleLine;

        const auto& feature = features.at(symbolInstance.layoutFeatureIndex);

        // Insert final placement into collision tree and add glyphs/icons to buffers

        if (hasText && feature.formattedText) {
            optional<std::size_t> lastAddedSection;
            if (singleLine) {
                optional<std::size_t> placedTextIndex;
                lastAddedSection = addSymbolGlyphQuads(*bucket, symbolInstance, feature, symbolInstance.writingModes, placedTextIndex, symbolInstance.rightJustifiedGlyphQuads(), lastAddedSection);
                symbolInstance.placedRightTextIndex = placedTextIndex;
                symbolInstance.placedCenterTextIndex = placedTextIndex;
                symbolInstance.placedLeftTextIndex = placedTextIndex;
            } else {
                if (symbolInstance.rightJustifiedGlyphQuadsSize) {
                    lastAddedSection = addSymbolGlyphQuads(*bucket, symbolInstance, feature, symbolInstance.writingModes, symbolInstance.placedRightTextIndex, symbolInstance.rightJustifiedGlyphQuads(), lastAddedSection);
                }
                if (symbolInstance.centerJustifiedGlyphQuadsSize) {
                    lastAddedSection = addSymbolGlyphQuads(*bucket, symbolInstance, feature, symbolInstance.writingModes, symbolInstance.placedCenterTextIndex, symbolInstance.centerJustifiedGlyphQuads(), lastAddedSection);
                }
                if (symbolInstance.leftJustifiedGlyphQuadsSize) {
                    lastAddedSection = addSymbolGlyphQuads(*bucket, symbolInstance, feature, symbolInstance.writingModes, symbolInstance.placedLeftTextIndex, symbolInstance.leftJustifiedGlyphQuads(), lastAddedSection);
                }
            }
            if (symbolInstance.writingModes & WritingModeType::Vertical && symbolInstance.verticalGlyphQuadsSize) {
                lastAddedSection = addSymbolGlyphQuads(*bucket, symbolInstance, feature, WritingModeType::Vertical, symbolInstance.placedVerticalTextIndex, symbolInstance.verticalGlyphQuads(), lastAddedSection);
            }
            assert(lastAddedSection); // True, as hasText == true;
            updatePaintPropertiesForSection(*bucket, feature, *lastAddedSection);
        }

        if (hasIcon) {
            if (symbolInstance.hasIcon) {
                const Range<float> sizeData = bucket->iconSizeBinder->getVertexSizeData(feature);
                bucket->icon.placedSymbols.emplace_back(symbolInstance.anchor.point, symbolInstance.anchor.segment, sizeData.min, sizeData.max,
                        symbolInstance.iconOffset, WritingModeType::None, symbolInstance.line(), std::vector<float>());
                symbolInstance.placedIconIndex = bucket->icon.placedSymbols.size() - 1;
                PlacedSymbol& iconSymbol = bucket->icon.placedSymbols.back();
                iconSymbol.vertexStartIndex = addSymbol(bucket->icon, sizeData, *symbolInstance.iconQuad(),
                                                        symbolInstance.anchor, iconSymbol, feature.sortKey);

                for (auto& pair : bucket->paintProperties) {
                    pair.second.iconBinders.populateVertexVectors(feature, bucket->icon.vertices.elements(), {}, {});
                }
            }
        }
        symbolInstance.releaseSharedData();
    }

    if (showCollisionBoxes) {
        addToDebugBuffers(*bucket);
    }
    if (bucket->hasData()){
        for (const auto& pair : layerPaintProperties) {
            if (!firstLoad) {
                bucket->justReloaded = true;
            }
            renderData.emplace(pair.first, LayerRenderData{bucket, pair.second});
        }
    }

