// Audio engine: music (XM players with crossfades) and synthesised sound effects.
// The browser pulls samples through dc_audio_render() from our JS plugin (www/dc_plugin.js),
// which starts the AudioContext on the first user interaction. Desktop builds play through
// the system's sound output (module `native` below).

use crate::sfx;
use crate::tracks::TRACKS;
use crate::xm::{self, Module, Player};
use std::cell::RefCell;
use std::rc::Rc;

// Music categories; the tracks themselves are listed in tracks.rs (generated by the composer)
#[derive(Clone, Copy, PartialEq, Eq, Debug)]
pub enum Category {
    Title,
    Build,
    Battle,
    Assault,
    BossPaladin,
    BossWarden,
    Torture,
    Temple,
    Victory,
    Defeat,
    Surface,       // above ground: flute, harp, birdsong
    SurfaceBattle, // fighting above ground
}

// indices of all tracks of a category, in play order
pub fn tracks_in(c: Category) -> Vec<usize> {
    TRACKS.iter().enumerate().filter(|(_, t)| t.1 == c).map(|(i, _)| i).collect()
}

// the calm tracks the music player offers (no battle, victory or defeat music)
pub fn player_tracks() -> Vec<usize> {
    use Category as C;
    TRACKS.iter().enumerate().filter(|(_, t)| matches!(t.1, C::Title | C::Build | C::Surface | C::Torture | C::Temple)).map(|(i, _)| i).collect()
}

pub fn track_id(t: usize) -> &'static str {
    TRACKS.get(t).map_or("", |t| t.0)
}

pub fn track_by_id(id: &str) -> Option<usize> {
    if id.is_empty() {
        return None;
    }
    TRACKS.iter().position(|t| t.0 == id)
}

// the song title stored in the XM module (without the "DungeonCraft - " prefix)
pub fn track_title(t: usize) -> String {
    let Some(d) = TRACKS.get(t).map(|t| t.2) else { return String::new() };
    let raw = d.get(17..37).unwrap_or(&[]);
    let name: String = raw.iter().take_while(|&&b| b != 0).map(|&b| b as char).collect();
    let name = name.trim().trim_start_matches("DungeonCraft - ").trim().to_string();
    if name.is_empty() {
        track_id(t).to_string()
    } else {
        name
    }
}

const MUSIC_GAIN: f32 = 0.45; // our replayer is ~4x louder than libopenmpt; leaves headroom for effects
const SFX_GAIN: f32 = 0.55;

struct MusicVoice {
    player: Player,
    gain: f32,
    target: f32,
    speed: f32, // gain change per second
}

struct SfxVoice {
    data: Rc<Vec<f32>>,
    pos: usize,
    l: f32,
    r: f32,
}

struct Engine {
    rate: f32,
    modules: Vec<Rc<Module>>,
    music: Vec<MusicVoice>,
    voices: Vec<SfxVoice>,
    sfx: Vec<Rc<Vec<f32>>>,
    buf: Vec<f32>,
}

// Requests that arrive before the browser allows audio are remembered here
struct State {
    music_vol: f32,
    sfx_vol: f32,
    muted: bool,
    track: Option<usize>,
    engine: Option<Engine>,
}

thread_local! {
    static STATE: RefCell<State> = RefCell::new(State { music_vol: 0.6, sfx_vol: 0.7, muted: false, track: None, engine: None });
}

impl Engine {
    fn new(rate: f32) -> Engine {
        let modules = TRACKS.iter().map(|(_, _, d)| Rc::new(xm::load(d).expect("built-in music"))).collect();
        let sfx = sfx::generate_all(rate).into_iter().map(Rc::new).collect();
        Engine { rate, modules, music: Vec::new(), voices: Vec::new(), sfx, buf: Vec::new() }
    }

    fn start_track(&mut self, t: usize, fade: f32) {
        let speed = 1.0 / fade.max(0.01);
        for v in self.music.iter_mut() {
            v.target = 0.0;
            v.speed = speed;
        }
        let player = Player::new(self.modules[t.min(self.modules.len() - 1)].clone(), self.rate);
        let instant = self.music.is_empty() || fade <= 0.0;
        self.music.push(MusicVoice { player, gain: if instant { 1.0 } else { 0.0 }, target: 1.0, speed });
    }

