project-kyoku/include/precisionevaluator.h

#ifndef PRECISIONEVALUATOR_H
#define PRECISIONEVALUATOR_H

#include <numeric>
#include <type_traits>
#include <vector>
#include <cmath>

#include <SFML/System/Clock.hpp>

using microsec = sf::Int64;

template<typename GRADE, typename = std::enable_if_t<std::is_enum<GRADE>::value>>
class PrecisionEvaluator
{
public:
    PrecisionEvaluator(const std::vector<microsec>& intervals, microsec offset) :
        _offset(offset),
        _intervals(intervals)
    {
        microsec&& handling_offset = std::accumulate(intervals.begin(), intervals.end(), 0);
        _start_handling_offset = _offset - handling_offset;
        _end_handling_offset = _offset + handling_offset;
    }

    inline microsec offset() const noexcept
    {
        return _offset;
    }

    inline bool isActive(microsec music_play_offset) const noexcept
    {
        return music_play_offset > _start_handling_offset
            && music_play_offset < _end_handling_offset;
    }

    inline GRADE calculatePrecision(microsec odds) const
    {
        microsec shift_from_perfect = std::abs(odds - offset());

        std::size_t raw_grade;
        for (raw_grade = 0; raw_grade < _intervals.size(); ++raw_grade)
        {
            if (shift_from_perfect <= _intervals.at(raw_grade))
                break;
        }

        return static_cast<GRADE>(raw_grade);
    }

private:
    microsec _offset;
    microsec _start_handling_offset;
    microsec _end_handling_offset;

    /* Amount of values in enum instanced as GRADES
     * represents capacity of _intervals.
     * So, for each V value in GRADES enum, _intervals[V]
     * should return time shift from V - 1.
     * V0 is PERFECT SCORE and the last V represents the worst
     * grades which is death of note by expiration */

    const std::vector<microsec>& _intervals;
};

#endif // PRECISIONEVALUATOR_H