//! Sub anchor: replaces the band below the split with a clean mono sine that follows the
//! bass pitch, holds one level for every note and restarts at the same phase on each note.
//!
//! The audio path is delayed by a fixed lookahead. Detection runs on the undelayed input, so
//! a note's pitch is known before its delayed attack leaves the plugin, and the sine starts
//! exactly on that attack.
//!
//! Ghost harmonics add the sub's own harmonics above a chosen frequency, so the note
//! reads on speakers without sub. The band above the split is measured per harmonic and
//! only the harmonics the patch lacks are filled: a harmonic the patch already has would
//! meet the added one at an unrelated phase and could cancel.
//!
//! The sine only plays while the note is sure. While tracking is unsure, the original sub
//! comes back in its place (Replace) or the added sine fades out (Enhance), so a wrong guess
//! never plays a wrong sub note.
//!
//! Kick lock reads the kick from the sidechain. Hits are found on the undelayed sidechain,
//! so with the lookahead each hit ducks the sub exactly when the delayed kick plays, and
//! restarts the sub's phase at the kick plus an offset, also before the kick. The audition
//! plays each offset of a sweep for a few kicks and measures how kick and sub sum in the
//! low band for each one; what sums loudest is not always what sounds like one hit.
mod settings;
use common_dsp::meter::HarmonicMeter;
use common_dsp::svf::{Svf, SvfCoef};
use common_dsp::tracker::{Fallback, NoteEvent, Tracker, TrackerConfig};
use common_dsp::{coefficient, db_to_gain, hz_to_midi, midi_to_hz, Biquad, Crossover};
pub use settings::{Mode, Settings, Source, KICK_OFFSET_MAX};
use std::f32::consts::TAU;

/// Detectable fundamental range. The lowest sets the lookahead (two periods).
pub const MIN_HZ: f32 = TrackerConfig::SUB.min_hz;
pub const MAX_HZ: f32 = TrackerConfig::SUB.max_hz;
pub const SCOPE: usize = 256;
const ATTACK_MS: f32 = 2.;
const RELEASE_MS: f32 = 15.;
const CROSSFADE_MS: f32 = 3.;
/// Crossfade between the sine and the original sub when tracking turns unsure or sure.
const TRUST_MS: f32 = 15.;
/// Highest Ghost harmonic. Harmonic 10 of a 30 Hz sub is 300 Hz.
pub const GHOST_TOP: usize = 10;
/// Ghost harmonics shown and generated: 2..=GHOST_TOP.
pub const GHOST_COUNT: usize = GHOST_TOP - 1;
/// Measurement window per note. Resolves harmonics of fundamentals down to about 35 Hz.
const GHOST_WINDOW_MS: f32 = 60.;
/// Harmonics fade in over this many octaves above the Ghost edge, so a gliding note
/// does not switch them on with a step.
const GHOST_RAMP_OCT: f32 = 0.5;
/// Offsets the audition steps through, in ms.
pub const AUDITION: [f32; 13] = [
    -30., -25., -20., -15., -10., -5., 0., 5., 10., 15., 20., 25., 30.,
];
/// Kicks each audition offset plays for.
pub const AUDITION_HITS: u32 = 4;
/// A kick is a rise of the fast sidechain envelope this far above the slow one...
const KICK_RISE: f32 = 2.8;
/// ...above this level (−45 dBFS)...
const KICK_FLOOR: f32 = 0.0056;
/// ...at least this long after the previous kick.
const KICK_HOLD_MS: f32 = 60.;
/// Kick and sub are compared below this frequency, over this long after each hit.
const KICK_LOW_HZ: f32 = 150.;
const SUM_MS: f32 = 60.;
const DUCK_ATTACK_MS: f32 = 1.;
const PENDING: usize = 16;
/// Small speaker listen: a phone-like band, summed to mono.
pub const PHONE_LOW: f32 = 400.;
pub const PHONE_HIGH: f32 = 7000.;

#[derive(Clone, Copy, Debug, Default)]
pub struct Monitor {
    /// Hear only the generated sub and Ghost harmonics.
    pub solo: bool,
    /// Hear the output through a phone-like speaker band, in mono.
    pub phone: bool,
    /// Step the kick offset through `AUDITION`, `AUDITION_HITS` kicks each.
