#include <mbgl/layout/merge_lines.hpp>
#include <mbgl/layout/symbol_feature.hpp>

#include <boost/functional/hash.hpp>

namespace mbgl {
namespace util {

using Index = std::unordered_map<size_t, unsigned int>;

unsigned int mergeFromRight(std::vector<SymbolFeature> &features,
                            Index &rightIndex,
                            Index::iterator left,
                            size_t rightKey,
                            GeometryCollection &geom) {

    unsigned int index = left->second;
    rightIndex.erase(left);
    rightIndex[rightKey] = index;
    features[index].geometry[0].pop_back();
    features[index].geometry[0].insert(
        features[index].geometry[0].end(), geom[0].begin(), geom[0].end());
    geom[0].clear();
    return index;
}

unsigned int mergeFromLeft(std::vector<SymbolFeature> &features,
                           Index &leftIndex,
                           size_t leftKey,
                           Index::iterator right,
                           GeometryCollection &geom) {

    unsigned int index = right->second;
    leftIndex.erase(right);
    leftIndex[leftKey] = index;
    geom[0].pop_back();
    geom[0].insert(
        geom[0].end(), features[index].geometry[0].begin(), features[index].geometry[0].end());
    features[index].geometry[0].clear();
    std::swap(features[index].geometry[0], geom[0]);
    return index;
}

enum class Side {
    Left = false,
    Right = true,
};

size_t
getKey(const std::u16string& text, const GeometryCollection& geom, Side side) {
    const GeometryCoordinate& coord = side == Side::Right ? geom[0].back() : geom[0].front();

    auto hash = std::hash<std::u16string>()(text);
    boost::hash_combine(hash, coord.x);
    boost::hash_combine(hash, coord.y);
    return hash;
}

void mergeLines(std::vector<SymbolFeature> &features) {

    Index leftIndex;
    Index rightIndex;

    for (unsigned int k = 0; k < features.size(); k++) {
        SymbolFeature &feature = features[k];
        GeometryCollection &geometry = feature.geometry;

        if (!feature.text) {
            continue;
        }

        const auto leftKey = getKey(*feature.text, geometry, Side::Left);
        const auto rightKey = getKey(*feature.text, geometry, Side::Right);

        const auto left = rightIndex.find(leftKey);
        const auto right = leftIndex.find(rightKey);

        if ((left != rightIndex.end()) && (right != leftIndex.end()) &&
            (left->second != right->second)) {
            // found lines with the same text adjacent to both ends of the current line, merge all
            // three
            unsigned int j = mergeFromLeft(features, leftIndex, leftKey, right, geometry);
            unsigned int i =
                mergeFromRight(features, rightIndex, left, rightKey, features[j].geometry);

            leftIndex.erase(leftKey);
            rightIndex.erase(rightKey);
            rightIndex[getKey(*feature.text, features[i].geometry, Side::Right)] = i;

        } else if (left != rightIndex.end()) {
            // found mergeable line adjacent to the start of the current line, merge
            mergeFromRight(features, rightIndex, left, rightKey, geometry);

        } else if (right != leftIndex.end()) {
            // found mergeable line adjacent to the end of the current line, merge
            mergeFromLeft(features, leftIndex, leftKey, right, geometry);

        } else {
            // no adjacent lines, add as a new item
            leftIndex[leftKey] = k;
            rightIndex[rightKey] = k;
        }
    }
}

} // end namespace util
} // end namespace mbgl