// 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>
#include <type_traits>

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; }

// The largest magnitude, in beats or in milliseconds, the conversions below are required to
// keep finite. `fromBpm` validates against it and every caller caps its own domain to it, so
// the two halves of the totality claim meet at one number. Astronomically above anything
// musical — a billion milliseconds is eleven days — so nothing real is excluded.
inline constexpr double kMaxConvertibleMagnitude = 1e9;

class Tempo {
public:
    // Rejects rather than clamps, alone among this module's doors: an unusable BPM has no
    // nearest usable one to fall to. See this directory's CLAUDE.md for the rule.
    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_;
};

static_assert(!std::is_default_constructible_v<Tempo>,
              "Tempo must not be constructible without a validated BPM");
static_assert(!std::is_constructible_v<Tempo, double>,
              "fromBpm must be the only way to give a Tempo a value");

}  // namespace reasampler::instrument::note