    pub audition: bool,
}

#[derive(Clone, Copy, Debug)]
pub struct AnalyzerFrame {
    /// Current sub frequency in Hz, 0 when silent.
    pub hz: f32,
    /// MIDI note of the current sub, rounded.
    pub note: Option<u8>,
    /// Tracking is unsure: the original sub plays instead of the sine.
    pub neutral: bool,
    pub low_db: f32,
    pub sub_db: f32,
    /// Harmonics 2..=GHOST_TOP of the current note, peak dB relative to the sub: what the
    /// patch carries above the split, and what Ghost adds. −120 when absent.
    pub patch_harmonics: [f32; GHOST_COUNT],
    pub ghost_harmonics: [f32; GHOST_COUNT],
    /// Lowest frequency Ghost fills, after the split.
    pub ghost_edge: f32,
    /// Kicks found in the sidechain since the plugin started.
    pub kick_hits: u32,
    /// Kick plus sub against kick and sub apart, low band, dB, after the last hit. +3 is a
    /// full sum of equal levels, 0 unrelated, below 0 they cancel. NaN before a hit.
    pub kick_sum_db: f32,
    /// Offset the sub restarted with on the latest kick, in ms.
    pub kick_offset: f32,
    /// Measured sum per audition offset, dB; NaN where not measured yet.
    pub audition_sums: [f32; AUDITION.len()],
    /// Original low band and new sub, triggered on a rising zero crossing of the sub.
    pub scope_low: [f32; SCOPE],
    pub scope_sub: [f32; SCOPE],
    /// Duration of the scope window in milliseconds.
    pub scope_ms: f32,
    pub latency: u32,
    pub sample_rate: f32,
}
impl Default for AnalyzerFrame {
    fn default() -> Self {
        Self {
            hz: 0.,
            note: None,
            neutral: false,
            low_db: -120.,
            sub_db: -120.,
            patch_harmonics: [-120.; GHOST_COUNT],
            ghost_harmonics: [-120.; GHOST_COUNT],
            ghost_edge: 300.,
            kick_hits: 0,
            kick_sum_db: f32::NAN,
            kick_offset: 0.,
            audition_sums: [f32::NAN; AUDITION.len()],
            scope_low: [0.; SCOPE],
            scope_sub: [0.; SCOPE],
            scope_ms: 60.,
            latency: 0,
            sample_rate: 48000.,
        }
    }
}

#[derive(Clone, Copy, Debug, Default)]
struct Voice {
    phase: f32,
    hz: f32,
    target: f32,
    amp: f32,
    releasing: bool,
}

/// Sine voices and per-note state, driven by tracker events at output time.
#[derive(Clone, Copy, Debug, Default)]
struct Synth {
    voice: Voice,
    old: Voice,
    old_gain: f32,
    note_peak: f32,
    /// Set when a note starts or changes pitch; the Ghost measurement starts over.
    fresh: bool,
}
impl Synth {
    fn event(&mut self, s: &Settings, e: NoteEvent) {
        match e {
            NoteEvent::Start { pitch, glide } => self.start(s, pitch, glide),
            NoteEvent::Move { pitch } => {
                if !s.snap {
                    self.voice.target = midi_to_hz(pitch + 12. * s.octave as f32);
                }
            }
            NoteEvent::Stop => self.voice.releasing = true,
        }
    }
    fn start(&mut self, s: &Settings, pitch: f32, glide: bool) {
        let note = if s.snap { pitch.round() } else { pitch };
        let hz = midi_to_hz(note + 12. * s.octave as f32);
        let audible = self.voice.amp > 1e-4 && !self.voice.releasing;
        if glide && audible {
            self.voice.target = hz;
            return;
        }
        if s.retrigger || !audible {
            if self.voice.amp > 1e-4 {
                // Restarting the phase mid-cycle would click; the old cycle fades out instead.
                self.old = self.voice;
                self.old_gain = 1.;
            }
            self.voice = Voice {
                phase: s.phase / 360.,
                hz,
                target: hz,
                amp: 0.,
                releasing: false,
            };
        } else {
            self.voice.target = hz;
            self.voice.hz = hz;
        }
        self.note_peak = 0.;
        self.fresh = true;
    }
    /// Restarts a sounding sub at the start phase, keeping its pitch.
