//! Audio engine — owns the cpal input/output streams, the Opus
//! encoder, and the tsclientlib `AudioHandler` for decode+mix.
//!
//! The engine is started after a protocol connection is established
//! and stopped before disconnect. It does not retry on device
//! change.

use std::sync::atomic::{AtomicBool, AtomicU32, Ordering};
use std::sync::{Arc, Mutex};

use cpal::traits::{DeviceTrait, HostTrait, StreamTrait};
use cpal::{SampleFormat, SizedSample};
use tokio::sync::mpsc;
use tracing::{debug, error, info, warn};

use audiopus::coder::Encoder as OpusEncoder;
use audiopus::{Application as OpusApp, Channels as OpusChannels, SampleRate as OpusSampleRate};

use tsclientlib::audio::AudioHandler;

use chanora_protocol::{
    AudioData, CodecType, InboundVoice, OutAudio, OutPacket,
};

use crate::AudioError;

/// Stable Chanora-side identifier for AudioHandler bookkeeping.
/// We only ever have one connection at a time (DEC-006), so this is
/// trivially unique.
#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
pub struct SessionAudioId(pub u64);

/// Audio framing: 48 kHz mono, 20 ms = 960 samples per frame.
const SAMPLE_RATE: u32 = 48_000;
const FRAME_SAMPLES: usize = 48_000 / 50; // 960
const MAX_OPUS_FRAME: usize = 1275;

/// Engine configuration.
#[derive(Debug, Clone)]
pub struct AudioEngineConfig {
    /// Input gain applied before encoding (1.0 = pass-through).
    pub mic_gain: f32,
    /// Initial PTT state. When false the encoder is bypassed and no
    /// outbound packets are produced.
    pub ptt_initial: bool,
    /// Audio-effect toggles. The struct is honoured by *naming* but
    /// the filters themselves are still no-op in Beta — see the
    /// crate-level docs and DEC-007/008/009/010.
    pub effects: crate::AudioEffects,
    /// A.5 mobile: prefer the OS-provided "voice communication"
    /// audio source on mobile platforms (Android
    /// `MediaRecorder.AudioSource.VOICE_COMMUNICATION`, iOS
    /// `AVAudioSession.Mode.voiceChat`). On Linux desktop this is
    /// ignored — the DSP chain stays a no-op and we use the
    /// default ALSA/PipeWire source.
    ///
    /// Beta status: the *config flag* is plumbed through every
    /// layer; the *Android-side preset switch* is documented but
    /// not yet wired through cpal, which currently uses the
    /// AAudio default input. RISK-AUDIO-MOBILE-001 tracks this gap.
    /// Setting `true` is a forward-compatible no-op for Beta and
    /// will become active once cpal exposes input-preset hooks (or
    /// when Chanora ships an Oboe-based fork).
    pub mobile_voice_preset: bool,
}

impl Default for AudioEngineConfig {
    fn default() -> Self {
        Self {
            mic_gain: 1.0,
            ptt_initial: false,
            effects: crate::AudioEffects::default(),
            mobile_voice_preset: true,
        }
    }
}

/// Running audio engine. Drop = stop.
pub struct AudioEngine {
    ptt: Arc<AtomicBool>,
    frames_sent: Arc<AtomicU32>,
    frames_received: Arc<AtomicU32>,

    // Streams must be dropped to stop audio. Both are `!Send` because
    // cpal's Stream isn't Send on some backends; we keep them in an
    // Option wrapped by Mutex so stop() can move them out.
    _input_stream: Mutex<Option<cpal::Stream>>,
    _output_stream: Mutex<Option<cpal::Stream>>,
    // Hand the inbound-voice forwarder task a shutdown signal.
    shutdown_tx: Option<tokio::sync::oneshot::Sender<()>>,
    /// True if the capture stream actually opened. If false (typical
    /// in headless environments with null sources, or where the user
    /// denied microphone permission), PTT becomes a no-op and
    /// `frames_sent` stays at 0.
    capture_active: bool,
}

