project-kyoku/src/tools/bpmcalculator.cpp

#include "tools/bpmcalculator.h"
#include <cmath>
#include <numeric>
#include <iostream>

constexpr float MICROSECONDS_IN_MINUTE_f = 60000000.;

BPMCalculator::BPMCalculator(const std::shared_ptr<Music>& music) :
    _music(music)
{
    reset();
}

void BPMCalculator::reset()
{
    _calculating = false;
    _deltas.clear();
    _previous_click_offset = 0;
    _approximated_bpm = 0;
    _need_recalculate = true;
}

void BPMCalculator::setMusic(const std::shared_ptr<Music>& music)
{
    _music = music;
    reset();
}

std::shared_ptr<Music> BPMCalculator::music() const
{
    return _music;
}

void BPMCalculator::start()
{
    reset();

    _calculating = true;
}

void BPMCalculator::stop()
{
    _calculating = false;
}

void BPMCalculator::click()
{
    if (!_calculating)
        return;

    const microsec click_offset = _music->fetchOffset();
    _need_recalculate = true;

    if (_previous_click_offset == 0)
    {
        _previous_click_offset = click_offset;
        return;
    }

    const microsec delta = click_offset - _previous_click_offset;
    _deltas.emplace_back(delta);

    _previous_click_offset = click_offset;
}

float BPMCalculator::fetchCurrentBPMApproximation()
{
    if (!_need_recalculate)
        return _approximated_bpm;

    _need_recalculate = false;

    const microsec sum = std::accumulate(_deltas.begin(), _deltas.end(), 0);
    bool hasEnoughDeltas = _deltas.size() >= 8;

    _approximated_bpm = (!hasEnoughDeltas)
                      ?  0.
                      :  calculateBPM(sum, _deltas.size());

    return _approximated_bpm;
}

float BPMCalculator::calculateBPM(microsec all_microseconds, std::size_t beats_amount) const
{
    if (beats_amount == 0)
        return 0;

    float relation = static_cast<float>(all_microseconds)
                   / static_cast<float>(beats_amount);

    return static_cast<float>(1. / relation);
}

microsec BPMCalculator::getStartingOffset() const
{
    return _first_click_offset;
}

void BPMCalculator::setStartingOffset(microsec offset)
{
    _first_click_offset = offset;
}

void BPMCalculator::moveStartingOffsetBy(microsec shift)
{
    _first_click_offset += shift;
}

microsec BPMCalculator::fetchTimeUntilNextBeat()
{
    const microsec actual_offset = _music->fetchOffset() - _first_click_offset;

    return fetchBeatInterval() % actual_offset;
}

microsec BPMCalculator::fetchBeatInterval()
{
    return static_cast<microsec>(1. / fetchCurrentBPMApproximation());
}