    fn kick(&mut self, s: &Settings) {
        let v = self.voice;
        if v.amp <= 1e-4 || v.releasing {
            return;
        }
        self.old = v;
        self.old_gain = 1.;
        self.voice = Voice {
            phase: s.phase / 360.,
            amp: 0.,
            ..v
        };
    }
}

#[derive(Clone, Copy, Debug, Default)]
struct Pending {
    /// Output-time sample.
    at: u64,
    /// Restart the sub (true) or duck it and start measuring (false).
    restart: bool,
    offset: f32,
    /// Audition offset index this hit belongs to.
    slot: Option<usize>,
}

/// Kick detection, scheduling, ducking and the sum measurement.
struct Kick {
    clock: u64,
    fast: f32,
    slow: f32,
    fast_coef: f32,
    slow_coef: f32,
    hold: usize,
    pending: [Option<Pending>; PENDING],
    delay: Vec<f32>,
    delay_at: usize,
    low: Biquad,
    duck: f32,
    rising: bool,
    attack: f32,
    measure: usize,
    measure_slot: Option<usize>,
    energy: [f32; 3],
    hits: u32,
    sum_db: f32,
    offset: f32,
    auditioning: bool,
    slot: usize,
    slot_hits: u32,
    sums: [f32; AUDITION.len()],
    counts: [u32; AUDITION.len()],
}
impl Kick {
    fn new(rate: f32, latency: usize) -> Self {
        Self {
            clock: 0,
            fast: 0.,
            slow: 0.,
            fast_coef: coefficient(rate, 0.5),
            slow_coef: coefficient(rate, 30.),
            hold: 0,
            pending: [None; PENDING],
            delay: vec![0.; latency + 1],
            delay_at: 0,
            low: Biquad::lowpass(rate, KICK_LOW_HZ, std::f32::consts::FRAC_1_SQRT_2),
            duck: 0.,
            rising: false,
            attack: coefficient(rate, DUCK_ATTACK_MS / 3.),
            measure: 0,
            measure_slot: None,
            energy: [0.; 3],
            hits: 0,
            sum_db: f32::NAN,
            offset: 0.,
            auditioning: false,
            slot: 0,
            slot_hits: 0,
            sums: [f32::NAN; AUDITION.len()],
            counts: [0; AUDITION.len()],
        }
    }
    fn reset(&mut self) {
        self.fast = 0.;
        self.slow = 0.;
        self.hold = 0;
        self.pending = [None; PENDING];
        self.delay.fill(0.);
        self.low.reset();
        self.duck = 0.;
        self.rising = false;
        self.measure = 0;
        self.measure_slot = None;
        self.sum_db = f32::NAN;
        self.slot = 0;
        self.slot_hits = 0;
        self.sums = [f32::NAN; AUDITION.len()];
        self.counts = [0; AUDITION.len()];
    }
    fn schedule(&mut self, p: Pending) {
        if let Some(free) = self.pending.iter_mut().find(|p| p.is_none()) {
            *free = Some(p);
        }
    }
}

pub struct Engine {
    rate: f32,
    channels: usize,
    settings: Settings,
    latency: usize,
    delay: Vec<[f32; 2]>,
    delay_at: usize,
    crossover: [Crossover; 2],
    tracker: Tracker,
    synth: Synth,
    glide: f32,
    low_env: f32,
    env_coef: f32,
    smooth: f32,
    level: f32,
    keep: f32,
    output: f32,
    bypass: f32,
    fallback: Fallback,
    neutral: bool,
    /// 1 while the sine plays, 0 while the original sub stands in for it.
    trust: f32,
    trust_coef: f32,
    meter_coef: f32,
    low_power: f32,
    sub_power: f32,
    scope_low: [f32; 2 * SCOPE],
    scope_sub: [f32; 2 * SCOPE],
    scope_at: usize,
    scope_stride: usize,
    scope_count: usize,
    meter: HarmonicMeter,
    /// Linear peak of the patch's harmonic k (index k − 2) above the split, this note.
    patch: [f32; GHOST_COUNT],
    /// Smoothed Ghost gain per harmonic, relative to the sub's peak.
