librespot/playback/src/player.rs

use byteorder::{LittleEndian, ReadBytesExt};
use futures;
use futures::{future, Async, Future, Poll, Stream};
use std;
use std::borrow::Cow;
use std::cmp::max;
use std::io::{Read, Result, Seek, SeekFrom};
use std::mem;
use std::thread;
use std::time::{Duration, Instant};

use crate::config::{Bitrate, PlayerConfig};
use librespot_core::session::Session;
use librespot_core::spotify_id::SpotifyId;

use librespot_core::util::SeqGenerator;

use crate::audio::{AudioDecrypt, AudioFile, StreamLoaderController};
use crate::audio::{VorbisDecoder, VorbisPacket};
use crate::audio::{
    READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS, READ_AHEAD_BEFORE_PLAYBACK_SECONDS,
    READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS, READ_AHEAD_DURING_PLAYBACK_SECONDS,
};
use crate::audio_backend::Sink;
use crate::metadata::{AudioItem, FileFormat};
use crate::mixer::AudioFilter;

const PRELOAD_NEXT_TRACK_BEFORE_END_DURATION_MS: u32 = 30000;

pub struct Player {
    commands: Option<futures::sync::mpsc::UnboundedSender<PlayerCommand>>,
    thread_handle: Option<thread::JoinHandle<()>>,
    play_request_id_generator: SeqGenerator<u64>,
}

struct PlayerInternal {
    session: Session,
    config: PlayerConfig,
    commands: futures::sync::mpsc::UnboundedReceiver<PlayerCommand>,

    state: PlayerState,
    preload: PlayerPreload,
    sink: Box<dyn Sink>,
    sink_running: bool,
    audio_filter: Option<Box<dyn AudioFilter + Send>>,
    event_senders: Vec<futures::sync::mpsc::UnboundedSender<PlayerEvent>>,
}

enum PlayerCommand {
    Load {
        track_id: SpotifyId,
        play_request_id: u64,
        play: bool,
        position_ms: u32,
    },
    Preload {
        track_id: SpotifyId,
    },
    Play,
    Pause,
    Stop,
    Seek(u32),
    AddEventSender(futures::sync::mpsc::UnboundedSender<PlayerEvent>),
    EmitVolumeSetEvent(u16),
}

#[derive(Debug, Clone)]
pub enum PlayerEvent {
    Loading {
        play_request_id: u64,
        track_id: SpotifyId,
        position_ms: u32,
    },
    Started {
        play_request_id: u64,
        track_id: SpotifyId,
        position_ms: u32,
    },
    Playing {
        play_request_id: u64,
        track_id: SpotifyId,
        position_ms: u32,
        duration_ms: u32,
    },
    Changed {
        old_track_id: SpotifyId,
        new_track_id: SpotifyId,
    },
    TimeToPreloadNextTrack {
        play_request_id: u64,
        track_id: SpotifyId,
    },
    EndOfTrack {
        play_request_id: u64,
        track_id: SpotifyId,
    },
    Paused {
        play_request_id: u64,
        track_id: SpotifyId,
        position_ms: u32,
        duration_ms: u32,
    },
    Stopped {
        play_request_id: u64,
        track_id: SpotifyId,
    },
    VolumeSet {
        volume: u16,
    },
}

impl PlayerEvent {
    pub fn get_play_request_id(&self) -> Option<u64> {
        use PlayerEvent::*;
        match self {
            Loading {
                play_request_id, ..
            }
            | Started {
                play_request_id, ..
            }
            | Playing {
                play_request_id, ..
            }
            | TimeToPreloadNextTrack {
                play_request_id, ..
            }
            | EndOfTrack {
                play_request_id, ..
            }
            | Paused {
                play_request_id, ..
            }
            | Stopped {
                play_request_id, ..
            } => Some(*play_request_id),
            Changed { .. } | VolumeSet { .. } => None,
        }
    }
}

pub type PlayerEventChannel = futures::sync::mpsc::UnboundedReceiver<PlayerEvent>;

#[derive(Clone, Copy, Debug)]
struct NormalisationData {
    track_gain_db: f32,
    track_peak: f32,
    album_gain_db: f32,
    album_peak: f32,
}

impl NormalisationData {
    fn parse_from_file<T: Read + Seek>(mut file: T) -> Result<NormalisationData> {
        const SPOTIFY_NORMALIZATION_HEADER_START_OFFSET: u64 = 144;
        file.seek(SeekFrom::Start(SPOTIFY_NORMALIZATION_HEADER_START_OFFSET))
            .unwrap();

        let track_gain_db = file.read_f32::<LittleEndian>().unwrap();
        let track_peak = file.read_f32::<LittleEndian>().unwrap();
        let album_gain_db = file.read_f32::<LittleEndian>().unwrap();
        let album_peak = file.read_f32::<LittleEndian>().unwrap();

        let r = NormalisationData {
            track_gain_db: track_gain_db,
            track_peak: track_peak,
            album_gain_db: album_gain_db,
            album_peak: album_peak,
        };

