#include <mbgl/tile/geometry_tile.hpp>
#include <mbgl/tile/tile_id.hpp>

namespace mbgl {

static double signedArea(const GeometryCoordinates& ring) {
    double sum = 0;

    for (std::size_t i = 0, len = ring.size(), j = len - 1; i < len; j = i++) {
        const GeometryCoordinate& p1 = ring[i];
        const GeometryCoordinate& p2 = ring[j];
        sum += (p2.x - p1.x) * (p1.y + p2.y);
    }

    return sum;
}

std::vector<GeometryCollection> classifyRings(const GeometryCollection& rings) {
    std::vector<GeometryCollection> polygons;

    std::size_t len = rings.size();

    if (len <= 1) {
        polygons.push_back(rings);
        return polygons;
    }

    GeometryCollection polygon;
    int8_t ccw = 0;

    for (std::size_t i = 0; i < len; i++) {
        double area = signedArea(rings[i]);

        if (area == 0)
            continue;

        if (ccw == 0)
            ccw = (area < 0 ? -1 : 1);

        if (ccw == (area < 0 ? -1 : 1) && !polygon.empty()) {
            polygons.push_back(polygon);
            polygon.clear();
        }

        polygon.push_back(rings[i]);
    }

    if (!polygon.empty())
        polygons.push_back(polygon);

    return polygons;
}

static Feature::geometry_type convertGeometry(const GeometryTileFeature& geometryTileFeature, const CanonicalTileID& tileID) {
    const double size = util::EXTENT * std::pow(2, tileID.z);
    const double x0 = util::EXTENT * tileID.x;
    const double y0 = util::EXTENT * tileID.y;

    auto tileCoordinatesToLatLng = [&] (const Point<int16_t>& p) {
        double y2 = 180 - (p.y + y0) * 360 / size;
        return Point<double>(
            (p.x + x0) * 360 / size - 180,
            360.0 / M_PI * std::atan(std::exp(y2 * M_PI / 180)) - 90.0
        );
    };

    GeometryCollection geometries = geometryTileFeature.getGeometries();

    switch (geometryTileFeature.getType()) {
        case FeatureType::Unknown: {
            assert(false);
            return Point<double>(NAN, NAN);
        }

        case FeatureType::Point: {
            MultiPoint<double> multiPoint;
            for (const auto& p : geometries.at(0)) {
                multiPoint.push_back(tileCoordinatesToLatLng(p));
            }
            if (multiPoint.size() == 1) {
                return multiPoint[0];
            } else {
                return multiPoint;
            }
        }

        case FeatureType::LineString: {
            MultiLineString<double> multiLineString;
            for (const auto& g : geometries) {
                LineString<double> lineString;
                for (const auto& p : g) {
                    lineString.push_back(tileCoordinatesToLatLng(p));
                }
                multiLineString.push_back(std::move(lineString));
            }
            if (multiLineString.size() == 1) {
                return multiLineString[0];
            } else {
                return multiLineString;
            }
        }

        case FeatureType::Polygon: {
            MultiPolygon<double> multiPolygon;
            for (const auto& pg : classifyRings(geometries)) {
                Polygon<double> polygon;
                for (const auto& r : pg) {
                    LinearRing<double> linearRing;
                    for (const auto& p : r) {
                        linearRing.push_back(tileCoordinatesToLatLng(p));
                    }
                    polygon.push_back(std::move(linearRing));
                }
                multiPolygon.push_back(std::move(polygon));
            }
            if (multiPolygon.size() == 1) {
                return multiPolygon[0];
            } else {
                return multiPolygon;
            }
        }
    }

    // Unreachable, but placate GCC.
    return Point<double>();
}

Feature convertFeature(const GeometryTileFeature& geometryTileFeature, const CanonicalTileID& tileID) {
    Feature feature { convertGeometry(geometryTileFeature, tileID) };
    feature.properties = geometryTileFeature.getProperties();
    feature.id = geometryTileFeature.getID();
    return feature;
}

} // namespace mbgl