    fill: [f32; GHOST_COUNT],
    phone_coefs: [SvfCoef; 3],
    phone: [Svf; 3],
    kick: Kick,
}

impl Engine {
    pub fn new(rate: f32, channels: usize) -> Result<Self, &'static str> {
        if !(8000.0..=768000.).contains(&rate) {
            return Err("unsupported sample rate");
        }
        if !(1..=2).contains(&channels) {
            return Err("unsupported channel count");
        }
        let tracker = Tracker::new(rate, TrackerConfig::SUB);
        let latency = tracker.latency();
        let settings = Settings::default();
        let mut e = Self {
            rate,
            channels,
            settings,
            latency,
            delay: vec![[0.; 2]; latency + 1],
            delay_at: 0,
            crossover: [Crossover::new(rate, settings.split); 2],
            tracker,
            synth: Synth::default(),
            glide: 1.,
            low_env: 0.,
            env_coef: coefficient(rate, 10.),
            smooth: coefficient(rate, 10.),
            level: db_to_gain(settings.level),
            keep: 0.,
            output: 1.,
            bypass: 0.,
            fallback: Fallback::default(),
            neutral: false,
            trust: 1.,
            trust_coef: coefficient(rate, TRUST_MS / 3.),
            meter_coef: coefficient(rate, 150.),
            low_power: 0.,
            sub_power: 0.,
            scope_low: [0.; 2 * SCOPE],
            scope_sub: [0.; 2 * SCOPE],
            scope_at: 0,
            scope_stride: ((rate * 0.06) / SCOPE as f32).round().max(1.) as usize,
            scope_count: 0,
            meter: HarmonicMeter::new(rate, GHOST_WINDOW_MS),
            patch: [0.; GHOST_COUNT],
            fill: [0.; GHOST_COUNT],
            phone_coefs: [
                // Fourth-order Butterworth high-pass, second-order low-pass.
                SvfCoef::highpass(rate, PHONE_LOW, 0.541),
                SvfCoef::highpass(rate, PHONE_LOW, 1.307),
                SvfCoef::lowpass(rate, PHONE_HIGH.min(0.45 * rate), 0.707),
            ],
            phone: [Svf::default(); 3],
            kick: Kick::new(rate, latency),
        };
        e.set_settings(settings)?;
        Ok(e)
    }
    pub fn latency_samples(&self) -> u32 {
        self.latency as u32
    }
    pub fn channels(&self) -> usize {
        self.channels
    }
    pub fn settings(&self) -> Settings {
        self.settings
    }
    pub fn set_settings(&mut self, s: Settings) -> Result<(), &'static str> {
        s.validate()?;
        let old = self.settings;
        if (s.split - old.split).abs() > 1e-3 {
            for x in &mut self.crossover {
                x.retune(self.rate, s.split);
            }
        }
        if self
            .tracker
            .set(s.pitch.source(s.source.mode(), s.gate, s.glide > 0.))
        {
            self.synth.voice.releasing = true;
        }
        self.glide = if s.glide <= 0. {
            1.
        } else {
            coefficient(self.rate, s.glide / 3.)
        };
        self.settings = s;
        Ok(())
    }
    pub fn reset(&mut self) {
        self.delay.fill([0.; 2]);
        for x in &mut self.crossover {
            x.reset();
        }
        self.tracker.reset();
        self.synth = Synth::default();
        self.fallback.reset();
        self.neutral = false;
        self.trust = 1.;
        self.low_env = 0.;
        self.low_power = 0.;
        self.sub_power = 0.;
        self.scope_low = [0.; 2 * SCOPE];
        self.scope_sub = [0.; 2 * SCOPE];
        self.meter.reset();
        self.patch = [0.; GHOST_COUNT];
        self.fill = [0.; GHOST_COUNT];
        for f in &mut self.phone {
            f.reset();
        }
        self.kick.reset();
    }
    /// Lowest frequency Ghost fills.
    fn ghost_edge(&self) -> f32 {
        self.settings.ghost_from.max(self.settings.split)
    }
    /// Moves each Ghost gain toward what the patch lacks at the current note.
    fn update_fill(&mut self) {
        let s = &self.settings;
        let v = self.synth.voice;
        let amount = s.ghost * 0.01;
        let edge = self.ghost_edge();
        let sub = self.level.max(1e-6);
        for (i, fill) in self.fill.iter_mut().enumerate() {
            let k = (i + 2) as f32;
            let f = k * v.hz;
            let target = if amount > 0. && v.hz > 0. && f < 0.45 * self.rate {
                let ramp = ((f / edge).log2() / GHOST_RAMP_OCT).clamp(0., 1.);
                // A 1/k slope, like a saw; at 100 % harmonic k sits at 2/k of the sub.
                let want = amount * 2. / k * ramp;
                (want - self.patch[i] / sub).max(0.)