        Ok(r)
    }

    fn get_factor(config: &PlayerConfig, data: NormalisationData) -> f32 {
        let mut normalisation_factor = f32::powf(
            10.0,
            (data.track_gain_db + config.normalisation_pregain) / 20.0,
        );

        if normalisation_factor * data.track_peak > 1.0 {
            warn!("Reducing normalisation factor to prevent clipping. Please add negative pregain to avoid.");
            normalisation_factor = 1.0 / data.track_peak;
        }

        debug!("Normalisation Data: {:?}", data);
        debug!("Applied normalisation factor: {}", normalisation_factor);

        normalisation_factor
    }
}

impl Player {
    pub fn new<F>(
        config: PlayerConfig,
        session: Session,
        audio_filter: Option<Box<dyn AudioFilter + Send>>,
        sink_builder: F,
    ) -> (Player, PlayerEventChannel)
    where
        F: FnOnce() -> Box<dyn Sink> + Send + 'static,
    {
        let (cmd_tx, cmd_rx) = futures::sync::mpsc::unbounded();
        let (event_sender, event_receiver) = futures::sync::mpsc::unbounded();

        let handle = thread::spawn(move || {
            debug!("new Player[{}]", session.session_id());

            let internal = PlayerInternal {
                session: session,
                config: config,
                commands: cmd_rx,

                state: PlayerState::Stopped,
                preload: PlayerPreload::None,
                sink: sink_builder(),
                sink_running: false,
                audio_filter: audio_filter,
                event_senders: [event_sender].to_vec(),
            };

            let _ = internal.wait();
            debug!("PlayerInternal thread finished.");
        });

        (
            Player {
                commands: Some(cmd_tx),
                thread_handle: Some(handle),
                play_request_id_generator: SeqGenerator::new(0),
            },
            event_receiver,
        )
    }

    fn command(&self, cmd: PlayerCommand) {
        self.commands.as_ref().unwrap().unbounded_send(cmd).unwrap();
    }

    pub fn load(&mut self, track_id: SpotifyId, start_playing: bool, position_ms: u32) -> u64 {
        let play_request_id = self.play_request_id_generator.get();
        self.command(PlayerCommand::Load {
            track_id,
            play_request_id,
            play: start_playing,
            position_ms,
        });

        play_request_id
    }

    pub fn preload(&self, track_id: SpotifyId) {
        self.command(PlayerCommand::Preload { track_id });
    }

    pub fn play(&self) {
        self.command(PlayerCommand::Play)
    }

    pub fn pause(&self) {
        self.command(PlayerCommand::Pause)
    }

    pub fn stop(&self) {
        self.command(PlayerCommand::Stop)
    }

    pub fn seek(&self, position_ms: u32) {
        self.command(PlayerCommand::Seek(position_ms));
    }

    pub fn get_player_event_channel(&self) -> PlayerEventChannel {
        let (event_sender, event_receiver) = futures::sync::mpsc::unbounded();
        self.command(PlayerCommand::AddEventSender(event_sender));
        event_receiver
    }

    pub fn get_end_of_track_future(&self) -> Box<dyn Future<Item = (), Error = ()>> {
        let result = self
            .get_player_event_channel()
            .filter(|event| match event {
                PlayerEvent::EndOfTrack { .. } | PlayerEvent::Stopped { .. } => true,
                _ => false,
            })
            .into_future()
            .map_err(|_| ())
            .map(|_| ());
        Box::new(result)
    }

    pub fn emit_volume_set_event(&self, volume: u16) {
        self.command(PlayerCommand::EmitVolumeSetEvent(volume));
    }
}

impl Drop for Player {
    fn drop(&mut self) {
        debug!("Shutting down player thread ...");
        self.commands = None;
        if let Some(handle) = self.thread_handle.take() {
            match handle.join() {
                Ok(_) => (),
                Err(_) => error!("Player thread panicked!"),
            }
        }
    }
}

struct PlayerLoadedTrackData {
    decoder: Decoder,
    normalisation_factor: f32,
    stream_loader_controller: StreamLoaderController,
    bytes_per_second: usize,
    duration_ms: u32,
    stream_position_pcm: u64,
}

enum PlayerPreload {
    None,
    Loading {
        track_id: SpotifyId,
        loader: Box<dyn Future<Item = PlayerLoadedTrackData, Error = ()>>,
    },
    Ready {
        track_id: SpotifyId,
        loaded_track: PlayerLoadedTrackData,
    },
}

type Decoder = VorbisDecoder<Subfile<AudioDecrypt<AudioFile>>>;

enum PlayerState {
    Stopped,
    Loading {
        track_id: SpotifyId,
        play_request_id: u64,
        start_playback: bool,
        loader: Box<dyn Future<Item = PlayerLoadedTrackData, Error = ()>>,
    },
    Paused {
        track_id: SpotifyId,
        play_request_id: u64,
        decoder: Decoder,
        normalisation_factor: f32,
        stream_loader_controller: StreamLoaderController,
        bytes_per_second: usize,
        duration_ms: u32,
        stream_position_pcm: u64,
        suggested_to_preload_next_track: bool,
    },
    Playing {
        track_id: SpotifyId,
        play_request_id: u64,
        decoder: Decoder,
        normalisation_factor: f32,
        stream_loader_controller: StreamLoaderController,
        bytes_per_second: usize,
        duration_ms: u32,
        stream_position_pcm: u64,
        reported_nominal_start_time: Option<Instant>,
        suggested_to_preload_next_track: bool,
    },
    EndOfTrack {
        track_id: SpotifyId,
        play_request_id: u64,
        loaded_track: Option<PlayerLoadedTrackData>,
    },
    Invalid,
}

impl PlayerState {
    fn is_playing(&self) -> bool {
        use self::PlayerState::*;
        match *self {
            Stopped | EndOfTrack { .. } | Paused { .. } | Loading { .. } => false,
            Playing { .. } => true,
            Invalid => panic!("invalid state"),
        }
    }

    fn is_stopped(&self) -> bool {
        use self::PlayerState::*;
        match *self {
            Stopped => true,
            _ => false,
        }
    }

