Difference.h

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#pragma once

#include "filter/IFilter.h"
#include <algorithm>

namespace ai {

class Difference: public IFilter {
public:
    FILTER_ACTION_CLASS(Difference)
    FILTER_ACTION_FACTORY(Difference)

    void filter (const AIPtr& entity) override;
};

inline void Difference::filter (const AIPtr& entity) {
    FilteredEntities& filtered = getFilteredEntities(entity);
    // create a copy
    const FilteredEntities alreadyFiltered = filtered;
    // now clear the entity list
    filtered.clear();

    std::vector<FilteredEntities> filteredArray(_filters.size());
    int n = 0;
    size_t max = 0u;
    for (auto& f : _filters) {
        f->filter(entity);
        filteredArray[n++] = filtered;
        max = std::max(filtered.size(), max);
        // safe and clear
        filtered.clear();
    }

    for (size_t i = 0; i < filteredArray.size(); ++i) {
        std::sort(filteredArray[i].begin(), filteredArray[i].end());
    }

    FilteredEntities result(max);
    std::set_difference(
            filteredArray[0].begin(), filteredArray[0].end(),
            filteredArray[1].begin(), filteredArray[1].end(),
            std::back_inserter(result));

    if (filteredArray.size() >= 2) {
        FilteredEntities buffer(max);
        for (size_t i = 2; i < filteredArray.size(); ++i) {
            buffer.clear();
            std::sort(result.begin(), result.end());
            std::set_difference(
                    result.begin(), result.end(),
                    filteredArray[i].begin(), filteredArray[i].end(),
                    std::back_inserter(buffer));
            std::swap(result, buffer);
        }
    }

    filtered.reserve(alreadyFiltered.size() + max);
    for (auto& e : alreadyFiltered) {
        filtered.push_back(e);
    }
    for (auto& e : result) {
        filtered.push_back(e);
    }
}

}