extern crate asio_sys as sys;
extern crate num_traits;

use self::num_traits::PrimInt;
use super::asio_utils as au;
use super::Device;
use std;
use std::mem;
use std::sync::atomic::{AtomicUsize, Ordering};
use std::sync::{Arc, Mutex};
use std::thread;
use std::time::Duration;
use BackendSpecificError;
use BuildStreamError;
use Format;
use PauseStreamError;
use PlayStreamError;
use SampleFormat;
use StreamData;
use StreamDataResult;
use UnknownTypeInputBuffer;
use UnknownTypeOutputBuffer;

/// Controls all streams
pub struct EventLoop {
    /// The input and output ASIO streams
    asio_streams: Arc<Mutex<sys::AsioStreams>>,
    /// List of all CPAL streams
    cpal_streams: Arc<Mutex<Vec<Option<Stream>>>>,
    /// Total stream count
    stream_count: AtomicUsize,
    /// The CPAL callback that the user gives to fill the buffers.
    callbacks: Arc<Mutex<Option<&'static mut (FnMut(StreamId, StreamDataResult) + Send)>>>,
}

/// Id for each stream.
/// Created depending on the number they are created.
/// Starting at one! not zero.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct StreamId(usize);

/// CPAL stream.
/// This decouples the many cpal streams
/// from the single input and single output
/// ASIO streams.
/// Each stream can be playing or paused.
struct Stream {
    playing: bool,
    // The driver associated with this stream.
    driver: Arc<sys::Driver>,
}

#[derive(Default)]
struct I16Buffer {
    cpal: Vec<i16>,
    channel: Vec<Vec<i16>>,
}

#[derive(Default)]
struct F32Buffer {
    cpal: Vec<f32>,
    channel: Vec<Vec<f32>>,
}
struct Buffers {
    i16_buff: I16Buffer,
    //u16_buff: U16Buffer,
    f32_buff: F32Buffer,
}

enum Endian {
    Little,
    Big,
}

impl EventLoop {
    pub fn new() -> EventLoop {
        EventLoop {
            asio_streams: Arc::new(Mutex::new(sys::AsioStreams {
                input: None,
                output: None,
            })),
            cpal_streams: Arc::new(Mutex::new(Vec::new())),
            // This is why the Id's count from one not zero
            // because at this point there is no streams
            stream_count: AtomicUsize::new(0),
            callbacks: Arc::new(Mutex::new(None)),
        }
    }

    fn check_format(
        &self,
        driver: &sys::Driver,
        format: &Format,
        num_asio_channels: u16,
    ) -> Result<(), BuildStreamError> {
        let Format {
            channels,
            sample_rate,
            data_type,
        } = format;
        // Try and set the sample rate to what the user selected.
        let sample_rate = sample_rate.0.into();
        if sample_rate != driver.sample_rate().map_err(build_stream_err)? {
            if driver.can_sample_rate(sample_rate).map_err(build_stream_err)? {
                driver
                    .set_sample_rate(sample_rate)
                    .map_err(build_stream_err)?;
            } else {
                return Err(BuildStreamError::FormatNotSupported);
            }
        }
        // unsigned formats are not supported by asio
        match data_type {
            SampleFormat::I16 | SampleFormat::F32 => (),
            SampleFormat::U16 => return Err(BuildStreamError::FormatNotSupported),
        }
        if *channels > num_asio_channels {
            return Err(BuildStreamError::FormatNotSupported);
        }
        Ok(())
    }