    fn decoder(&mut self) -> Option<&mut Decoder> {
        use self::PlayerState::*;
        match *self {
            Stopped | EndOfTrack { .. } | Loading { .. } => None,
            Paused {
                ref mut decoder, ..
            }
            | Playing {
                ref mut decoder, ..
            } => Some(decoder),
            Invalid => panic!("invalid state"),
        }
    }

    fn stream_loader_controller(&mut self) -> Option<&mut StreamLoaderController> {
        use self::PlayerState::*;
        match *self {
            Stopped | EndOfTrack { .. } | Loading { .. } => None,
            Paused {
                ref mut stream_loader_controller,
                ..
            }
            | Playing {
                ref mut stream_loader_controller,
                ..
            } => Some(stream_loader_controller),
            Invalid => panic!("invalid state"),
        }
    }

    fn playing_to_end_of_track(&mut self) {
        use self::PlayerState::*;
        match mem::replace(self, Invalid) {
            Playing {
                track_id,
                play_request_id,
                decoder,
                duration_ms,
                bytes_per_second,
                normalisation_factor,
                stream_loader_controller,
                stream_position_pcm,
                ..
            } => {
                *self = EndOfTrack {
                    track_id,
                    play_request_id,
                    loaded_track: Some(PlayerLoadedTrackData {
                        decoder,
                        duration_ms,
                        bytes_per_second,
                        normalisation_factor,
                        stream_loader_controller,
                        stream_position_pcm,
                    }),
                };
            }
            _ => panic!("Called playing_to_end_of_track in non-playing state."),
        }
    }

    fn paused_to_playing(&mut self) {
        use self::PlayerState::*;
        match ::std::mem::replace(self, Invalid) {
            Paused {
                track_id,
                play_request_id,
                decoder,
                normalisation_factor,
                stream_loader_controller,
                duration_ms,
                bytes_per_second,
                stream_position_pcm,
                suggested_to_preload_next_track,
            } => {
                *self = Playing {
                    track_id,
                    play_request_id,
                    decoder,
                    normalisation_factor,
                    stream_loader_controller,
                    duration_ms,
                    bytes_per_second,
                    stream_position_pcm,
                    reported_nominal_start_time: None,
                    suggested_to_preload_next_track,
                };
            }
            _ => panic!("invalid state"),
        }
    }

    fn playing_to_paused(&mut self) {
        use self::PlayerState::*;
        match ::std::mem::replace(self, Invalid) {
            Playing {
                track_id,
                play_request_id,
                decoder,
                normalisation_factor,
                stream_loader_controller,
                duration_ms,
                bytes_per_second,
                stream_position_pcm,
                reported_nominal_start_time: _,
                suggested_to_preload_next_track,
            } => {
                *self = Paused {
                    track_id,
                    play_request_id,
                    decoder,
                    normalisation_factor,
                    stream_loader_controller,
                    duration_ms,
                    bytes_per_second,
                    stream_position_pcm,
                    suggested_to_preload_next_track,
                };
            }
            _ => panic!("invalid state"),
        }
    }
}

struct PlayerTrackLoader {
    session: Session,
    config: PlayerConfig,
}

impl PlayerTrackLoader {
    fn find_available_alternative<'a>(&self, audio: &'a AudioItem) -> Option<Cow<'a, AudioItem>> {
        if audio.available {
            Some(Cow::Borrowed(audio))
        } else {
            if let Some(alternatives) = &audio.alternatives {
                let alternatives = alternatives
                    .iter()
                    .map(|alt_id| AudioItem::get_audio_item(&self.session, *alt_id));
                let alternatives = future::join_all(alternatives).wait().unwrap();
                alternatives
                    .into_iter()
                    .find(|alt| alt.available)
                    .map(Cow::Owned)
            } else {
                None
            }
        }
    }

    fn stream_data_rate(&self, format: FileFormat) -> usize {
        match format {
            FileFormat::OGG_VORBIS_96 => 12 * 1024,
            FileFormat::OGG_VORBIS_160 => 20 * 1024,
            FileFormat::OGG_VORBIS_320 => 40 * 1024,
            FileFormat::MP3_256 => 32 * 1024,
            FileFormat::MP3_320 => 40 * 1024,
            FileFormat::MP3_160 => 20 * 1024,
            FileFormat::MP3_96 => 12 * 1024,
            FileFormat::MP3_160_ENC => 20 * 1024,
            FileFormat::MP4_128_DUAL => 16 * 1024,
            FileFormat::OTHER3 => 40 * 1024, // better some high guess than nothing
            FileFormat::AAC_160 => 20 * 1024,
            FileFormat::AAC_320 => 40 * 1024,
            FileFormat::MP4_128 => 16 * 1024,
            FileFormat::OTHER5 => 40 * 1024, // better some high guess than nothing
        }
    }

    fn load_track(&self, spotify_id: SpotifyId, position_ms: u32) -> Option<PlayerLoadedTrackData> {
        let audio = match AudioItem::get_audio_item(&self.session, spotify_id).wait() {
            Ok(audio) => audio,
            Err(_) => {
                error!("Unable to load audio item.");
                return None;
            }
        };

        info!("Loading <{}> with Spotify URI <{}>", audio.name, audio.uri);

        let audio = match self.find_available_alternative(&audio) {
            Some(audio) => audio,
            None => {
                warn!("<{}> is not available", audio.uri);
                return None;
            }
        };

        assert!(audio.duration >= 0);
        let duration_ms = audio.duration as u32;