            } else {
                0.
            };
            *fill += (target - *fill) * self.smooth;
        }
    }
    /// Ghost harmonics for a voice at `phase`, without the voice's amplitude.
    #[inline]
    fn ghost(&self, phase: f32) -> f32 {
        let mut out = 0.;
        for (i, &g) in self.fill.iter().enumerate() {
            if g > 1e-5 {
                out += g * (TAU * ((i + 2) as f32 * phase).fract()).sin();
            }
        }
        out
    }
    /// MIDI note start at the current input sample. Used when the source is MIDI.
    pub fn note_on(&mut self, note: u8) {
        self.tracker.note_on(note);
    }
    pub fn note_off(&mut self, note: u8) {
        self.tracker.note_off(note);
    }
    #[inline]
    fn shape(&self, x: f32) -> f32 {
        let drive = self.settings.drive * 0.01;
        if drive <= 0. {
            return x;
        }
        let k = 1. + 6. * drive;
        (k * x).tanh() / k.tanh()
    }
    /// The shaped sub and the Ghost harmonics, before level and dynamics.
    fn oscillator(&mut self) -> (f32, f32) {
        let attack = 1. / (self.rate * ATTACK_MS * 0.001);
        let release = 1. / (self.rate * RELEASE_MS * 0.001);
        let v = &mut self.synth.voice;
        v.amp = if v.releasing {
            (v.amp - release).max(0.)
        } else {
            (v.amp + attack).min(1.)
        };
        v.hz += (v.target - v.hz) * self.glide;
        let (mut out, mut ghost) = (0., 0.);
        let v = self.synth.voice;
        if v.amp > 0. {
            out += (TAU * v.phase).sin() * v.amp;
            ghost += self.ghost(v.phase) * v.amp;
            self.synth.voice.phase = (v.phase + v.hz / self.rate).fract();
        }
        let s = self.synth;
        if s.old_gain > 0. {
            let o = s.old;
            out += (TAU * o.phase).sin() * o.amp * s.old_gain;
            ghost += self.ghost(o.phase) * o.amp * s.old_gain;
            let s = &mut self.synth;
            s.old.phase = (o.phase + o.hz / self.rate).fract();
            s.old_gain = (s.old_gain - 1. / (self.rate * CROSSFADE_MS * 0.001)).max(0.);
        }
        (self.shape(out), ghost)
    }
    /// One sample without a sidechain.
    pub fn process_sample(&mut self, x: [f32; 2], monitor: Monitor) -> [f32; 2] {
        self.process_with_kick(x, 0., monitor)
    }
    /// Finds kicks in the undelayed sidechain and schedules their duck and restart.
    fn detect_kick(&mut self, side: f32, audition: bool) {
        let rate = self.rate;
        let s = self.settings;
        let k = &mut self.kick;
        if audition != k.auditioning {
            k.auditioning = audition;
            k.slot = 0;
            k.slot_hits = 0;
            k.sums = [f32::NAN; AUDITION.len()];
            k.counts = [0; AUDITION.len()];
        }
        let level = side.abs();
        k.fast += (level - k.fast) * k.fast_coef;
        k.slow += (level - k.slow) * k.slow_coef;
        k.hold = k.hold.saturating_sub(1);
        if !s.kick_lock || k.hold > 0 || k.fast < KICK_FLOOR || k.fast < KICK_RISE * k.slow {
            return;
        }
        k.hold = (rate * KICK_HOLD_MS * 0.001) as usize;
        let (offset, slot) = if audition {
            let slot = k.slot;
            k.slot_hits += 1;
            if k.slot_hits >= AUDITION_HITS {
                k.slot_hits = 0;
                k.slot = (k.slot + 1) % AUDITION.len();
            }
            (AUDITION[slot], Some(slot))
        } else {
            (s.kick_offset, None)
        };
        // The delayed kick leaves the plugin `latency` samples from now.
        let at = k.clock + self.latency as u64;
        let shift = (offset * 0.001 * rate).round() as i64;
        let duck = Pending {
            at,
            restart: false,
            offset,
            slot,
        };
        k.schedule(duck);
        k.schedule(Pending {
            at: (at as i64 + shift).max(0) as u64,
            restart: true,
            ..duck
        });
    }
    /// Runs the kick events due at this output sample. Returns the duck gain for the sub.
