crabshell-services 0.1.0

//! Audio: the default sink's volume and mute, from the PulseAudio server,
//! which pipewire-pulse serves on PipeWire systems.
//!
//! libpulse runs its mainloop on a thread of its own. Every libpulse call
//! from this side runs on the main thread under the mainloop's lock.
//! libpulse's callbacks run on its thread and only send a message over a
//! calloop channel, so the signal is set on the main thread like any other.

use std::cell::{OnceCell, RefCell};
use std::rc::Rc;
use std::sync::{Arc, Once};
use std::time::{Duration, Instant};

use calloop::channel::Sender;
use calloop::timer::TimeoutAction;
use crabshell_reactive::{ReadSignal, Signal};
use crabshell_ui::Cx;
use libpulse_binding::callbacks::ListResult;
use libpulse_binding::context::introspect::{Introspector, ServerInfo, SinkInfo};
use libpulse_binding::context::subscribe::{Facility, InterestMaskSet};
use libpulse_binding::context::{Context, FlagSet, State};
use libpulse_binding::mainloop::threaded::Mainloop;
use libpulse_binding::volume::{ChannelVolumes, Volume};

use crate::Shared;

#[cfg(test)]
mod tests;

/// How long the service waits before each reconnect.
pub(crate) const RETRY: Duration = Duration::from_secs(2);

/// How long the service keeps trying, from startup and from each drop of
/// a working connection.
pub(crate) const RETRY_FOR: Duration = Duration::from_secs(60);

/// How long a command's result stands in for the server's reads.
pub(crate) const SETTLE: Duration = Duration::from_millis(250);

/// Where the audio server is.
pub(crate) struct Server {
  /// In libpulse's server syntax. `None` for libpulse's default, which
  /// `PULSE_SERVER` and client.conf can set.
  pub(crate) address: Option<String>,
  /// How long to wait before each reconnect: [`RETRY`], less in tests.
  pub(crate) retry: Duration,
  /// How long to keep trying: [`RETRY_FOR`], less in tests.
  pub(crate) retry_for: Duration,
}

/// The default sink: where sound goes unless an app picks another.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Sink {
  /// Its name on the server, such as
  /// `alsa_output.pci-0000_03_00.6.analog-stereo`.
  pub name: String,
  /// The average of its channels' volumes, rounded as `pactl` rounds
  /// them. 100 is full volume, and other apps can set more.
  pub volume_percent: u32,
  /// Whether it is muted.
  pub muted: bool,
}

/// The audio service, from `cx.audio()`. Cloning it is cheap.
#[derive(Clone)]
pub struct Audio {
  sink: ReadSignal<Option<Sink>>,
  /// `None` on a context the shell didn't set up.
  service: Option<Rc<AudioService>>,
}

impl Audio {
  /// The default sink. `None` while there is no audio server or the
  /// server has no sink. Every caller gets the same signal.
  pub fn default_sink(&self) -> ReadSignal<Option<Sink>> {
    self.sink
  }

  /// Changes the default sink's volume by `percent`, louder when
  /// positive, and keeps it within 0-100%, so a step from above 100%
  /// lands on 100%. Every channel moves by the same amount, keeping their
  /// balance, except that one reaching 0% or 100% stops there. With no
  /// sink or no server it does nothing.
  pub fn change_volume(&self, percent: i32) {
    self.command(|pulse| pulse.change_volume(percent));
  }

  /// Mutes the default sink, or unmutes it. With no sink or no server it
  /// does nothing.
  pub fn toggle_mute(&self) {
    self.command(Pulse::toggle_mute);
  }

  fn command(&self, command: impl FnOnce(&mut Pulse)) {
    let mut pulse = self
      .service
      .as_ref()
      .map(|service| service.pulse.borrow_mut());
    match pulse.as_deref_mut().and_then(Option::as_mut) {
      Some(pulse) => command(pulse),
      None => tracing::debug!("no audio service: nothing to change"),
    }
  }
}