        // (Most) podcasts seem to support only 96 bit Vorbis, so fall back to it
        let formats = match self.config.bitrate {
            Bitrate::Bitrate96 => [
                FileFormat::OGG_VORBIS_96,
                FileFormat::OGG_VORBIS_160,
                FileFormat::OGG_VORBIS_320,
            ],
            Bitrate::Bitrate160 => [
                FileFormat::OGG_VORBIS_160,
                FileFormat::OGG_VORBIS_96,
                FileFormat::OGG_VORBIS_320,
            ],
            Bitrate::Bitrate320 => [
                FileFormat::OGG_VORBIS_320,
                FileFormat::OGG_VORBIS_160,
                FileFormat::OGG_VORBIS_96,
            ],
        };
        let format = formats
            .iter()
            .find(|format| audio.files.contains_key(format))
            .unwrap();

        let file_id = match audio.files.get(&format) {
            Some(&file_id) => file_id,
            None => {
                warn!("<{}> in not available in format {:?}", audio.name, format);
                return None;
            }
        };

        let bytes_per_second = self.stream_data_rate(*format);
        let play_from_beginning = position_ms == 0;

        let key = self.session.audio_key().request(spotify_id, file_id);
        let encrypted_file = AudioFile::open(
            &self.session,
            file_id,
            bytes_per_second,
            play_from_beginning,
        );

        let encrypted_file = match encrypted_file.wait() {
            Ok(encrypted_file) => encrypted_file,
            Err(_) => {
                error!("Unable to load encrypted file.");
                return None;
            }
        };

        let mut stream_loader_controller = encrypted_file.get_stream_loader_controller();

        if play_from_beginning {
            // No need to seek -> we stream from the beginning
            stream_loader_controller.set_stream_mode();
        } else {
            // we need to seek -> we set stream mode after the initial seek.
            stream_loader_controller.set_random_access_mode();
        }

        let key = match key.wait() {
            Ok(key) => key,
            Err(_) => {
                error!("Unable to load decryption key");
                return None;
            }
        };

        let mut decrypted_file = AudioDecrypt::new(key, encrypted_file);

        let normalisation_factor = match NormalisationData::parse_from_file(&mut decrypted_file) {
            Ok(normalisation_data) => {
                NormalisationData::get_factor(&self.config, normalisation_data)
            }
            Err(_) => {
                warn!("Unable to extract normalisation data, using default value.");
                1.0 as f32
            }
        };

        let audio_file = Subfile::new(decrypted_file, 0xa7);

        let mut decoder = VorbisDecoder::new(audio_file).unwrap();

        if position_ms != 0 {
            match decoder.seek(position_ms as i64) {
                Ok(_) => (),
                Err(err) => error!("Vorbis error: {:?}", err),
            }
            stream_loader_controller.set_stream_mode();
        }
        let stream_position_pcm = PlayerInternal::position_ms_to_pcm(position_ms);
        info!("<{}> ({} ms) loaded", audio.name, audio.duration);
        Some(PlayerLoadedTrackData {
            decoder,
            normalisation_factor,
            stream_loader_controller,
            bytes_per_second,
            duration_ms,
            stream_position_pcm,
        })
    }
}

impl Future for PlayerInternal {
    type Item = ();
    type Error = ();

    fn poll(&mut self) -> Poll<(), ()> {
        loop {
            let mut all_futures_completed_or_not_ready = true;

            // process commands that were sent to us
            let cmd = match self.commands.poll() {
                Ok(Async::Ready(None)) => return Ok(Async::Ready(())), // client has disconnected - shut down.
                Ok(Async::Ready(Some(cmd))) => {
                    all_futures_completed_or_not_ready = false;
                    Some(cmd)
                }
                Ok(Async::NotReady) => None,
                Err(_) => None,
            };

            if let Some(cmd) = cmd {
                self.handle_command(cmd);
            }

            // Handle loading of a new track to play
            if let PlayerState::Loading {
                ref mut loader,
                track_id,
                start_playback,
                play_request_id,
            } = self.state
            {
                match loader.poll() {
                    Ok(Async::Ready(loaded_track)) => {
                        self.start_playback(
                            track_id,
                            play_request_id,
                            loaded_track,
                            start_playback,
                            false,
                        );
                        if let PlayerState::Loading { .. } = self.state {
                            panic!("The state wasn't changed by start_playback()");
                        }
                    }
                    Ok(Async::NotReady) => (),
                    Err(_) => {
                        self.handle_player_stop();
                        assert!(self.state.is_stopped());
                    }
                }
            }

            // handle pending preload requests.
            if let PlayerPreload::Loading {
                ref mut loader,
                track_id,
            } = self.preload
            {
                match loader.poll() {
                    Ok(Async::Ready(loaded_track)) => {
                        self.preload = PlayerPreload::Ready {
                            track_id,
                            loaded_track,
                        };
                    }
                    Ok(Async::NotReady) => (),
                    Err(_) => {
                        self.preload = PlayerPreload::None;
                    }
                }
            }

            if self.state.is_playing() {
                self.ensure_sink_running();
            }

            if self.sink_running {
                let mut current_normalisation_factor: f32 = 1.0;

                let packet = if let PlayerState::Playing {
                    track_id,
                    play_request_id,
                    ref mut decoder,
                    normalisation_factor,
                    ref mut stream_position_pcm,
                    ref mut reported_nominal_start_time,
                    duration_ms,
                    ..
                } = self.state
                {
                    current_normalisation_factor = normalisation_factor;
                    let packet = decoder.next_packet().expect("Vorbis error");

                    if let Some(ref packet) = packet {
                        *stream_position_pcm =
                            *stream_position_pcm + (packet.data().len() / 2) as u64;
                        let stream_position_millis = Self::position_pcm_to_ms(*stream_position_pcm);