// cpal::Stream is not Send. We keep the engine pinned to the thread
// it was constructed on — `chanora_core` spawns it inside a
// `tokio::task::spawn_blocking` so the streams stay on that worker.
// This `unsafe impl Send` is necessary because the outer Arc<AudioEngine>
// is stored in core's session and must move into a task. The streams
// themselves are only mutated through the Mutex and are dropped on
// the same thread that owns them.
//
// SAFETY: cpal's Stream is not Send because the underlying audio API
// callback thread may not be transferable. We never invoke methods on
// the streams from any thread but the owning one; we only ever *drop*
// them, which cpal documents as safe from any thread for ALSA and
// PipeWire (Linux backend used here). For Windows/macOS the contract
// may differ; production Beta+ work must revisit per-platform.
unsafe impl Send for AudioEngine {}
unsafe impl Sync for AudioEngine {}

impl AudioEngine {
    /// Start the engine: open capture + playback streams, spawn the
    /// inbound-voice forwarder, return a handle.
    pub fn start(
        cfg: AudioEngineConfig,
        voice_out_tx: mpsc::Sender<OutPacket>,
        mut voice_in_rx: mpsc::Receiver<InboundVoice>,
    ) -> Result<Self, AudioError> {
        let host = cpal::default_host();
        let in_dev = host
            .default_input_device()
            .ok_or(AudioError::NoInputDevice)?;
        let out_dev = host
            .default_output_device()
            .ok_or(AudioError::NoOutputDevice)?;

        info!(
            target: "chanora_audio",
            in_device = %in_dev.name().unwrap_or_default(),
            out_device = %out_dev.name().unwrap_or_default(),
            "starting audio engine"
        );

        // A.5 mobile-only preset acknowledgement. On Linux desktop
        // the flag is ignored; on Android we log it so a future cpal
        // / Oboe wiring can be observed in the diagnostic export.
        #[cfg(target_os = "android")]
        {
            if cfg.mobile_voice_preset {
                info!(
                    target: "chanora_audio",
                    "android: mobile_voice_preset requested (RISK-AUDIO-MOBILE-001 — flag plumbed, switch pending cpal upstream)"
                );
            }
            if cfg.effects.aec || cfg.effects.noise_suppression {
                info!(
                    target: "chanora_audio",
                    aec = cfg.effects.aec,
                    ns = cfg.effects.noise_suppression,
                    "android: effects requested; awaiting OS-source switch to engage hardware AEC/NS"
                );
            }
        }
        #[cfg(target_os = "ios")]
        {
            if cfg.mobile_voice_preset {
                info!(
                    target: "chanora_audio",
                    "ios: voice-chat session mode requested (binding pending — Chanora iOS audio is documented-only for Beta)"
                );
            }
        }

        let ptt = Arc::new(AtomicBool::new(cfg.ptt_initial));
        let frames_sent = Arc::new(AtomicU32::new(0));
        let frames_received = Arc::new(AtomicU32::new(0));

        // ---------- Capture ----------
        // Capture is best-effort. If the platform default input
        // device refuses any supported config (typical for
        // headless null sources or for users who deny the mic
        // permission) we log and continue — playback alone is
        // still useful. PTT becomes a no-op in that case.
        let capture_result = try_open_capture(
            &in_dev,
            voice_out_tx,
            ptt.clone(),
            frames_sent.clone(),
            cfg.mic_gain,
        );
        let (input_stream, capture_active) = match capture_result {
            Ok(s) => (Some(s), true),
            Err(e) => {
                warn!(
                    target: "chanora_audio",
                    error = %e,
                    "capture stream unavailable; continuing with playback only"
                );
                (None, false)
            }
        };
        if let Some(s) = &input_stream {
            s.play()
                .map_err(|e| AudioError::Backend(format!("input play: {e}")))?;
        }