/// `cx.audio()`.
pub(crate) fn audio(cx: &Cx) -> Audio {
  if let Some(service) = cx.service::<AudioService>() {
    return service.audio();
  }
  static LOGGED: Once = Once::new();
  LOGGED.call_once(|| {
    tracing::warn!("cx.audio() needs the services the shell provides; there is no sink");
  });
  Audio {
    sink: cx.signal(None).read_only(),
    service: None,
  }
}

/// The audio service of one shell. It connects on first use.
pub(crate) struct AudioService {
  shared: Rc<Shared>,
  /// The default sink, under the root owner. Made on first use.
  sink: OnceCell<Signal<Option<Sink>>>,
  /// libpulse, from first use on. `None` before that, and if libpulse
  /// couldn't start its thread.
  pulse: RefCell<Option<Pulse>>,
}

/// What libpulse's thread sends: the generation of the context it came
/// from, and what happened.
pub(crate) type Message = (u32, Event);

pub(crate) enum Event {
  /// The context's state changed.
  State,
  /// The server changed, maybe its default sink.
  Server,
  /// The sink with this index changed.
  Sink(u32),
  /// The server's default sink name.
  Default(Option<String>),
  /// The sink asked for by name, or `None` for no such sink.
  Info(Option<Info>),
}

impl AudioService {
  pub(crate) fn new(shared: Rc<Shared>) -> AudioService {
    AudioService {
      shared,
      sink: OnceCell::new(),
      pulse: RefCell::new(None),
    }
  }

  fn audio(self: &Rc<Self>) -> Audio {
    let sink = *self.sink.get_or_init(|| {
      // On the loop's next turn, so `cx.audio()` never waits on libpulse.
      self.after(Duration::ZERO, AudioService::start);
      self.shared.root.signal(None)
    });
    Audio {
      sink: sink.read_only(),
      service: Some(Rc::clone(self)),
    }
  }

  /// Starts libpulse's thread and the first connection. Neither waits
  /// for the server.
  fn start(self: &Rc<Self>) {
    let Some(server) = &self.shared.config.audio else {
      return tracing::info!("no audio server is set, so there is no sink");
    };
    let sink = *self
      .sink
      .get()
      .expect("the sink is made before libpulse starts");
    let Some(event_loop) = self.shared.event_loop() else {
      return;
    };
    let Some(mut mainloop) = Mainloop::new() else {
      tracing::error!("libpulse couldn't make its mainloop: no audio");
      return;
    };
    if let Err(error) = mainloop.start() {
      tracing::error!(%error, "libpulse's thread didn't start: no audio");
      return;
    }
    let (sender, channel) = calloop::channel::channel();
    // From here on, dropping `pulse` stops libpulse's thread.
    let pulse = Pulse {
      intro: None,
      context: None,
      mainloop,
      sender: Arc::new(sender),
      generation: 0,
      shown: None,
      asked: None,
      sink,
      down: false,
      retry_until: Instant::now() + server.retry_for,
    };
    let service = Rc::clone(self);
    let on_message = Box::new(move |message| service.on_message(message));
    if event_loop.insert_audio_channel(channel, on_message) {
      *self.pulse.borrow_mut() = Some(pulse);
      self.connect();
    }
  }

  /// Connects to the server, or tries again later.
  fn connect(self: &Rc<Self>) {
    let mut pulse = self.pulse.borrow_mut();
    let (Some(pulse), Some(server)) = (pulse.as_mut(), &self.shared.config.audio) else {
      return;
    };
    // The root is gone, and the shell with it.
    if pulse.sink.try_with(|_| ()).is_none() {
      return;
    }
    if let Err(why) = pulse.connect(server.address.as_deref()) {
      self.lost(pulse, &why);
    }
  }

  fn on_message(self: &Rc<Self>, (generation, event): Message) {
    let mut pulse = self.pulse.borrow_mut();
    // A message from a context that is gone is stale.
    let Some(pulse) = pulse
      .as_mut()
      .filter(|pulse| pulse.generation == generation)
    else {
      return;
    };
    match event {
      Event::State => {
        if let Err(why) = pulse.on_state() {
          self.lost(pulse, &why);
        }
      }
      Event::Server => pulse.read_default(),
      Event::Sink(index) if pulse.shown.as_ref().is_some_and(|s| s.index == index) => {
        pulse.read_default();
      }
      Event::Sink(_) => {}
      Event::Default(name) => pulse.read_sink(name),
      Event::Info(info) => pulse.show(info),
    }
  }