                        let notify_about_position = match *reported_nominal_start_time {
                            None => true,
                            Some(reported_nominal_start_time) => {
                                // only notify if we're behind. If we're ahead it's probably due to a buffer of the backend and we;re actually in time.
                                let lag = (Instant::now() - reported_nominal_start_time).as_millis()
                                    as i64
                                    - stream_position_millis as i64;
                                if lag > 1000 {
                                    true
                                } else {
                                    false
                                }
                            }
                        };
                        if notify_about_position {
                            *reported_nominal_start_time = Some(
                                Instant::now()
                                    - Duration::from_millis(stream_position_millis as u64),
                            );
                            self.send_event(PlayerEvent::Playing {
                                track_id,
                                play_request_id,
                                position_ms: stream_position_millis as u32,
                                duration_ms,
                            });
                        }
                    }

                    Some(packet)
                } else {
                    None
                };

                if let Some(packet) = packet {
                    self.handle_packet(packet, current_normalisation_factor);
                }
            }

            if let PlayerState::Playing {
                track_id,
                play_request_id,
                duration_ms,
                stream_position_pcm,
                ref mut stream_loader_controller,
                ref mut suggested_to_preload_next_track,
                ..
            }
            | PlayerState::Paused {
                track_id,
                play_request_id,
                duration_ms,
                stream_position_pcm,
                ref mut stream_loader_controller,
                ref mut suggested_to_preload_next_track,
                ..
            } = self.state
            {
                let stream_position_millis = Self::position_pcm_to_ms(stream_position_pcm);
                if (!*suggested_to_preload_next_track)
                    && ((duration_ms as i64 - stream_position_millis as i64)
                        < PRELOAD_NEXT_TRACK_BEFORE_END_DURATION_MS as i64)
                    && stream_loader_controller.range_to_end_available()
                {
                    *suggested_to_preload_next_track = true;
                    self.send_event(PlayerEvent::TimeToPreloadNextTrack {
                        track_id,
                        play_request_id,
                    });
                }
            }

            if self.session.is_invalid() {
                return Ok(Async::Ready(()));
            }

            if (!self.sink_running) && all_futures_completed_or_not_ready {
                return Ok(Async::NotReady);
            }
        }
    }
}

impl PlayerInternal {
    fn position_pcm_to_ms(position_pcm: u64) -> u32 {
        (position_pcm * 10 / 441) as u32
    }

    fn position_ms_to_pcm(position_ms: u32) -> u64 {
        position_ms as u64 * 441 / 10
    }

    fn ensure_sink_running(&mut self) {
        if !self.sink_running {
            trace!("== Starting sink ==");
            match self.sink.start() {
                Ok(()) => self.sink_running = true,
                Err(err) => error!("Could not start audio: {}", err),
            }
        }
    }

    fn ensure_sink_stopped(&mut self) {
        if self.sink_running {
            trace!("== Stopping sink ==");
            self.sink.stop().unwrap();
            self.sink_running = false;
        }
    }

    fn handle_player_stop(&mut self) {
        match self.state {
            PlayerState::Playing {
                track_id,
                play_request_id,
                ..
            }
            | PlayerState::Paused {
                track_id,
                play_request_id,
                ..
            }
            | PlayerState::EndOfTrack {
                track_id,
                play_request_id,
                ..
            }
            | PlayerState::Loading {
                track_id,
                play_request_id,
                ..
            } => {
                self.ensure_sink_stopped();
                self.send_event(PlayerEvent::Stopped {
                    track_id,
                    play_request_id,
                });
                self.state = PlayerState::Stopped;
            }
            PlayerState::Stopped => (),
            PlayerState::Invalid => panic!("invalid state"),
        }
    }

    fn handle_play(&mut self) {
        if let PlayerState::Paused {
            track_id,
            play_request_id,
            stream_position_pcm,
            ..
        } = self.state
        {
            self.state.paused_to_playing();

            let position_ms = Self::position_pcm_to_ms(stream_position_pcm);
            self.send_event(PlayerEvent::Started {
                track_id,
                play_request_id,
                position_ms,
            });
            self.ensure_sink_running();
        } else {
            warn!("Player::play called from invalid state");
        }
    }

    fn handle_pause(&mut self) {
        if let PlayerState::Playing {
            track_id,
            play_request_id,
            stream_position_pcm,
            duration_ms,
            ..
        } = self.state
        {
            self.state.playing_to_paused();

            self.ensure_sink_stopped();
            let position_ms = Self::position_pcm_to_ms(stream_position_pcm);
            self.send_event(PlayerEvent::Paused {
                track_id,
                play_request_id,
                position_ms,
                duration_ms,
            });
        } else {
            warn!("Player::pause called from invalid state");
        }
    }

    fn handle_packet(&mut self, packet: Option<VorbisPacket>, normalisation_factor: f32) {
        match packet {
            Some(mut packet) => {
                if packet.data().len() > 0 {
                    if let Some(ref editor) = self.audio_filter {
                        editor.modify_stream(&mut packet.data_mut())
                    };

                    if self.config.normalisation && normalisation_factor != 1.0 {
                        for x in packet.data_mut().iter_mut() {
                            *x = (*x as f32 * normalisation_factor) as i16;
                        }
                    }

                    if let Err(err) = self.sink.write(&packet.data()) {
                        error!("Could not write audio: {}", err);
                        self.ensure_sink_stopped();
                    }
                }
            }

