tempo_analyzer.h

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#pragma once
 
#include "fl/audio/audio_detector.h"
#include "fl/audio/silence_envelope.h"
#include "fl/math/filter/filter.h"
#include "fl/stl/function.h"
#include "fl/stl/vector.h"
#include "fl/stl/deque.h"
#include "fl/stl/noexcept.h"
 
namespace fl {
namespace audio {
namespace detector {
 
class TempoAnalyzer : public Detector {
public:
    TempoAnalyzer() FL_NOEXCEPT;
    ~TempoAnalyzer() FL_NOEXCEPT override;
 
    void update(shared_ptr<Context> context) override;
    void fireCallbacks() override;
    bool needsFFT() const override { return true; }
    bool needsFFTHistory() const override { return true; }
    const char* getName() const override { return "TempoAnalyzer"; }
    void reset() override;
 
    // Callbacks (multiple listeners supported)
    function_list<void(float bpm)> onTempo;
    function_list<void(float bpm, float confidence)> onTempoWithConfidence;
    function_list<void(float bpm)> onTempoChange;
    function_list<void()> onTempoStable;
    function_list<void()> onTempoUnstable;
 
    // State access
    float getBPM() const { return mCurrentBPM; }
    float getConfidence() const { return mConfidence; }
    bool isStable() const { return mIsStable; }
    float getStability() const { return mStability; }
 
    // Configuration
    void setMinBPM(float minBPM) { mMinBPM = minBPM; }
    void setMaxBPM(float maxBPM) { mMaxBPM = maxBPM; }
    void setStabilityThreshold(float threshold) { mStabilityThreshold = threshold; }
 
    // Scoring (public for testability)
    float calculateIntervalScore(u32 interval);
 
private:
    // Current tempo state
    float mCurrentBPM;
    float mConfidence;
    bool mIsStable;
    float mStability;
    float mMinBPM;
    float mMaxBPM;
    float mStabilityThreshold;
 
    // Tempo hypothesis tracking
    struct TempoHypothesis {
        float bpm;
        float score;
        u32 lastOnsetTime;
        u32 onsetCount;
    };
    vector<TempoHypothesis> mHypotheses;
    static constexpr size MAX_HYPOTHESES = 5;
 
    // Onset detection state
    deque<u32> mOnsetTimes;
    static constexpr size MAX_ONSET_HISTORY = 50;
    vector<float> mPreviousMagnitudes;  // Per-bin magnitudes for spectral flux
    float mPreviousFlux;                // Previous frame's total flux (for threshold)
    float mAdaptiveThreshold;
    MovingAverage<float, 43> mFluxAvg;
    static constexpr size FLUX_HISTORY_SIZE = 43;  // ~1 second at 43fps
 
    // Callback state tracking
    bool mWasStable = false;
    bool mBpmChanged = false;
    float mPreviousBPM = 120.0f;
 
    // Stability tracking (MedianFilter rejects half/double-tempo outliers)
    MedianFilter<float, 21> mBPMMedian;
    deque<float> mBPMHistory;
    static constexpr size BPM_HISTORY_SIZE = 20;
    u32 mStableFrameCount;
    static constexpr u32 STABLE_FRAMES_REQUIRED = 10;
 
    // Tempo range constraints
    static constexpr u32 MIN_BEAT_INTERVAL_MS = 250;  // Max 240 BPM
    static constexpr u32 MAX_BEAT_INTERVAL_MS = 2000; // Min 30 BPM
 
    shared_ptr<const fft::Bins> mRetainedFFT;
 
    // Silence gate for confidence. Decays confidence (not BPM) toward 0 with
    // tau ~2s during silence; the BPM estimate itself is preserved so that
    // when audio returns, beat sync resumes from the same tempo. Musical tempo
    // has natural persistence — snapping too fast feels wrong to users.
    SilenceEnvelope mConfidenceEnvelope;
 
    // Timestamp of the previous update() call, used to compute dt for the
    // envelope. Zero means "no previous frame" and the envelope skips decay
    // for that one-off call.
    u32 mPrevTimestamp = 0;
    bool mHasPrevTimestamp = false;
 
    // Internal methods
    float calculateSpectralFlux(const fft::Bins& fft);
    void updateAdaptiveThreshold();
    bool detectOnset(u32 timestamp);
    void updateHypotheses(u32 timestamp);
    void pruneHypotheses();
    void updateCurrentTempo();
    void updateStability();
    float calculateTempoConfidence(const TempoHypothesis& hyp);
};
 
} // namespace detector
} // namespace audio
} // namespace fl