    fn kick_events(&mut self) -> f32 {
        let s = self.settings;
        let clock = self.kick.clock;
        for i in 0..PENDING {
            let Some(p) = self.kick.pending[i] else {
                continue;
            };
            if p.at > clock {
                continue;
            }
            self.kick.pending[i] = None;
            if p.restart {
                self.synth.kick(&s);
                self.kick.offset = p.offset;
            } else {
                let k = &mut self.kick;
                k.hits += 1;
                k.rising = true;
                k.measure = (self.rate * SUM_MS * 0.001) as usize;
                k.measure_slot = p.slot;
                k.energy = [0.; 3];
            }
        }
        let k = &mut self.kick;
        if k.rising {
            k.duck += (1. - k.duck) * k.attack;
            if k.duck > 0.98 {
                k.rising = false;
            }
        } else {
            k.duck -= k.duck * coefficient(self.rate, s.kick_release / 3.);
        }
        if !s.kick_lock {
            k.duck = 0.;
        }
        1. - (1. - db_to_gain(-s.kick_duck)) * k.duck
    }
    /// Adds one sample of the delayed kick's and the sub's low band to the sum measurement.
    fn measure_kick(&mut self, kick: f32, sub: f32) {
        let k = &mut self.kick;
        if k.measure == 0 {
            return;
        }
        k.energy[0] += (kick + sub) * (kick + sub);
        k.energy[1] += kick * kick;
        k.energy[2] += sub * sub;
        k.measure -= 1;
        if k.measure > 0 {
            return;
        }
        let apart = k.energy[1] + k.energy[2];
        if apart < 1e-9 {
            return;
        }
        k.sum_db = 10. * (k.energy[0] / apart).max(1e-6).log10();
        if let Some(slot) = k.measure_slot {
            let n = k.counts[slot] as f32;
            let old = if n > 0. { k.sums[slot] } else { 0. };
            k.sums[slot] = (old * n + k.sum_db) / (n + 1.);
            k.counts[slot] += 1;
        }
    }
    /// One sample with the kick's sidechain (mono) for Kick lock.
    pub fn process_with_kick(&mut self, x: [f32; 2], kick: f32, monitor: Monitor) -> [f32; 2] {
        self.detect_kick(kick, monitor.audition);
        let len = self.kick.delay.len();
        self.kick.delay[self.kick.delay_at] = kick;
        self.kick.delay_at = (self.kick.delay_at + 1) % len;
        let kick_late = self.kick.delay[self.kick.delay_at];
        let mono = if self.channels == 2 {
            0.5 * (x[0] + x[1])
        } else {
            x[0]
        };
        let (synth, settings) = (&mut self.synth, &self.settings);
        self.tracker.process(mono, |e| synth.event(settings, e));
        self.neutral = self.fallback.neutral(self.tracker.state());
        let len = self.delay.len();
        self.delay[self.delay_at] = x;
        self.delay_at = (self.delay_at + 1) % len;
        // The slot after the newest write is the oldest: exactly `latency` samples ago.
        let y = self.delay[self.delay_at];
        let s = self.settings;
        let (l0, h0) = self.crossover[0].process(y[0]);
        let (l1, h1) = if self.channels == 2 {
            self.crossover[1].process(y[1])
        } else {
            (l0, h0)
        };
        let low = 0.5 * (l0 + l1);
        if std::mem::take(&mut self.synth.fresh) {
            // A new note: measure its harmonics from its first sample. Until the first
            // window completes they count as missing.
            self.meter.reset();
            self.patch = [0.; GHOST_COUNT];
        }
        let v = self.synth.voice;
        let hz = if v.amp > 0. && !v.releasing { v.hz } else { 0. };
        if self.meter.push(0.5 * (h0 + h1), hz) && self.meter.hz() > 0. {
            for (p, db) in self.patch.iter_mut().zip(&self.meter.levels()[1..]) {
                *p = if *db > -119. { db_to_gain(*db) } else { 0. };
            }
        }
        self.low_env += (low * low - self.low_env) * self.env_coef;
        let env = self.low_env.sqrt();
        if !self.synth.voice.releasing {
            self.synth.note_peak = self.synth.note_peak.max(env);
        }
        let follow = if self.synth.note_peak > 1e-6 {
            (env / self.synth.note_peak).min(1.)