            None => {
                self.state.playing_to_end_of_track();
                if let PlayerState::EndOfTrack {
                    track_id,
                    play_request_id,
                    ..
                } = self.state
                {
                    self.send_event(PlayerEvent::EndOfTrack {
                        track_id,
                        play_request_id,
                    })
                } else {
                    unreachable!();
                }
            }
        }
    }

    fn start_playback(
        &mut self,
        track_id: SpotifyId,
        play_request_id: u64,
        loaded_track: PlayerLoadedTrackData,
        start_playback: bool,
        state_is_invalid_because_the_same_track_is_getting_repeated: bool,
    ) {
        let position_ms = Self::position_pcm_to_ms(loaded_track.stream_position_pcm);

        match self.state {
            PlayerState::Playing {
                track_id: old_track_id,
                ..
            }
            | PlayerState::Paused {
                track_id: old_track_id,
                ..
            }
            | PlayerState::EndOfTrack {
                track_id: old_track_id,
                ..
            } => self.send_event(PlayerEvent::Changed {
                old_track_id: old_track_id,
                new_track_id: track_id,
            }),
            PlayerState::Stopped => self.send_event(PlayerEvent::Started {
                track_id,
                play_request_id,
                position_ms,
            }),
            PlayerState::Loading { .. } => (),
            PlayerState::Invalid { .. } => {
                if state_is_invalid_because_the_same_track_is_getting_repeated {
                    self.send_event(PlayerEvent::Changed {
                        old_track_id: track_id,
                        new_track_id: track_id,
                    })
                } else {
                    panic!("Player is in an invalid state.")
                }
            }
        }

        if start_playback {
            self.ensure_sink_running();

            self.send_event(PlayerEvent::Playing {
                track_id,
                play_request_id,
                position_ms,
                duration_ms: loaded_track.duration_ms,
            });

            self.state = PlayerState::Playing {
                track_id: track_id,
                play_request_id: play_request_id,
                decoder: loaded_track.decoder,
                normalisation_factor: loaded_track.normalisation_factor,
                stream_loader_controller: loaded_track.stream_loader_controller,
                duration_ms: loaded_track.duration_ms,
                bytes_per_second: loaded_track.bytes_per_second,
                stream_position_pcm: loaded_track.stream_position_pcm,
                reported_nominal_start_time: Some(
                    Instant::now() - Duration::from_millis(position_ms as u64),
                ),
                suggested_to_preload_next_track: false,
            };
        } else {
            self.state = PlayerState::Paused {
                track_id: track_id,
                play_request_id: play_request_id,
                decoder: loaded_track.decoder,
                normalisation_factor: loaded_track.normalisation_factor,
                stream_loader_controller: loaded_track.stream_loader_controller,
                duration_ms: loaded_track.duration_ms,
                bytes_per_second: loaded_track.bytes_per_second,
                stream_position_pcm: loaded_track.stream_position_pcm,
                suggested_to_preload_next_track: false,
            };

            self.send_event(PlayerEvent::Paused {
                track_id,
                play_request_id,
                position_ms,
                duration_ms: loaded_track.duration_ms,
            });
        }
    }

    fn handle_command(&mut self, cmd: PlayerCommand) {
        debug!("command={:?}", cmd);
        match cmd {
            PlayerCommand::Load {
                track_id,
                play_request_id,
                play,
                position_ms,
            } => {
                // emit the correct player event
                match self.state {
                    PlayerState::Playing {
                        track_id: old_track_id,
                        ..
                    }
                    | PlayerState::Paused {
                        track_id: old_track_id,
                        ..
                    }
                    | PlayerState::EndOfTrack {
                        track_id: old_track_id,
                        ..
                    }
                    | PlayerState::Loading {
                        track_id: old_track_id,
                        ..
                    } => self.send_event(PlayerEvent::Changed {
                        old_track_id: old_track_id,
                        new_track_id: track_id,
                    }),
                    PlayerState::Stopped => self.send_event(PlayerEvent::Started {
                        track_id,
                        play_request_id,
                        position_ms,
                    }),
                    PlayerState::Invalid { .. } => panic!("Player is in an invalid state."),
                }

                let mut load_command_processed = false;

                // Check if there's a matching loaded track in the EndOfTrack player state.
                // This is the case if we're repeating the same track again.
                if let PlayerState::EndOfTrack {
                    track_id: previous_track_id,
                    ref mut loaded_track,
                    ..
                } = self.state
                {
                    if previous_track_id == track_id {
                        let loaded_track = mem::replace(&mut *loaded_track, None);
                        if let Some(mut loaded_track) = loaded_track {
                            if Self::position_ms_to_pcm(position_ms)
                                != loaded_track.stream_position_pcm
                            {
                                loaded_track
                                    .stream_loader_controller
                                    .set_random_access_mode();
                                let _ = loaded_track.decoder.seek(position_ms as i64); // This may be blocking.
                                                                                       // But most likely the track is fully
                                                                                       // loaded already because we played
                                                                                       // to the end of it.
                                loaded_track.stream_loader_controller.set_stream_mode();
                                loaded_track.stream_position_pcm =
                                    Self::position_ms_to_pcm(position_ms);
                            }
                            self.start_playback(
                                track_id,
                                play_request_id,
                                loaded_track,
                                play,
                                false,
                            );
                            load_command_processed = true;
                        }
                    }
                }

                // Check if we are already playing the track. If so, just do a seek and update our info.
                if let PlayerState::Playing {
                    track_id: current_track_id,
                    ref mut stream_position_pcm,
                    ref mut decoder,
                    ref mut stream_loader_controller,
                    ..
                }
                | PlayerState::Paused {
                    track_id: current_track_id,
                    ref mut stream_position_pcm,
                    ref mut decoder,
                    ref mut stream_loader_controller,
                    ..
                } = self.state
                {
                    if current_track_id == track_id {
                        if Self::position_ms_to_pcm(position_ms) != *stream_position_pcm {
                            stream_loader_controller.set_random_access_mode();
                            let _ = decoder.seek(position_ms as i64); // This may be blocking.
                            stream_loader_controller.set_stream_mode();
                            *stream_position_pcm = Self::position_ms_to_pcm(position_ms);
                        }