        // ---------- Playback ----------
        let audio_handler: Arc<Mutex<AudioHandler<SessionAudioId>>> =
            Arc::new(Mutex::new(AudioHandler::new()));

        let out_cfg = out_dev
            .default_output_config()
            .map_err(|e| AudioError::StreamConfig(format!("output default: {e}")))?;
        let out_format = out_cfg.sample_format();
        // AudioHandler::fill_buffer expects 48 kHz stereo f32.
        let out_stream_cfg = cpal::StreamConfig {
            channels: 2,
            sample_rate: cpal::SampleRate(SAMPLE_RATE),
            buffer_size: cpal::BufferSize::Default,
        };

        let output_stream = match out_format {
            SampleFormat::F32 => build_output_stream::<f32>(
                &out_dev,
                &out_stream_cfg,
                audio_handler.clone(),
            )?,
            SampleFormat::I16 => build_output_stream::<i16>(
                &out_dev,
                &out_stream_cfg,
                audio_handler.clone(),
            )?,
            SampleFormat::U16 => build_output_stream::<u16>(
                &out_dev,
                &out_stream_cfg,
                audio_handler.clone(),
            )?,
            other => {
                return Err(AudioError::StreamConfig(format!(
                    "unsupported output format: {other:?}"
                )))
            }
        };
        output_stream
            .play()
            .map_err(|e| AudioError::Backend(format!("output play: {e}")))?;

        // ---------- Inbound forwarder ----------
        let (shutdown_tx, mut shutdown_rx) = tokio::sync::oneshot::channel();
        let handler_for_task = audio_handler.clone();
        let frames_received_for_task = frames_received.clone();
        tokio::spawn(async move {
            loop {
                tokio::select! {
                    _ = &mut shutdown_rx => {
                        debug!(target: "chanora_audio", "inbound forwarder shutting down");
                        break;
                    }
                    item = voice_in_rx.recv() => {
                        match item {
                            Some(v) => {
                                let id = SessionAudioId(v.from_client);
                                let mut h = handler_for_task.lock().unwrap();
                                if let Err(e) = h.handle_packet(id, v.packet) {
                                    debug!(target: "chanora_audio", error = %e, "decode failed");
                                } else {
                                    frames_received_for_task.fetch_add(1, Ordering::Relaxed);
                                }
                            }
                            None => break,
                        }
                    }
                }
            }
        });

        Ok(Self {
            ptt,
            frames_sent,
            frames_received,
            _input_stream: Mutex::new(input_stream),
            _output_stream: Mutex::new(Some(output_stream)),
            shutdown_tx: Some(shutdown_tx),
            capture_active,
        })
    }

    /// Stop the engine. Idempotent.
    pub fn stop(&mut self) {
        if let Some(tx) = self.shutdown_tx.take() {
            let _ = tx.send(());
        }
        // Drop the streams, which stops their callback threads.
        let _ = self._input_stream.lock().unwrap().take();
        let _ = self._output_stream.lock().unwrap().take();
        info!(target: "chanora_audio", "audio engine stopped");
    }

    /// Set the push-to-talk active state. When false, captured audio
    /// is discarded before encoding. No-op if capture is inactive.
    pub fn set_ptt(&self, active: bool) {
        self.ptt.store(active, Ordering::Relaxed);
    }

    /// Current PTT state.
    pub fn ptt(&self) -> bool {
        self.ptt.load(Ordering::Relaxed)
    }

    /// True if the capture stream opened. When false, the engine
    /// runs in playback-only mode and PTT is a no-op.
    pub fn capture_active(&self) -> bool {
        self.capture_active
    }

    /// Number of Opus frames sent since the engine started.
    pub fn frames_sent(&self) -> u32 {
        self.frames_sent.load(Ordering::Relaxed)
    }

    /// Number of inbound voice packets received and decoded.
    pub fn frames_received(&self) -> u32 {
        self.frames_received.load(Ordering::Relaxed)
    }
}

impl Drop for AudioEngine {
    fn drop(&mut self) {
        self.stop();
    }
}

// ---------- Capture pipeline ----------

fn try_open_capture(
    in_dev: &cpal::Device,
    voice_out_tx: mpsc::Sender<OutPacket>,
    ptt: Arc<AtomicBool>,
    frames_sent: Arc<AtomicU32>,
    mic_gain: f32,
) -> Result<cpal::Stream, AudioError> {
    let in_cfg = in_dev
        .default_input_config()
        .map_err(|e| AudioError::StreamConfig(format!("input default: {e}")))?;
    let in_sample_rate = in_cfg.sample_rate().0;
    let in_channels = in_cfg.channels() as usize;
    let in_format = in_cfg.sample_format();
    let in_stream_cfg: cpal::StreamConfig = in_cfg.into();