    /// Create a new CPAL Input Stream.
    /// If there is no ASIO Input Stream
    /// it will be created.
    fn get_input_stream(
        &self,
        driver: &sys::Driver,
        format: &Format,
        device: &Device,
    ) -> Result<usize, BuildStreamError> {
        match device.default_input_format() {
            Ok(f) => {
                let num_asio_channels = f.channels;
                self.check_format(driver, format, num_asio_channels)
            },
            Err(_) => Err(BuildStreamError::FormatNotSupported),
        }?;
        let num_channels = format.channels as usize;
        let ref mut streams = *self.asio_streams.lock().unwrap();
        // Either create a stream if thers none or had back the
        // size of the current one.
        match streams.input {
            Some(ref input) => Ok(input.buffer_size as usize),
            None => {
                let output = streams.output.take();
                driver
                    .prepare_input_stream(output, num_channels)
                    .map(|new_streams| {
                        let bs = match new_streams.input {
                            Some(ref inp) => inp.buffer_size as usize,
                            None => unreachable!(),
                        };
                        *streams = new_streams;
                        bs
                    }).map_err(|ref e| {
                        println!("Error preparing stream: {}", e);
                        BuildStreamError::DeviceNotAvailable
                    })
            }
        }
    }

    /// Create a new CPAL Output Stream.
    /// If there is no ASIO Output Stream
    /// it will be created.
    fn get_output_stream(
        &self,
        driver: &sys::Driver,
        format: &Format,
        device: &Device,
    ) -> Result<usize, BuildStreamError> {
        match device.default_output_format() {
            Ok(f) => {
                let num_asio_channels = f.channels;
                self.check_format(driver, format, num_asio_channels)
            },
            Err(_) => Err(BuildStreamError::FormatNotSupported),
        }?;
        let num_channels = format.channels as usize;
        let ref mut streams = *self.asio_streams.lock().unwrap();
        // Either create a stream if thers none or had back the
        // size of the current one.
        match streams.output {
            Some(ref output) => Ok(output.buffer_size as usize),
            None => {
                let input = streams.input.take();
                driver
                    .prepare_output_stream(input, num_channels)
                    .map(|new_streams| {
                        let bs = match new_streams.output {
                            Some(ref out) => out.buffer_size as usize,
                            None => unreachable!(),
                        };
                        *streams = new_streams;
                        bs
                    }).map_err(|ref e| {
                        println!("Error preparing stream: {}", e);
                        BuildStreamError::DeviceNotAvailable
                    })
            }
        }
    }

    /// Builds a new cpal input stream
    pub fn build_input_stream(
        &self,
        device: &Device,
        format: &Format,
    ) -> Result<StreamId, BuildStreamError> {
        let Device { driver, .. } = device;
        let num_channels = format.channels.clone();
        let stream_type = driver.data_type().map_err(build_stream_err)?;
        let stream_buffer_size = self.get_input_stream(&driver, format, device)?;
        let cpal_num_samples = stream_buffer_size * num_channels as usize;
        let count = self.stream_count.fetch_add(1, Ordering::SeqCst);
        let asio_streams = self.asio_streams.clone();
        let cpal_streams = self.cpal_streams.clone();
        let callbacks = self.callbacks.clone();

        let channel_len = cpal_num_samples / num_channels as usize;

        // Create buffers depending on data type
        // TODO the naming of cpal and channel is confusing.
        // change it to:
        // cpal -> interleaved
        // channels -> per_channel
        let mut buffers = match format.data_type {
            SampleFormat::I16 => Buffers {
                i16_buff: I16Buffer {
                    cpal: vec![0 as i16; cpal_num_samples],
                    channel: (0..num_channels)
                        .map(|_| Vec::with_capacity(channel_len))
                        .collect(),
                },
                f32_buff: F32Buffer::default(),
            },
            SampleFormat::F32 => Buffers {
                i16_buff: I16Buffer::default(),
                f32_buff: F32Buffer {
                    cpal: vec![0 as f32; cpal_num_samples],
                    channel: (0..num_channels)
                        .map(|_| Vec::with_capacity(channel_len))
                        .collect(),
                },
            },
            _ => unimplemented!(),
        };

        // Set the input callback.
        // This is most performance critical part of the ASIO bindings.
        sys::set_callback(move |index| unsafe {
            // if not playing return early
            {
                if let Some(s) = cpal_streams.lock().unwrap().get(count) {
                    if let Some(s) = s {
                        if !s.playing {
                            return ();
                        }
                    }
                }
            }
            // Get the stream
            let stream_lock = asio_streams.lock().unwrap();
            let ref asio_stream = match stream_lock.input {
                Some(ref asio_stream) => asio_stream,
                None => return (),
            };