                        let old_state = mem::replace(&mut self.state, PlayerState::Invalid);

                        if let PlayerState::Playing {
                            stream_position_pcm,
                            decoder,
                            stream_loader_controller,
                            bytes_per_second,
                            duration_ms,
                            normalisation_factor,
                            ..
                        }
                        | PlayerState::Paused {
                            stream_position_pcm,
                            decoder,
                            stream_loader_controller,
                            bytes_per_second,
                            duration_ms,
                            normalisation_factor,
                            ..
                        } = old_state
                        {
                            let loaded_track = PlayerLoadedTrackData {
                                decoder,
                                normalisation_factor,
                                stream_loader_controller,
                                bytes_per_second,
                                duration_ms,
                                stream_position_pcm,
                            };

                            self.start_playback(
                                track_id,
                                play_request_id,
                                loaded_track,
                                play,
                                true,
                            );

                            load_command_processed = true;
                        } else {
                            unreachable!();
                        }
                    }
                }

                // Check if the requested track has been preloaded already. If so use the preloaded data.
                if !load_command_processed {
                    if let PlayerPreload::Ready {
                        track_id: loaded_track_id,
                        ..
                    } = self.preload
                    {
                        if track_id == loaded_track_id {
                            let preload = std::mem::replace(&mut self.preload, PlayerPreload::None);
                            if let PlayerPreload::Ready {
                                track_id,
                                mut loaded_track,
                            } = preload
                            {
                                if Self::position_ms_to_pcm(position_ms)
                                    != loaded_track.stream_position_pcm
                                {
                                    loaded_track
                                        .stream_loader_controller
                                        .set_random_access_mode();
                                    let _ = loaded_track.decoder.seek(position_ms as i64); // This may be blocking
                                    loaded_track.stream_loader_controller.set_stream_mode();
                                }
                                self.start_playback(
                                    track_id,
                                    play_request_id,
                                    loaded_track,
                                    play,
                                    false,
                                );
                                load_command_processed = true;
                            }
                        }
                    }
                }

                // We need to load the track - either from scratch or by completing a preload.
                // In any case we go into a Loading state to load the track.
                if !load_command_processed {
                    self.ensure_sink_stopped();

                    self.send_event(PlayerEvent::Loading {
                        track_id,
                        play_request_id,
                        position_ms,
                    });

                    let loader = if let PlayerPreload::Loading {
                        track_id: loaded_track_id,
                        ..
                    } = self.preload
                    {
                        if (track_id == loaded_track_id) && (position_ms == 0) {
                            let mut preload = PlayerPreload::None;
                            std::mem::swap(&mut preload, &mut self.preload);
                            if let PlayerPreload::Loading { loader, .. } = preload {
                                Some(loader)
                            } else {
                                None
                            }
                        } else {
                            None
                        }
                    } else {
                        None
                    };

                    self.preload = PlayerPreload::None;

                    let loader = loader
                        .or_else(|| Some(self.load_track(track_id, position_ms)))
                        .unwrap();

                    self.state = PlayerState::Loading {
                        track_id,
                        play_request_id,
                        start_playback: play,
                        loader,
                    };
                }
            }

            PlayerCommand::Preload { track_id } => {
                debug!("Preloading track");
                let mut preload_track = true;

                if let PlayerPreload::Loading {
                    track_id: currently_loading,
                    ..
                }
                | PlayerPreload::Ready {
                    track_id: currently_loading,
                    ..
                } = self.preload
                {
                    if currently_loading == track_id {
                        // we're already loading the requested track.
                        preload_track = false;
                    } else {
                        // we're loading something else - cancel it.
                        self.preload = PlayerPreload::None;
                    }
                }

                if let PlayerState::Playing {
                    track_id: current_track_id,
                    ..
                }
                | PlayerState::Paused {
                    track_id: current_track_id,
                    ..
                }
                | PlayerState::EndOfTrack {
                    track_id: current_track_id,
                    ..
                } = self.state
                {
                    if current_track_id == track_id {
                        // we already have the requested track loaded.
                        preload_track = false;
                    }
                }

                if preload_track {
                    let loader = self.load_track(track_id, 0);
                    self.preload = PlayerPreload::Loading { track_id, loader }
                }
            }

            PlayerCommand::Seek(position_ms) => {
                if let Some(stream_loader_controller) = self.state.stream_loader_controller() {
                    stream_loader_controller.set_random_access_mode();
                }
                if let Some(decoder) = self.state.decoder() {
                    match decoder.seek(position_ms as i64) {
                        Ok(_) => {
                            if let PlayerState::Playing {
                                ref mut stream_position_pcm,
                                ..
                            }
                            | PlayerState::Paused {
                                ref mut stream_position_pcm,
                                ..
                            } = self.state
                            {
                                *stream_position_pcm = Self::position_ms_to_pcm(position_ms);
                            }
                        }
                        Err(err) => error!("Vorbis error: {:?}", err),
                    }
                } else {
                    warn!("Player::seek called from invalid state");
                }