    let opus_enc = OpusEncoder::new(
        OpusSampleRate::Hz48000,
        OpusChannels::Mono,
        OpusApp::Voip,
    )
    .map_err(|e| AudioError::Opus(format!("encoder new: {e}")))?;

    let capture_state = Arc::new(Mutex::new(CaptureState::new(
        opus_enc,
        in_sample_rate,
        in_channels,
        mic_gain,
        voice_out_tx,
        ptt,
        frames_sent,
    )));

    let stream = match in_format {
        SampleFormat::F32 => build_input_stream::<f32>(in_dev, &in_stream_cfg, capture_state)?,
        SampleFormat::I16 => build_input_stream::<i16>(in_dev, &in_stream_cfg, capture_state)?,
        SampleFormat::U16 => build_input_stream::<u16>(in_dev, &in_stream_cfg, capture_state)?,
        other => {
            return Err(AudioError::StreamConfig(format!(
                "unsupported input format: {other:?}"
            )))
        }
    };
    Ok(stream)
}

struct CaptureState {
    encoder: OpusEncoder,
    in_sample_rate: u32,
    in_channels: usize,
    mic_gain: f32,
    /// 48 kHz mono buffer accumulated to FRAME_SAMPLES before each encode.
    pcm_accum: Vec<f32>,
    /// Resampling state for non-48k sources (very simple linear resampler).
    resample_pos: f64,
    opus_out: [u8; MAX_OPUS_FRAME],
    voice_out_tx: mpsc::Sender<OutPacket>,
    ptt: Arc<AtomicBool>,
    frames_sent: Arc<AtomicU32>,
}

impl CaptureState {
    fn new(
        encoder: OpusEncoder,
        in_sample_rate: u32,
        in_channels: usize,
        mic_gain: f32,
        voice_out_tx: mpsc::Sender<OutPacket>,
        ptt: Arc<AtomicBool>,
        frames_sent: Arc<AtomicU32>,
    ) -> Self {
        Self {
            encoder,
            in_sample_rate,
            in_channels,
            mic_gain,
            pcm_accum: Vec::with_capacity(FRAME_SAMPLES * 2),
            resample_pos: 0.0,
            opus_out: [0u8; MAX_OPUS_FRAME],
            voice_out_tx,
            ptt,
            frames_sent,
        }
    }

    /// Consume an arbitrary-rate, multichannel cpal buffer; produce
    /// 48 kHz mono frames; encode and send on PTT.
    fn ingest<T: ToF32 + Copy>(&mut self, buf: &[T]) {
        if !self.ptt.load(Ordering::Relaxed) {
            // Drain accumulator while muted so we don't pop on PTT release.
            self.pcm_accum.clear();
            return;
        }

        // 1. Down-mix to mono + gain.
        let mono: Vec<f32> = buf
            .chunks(self.in_channels)
            .map(|frame| {
                let sum: f32 = frame.iter().map(|s| s.to_f32_sample()).sum();
                (sum / frame.len() as f32) * self.mic_gain
            })
            .collect();

        // 2. Resample to 48 kHz if needed.
        if self.in_sample_rate == SAMPLE_RATE {
            self.pcm_accum.extend_from_slice(&mono);
        } else {
            self.resample_into_accum(&mono);
        }

        // 3. Encode any complete frames.
        while self.pcm_accum.len() >= FRAME_SAMPLES {
            let frame: Vec<f32> = self.pcm_accum.drain(..FRAME_SAMPLES).collect();
            match self.encoder.encode_float(&frame, &mut self.opus_out[..]) {
                Ok(len) => {
                    let packet = OutAudio::new(&AudioData::C2S {
                        id: 0,
                        codec: CodecType::OpusVoice,
                        data: &self.opus_out[..len],
                    });
                    match self.voice_out_tx.try_send(packet) {
                        Ok(()) => {
                            self.frames_sent.fetch_add(1, Ordering::Relaxed);
                        }
                        Err(mpsc::error::TrySendError::Full(_)) => {
                            warn!(target: "chanora_audio", "voice_out queue full; dropping frame");
                        }
                        Err(mpsc::error::TrySendError::Closed(_)) => {
                            warn!(target: "chanora_audio", "voice_out closed; stopping send");
                        }
                    }
                }
                Err(e) => {
                    error!(target: "chanora_audio", error = %e, "opus encode failed");
                }
            }
        }
    }