}

void SymbolLayout::updatePaintPropertiesForSection(SymbolBucket& bucket,
                                                   const SymbolFeature& feature,
                                                   std::size_t sectionIndex) {
    const auto& formattedSection = sectionOptionsToValue((*feature.formattedText).sectionAt(sectionIndex));
    for (auto& pair : bucket.paintProperties) {
        pair.second.textBinders.populateVertexVectors(feature, bucket.text.vertices.elements(), {}, {}, formattedSection);
    }
}

std::size_t SymbolLayout::addSymbolGlyphQuads(SymbolBucket& bucket,
                                              SymbolInstance& symbolInstance,
                                              const SymbolFeature& feature,
                                              WritingModeType writingMode,
                                              optional<size_t>& placedIndex,
                                              const SymbolQuads& glyphQuads,
                                              optional<std::size_t> lastAddedSection) {
    const Range<float> sizeData = bucket.textSizeBinder->getVertexSizeData(feature);
    const bool hasFormatSectionOverrides = bucket.hasFormatSectionOverrides();

    bucket.text.placedSymbols.emplace_back(symbolInstance.anchor.point, symbolInstance.anchor.segment, sizeData.min, sizeData.max,
            symbolInstance.textOffset, writingMode, symbolInstance.line(), CalculateTileDistances(symbolInstance.line(), symbolInstance.anchor));
    placedIndex = bucket.text.placedSymbols.size() - 1;
    PlacedSymbol& placedSymbol = bucket.text.placedSymbols.back();

    bool firstSymbol = true;
    for (const auto& symbolQuad : glyphQuads) {
        if (hasFormatSectionOverrides) {
            if (lastAddedSection && *lastAddedSection != symbolQuad.sectionIndex) {
                updatePaintPropertiesForSection(bucket, feature, *lastAddedSection);
            }
            lastAddedSection = symbolQuad.sectionIndex;
        }
        size_t index = addSymbol(bucket.text, sizeData, symbolQuad, symbolInstance.anchor, placedSymbol, feature.sortKey);
        if (firstSymbol) {
            placedSymbol.vertexStartIndex = index;
            firstSymbol = false;
        }
    }

    return lastAddedSection ? *lastAddedSection : 0u;
}

size_t SymbolLayout::addSymbol(SymbolBucket::Buffer& buffer,
                               const Range<float> sizeData,
                               const SymbolQuad& symbol,
                               const Anchor& labelAnchor,
                               PlacedSymbol& placedSymbol,
                               float sortKey) {
    constexpr const uint16_t vertexLength = 4;

    const auto &tl = symbol.tl;
    const auto &tr = symbol.tr;
    const auto &bl = symbol.bl;
    const auto &br = symbol.br;
    const auto &tex = symbol.tex;

    if (buffer.segments.empty() ||
        buffer.segments.back().vertexLength + vertexLength > std::numeric_limits<uint16_t>::max() ||
        fabs(buffer.segments.back().sortKey - sortKey) > std::numeric_limits<float>::epsilon()) {
        buffer.segments.emplace_back(buffer.vertices.elements(), buffer.triangles.elements(), 0ul, 0ul, sortKey);
    }

    // We're generating triangle fans, so we always start with the first
    // coordinate in this polygon.
    auto& segment = buffer.segments.back();
    assert(segment.vertexLength <= std::numeric_limits<uint16_t>::max());
    uint16_t index = segment.vertexLength;

    // coordinates (2 triangles)
    buffer.vertices.emplace_back(SymbolSDFIconProgram::layoutVertex(labelAnchor.point, tl, symbol.glyphOffset.y, tex.x, tex.y, sizeData));
    buffer.vertices.emplace_back(SymbolSDFIconProgram::layoutVertex(labelAnchor.point, tr, symbol.glyphOffset.y, tex.x + tex.w, tex.y, sizeData));
    buffer.vertices.emplace_back(SymbolSDFIconProgram::layoutVertex(labelAnchor.point, bl, symbol.glyphOffset.y, tex.x, tex.y + tex.h, sizeData));
    buffer.vertices.emplace_back(SymbolSDFIconProgram::layoutVertex(labelAnchor.point, br, symbol.glyphOffset.y, tex.x + tex.w, tex.y + tex.h, sizeData));

    // Dynamic/Opacity vertices are initialized so that the vertex count always agrees with
    // the layout vertex buffer, but they will always be updated before rendering happens
    auto dynamicVertex = SymbolSDFIconProgram::dynamicLayoutVertex(labelAnchor.point, 0);
    buffer.dynamicVertices.emplace_back(dynamicVertex);
    buffer.dynamicVertices.emplace_back(dynamicVertex);
    buffer.dynamicVertices.emplace_back(dynamicVertex);
    buffer.dynamicVertices.emplace_back(dynamicVertex);

    auto opacityVertex = SymbolSDFIconProgram::opacityVertex(1.0, 1.0);
    buffer.opacityVertices.emplace_back(opacityVertex);
    buffer.opacityVertices.emplace_back(opacityVertex);
    buffer.opacityVertices.emplace_back(opacityVertex);
    buffer.opacityVertices.emplace_back(opacityVertex);

