note: land the programmed capture-signal model — division ladder, tempo resolution, anchored offsets, one record and one resolver

src/core/instrument/note/tempo.h

@@ -0,0 +1,37 @@
+// tempo — a validated project tempo and every beats <-> seconds <-> ms conversion a
+// beat-denominated capture value resolves through.
+//
+// A BEAT IS A QUARTER NOTE — REAPER states project tempo in quarter notes per minute
+// regardless of time signature, so a division resolves without one.
+
+#pragma once
+
+#include <optional>
+
+namespace reasampler::instrument::note {
+
+inline constexpr double kMsPerSecond = 1000.0;
+
+constexpr double msToSeconds(double ms) { return ms / kMsPerSecond; }
+constexpr double secondsToMs(double seconds) { return seconds * kMsPerSecond; }
+
+class Tempo {
+public:
+    // The only place a bad BPM is rejected, which is what lets every conversion below be
+    // total — no resolver downstream needs a failure path.
+    static std::optional<Tempo> fromBpm(double beatsPerMinute);
+
+    double bpm() const { return bpm_; }
+    double secondsPerBeat() const;
+
+    double beatsToSeconds(double beats) const;
+    double secondsToBeats(double seconds) const;
+    double beatsToMs(double beats) const;
+    double msToBeats(double ms) const;
+
+private:
+    explicit Tempo(double beatsPerMinute) : bpm_(beatsPerMinute) {}
+    double bpm_;
+};
+
+}  // namespace reasampler::instrument::note