            // Get the callback
            let mut callbacks = callbacks.lock().unwrap();

            // Theres only a single callback because theres only one event loop
            let callback = match callbacks.as_mut() {
                Some(callback) => callback,
                None => return (),
            };

            // Macro to convert sample from ASIO to CPAL type
            macro_rules! convert_sample {
                // floats types required different conversion
                (f32,
                f32,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    *$Sample
                };
                (f64,
                f64,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    *$Sample
                };
                (f64,
                f32,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    *$Sample as f32
                };
                (f32,
                f64,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    *$Sample as f64
                };
                ($AsioTypeIdent:ident,
                f32,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    (*$Sample as f64 / ::std::$AsioTypeIdent::MAX as f64) as f32
                };
                ($AsioTypeIdent:ident,
                f64,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    *$Sample as f64 / ::std::$AsioTypeIdent::MAX as f64
                };
                (f32,
                $SampleType:ty,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    (*$Sample as f64 * ::std::$SampleTypeIdent::MAX as f64) as $SampleType
                };
                (f64,
                $SampleType:ty,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    (*$Sample as f64 * ::std::$SampleTypeIdent::MAX as f64) as $SampleType
                };
                ($AsioTypeIdent:ident,
                $SampleType:ty,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    (*$Sample as i64 * ::std::$SampleTypeIdent::MAX as i64
                        / ::std::$AsioTypeIdent::MAX as i64) as $SampleType
                };
            };
            // This creates gets the buffer and interleaves it.
            // It allows it to be done based on the sample type.
            macro_rules! try_callback {
                ($SampleFormat:ident,
                $SampleType:ty,
                $SampleTypeIdent:ident,
                $AsioType:ty,
                $AsioTypeIdent:ident,
                $Buffers:expr,
                $BuffersType:ty,
                $BuffersTypeIdent:ident,
                $Endianness:expr,
                $ConvertEndian:expr
                ) => {
                    // For each channel write the asio buffer to
                    // the cpal buffer

                    for (i, channel) in $Buffers.channel.iter_mut().enumerate() {
                        let buff_ptr = asio_stream.buffer_infos[i].buffers[index as usize]
                            as *mut $AsioType;
                        let asio_buffer: &'static [$AsioType] = std::slice::from_raw_parts(
                            buff_ptr,
                            asio_stream.buffer_size as usize,
                        );
                        for asio_s in asio_buffer.iter() {
                            channel.push($ConvertEndian(
                                convert_sample!(
                                    $AsioTypeIdent,
                                    $SampleType,
                                    $SampleTypeIdent,
                                    asio_s
                                ),
                                $Endianness,
                            ));
                        }
                    }

                    // interleave all the channels
                    {
                        let $BuffersTypeIdent {
                            cpal: ref mut c_buffer,
                            channel: ref mut channels,
                        } = $Buffers;
                        au::interleave(&channels, c_buffer);
                        // Clear the per channel buffers
                        for c in channels.iter_mut() {
                            c.clear();
                        }
                    }

