//! Integrated loudness measurement in LUFS per ITU-R BS.1770-4.

/// Measure integrated LUFS loudness per ITU-R BS.1770-4.
/// Returns -70.0 for silence/near-silence where gating produces no result.
pub fn measure_lufs(samples: &[f32], sample_rate: u32) -> f64 {
    if samples.is_empty() || sample_rate == 0 {
        return -70.0;
    }
    let mut meter = bs1770::ChannelLoudnessMeter::new(sample_rate);
    meter.push(samples.iter().copied());
    let windows = meter.into_100ms_windows();
    let power = bs1770::gated_mean(windows.as_ref());
    let lkfs = power.loudness_lkfs() as f64;
    if lkfs.is_nan() || lkfs.is_infinite() {
        -70.0
    } else {
        lkfs
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn silence_is_very_quiet() {
        let silence = vec![0.0f32; 48000];
        let lufs = measure_lufs(&silence, 48000);
        // Silence should be extremely quiet (negative infinity or very low)
        assert!(lufs < -60.0, "silence LUFS should be < -60, got {lufs}");
    }

    #[test]
    fn loud_sine_is_near_zero() {
        let samples: Vec<f32> = (0..48000)
            .map(|i| (2.0 * std::f32::consts::PI * 1000.0 * i as f32 / 48000.0).sin())
            .collect();
        let lufs = measure_lufs(&samples, 48000);
        // A 1kHz full-scale sine should be around -3 LUFS
        assert!(
            lufs > -10.0 && lufs < 0.0,
            "full-scale sine LUFS should be near -3, got {lufs}"
        );
    }
}