    // add the two triangles, referencing the four coordinates we just inserted.
    buffer.triangles.emplace_back(index + 0, index + 1, index + 2);
    buffer.triangles.emplace_back(index + 1, index + 2, index + 3);

    segment.vertexLength += vertexLength;
    segment.indexLength += 6;

    placedSymbol.glyphOffsets.push_back(symbol.glyphOffset.x);

    return index;
}

void SymbolLayout::addToDebugBuffers(SymbolBucket& bucket) {

    if (!hasSymbolInstances()) {
        return;
    }

    for (const SymbolInstance &symbolInstance : symbolInstances) {
        auto populateCollisionBox = [&](const auto& feature) {
            SymbolBucket::CollisionBuffer& collisionBuffer = feature.alongLine ?
                static_cast<SymbolBucket::CollisionBuffer&>(bucket.getOrCreateCollisionCircleBuffer()) :
                static_cast<SymbolBucket::CollisionBuffer&>(bucket.getOrCreateCollisionBox());
            for (const CollisionBox &box : feature.boxes) {
                auto& anchor = box.anchor;

                Point<float> tl{box.x1, box.y1};
                Point<float> tr{box.x2, box.y1};
                Point<float> bl{box.x1, box.y2};
                Point<float> br{box.x2, box.y2};

                static constexpr std::size_t vertexLength = 4;
                const std::size_t indexLength = feature.alongLine ? 6 : 8;

                if (collisionBuffer.segments.empty() || collisionBuffer.segments.back().vertexLength + vertexLength > std::numeric_limits<uint16_t>::max()) {
                    collisionBuffer.segments.emplace_back(collisionBuffer.vertices.elements(),
                      feature.alongLine ? bucket.collisionCircle->triangles.elements() : bucket.collisionBox->lines.elements());
                }

                auto& segment = collisionBuffer.segments.back();
                uint16_t index = segment.vertexLength;

                collisionBuffer.vertices.emplace_back(CollisionBoxProgram::layoutVertex(anchor, symbolInstance.anchor.point, tl));
                collisionBuffer.vertices.emplace_back(CollisionBoxProgram::layoutVertex(anchor, symbolInstance.anchor.point, tr));
                collisionBuffer.vertices.emplace_back(CollisionBoxProgram::layoutVertex(anchor, symbolInstance.anchor.point, br));
                collisionBuffer.vertices.emplace_back(CollisionBoxProgram::layoutVertex(anchor, symbolInstance.anchor.point, bl));

                // Dynamic vertices are initialized so that the vertex count always agrees with
                // the layout vertex buffer, but they will always be updated before rendering happens
                auto dynamicVertex = CollisionBoxProgram::dynamicVertex(false, false, {});
                collisionBuffer.dynamicVertices.emplace_back(dynamicVertex);
                collisionBuffer.dynamicVertices.emplace_back(dynamicVertex);
                collisionBuffer.dynamicVertices.emplace_back(dynamicVertex);
                collisionBuffer.dynamicVertices.emplace_back(dynamicVertex);

                if (feature.alongLine) {
                    bucket.collisionCircle->triangles.emplace_back(index, index + 1, index + 2);
                    bucket.collisionCircle->triangles.emplace_back(index, index + 2, index + 3);
                } else {
                    bucket.collisionBox->lines.emplace_back(index + 0, index + 1);
                    bucket.collisionBox->lines.emplace_back(index + 1, index + 2);
                    bucket.collisionBox->lines.emplace_back(index + 2, index + 3);
                    bucket.collisionBox->lines.emplace_back(index + 3, index + 0);
                }

                segment.vertexLength += vertexLength;
                segment.indexLength += indexLength;
            }
        };
        populateCollisionBox(symbolInstance.textCollisionFeature);
        populateCollisionBox(symbolInstance.iconCollisionFeature);
    }
}

} // namespace mbgl