                    // Call the users callback with the buffer
                    callback(
                        StreamId(count),
                        Ok(StreamData::Input {
                            buffer: UnknownTypeInputBuffer::$SampleFormat(::InputBuffer {
                                buffer: &$Buffers.cpal,
                            }),
                        }),
                    );
                };
            };
            // Call the right buffer handler depending on types
            match stream_type {
                sys::AsioSampleType::ASIOSTInt32LSB => {
                    try_callback!(
                        I16,
                        i16,
                        i16,
                        i32,
                        i32,
                        buffers.i16_buff,
                        I16Buffer,
                        I16Buffer,
                        Endian::Little,
                        convert_endian_from
                    );
                }
                sys::AsioSampleType::ASIOSTInt16LSB => {
                    try_callback!(
                        I16,
                        i16,
                        i16,
                        i16,
                        i16,
                        buffers.i16_buff,
                        I16Buffer,
                        I16Buffer,
                        Endian::Little,
                        convert_endian_from
                    );
                }
                sys::AsioSampleType::ASIOSTInt32MSB => {
                    try_callback!(
                        I16,
                        i16,
                        i16,
                        i32,
                        i32,
                        buffers.i16_buff,
                        I16Buffer,
                        I16Buffer,
                        Endian::Big,
                        convert_endian_from
                    );
                }
                sys::AsioSampleType::ASIOSTInt16MSB => {
                    try_callback!(
                        I16,
                        i16,
                        i16,
                        i16,
                        i16,
                        buffers.i16_buff,
                        I16Buffer,
                        I16Buffer,
                        Endian::Big,
                        convert_endian_from
                    );
                }
                sys::AsioSampleType::ASIOSTFloat32LSB => {
                    try_callback!(
                        F32,
                        f32,
                        f32,
                        f32,
                        f32,
                        buffers.f32_buff,
                        F32Buffer,
                        F32Buffer,
                        Endian::Little,
                        |a, _| a
                    );
                }
                sys::AsioSampleType::ASIOSTFloat64LSB => {
                    try_callback!(
                        F32,
                        f32,
                        f32,
                        f64,
                        f64,
                        buffers.f32_buff,
                        F32Buffer,
                        F32Buffer,
                        Endian::Little,
                        |a, _| a
                    );
                }
                sys::AsioSampleType::ASIOSTFloat32MSB => {
                    try_callback!(
                        F32,
                        f32,
                        f32,
                        f32,
                        f32,
                        buffers.f32_buff,
                        F32Buffer,
                        F32Buffer,
                        Endian::Big,
                        |a, _| a
                    );
                }
                sys::AsioSampleType::ASIOSTFloat64MSB => {
                    try_callback!(
                        F32,
                        f32,
                        f32,
                        f64,
                        f64,
                        buffers.f32_buff,
                        F32Buffer,
                        F32Buffer,
                        Endian::Big,
                        |a, _| a
                    );
                }
                _ => println!("unsupported format {:?}", stream_type),
            }
        });
        // Create stream and set to paused
        self.cpal_streams
            .lock()
            .unwrap()
            .push(Some(Stream { driver: driver.clone(), playing: false }));

        Ok(StreamId(count))
    }

    /// Create the an output cpal stream.
    pub fn build_output_stream(
        &self,
        device: &Device,
        format: &Format,
    ) -> Result<StreamId, BuildStreamError> {
        let Device { driver, .. } = device;
        let num_channels = format.channels.clone();
        let stream_type = driver.data_type().map_err(build_stream_err)?;
        let stream_buffer_size = self.get_output_stream(&driver, format, device)?;
        let cpal_num_samples = stream_buffer_size * num_channels as usize;
        let count = self.stream_count.fetch_add(1, Ordering::SeqCst);
        let asio_streams = self.asio_streams.clone();
        let cpal_streams = self.cpal_streams.clone();
        let callbacks = self.callbacks.clone();
        let channel_len = cpal_num_samples / num_channels as usize;

        // Create buffers depending on data type
        let mut re_buffers = match format.data_type {
            SampleFormat::I16 => Buffers {
                i16_buff: I16Buffer {
                    cpal: vec![0 as i16; cpal_num_samples],
                    channel: (0..num_channels)
                        .map(|_| Vec::with_capacity(channel_len))
                        .collect(),
                },
                f32_buff: F32Buffer::default(),
            },
            SampleFormat::F32 => Buffers {
                i16_buff: I16Buffer::default(),
                f32_buff: F32Buffer {
                    cpal: vec![0 as f32; cpal_num_samples],
                    channel: (0..num_channels)
                        .map(|_| Vec::with_capacity(channel_len))
                        .collect(),
                },
            },
            _ => unimplemented!(),
        };

        sys::set_callback(move |index| unsafe {
            // if not playing return early
            {
                if let Some(s) = cpal_streams.lock().unwrap().get(count) {
                    if let Some(s) = s {
                        if !s.playing {
                            return ();
                        }
                    }
                }
            }
            // Get the stream
            let stream_lock = asio_streams.lock().unwrap();
            let ref asio_stream = match stream_lock.output {
                Some(ref asio_stream) => asio_stream,
                None => return (),
            };

