librespot/src/metadata.rs

use protobuf::{self, Message};
use std::any::{Any, TypeId};
use std::collections::HashMap;
use std::fmt;
use std::slice::bytes::copy_memory;
use std::sync::{mpsc, Arc, Condvar, Mutex, MutexGuard, Weak};
use std::thread;

use librespot_protocol as protocol;
use mercury::{MercuryRequest, MercuryMethod};
use subsystem::Subsystem;
use util::{SpotifyId, FileId};

pub trait MetadataTrait : Send + Any + 'static {
    type Message: protobuf::MessageStatic;
    fn from_msg(msg: &Self::Message) -> Self;
    fn base_url() -> &'static str;
    fn request(r: MetadataRef<Self>) -> MetadataRequest;
}

#[derive(Debug)]
pub struct Track {
    pub name: String,
    pub album: SpotifyId,
    pub files: Vec<FileId>
}

impl MetadataTrait for Track {
    type Message = protocol::metadata::Track;
    fn from_msg(msg: &Self::Message) -> Self {
        Track {
            name: msg.get_name().to_string(),
            album: SpotifyId::from_raw(msg.get_album().get_gid()),
            files: msg.get_file().iter()
                .map(|file| {
                    let mut dst = [0u8; 20];
                    copy_memory(&file.get_gid(), &mut dst);
                    dst
                })
                .collect(),
        }
    }
    fn base_url() -> &'static str {
        "hm://metadata/3/track"
    }
    fn request(r: MetadataRef<Self>) -> MetadataRequest {
        MetadataRequest::Track(r)
    }
}

#[derive(Debug)]
pub struct Album {
    pub name: String,
    pub artists: Vec<SpotifyId>,
    pub covers: Vec<FileId>
}

impl MetadataTrait for Album {
    type Message = protocol::metadata::Album;
    fn from_msg(msg: &Self::Message) -> Self {
        Album {
            name: msg.get_name().to_string(),
            artists: msg.get_artist().iter()
                .map(|a| SpotifyId::from_raw(a.get_gid()))
                .collect(),
            covers: msg.get_cover_group().get_image().iter()
                .map(|image| {
                    let mut dst = [0u8; 20];
                    copy_memory(&image.get_file_id(), &mut dst);
                    dst
                })
                .collect(),
        }
    }
    fn base_url() -> &'static str {
        "hm://metadata/3/album"
    }
    fn request(r: MetadataRef<Self>) -> MetadataRequest {
        MetadataRequest::Album(r)
    }
}

#[derive(Debug)]
pub struct Artist {
    pub name: String,
}

impl MetadataTrait for Artist {
    type Message = protocol::metadata::Artist;
    fn from_msg(msg: &Self::Message) -> Self {
        Artist {
            name: msg.get_name().to_string(),
        }
    }
    fn base_url() -> &'static str {
        "hm://metadata/3/artist"
    }
    fn request(r: MetadataRef<Self>) -> MetadataRequest {
        MetadataRequest::Artist(r)
    }
}

#[derive(Debug)]
pub enum MetadataState<T> {
    Loading,
    Loaded(T),
    Error,
}

pub struct Metadata<T: MetadataTrait> {
    id: SpotifyId,
    state: Mutex<MetadataState<T>>,
    cond: Condvar
}

pub type MetadataRef<T> = Arc<Metadata<T>>;

pub type TrackRef = MetadataRef<Track>;
pub type AlbumRef = MetadataRef<Album>;
pub type ArtistRef = MetadataRef<Artist>;

pub struct MetadataCache {
    metadata: mpsc::Sender<MetadataRequest>,
    cache: HashMap<(SpotifyId, TypeId), Box<Any + 'static>>
}

impl MetadataCache {
    pub fn new(metadata: mpsc::Sender<MetadataRequest>) -> MetadataCache {
        MetadataCache {
            metadata: metadata,
            cache: HashMap::new()
        }
    }

    pub fn get<T: MetadataTrait>(&mut self, id: SpotifyId)
      -> MetadataRef<T> {
        let key = (id, TypeId::of::<T>());

        self.cache.get(&key)
            .and_then(|x| x.downcast_ref::<Weak<Metadata<T>>>())
            .and_then(|x| x.upgrade())
            .unwrap_or_else(|| {
                let x : MetadataRef<T> = Arc::new(Metadata{
                    id: id,
                    state: Mutex::new(MetadataState::Loading),
                    cond: Condvar::new()
                });

                self.cache.insert(key, Box::new(x.downgrade()));
                self.metadata.send(T::request(x.clone())).unwrap();
                x
            })
    }
}

impl <T: MetadataTrait> Metadata<T> {
    pub fn id(&self) -> SpotifyId {
        self.id
    }

    pub fn lock(&self) -> MutexGuard<MetadataState<T>> {
        self.state.lock().unwrap()
    }

    pub fn wait(&self) -> MutexGuard<MetadataState<T>> {
        let mut handle = self.lock();
        while handle.is_loading() {
            handle = self.cond.wait(handle).unwrap();
        }
        handle
    }

    pub fn set(&self, state: MetadataState<T>) {
        let mut handle = self.lock();
        *handle = state;
        self.cond.notify_all();
    }
}

impl <T: MetadataTrait + fmt::Debug> fmt::Debug for Metadata<T> {
    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        write!(f, "Metadata<>({:?}, {:?})", self.id, *self.lock())
    }
}

impl <T: MetadataTrait> MetadataState<T> {
    pub fn is_loading(&self) -> bool {
        match *self {
            MetadataState::Loading => true,
            _ => false
        }
    }

    pub fn is_loaded(&self) -> bool {
        match *self {
            MetadataState::Loaded(_) => true,
            _ => false
        }
    }

    pub fn unwrap<'s>(&'s self) -> &'s T {
        match *self {
            MetadataState::Loaded(ref data) => data,
            _ => panic!("Not loaded")
        }
    }
}

#[derive(Debug)]
pub enum MetadataRequest {
    Artist(ArtistRef),
    Album(AlbumRef),
    Track(TrackRef)
}

pub struct MetadataManager {
    requests: mpsc::Receiver<MetadataRequest>,
    mercury: mpsc::Sender<MercuryRequest>
}

impl MetadataManager {
    pub fn new(mercury: mpsc::Sender<MercuryRequest>) -> (MetadataManager,
                                                          mpsc::Sender<MetadataRequest>) {
        let (tx, rx) = mpsc::channel();
        (MetadataManager {
            requests: rx,
            mercury: mercury
        }, tx)
    }

    fn load<T: MetadataTrait> (&self, object: MetadataRef<T>) {
        let mercury = self.mercury.clone();
        thread::spawn(move || {
            let (tx, rx) = mpsc::channel();
            
            mercury.send(MercuryRequest {
                method: MercuryMethod::GET,
                url: format!("{}/{}", T::base_url(), object.id.to_base16()),
                mime: None,
                callback: Some(tx)
            }).unwrap();

            let response = rx.recv().unwrap();

            let msg : T::Message = protobuf::parse_from_bytes(
                response.payload.front().unwrap()).unwrap();

            object.set(MetadataState::Loaded(T::from_msg(&msg)));
        });
    }
}

impl Subsystem for MetadataManager {
    fn run(self) {
        for req in self.requests.iter() {
            match req {
                MetadataRequest::Artist(artist) => {
                    self.load(artist)
                }
                MetadataRequest::Album(album) => {
                    self.load(album)
                }
                MetadataRequest::Track(track) => {
                    self.load(track)
                }
            }
        }
    }
}