//! Gain adjustment: apply a dB offset with clipping protection.

/// Apply a gain offset in dB to all samples, clamping to [-1.0, 1.0].
pub fn apply_gain(samples: &mut [f32], db: f64) {
    if samples.is_empty() || db == 0.0 || !db.is_finite() {
        return;
    }

    let scale = 10.0_f64.powf(db / 20.0) as f32;
    for sample in samples.iter_mut() {
        *sample = (*sample * scale).clamp(-1.0, 1.0);
    }
}

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

    #[test]
    fn gain_plus_6db() {
        let mut samples = vec![0.25, -0.25, 0.1];
        apply_gain(&mut samples, 6.0);
        // +6 dB ≈ 2x
        let scale = 10.0_f64.powf(6.0 / 20.0) as f32;
        assert!((samples[0] - 0.25 * scale).abs() < 0.001);
        assert!((samples[1] - (-0.25 * scale)).abs() < 0.001);
    }

    #[test]
    fn gain_minus_6db() {
        let mut samples = vec![1.0, -1.0, 0.5];
        apply_gain(&mut samples, -6.0);
        let scale = 10.0_f64.powf(-6.0 / 20.0) as f32;
        assert!((samples[0] - scale).abs() < 0.001);
    }

    #[test]
    fn gain_zero_is_noop() {
        let original = vec![0.5, -0.5, 0.25];
        let mut samples = original.clone();
        apply_gain(&mut samples, 0.0);
        assert_eq!(samples, original);
    }

    #[test]
    fn gain_clips_to_bounds() {
        let mut samples = vec![0.5, -0.5];
        apply_gain(&mut samples, 24.0); // +24 dB ≈ 15.85x, will clip
        assert_eq!(samples[0], 1.0);
        assert_eq!(samples[1], -1.0);
    }

    #[test]
    fn gain_empty() {
        let mut samples: Vec<f32> = vec![];
        apply_gain(&mut samples, 6.0);
        assert!(samples.is_empty());
    }
}