            // Get the callback
            let mut callbacks = callbacks.lock().unwrap();

            // Theres only a single callback because theres only one event loop
            let callback = match callbacks.as_mut() {
                Some(callback) => callback,
                None => return (),
            };

            // Convert sample depending on the sample type
            macro_rules! convert_sample {
                ($AsioTypeIdent:ident,
                f64,
                f64,
                $Sample:expr
                ) => {
                    *$Sample
                };
                ($AsioTypeIdent:ident,
                f32,
                f32,
                $Sample:expr
                ) => {
                    *$Sample
                };
                ($AsioTypeIdent:ident,
                f64,
                f32,
                $Sample:expr
                ) => {
                    *$Sample as f64
                };
                ($AsioTypeIdent:ident,
                f32,
                f64,
                $Sample:expr
                ) => {
                    *$Sample as f32
                };
                ($AsioTypeIdent:ident,
                $AsioType:ty,
                f32,
                $Sample:expr
                ) => {
                    (*$Sample as f64 * ::std::$AsioTypeIdent::MAX as f64) as $AsioType
                };
                ($AsioTypeIdent:ident,
                $AsioType:ty,
                f64,
                $Sample:expr
                ) => {
                    (*$Sample as f64 * ::std::$AsioTypeIdent::MAX as f64) as $AsioType
                };
                ($AsioTypeIdent:ident,
                f32,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    (*$Sample as f64 / ::std::$SampleTypeIdent::MAX as f64) as f32
                };
                ($AsioTypeIdent:ident,
                f64,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    *$Sample as f64 / ::std::$SampleTypeIdent::MAX as f64
                };
                ($AsioTypeIdent:ident,
                $AsioType:ty,
                $SampleTypeIdent:ident,
                $Sample:expr
                ) => {
                    (*$Sample as i64 * ::std::$AsioTypeIdent::MAX as i64
                        / ::std::$SampleTypeIdent::MAX as i64) as $AsioType
                };
            };

            macro_rules! try_callback {
                ($SampleFormat:ident,
                $SampleType:ty,
                $SampleTypeIdent:ident,
                $AsioType:ty,
                $AsioTypeIdent:ident,
                $Buffers:expr,
                $BuffersType:ty,
                $BuffersTypeIdent:ident,
                $Endianness:expr,
                $ConvertEndian:expr
                ) => {
                    let mut my_buffers = $Buffers;
                    {
                        // call the callback to fill the buffer with
                        // users data
                        callback(
                            StreamId(count),
                            Ok(StreamData::Output {
                                buffer: UnknownTypeOutputBuffer::$SampleFormat(
                                    ::OutputBuffer {
                                        buffer: &mut my_buffers.cpal,
                                    },
                                ),
                            }),
                        );
                    }
                    // Deinter all the channels
                    {
                        let $BuffersTypeIdent {
                            cpal: ref mut c_buffer,
                            channel: ref mut channels,
                        } = my_buffers;
                        au::deinterleave(&c_buffer[..], channels);
                    }

                    // Silence the buffer that is about to be used.
                    // This checks if any other callbacks have already
                    // silenced this buffer. If not it will silence it
                    // and set the opposite buffer half to unsilenced.
                    let silence = match index {
                        0 => {
                            if !sys::SILENCE_FIRST.load(Ordering::SeqCst) {
                                sys::SILENCE_FIRST.store(true, Ordering::SeqCst);
                                sys::SILENCE_SECOND.store(false, Ordering::SeqCst);
                                true
                            } else {
                                false
                            }
                        }
                        1 => {
                            if !sys::SILENCE_SECOND.load(Ordering::SeqCst) {
                                sys::SILENCE_SECOND.store(true, Ordering::SeqCst);
                                sys::SILENCE_FIRST.store(false, Ordering::SeqCst);
                                true
                            } else {
                                false
                            }
                        }
                        _ => unreachable!(),
                    };