                // If we're playing, ensure, that we have enough data leaded to avoid a buffer underrun.
                if let Some(stream_loader_controller) = self.state.stream_loader_controller() {
                    stream_loader_controller.set_stream_mode();
                }

                self.preload_data_before_playback();

                if let PlayerState::Playing {
                    track_id,
                    play_request_id,
                    ref mut reported_nominal_start_time,
                    duration_ms,
                    ..
                } = self.state
                {
                    *reported_nominal_start_time =
                        Some(Instant::now() - Duration::from_millis(position_ms as u64));
                    self.send_event(PlayerEvent::Playing {
                        track_id,
                        play_request_id,
                        position_ms: position_ms,
                        duration_ms,
                    });
                }
                if let PlayerState::Paused {
                    track_id,
                    play_request_id,
                    duration_ms,
                    ..
                } = self.state
                {
                    self.send_event(PlayerEvent::Paused {
                        track_id,
                        play_request_id,
                        position_ms: position_ms,
                        duration_ms,
                    });
                }
            }

            PlayerCommand::Play => {
                self.handle_play();
            }

            PlayerCommand::Pause => {
                self.handle_pause();
            }

            PlayerCommand::Stop => self.handle_player_stop(),

            PlayerCommand::AddEventSender(sender) => self.event_senders.push(sender),

            PlayerCommand::EmitVolumeSetEvent(volume) => {
                self.send_event(PlayerEvent::VolumeSet { volume })
            }
        }
    }

    fn send_event(&mut self, event: PlayerEvent) {
        let mut index = 0;
        while index < self.event_senders.len() {
            match self.event_senders[index].unbounded_send(event.clone()) {
                Ok(_) => index += 1,
                Err(_) => {
                    self.event_senders.remove(index);
                }
            }
        }
    }

    fn load_track(
        &self,
        spotify_id: SpotifyId,
        position_ms: u32,
    ) -> Box<dyn Future<Item = PlayerLoadedTrackData, Error = ()>> {
        // This method creates a future that returns the loaded stream and associated info.
        // Ideally all work should be done using asynchronous code. However, seek() on the
        // audio stream is implemented in a blocking fashion. Thus, we can't turn it into future
        // easily. Instead we spawn a thread to do the work and return a one-shot channel as the
        // future to work with.

        let loader = PlayerTrackLoader {
            session: self.session.clone(),
            config: self.config.clone(),
        };

        let (result_tx, result_rx) = futures::sync::oneshot::channel();

        std::thread::spawn(move || {
            loader
                .load_track(spotify_id, position_ms)
                .and_then(move |data| {
                    let _ = result_tx.send(data);
                    Some(())
                });
        });

        Box::new(result_rx.map_err(|_| ()))
    }

    fn preload_data_before_playback(&mut self) {
        if let PlayerState::Playing {
            bytes_per_second,
            ref mut stream_loader_controller,
            ..
        } = self.state
        {
            // Request our read ahead range
            let request_data_length = max(
                (READ_AHEAD_DURING_PLAYBACK_ROUNDTRIPS
                    * (0.001 * stream_loader_controller.ping_time_ms() as f64)
                    * bytes_per_second as f64) as usize,
                (READ_AHEAD_DURING_PLAYBACK_SECONDS * bytes_per_second as f64) as usize,
            );
            stream_loader_controller.fetch_next(request_data_length);

            // Request the part we want to wait for blocking. This effecively means we wait for the previous request to partially complete.
            let wait_for_data_length = max(
                (READ_AHEAD_BEFORE_PLAYBACK_ROUNDTRIPS
                    * (0.001 * stream_loader_controller.ping_time_ms() as f64)
                    * bytes_per_second as f64) as usize,
                (READ_AHEAD_BEFORE_PLAYBACK_SECONDS * bytes_per_second as f64) as usize,
            );
            stream_loader_controller.fetch_next_blocking(wait_for_data_length);
        }
    }
}

impl Drop for PlayerInternal {
    fn drop(&mut self) {
        debug!("drop PlayerInternal[{}]", self.session.session_id());
    }
}

impl ::std::fmt::Debug for PlayerCommand {
    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
        match *self {
            PlayerCommand::Load {
                track_id,
                play,
                position_ms,
                ..
            } => f
                .debug_tuple("Load")
                .field(&track_id)
                .field(&play)
                .field(&position_ms)
                .finish(),
            PlayerCommand::Preload { track_id } => {
                f.debug_tuple("Preload").field(&track_id).finish()
            }
            PlayerCommand::Play => f.debug_tuple("Play").finish(),
            PlayerCommand::Pause => f.debug_tuple("Pause").finish(),
            PlayerCommand::Stop => f.debug_tuple("Stop").finish(),
            PlayerCommand::Seek(position) => f.debug_tuple("Seek").field(&position).finish(),
            PlayerCommand::AddEventSender(_) => f.debug_tuple("AddEventSender").finish(),
            PlayerCommand::EmitVolumeSetEvent(volume) => {
                f.debug_tuple("VolumeSet").field(&volume).finish()
            }
        }
    }
}

struct Subfile<T: Read + Seek> {
    stream: T,
    offset: u64,
}

impl<T: Read + Seek> Subfile<T> {
    pub fn new(mut stream: T, offset: u64) -> Subfile<T> {
        stream.seek(SeekFrom::Start(offset)).unwrap();
        Subfile {
            stream: stream,
            offset: offset,
        }
    }
}

impl<T: Read + Seek> Read for Subfile<T> {
    fn read(&mut self, buf: &mut [u8]) -> Result<usize> {
        self.stream.read(buf)
    }
}

impl<T: Read + Seek> Seek for Subfile<T> {
    fn seek(&mut self, mut pos: SeekFrom) -> Result<u64> {
        pos = match pos {
            SeekFrom::Start(offset) => SeekFrom::Start(offset + self.offset),
            x => x,
        };

        let newpos = self.stream.seek(pos)?;
        if newpos > self.offset {
            Ok(newpos - self.offset)
        } else {
            Ok(0)
        }
    }
}