  /// Drops the connection, shows no sink and tries again every `retry`
  /// until `retry_for` has passed since startup, or since a working
  /// connection dropped. Logs once per outage, not on every try, and
  /// once on giving up.
  fn lost(self: &Rc<Self>, pulse: &mut Pulse, why: &str) {
    let Some(Server {
      retry, retry_for, ..
    }) = self.shared.config.audio
    else {
      return;
    };
    let now = Instant::now();
    // It was ready, so the server was there: give it a new while.
    if pulse.intro.is_some() {
      pulse.retry_until = now + retry_for;
    }
    if pulse.disconnect() {
      tracing::warn!(
        reason = why,
        "no audio server, trying again every {retry:?} for up to {retry_for:?}"
      );
    }
    if now + retry > pulse.retry_until {
      // No timer from here on, so audio never wakes the shell again.
      return tracing::info!(
        "stopped trying to reach the audio server; it is tried again when the shell restarts"
      );
    }
    self.after(retry, AudioService::connect);
  }

  /// Runs `f` from the event loop once, `delay` from now.
  fn after(self: &Rc<Self>, delay: Duration, f: fn(&Rc<AudioService>)) {
    let Some(event_loop) = self.shared.event_loop() else {
      return;
    };
    let service = Rc::clone(self);
    let once = move || {
      f(&service);
      TimeoutAction::Drop
    };
    event_loop.insert_timer(Instant::now() + delay, Box::new(once));
  }
}

/// One shell's libpulse objects and what they last told us. It stays on
/// the main thread: `Mainloop` holds an `Rc`, so the compiler won't let it
/// go to another.
struct Pulse {
  // Declared before `mainloop`, so they drop before it.
  intro: Option<Introspector>,
  context: Option<Context>,
  mainloop: Mainloop,
  /// Shared by every callback. Each `Sender` wakes the loop when it
  /// drops, so a callback that holds its own would wake the shell when
  /// libpulse drops it, with nothing to read.
  sender: Arc<Sender<Message>>,
  /// Bumped when a context goes, so the messages it left behind are
  /// dropped.
  generation: u32,
  /// The default sink as last read.
  shown: Option<Info>,
  /// The default sink as the last command left it, and when that was
  /// sent. pipewire-pulse answers a read sent right after a set with the
  /// sink as it was before, so commands build on this instead until a
  /// read echoes it or [`SETTLE`] passes.
  asked: Option<(Info, Instant)>,
  sink: Signal<Option<Sink>>,
  /// Whether the server is gone and that was logged.
  down: bool,
  /// When the service stops trying to connect, if it can't.
  retry_until: Instant,
}

/// The default sink as libpulse reported it.
#[derive(Clone, PartialEq)]
pub(crate) struct Info {
  index: u32,
  name: String,
  volumes: ChannelVolumes,
  muted: bool,
}

impl Pulse {
  /// Makes a context and starts connecting it to `server`, or to
  /// libpulse's default for `None`.
  fn connect(&mut self, server: Option<&str>) -> Result<(), String> {
    let lock = Locked::new(&mut self.mainloop);
    let mut context = Context::new(&*lock.0, "crabshell").ok_or("libpulse made no context")?;
    let (sender, generation) = (Arc::clone(&self.sender), self.generation);
    context.set_state_callback(Some(Box::new(on_pa_thread(move || {
      let _ = sender.send((generation, Event::State));
    }))));
    // NOAUTOSPAWN: a retry must never start a daemon next to pipewire-pulse.
    let connected = context.connect(server, FlagSet::NOAUTOSPAWN, None);
    self.context = Some(context);
    connected.map_err(|error| format!("{error}"))
  }