    fn render(&mut self, frames: usize, music_vol: f32, sfx_vol: f32, muted: bool) {
        self.buf.clear();
        self.buf.resize(frames * 2, 0.0);
        let dt = frames as f32 / self.rate;
        for v in self.music.iter_mut() {
            if v.gain < v.target {
                v.gain = (v.gain + v.speed * dt).min(v.target);
            } else if v.gain > v.target {
                v.gain = (v.gain - v.speed * dt).max(v.target);
            }
            if v.gain > 0.0 {
                v.player.render(&mut self.buf, v.gain * music_vol * MUSIC_GAIN);
            }
        }
        self.music.retain(|v| v.gain > 0.0 || v.target > 0.0);
        let g = sfx_vol * SFX_GAIN;
        for v in self.voices.iter_mut() {
            let n = (v.data.len() - v.pos).min(frames);
            for k in 0..n {
                let s = v.data[v.pos + k] * g;
                self.buf[k * 2] += s * v.l;
                self.buf[k * 2 + 1] += s * v.r;
            }
            v.pos += n;
        }
        self.voices.retain(|v| v.pos < v.data.len());
        for x in self.buf.iter_mut() {
            *x = if muted { 0.0 } else { soft_clip(*x) };
        }
    }
}

fn soft_clip(x: f32) -> f32 {
    if x.abs() < 0.8 {
        x
    } else {
        x.signum() * (0.8 + 0.2 * ((x.abs() - 0.8) / 0.2).tanh())
    }
}

// ------------------------------------------------------------------ API for the game

pub fn set_volumes(music: f32, sfx: f32, muted: bool) {
    STATE.with(|s| {
        let mut s = s.borrow_mut();
        s.music_vol = music;
        s.sfx_vol = sfx;
        s.muted = muted;
    });
}

// Switch music with a crossfade (seconds); does nothing if the track already plays
pub fn play_music(t: usize, fade: f32) {
    STATE.with(|s| {
        let mut s = s.borrow_mut();
        if s.track == Some(t) {
            return;
        }
        s.track = Some(t);
        if let Some(e) = s.engine.as_mut() {
            e.start_track(t, fade);
        }
    });
}

// How often the current track has looped (0 before audio started)
pub fn music_loops() -> u32 {
    STATE.with(|s| {
        let s = s.borrow();
        s.engine.as_ref().and_then(|e| e.music.iter().rev().find(|v| v.target > 0.0)).map_or(0, |v| v.player.loops)
    })
}

pub fn current_track() -> Option<usize> {
    STATE.with(|s| s.borrow().track)
}

// pan: -1 (left) .. 1 (right)
pub fn play_sfx(index: usize, vol: f32, pan: f32) {
    STATE.with(|s| {
        let mut s = s.borrow_mut();
        if s.muted {
            return;
        }
        if let Some(e) = s.engine.as_mut() {
            if let Some(d) = e.sfx.get(index) {
                if e.voices.len() < 24 {
                    let p = (pan.clamp(-1.0, 1.0) + 1.0) * 0.5;
                    e.voices.push(SfxVoice { data: d.clone(), pos: 0, l: vol * (1.0 - p).sqrt(), r: vol * p.sqrt() });
                }
            }
        }
    });
}

// ------------------------------------------------------------------ called from JS

#[no_mangle]
pub extern "C" fn dc_audio_init(rate: f32) {
    STATE.with(|s| {
        let mut s = s.borrow_mut();
        if s.engine.is_some() {
            return;
        }
        let mut e = Engine::new(rate.clamp(8000.0, 192000.0));
        if let Some(t) = s.track {
            e.start_track(t, 0.0);
        }
        s.engine = Some(e);
    });
}

#[no_mangle]
pub extern "C" fn dc_audio_render(frames: u32) -> *const f32 {
    STATE.with(|s| {
        let mut s = s.borrow_mut();
        let (mv, sv, muted) = (s.music_vol, s.sfx_vol, s.muted);
        match s.engine.as_mut() {
            Some(e) => {
                e.render(frames as usize, mv, sv, muted);
                e.buf.as_ptr()
            }
            None => std::ptr::null(),
        }
    })
}

// ------------------------------------------------------------------ desktop sound output

// The game renders a little ahead into a queue each frame; the sound card's thread takes from it.
// The engine itself stays on the game thread, like in the browser.
#[cfg(not(target_arch = "wasm32"))]
pub mod native {
    use super::STATE;
    use cpal::traits::{DeviceTrait, HostTrait, StreamTrait};
    use std::cell::RefCell;
    use std::collections::VecDeque;
    use std::sync::{Arc, Mutex};

    // seconds rendered ahead: covers a slow frame or two
    const AHEAD: f32 = 0.07;

    struct Out {
        _stream: cpal::Stream,
        queue: Arc<Mutex<VecDeque<f32>>>, // interleaved stereo
        rate: f32,
    }

    thread_local! {
        static OUT: RefCell<Option<Out>> = const { RefCell::new(None) };
    }