        } else {
            1.
        };
        let dynamics = s.dynamics * 0.01;
        let shape = 1. - dynamics + dynamics * follow;
        self.level += (db_to_gain(s.level) - self.level) * self.smooth;
        self.keep += (s.keep * 0.01 - self.keep) * self.smooth;
        self.output += (db_to_gain(s.output) - self.output) * self.smooth;
        self.bypass += (f32::from(s.bypass) - self.bypass) * self.smooth;
        let duck = self.kick_events();
        self.update_fill();
        let (sub, ghost) = self.oscillator();
        self.trust += (f32::from(!self.neutral) - self.trust) * self.trust_coef;
        let gain = self.level * shape * duck * self.trust;
        let sub = sub * gain;
        let generated = sub + ghost * gain;
        if self.settings.kick_lock {
            let kick_low = self.kick.low.process(kick_late);
            self.measure_kick(kick_low, sub);
        }
        self.kick.clock += 1;
        self.low_power += (low * low - self.low_power) * self.meter_coef;
        self.sub_power += (sub * sub - self.sub_power) * self.meter_coef;
        self.scope_count += 1;
        if self.scope_count >= self.scope_stride {
            self.scope_count = 0;
            self.scope_low[self.scope_at] = low;
            self.scope_sub[self.scope_at] = generated;
            self.scope_at = (self.scope_at + 1) % (2 * SCOPE);
        }
        // Replace keeps `keep` of the original, and all of it while the sine is out.
        let keep = match s.mode {
            Mode::Replace => self.keep + (1. - self.keep) * (1. - self.trust),
            Mode::Enhance => 1.,
        };
        let wet = |l: f32, h: f32| {
            if monitor.solo {
                generated
            } else {
                h + keep * l + generated
            }
        };
        let w = [wet(l0, h0), wet(l1, h1)];
        let mut out = [0.; 2];
        for c in 0..self.channels {
            out[c] = (w[c] * self.output) * (1. - self.bypass) + y[c] * self.bypass;
        }
        if monitor.phone {
            let mut m = if self.channels == 2 {
                0.5 * (out[0] + out[1])
            } else {
                out[0]
            };
            for (f, c) in self.phone.iter_mut().zip(&self.phone_coefs) {
                m = f.process(c, m);
            }
            out = [m, if self.channels == 2 { m } else { 0. }];
        }
        out
    }
    pub fn take_analyzer(&self) -> AnalyzerFrame {
        let mut f = AnalyzerFrame {
            latency: self.latency as u32,
            sample_rate: self.rate,
            low_db: 10. * self.low_power.max(1e-12).log10() + 3.01,
            sub_db: 10. * self.sub_power.max(1e-12).log10() + 3.01,
            scope_ms: (self.scope_stride * SCOPE) as f32 / self.rate * 1000.,
            ghost_edge: self.ghost_edge(),
            kick_hits: self.kick.hits,
            kick_sum_db: self.kick.sum_db,
            kick_offset: self.kick.offset,
            audition_sums: self.kick.sums,
            neutral: self.neutral,
            ..AnalyzerFrame::default()
        };
        let sub = self.level.max(1e-6);
        let rel = |g: f32| {
            if g > 1e-6 {
                20. * (g / sub).log10()
            } else {
                -120.
            }
        };
        for i in 0..GHOST_COUNT {
            f.patch_harmonics[i] = rel(self.patch[i]);
            f.ghost_harmonics[i] = rel(self.fill[i] * sub);
        }
        let v = self.synth.voice;
        if v.amp > 0. && !v.releasing && !self.neutral {
            f.hz = v.hz;
            f.note = Some(hz_to_midi(v.hz).round().clamp(0., 127.) as u8);
        }
        // Trigger on the latest rising zero crossing that still leaves a full window behind it.
        let n = 2 * SCOPE;
        let oldest = self.scope_at;
        let mut start = oldest;
        for back in 0..SCOPE {
            let i = (oldest + SCOPE - back) % n;
            let prev = (i + n - 1) % n;
            if self.scope_sub[prev] < 0. && self.scope_sub[i] >= 0. {
                start = i;
                break;
            }
        }
        for k in 0..SCOPE {
            let i = (start + k) % n;
            f.scope_low[k] = self.scope_low[i];
            f.scope_sub[k] = self.scope_sub[i];
        }
        f
    }
}