  /// Acts on the context's new state. Once it is ready, subscribes to
  /// sink and server events and reads the default sink. `Err` when the
  /// connection failed or ended.
  fn on_state(&mut self) -> Result<(), String> {
    let lock = Locked::new(&mut self.mainloop);
    let Some(context) = self.context.as_mut() else {
      return Ok(());
    };
    match context.get_state() {
      // Several queued messages can each find it ready.
      State::Ready if self.intro.is_none() => {
        let (sender, generation) = (Arc::clone(&self.sender), self.generation);
        let on_event = move |facility, _, index| {
          let event = match facility {
            Some(Facility::Server) => Event::Server,
            Some(Facility::Sink) => Event::Sink(index),
            _ => return,
          };
          let _ = sender.send((generation, event));
        };
        context.set_subscribe_callback(Some(Box::new(on_pa_thread(on_event))));
        let interest = InterestMaskSet::SINK | InterestMaskSet::SERVER;
        context.subscribe(interest, on_pa_thread(|_| {}));
        self.intro = Some(context.introspect());
        drop(lock);
        if std::mem::take(&mut self.down) {
          tracing::info!("the audio server is back");
        } else {
          tracing::debug!("connected to the audio server");
        }
        self.read_default();
        Ok(())
      }
      State::Failed | State::Terminated => Err(format!("{}", context.errno())),
      _ => Ok(()),
    }
  }

  /// Runs `call` under the lock if the context is ready, and says
  /// whether it ran. libpulse returns no operation from a context that
  /// isn't, and the binding panics on that.
  fn when_ready(&mut self, call: impl FnOnce(&mut Introspector)) -> bool {
    let _lock = Locked::new(&mut self.mainloop);
    match (&self.context, &mut self.intro) {
      (Some(context), Some(intro)) if context.get_state() == State::Ready => {
        call(intro);
        true
      }
      _ => false,
    }
  }

  /// Asks the server for its default sink's name.
  fn read_default(&mut self) {
    let (sender, generation) = (Arc::clone(&self.sender), self.generation);
    self.when_ready(|intro| {
      // shortcut: on an error reply libpulse-binding panics on its thread instead of calling
      // this, and the panic hook prints it raw; logging it needs the C API, so `unsafe`.
      intro.get_server_info(on_pa_thread(move |info: &ServerInfo| {
        let name = info
          .default_sink_name
          .as_deref()
          .filter(|name| !name.is_empty());
        let _ = sender.send((generation, Event::Default(name.map(str::to_owned))));
      }));
    });
  }

  /// Asks for the sink called `name`, or shows none.
  fn read_sink(&mut self, name: Option<String>) {
    let Some(name) = name else {
      return self.show(None);
    };
    let (sender, generation) = (Arc::clone(&self.sender), self.generation);
    self.when_ready(|intro| {
      let mut found = None;
      let on_result = move |result: ListResult<&SinkInfo>| match result {
        ListResult::Item(info) => found = Info::read(info),
        ListResult::End | ListResult::Error => {
          let _ = sender.send((generation, Event::Info(found.take())));
        }
      };
      intro.get_sink_info_by_name(&name, on_pa_thread(on_result));
    });
  }

  /// Shows `info`, or no sink. The signal is set only when that changes
  /// what the bar shows, since every set repaints.
  fn show(&mut self, info: Option<Info>) {
    // An echo of the last command, or another sink, ends its stand-in.
    let stands = match (&self.asked, &info) {
      (Some((asked, _)), Some(read)) => read != asked && read.index == asked.index,
      _ => false,
    };
    if !stands {
      self.asked = None;
    }
    let sink = info.as_ref().map(Info::sink);
    self.shown = info;
    if self.sink.try_with(|shown| *shown != sink) == Some(true) {
      self.sink.set(sink);
    }
  }