    /// Simple linear resampler for `in_sample_rate → 48000`.
    /// Production quality work belongs in a Beta+ DSP module.
    fn resample_into_accum(&mut self, mono: &[f32]) {
        let ratio = self.in_sample_rate as f64 / SAMPLE_RATE as f64;
        let mut pos = self.resample_pos;
        while pos < mono.len() as f64 {
            let i = pos as usize;
            let frac = pos - i as f64;
            let a = mono[i];
            let b = if i + 1 < mono.len() { mono[i + 1] } else { a };
            self.pcm_accum
                .push((a as f64 + frac * (b - a) as f64) as f32);
            pos += ratio;
        }
        // Keep the leftover sub-sample offset for the next buffer.
        self.resample_pos = pos - mono.len() as f64;
    }
}

/// Per-sample format conversion to f32 in the range [-1.0, 1.0].
trait ToF32 {
    fn to_f32_sample(self) -> f32;
}
impl ToF32 for f32 {
    fn to_f32_sample(self) -> f32 {
        self
    }
}
impl ToF32 for i16 {
    fn to_f32_sample(self) -> f32 {
        f32::from(self) / f32::from(i16::MAX)
    }
}
impl ToF32 for u16 {
    fn to_f32_sample(self) -> f32 {
        (f32::from(self) - f32::from(i16::MAX) - 1.0) / f32::from(i16::MAX)
    }
}

fn build_input_stream<T>(
    device: &cpal::Device,
    config: &cpal::StreamConfig,
    state: Arc<Mutex<CaptureState>>,
) -> Result<cpal::Stream, AudioError>
where
    T: SizedSample + ToF32 + Send + 'static,
{
    let stream = device
        .build_input_stream(
            config,
            move |data: &[T], _| {
                let mut s = state.lock().unwrap();
                s.ingest(data);
            },
            move |e| {
                error!(target: "chanora_audio", error = %e, "input stream error");
            },
            None,
        )
        .map_err(|e| AudioError::Backend(format!("build_input_stream: {e}")))?;
    Ok(stream)
}

// ---------- Playback pipeline ----------

fn build_output_stream<T>(
    device: &cpal::Device,
    config: &cpal::StreamConfig,
    handler: Arc<Mutex<AudioHandler<SessionAudioId>>>,
) -> Result<cpal::Stream, AudioError>
where
    T: SizedSample + FromF32 + Send + 'static,
{
    // Reusable f32 scratch buffer. cpal callbacks ask for a max
    // buffer size known at construction time; we allocate per-call
    // because reusing across calls would need an Arc<Mutex<_>> and
    // we already hold one for the handler.
    let stream = device
        .build_output_stream(
            config,
            move |out: &mut [T], _| {
                let mut scratch = vec![0.0f32; out.len()];
                {
                    let mut h = handler.lock().unwrap();
                    h.fill_buffer(&mut scratch);
                }
                for (dst, src) in out.iter_mut().zip(scratch.into_iter()) {
                    *dst = T::from_f32_sample(src);
                }
            },
            move |e| {
                error!(target: "chanora_audio", error = %e, "output stream error");
            },
            None,
        )
        .map_err(|e| AudioError::Backend(format!("build_output_stream: {e}")))?;
    Ok(stream)
}

trait FromF32 {
    fn from_f32_sample(v: f32) -> Self;
}
impl FromF32 for f32 {
    fn from_f32_sample(v: f32) -> Self {
        v
    }
}
impl FromF32 for i16 {
    fn from_f32_sample(v: f32) -> Self {
        (v.clamp(-1.0, 1.0) * f32::from(i16::MAX)) as i16
    }
}
impl FromF32 for u16 {
    fn from_f32_sample(v: f32) -> Self {
        let s = (v.clamp(-1.0, 1.0) * f32::from(i16::MAX)) as i32;
        (s + i32::from(i16::MAX) + 1) as u16
    }
}