//! Weld engine: aligns the phase of the main layer to a sidechain layer so the two sum
//! instead of cancel. Allocation-free after `new`; zero latency.
mod settings;
pub use settings::{Listen, Settings};

/// Levels for the editor, published a few times per second.
#[derive(Debug, Clone, Copy, PartialEq)]
pub struct AnalyzerFrame {
    /// RMS of the main input in dBFS since the last frame.
    pub main_db: f32,
    /// RMS of the sidechain input in dBFS since the last frame.
    pub side_db: f32,
    /// Peak of the sidechain input in dBFS since the last frame.
    pub side_peak_db: f32,
    /// True once any sidechain sample above −90 dBFS arrived since activation.
    pub side_seen: bool,
    pub sample_rate: f32,
}
impl Default for AnalyzerFrame {
    fn default() -> Self {
        Self {
            main_db: -120.,
            side_db: -120.,
            side_peak_db: -120.,
            side_seen: false,
            sample_rate: 48000.,
        }
    }
}

fn db(power_or_amp: f32, power: bool) -> f32 {
    let v = power_or_amp.max(1e-12);
    if power {
        10. * v.log10()
    } else {
        20. * v.log10()
    }
    .max(-120.)
}

#[derive(Default)]
struct Levels {
    main: f64,
    side: f64,
    peak: f32,
    count: usize,
}

pub struct Engine {
    rate: f32,
    channels: usize,
    settings: Settings,
    gain: f32,
    target_gain: f32,
    gain_coef: f32,
    fresh: bool,
    levels: Levels,
    side_seen: bool,
}
impl Engine {
    pub fn new(rate: f32, channels: usize) -> Result<Self, &'static str> {
        if !(rate.is_finite() && (8000.0..=768000.).contains(&rate)) {
            return Err("unsupported sample rate");
        }
        if !(1..=2).contains(&channels) {
            return Err("unsupported channel count");
        }
        Ok(Self {
            rate,
            channels,
            settings: Settings::default(),
            gain: 1.,
            target_gain: 1.,
            gain_coef: 1. - (-1. / (0.02 * rate)).exp(),
            fresh: true,
            levels: Levels::default(),
            side_seen: false,
        })
    }
    pub const fn latency_samples(&self) -> u32 {
        0
    }
    pub fn channels(&self) -> usize {
        self.channels
    }
    pub fn settings(&self) -> &Settings {
        &self.settings
    }
    pub fn set_settings(&mut self, settings: Settings) -> Result<(), &'static str> {
        settings.validate()?;
        self.settings = settings;
        self.target_gain = 10f32.powf(settings.output / 20.);
        if self.fresh {
            self.gain = self.target_gain;
            self.fresh = false;
        }
        Ok(())
    }
    pub fn reset(&mut self) {
        self.gain = self.target_gain;
        self.levels = Levels::default();
    }
    /// One frame of main input `x` and sidechain input `side`. Mono uses index 0 only.
    #[inline]
    pub fn process_sample(&mut self, x: [f32; 2], side: [f32; 2]) -> [f32; 2] {
        let n = self.channels;
        let (mut m, mut s) = (0f32, 0f32);
        for c in 0..n {
            m += x[c];
            s += side[c];
            self.levels.peak = self.levels.peak.max(side[c].abs());
        }
        m /= n as f32;
        s /= n as f32;
        self.levels.main += (m * m) as f64;
        self.levels.side += (s * s) as f64;
        self.levels.count += 1;
        if s.abs() > 3e-5 {
            self.side_seen = true;
        }
        self.gain += (self.target_gain - self.gain) * self.gain_coef;
        if self.settings.bypass {
            return x;
        }
        let mut out = [0.; 2];
        for c in 0..n {
            let layer = x[c];
            out[c] = self.gain
                * match self.settings.listen {
                    Listen::Layer => layer,
                    Listen::Sum => layer + side[c],
                    Listen::SumDry => x[c] + side[c],
                };
        }
        out
    }
    /// Levels since the previous call.
    pub fn take_analyzer(&mut self) -> AnalyzerFrame {
        let n = self.levels.count.max(1) as f64;
        let frame = AnalyzerFrame {
            main_db: db((self.levels.main / n) as f32, true),
            side_db: db((self.levels.side / n) as f32, true),
            side_peak_db: db(self.levels.peak, false),
            side_seen: self.side_seen,
            sample_rate: self.rate,
        };
        self.levels = Levels::default();
        frame
    }
}