  /// What the next command builds on: the last one's result while it
  /// stands in, or else the last read.
  fn base(&self) -> Option<Info> {
    match &self.asked {
      Some((asked, at)) if at.elapsed() < SETTLE => Some(asked.clone()),
      _ => self.shown.clone(),
    }
  }

  fn change_volume(&mut self, percent: i32) {
    let Some(mut next) = self.base() else {
      return tracing::debug!("no default sink: the volume stays");
    };
    next.volumes = changed(next.volumes, percent);
    let sent = self.when_ready(|intro| {
      intro.set_sink_volume_by_name(&next.name, &next.volumes, None);
    });
    if sent {
      self.asked = Some((next, Instant::now()));
    } else {
      tracing::debug!("no audio server: the volume stays");
    }
  }

  fn toggle_mute(&mut self) {
    let Some(mut next) = self.base() else {
      return tracing::debug!("no default sink: nothing to mute");
    };
    next.muted = !next.muted;
    let sent = self.when_ready(|intro| {
      intro.set_sink_mute_by_name(&next.name, next.muted, None);
    });
    if sent {
      self.asked = Some((next, Instant::now()));
    } else {
      tracing::debug!("no audio server: nothing to mute");
    }
  }

  /// Drops the context and shows no sink. `true` when this starts an
  /// outage.
  fn disconnect(&mut self) -> bool {
    let lock = Locked::new(&mut self.mainloop);
    self.intro = None;
    if let Some(mut context) = self.context.take() {
      // Cleared first: disconnecting calls the state callback.
      context.set_state_callback(None);
      context.set_subscribe_callback(None);
      context.disconnect();
    }
    drop(lock);
    self.generation += 1;
    self.show(None);
    !std::mem::replace(&mut self.down, true)
  }
}

impl Drop for Pulse {
  fn drop(&mut self) {
    // Unlocked, as libpulse asks. Once its thread is gone, the context
    // and introspector drop with nothing running beside them.
    self.mainloop.stop();
  }
}

impl Info {
  /// Copies what we need out of libpulse's `info`, which lives only for
  /// the callback. A sink with no name or a bad volume is skipped.
  fn read(info: &SinkInfo) -> Option<Info> {
    let (Some(name), true) = (info.name.as_deref(), info.volume.is_valid()) else {
      tracing::warn!(
        index = info.index,
        "skipped a sink with no name or a bad volume"
      );
      return None;
    };
    Some(Info {
      index: info.index,
      name: name.to_owned(),
      volumes: info.volume,
      muted: info.mute,
    })
  }

  fn sink(&self) -> Sink {
    Sink {
      name: self.name.clone(),
      volume_percent: percent(self.volumes.avg()),
      muted: self.muted,
    }
  }
}

/// The mainloop's lock, held until this drops. libpulse's thread waits for
/// it, so it must be let go even on an early return or a panic.
struct Locked<'a>(&'a mut Mainloop);

impl<'a> Locked<'a> {
  fn new(mainloop: &'a mut Mainloop) -> Locked<'a> {
    mainloop.lock();
    Locked(mainloop)
  }
}

impl Drop for Locked<'_> {
  fn drop(&mut self) {
    self.0.unlock();
  }
}

/// libpulse runs its callbacks on its own thread but doesn't ask for
/// `Send`. Wrapping each one in this makes the compiler check it.
fn on_pa_thread<F: Send + 'static>(callback: F) -> F {
  callback
}

/// The percent `pactl get-sink-volume` shows for `volume`: 100 is
/// `PA_VOLUME_NORM`, and halves round up.
fn percent(volume: Volume) -> u32 {
  let norm = u64::from(Volume::NORMAL.0);
  // At most u32::MAX * 100 / norm, which fits.
  ((u64::from(volume.0) * 100 + norm / 2) / norm) as u32
}

/// `volumes` changed by `delta` percent. Every channel moves by the amount
/// that puts their average on the shown percent plus `delta`, kept within
/// 0-100%. A channel that would pass 0% or 100% stops there, and then the
/// average falls short of that.
fn changed(mut volumes: ChannelVolumes, delta: i32) -> ChannelVolumes {
  let norm = i64::from(Volume::NORMAL.0);
  let average = volumes.avg();
  let target = (i64::from(percent(average)) + i64::from(delta)).clamp(0, 100);
  let shift = (target * norm + 50) / 100 - i64::from(average.0);
  for volume in volumes.get_mut() {
    // Within 0..=norm, which fits.
    volume.0 = (i64::from(volume.0) + shift).clamp(0, norm) as u32;
  }
  volumes
}