project-kyoku/include/tools/bpmcalculator.h

#pragma once

#include "tools/music.h"
#include <memory>
#include <vector>

class BPMCalculator
{
public:
    explicit BPMCalculator(const std::shared_ptr<Music>& music);

    void setMusic(const std::shared_ptr<Music>& music);
    std::shared_ptr<Music> music() const;

    void start();
    void stop();
    void click();
    float fetchCurrentBPMApproximation();

    microsec getStartingOffset() const;
    void setStartingOffset(microsec offset);
    void moveStartingOffsetBy(microsec shift);

    microsec fetchTimeUntilNextBeat();
    microsec fetchBeatInterval();

private:
    bool _need_recalculate;
    bool _calculating;

    std::shared_ptr<Music> _music;
    std::vector<microsec> _deltas;
    microsec _previous_click_offset;
    microsec _first_click_offset;

    int _approximated_bpm;

    inline float calculateBPM(microsec all_microseconds, std::size_t beats_amount) const;
    inline void reset();
};