Implement BPMCalculator for internal bpm calculation in level editor

include/tools/bpmcalculator.h

@@ -0,0 +1,23 @@
+#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);
+
+    void startListening(const microsec& offset);
+    void stopListening();
+
+    void click();
+    int getCurrentApproximation() const;
+
+private:
+    std::shared_ptr<Music> _music;
+    std::vector<microsec> _deltas;
+    microsec _previous_click_offset;
+};

include/tools/mathutils.h

@@ -1,4 +1,5 @@
 #pragma once
+
 #include <SFML/System/Clock.hpp>
 
 using microsec = sf::Int64;

src/tools/bpmcalculator.cpp

@@ -0,0 +1,54 @@
+#include "tools/bpmcalculator.h"
+#include <cmath>
+#include <numeric>
+#include <iostream>
+
+constexpr microsec MICROSECONDS_IN_MINUTE = 60000000;
+
+BPMCalculator::BPMCalculator(const std::shared_ptr<Music>& music) :
+    _music(music),
+    _previous_click_offset(0)
+{}
+
+void BPMCalculator::setMusic(const std::shared_ptr<Music>& music)
+{
+    _music = music;
+}
+
+void BPMCalculator::startListening(const microsec &offset)
+{
+    _deltas.clear();
+    _previous_click_offset = 0;
+    _music->setOffset(offset);
+    _music->play();
+}
+
+void BPMCalculator::stopListening()
+{
+    _music->stop();
+}
+
+void BPMCalculator::click()
+{
+    const microsec click_offset = _music->fetchOffset();
+
+    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;
+}
+
+int BPMCalculator::getCurrentApproximation() const
+{
+    const microsec sum = std::accumulate(_deltas.begin(), _deltas.end(), 0);
+
+    return (sum == 0)
+         ?  0.
+         :  static_cast<int>(static_cast<float>(MICROSECONDS_IN_MINUTE) / (static_cast<float>(sum) / static_cast<float>(_deltas.size())));
+}