    // opens the default output device and starts the engine; without one the game stays silent
    pub fn start() {
        match open() {
            Ok(out) => {
                super::dc_audio_init(out.rate);
                OUT.with(|o| *o.borrow_mut() = Some(out));
            }
            Err(e) => eprintln!("DungeonCraft: no sound ({})", e),
        }
    }

    fn open() -> Result<Out, String> {
        let dev = cpal::default_host().default_output_device().ok_or("no output device")?;
        let cfg = dev.default_output_config().map_err(|e| e.to_string())?;
        let rate = cfg.sample_rate() as f32;
        let channels = cfg.channels() as usize;
        let queue = Arc::new(Mutex::new(VecDeque::new()));
        let sc: cpal::StreamConfig = cfg.config();
        use cpal::SampleFormat as F;
        let stream = match cfg.sample_format() {
            F::F32 => build::<f32>(&dev, &sc, channels, queue.clone()),
            F::I16 => build::<i16>(&dev, &sc, channels, queue.clone()),
            F::U16 => build::<u16>(&dev, &sc, channels, queue.clone()),
            F::I32 => build::<i32>(&dev, &sc, channels, queue.clone()),
            f => Err(format!("sample format {:?}", f)),
        }?;
        stream.play().map_err(|e| e.to_string())?;
        Ok(Out { _stream: stream, queue, rate })
    }

    fn build<T: cpal::SizedSample + cpal::FromSample<f32>>(dev: &cpal::Device, sc: &cpal::StreamConfig, channels: usize, queue: Arc<Mutex<VecDeque<f32>>>) -> Result<cpal::Stream, String> {
        let channels = channels.max(1);
        dev.build_output_stream(
            sc.clone(),
            move |out: &mut [T], _: &cpal::OutputCallbackInfo| {
                let mut q = queue.lock().unwrap_or_else(|e| e.into_inner());
                for frame in out.chunks_mut(channels) {
                    // an empty queue (a stalled frame) plays silence
                    let (l, r) = if q.len() >= 2 { (q.pop_front().unwrap_or(0.0), q.pop_front().unwrap_or(0.0)) } else { (0.0, 0.0) };
                    for (c, s) in frame.iter_mut().enumerate() {
                        let v = match (channels, c) {
                            (1, _) => (l + r) * 0.5,
                            (_, 0) => l,
                            (_, 1) => r,
                            _ => 0.0,
                        };
                        *s = T::from_sample(v);
                    }
                }
            },
            |e| eprintln!("DungeonCraft: sound output: {}", e),
            None,
        )
        .map_err(|e| e.to_string())
    }

    // called once per frame: tops the queue up to AHEAD seconds
    pub fn pump() {
        OUT.with(|o| {
            let o = o.borrow();
            let Some(o) = o.as_ref() else { return };
            let want = (o.rate * AHEAD) as usize;
            let have = o.queue.lock().unwrap_or_else(|e| e.into_inner()).len() / 2;
            if have >= want {
                return;
            }
            STATE.with(|s| {
                let mut s = s.borrow_mut();
                let (mv, sv, muted) = (s.music_vol, s.sfx_vol, s.muted);
                if let Some(e) = s.engine.as_mut() {
                    e.render(want - have, mv, sv, muted);
                    o.queue.lock().unwrap_or_else(|e| e.into_inner()).extend(e.buf.iter().copied());
                }
            });
        });
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn the_music_player_offers_only_calm_tracks_with_titles() {
        let l = player_tracks();
        assert!(l.len() > 20);
        for t in l {
            let id = track_id(t);
            assert!(!id.starts_with("battle") && !id.starts_with("victory") && id != "defeat" && !id.starts_with("assault"), "{}", id);
            assert!(!track_title(t).is_empty());
            assert_eq!(track_by_id(id), Some(t));
        }
        assert_eq!(track_by_id(""), None);
        assert_eq!(track_title(track_by_id("build13").unwrap()), "Underground River");
    }

    #[test]
    fn engine_crossfade_and_sfx() {
        dc_audio_init(48000.0);
        let build = tracks_in(Category::Build);
        let battle = tracks_in(Category::Battle);
        assert_eq!(build.len(), 19);
        assert_eq!(tracks_in(Category::Surface).len(), 4);
        assert_eq!(tracks_in(Category::SurfaceBattle).len(), 2);
        play_music(build[0], 0.0);
        let mut peak = 0.0f32;
        for k in 0..200 {
            if k == 50 {
                play_music(battle[0], 2.5);
            }
            if k % 10 == 0 {
                play_sfx(k % crate::game::SFX_ALL.len(), 1.0, 0.3);
            }
            let p = dc_audio_render(1024);
            assert!(!p.is_null());
            let buf = unsafe { std::slice::from_raw_parts(p, 2048) };
            for &v in buf {
                assert!(v.is_finite() && v.abs() <= 1.0);
                peak = peak.max(v.abs());
            }
        }
        assert!(peak > 0.05);
        assert_eq!(current_track(), Some(battle[0]));
    }
}