use std::f64::consts::PI;

#[derive(Clone)]
pub struct Biquad {
    b0: f64,
    b1: f64,
    b2: f64,
    a1: f64,
    a2: f64,
    x1: f64,
    x2: f64,
    y1: f64,
    y2: f64,
}

impl Biquad {
    pub fn lowpass(sample_rate: f64, cutoff: f64, q: f64) -> Self {
        let omega = 2.0 * PI * cutoff / sample_rate;
        let sin_omega = omega.sin();
        let cos_omega = omega.cos();
        let alpha = sin_omega / (2.0 * q);

        let a0 = 1.0 + alpha;

        Self {
            b0: ((1.0 - cos_omega) / 2.0) / a0,
            b1: (1.0 - cos_omega) / a0,
            b2: ((1.0 - cos_omega) / 2.0) / a0,
            a1: (-2.0 * cos_omega) / a0,
            a2: (1.0 - alpha) / a0,
            x1: 0.0,
            x2: 0.0,
            y1: 0.0,
            y2: 0.0,
        }
    }

    pub fn highpass(sample_rate: f64, cutoff: f64, q: f64) -> Self {
        let omega = 2.0 * PI * cutoff / sample_rate;
        let sin_omega = omega.sin();
        let cos_omega = omega.cos();
        let alpha = sin_omega / (2.0 * q);

        let a0 = 1.0 + alpha;

        Self {
            b0: ((1.0 + cos_omega) / 2.0) / a0,
            b1: (-(1.0 + cos_omega)) / a0,
            b2: ((1.0 + cos_omega) / 2.0) / a0,
            a1: (-2.0 * cos_omega) / a0,
            a2: (1.0 - alpha) / a0,
            x1: 0.0,
            x2: 0.0,
            y1: 0.0,
            y2: 0.0,
        }
    }
}