                    // For each channel write the cpal data to
                    // the asio buffer
                    for (i, channel) in my_buffers.channel.iter().enumerate() {
                        let buff_ptr = asio_stream.buffer_infos[i].buffers
                            [index as usize] as *mut $AsioType;
                        let asio_buffer: &'static mut [$AsioType] =
                            std::slice::from_raw_parts_mut(
                                buff_ptr,
                                asio_stream.buffer_size as usize,
                            );
                        for (asio_s, cpal_s) in asio_buffer.iter_mut().zip(channel) {
                            if silence {
                                *asio_s = 0.0 as $AsioType;
                            }
                            *asio_s += $ConvertEndian(
                                convert_sample!(
                                    $AsioTypeIdent,
                                    $AsioType,
                                    $SampleTypeIdent,
                                    cpal_s
                                ),
                                $Endianness,
                            );
                        }
                    }
                };
            }
            // Choose the buffer conversions based on the sample types
            match stream_type {
                sys::AsioSampleType::ASIOSTInt32LSB => {
                    try_callback!(
                        I16,
                        i16,
                        i16,
                        i32,
                        i32,
                        &mut re_buffers.i16_buff,
                        I16Buffer,
                        I16Buffer,
                        Endian::Little,
                        convert_endian_to
                    );
                }
                sys::AsioSampleType::ASIOSTInt16LSB => {
                    try_callback!(
                        I16,
                        i16,
                        i16,
                        i16,
                        i16,
                        &mut re_buffers.i16_buff,
                        I16Buffer,
                        I16Buffer,
                        Endian::Little,
                        convert_endian_to
                    );
                }
                sys::AsioSampleType::ASIOSTInt32MSB => {
                    try_callback!(
                        I16,
                        i16,
                        i16,
                        i32,
                        i32,
                        &mut re_buffers.i16_buff,
                        I16Buffer,
                        I16Buffer,
                        Endian::Big,
                        convert_endian_to
                    );
                }
                sys::AsioSampleType::ASIOSTInt16MSB => {
                    try_callback!(
                        I16,
                        i16,
                        i16,
                        i16,
                        i16,
                        &mut re_buffers.i16_buff,
                        I16Buffer,
                        I16Buffer,
                        Endian::Big,
                        convert_endian_to
                    );
                }
                sys::AsioSampleType::ASIOSTFloat32LSB => {
                    try_callback!(
                        F32,
                        f32,
                        f32,
                        f32,
                        f32,
                        &mut re_buffers.f32_buff,
                        F32Buffer,
                        F32Buffer,
                        Endian::Little,
                        |a, _| a
                    );
                }
                sys::AsioSampleType::ASIOSTFloat64LSB => {
                    try_callback!(
                        F32,
                        f32,
                        f32,
                        f64,
                        f64,
                        &mut re_buffers.f32_buff,
                        F32Buffer,
                        F32Buffer,
                        Endian::Little,
                        |a, _| a
                    );
                }
                sys::AsioSampleType::ASIOSTFloat32MSB => {
                    try_callback!(
                        F32,
                        f32,
                        f32,
                        f32,
                        f32,
                        &mut re_buffers.f32_buff,
                        F32Buffer,
                        F32Buffer,
                        Endian::Big,
                        |a, _| a
                    );
                }
                sys::AsioSampleType::ASIOSTFloat64MSB => {
                    try_callback!(
                        F32,
                        f32,
                        f32,
                        f64,
                        f64,
                        &mut re_buffers.f32_buff,
                        F32Buffer,
                        F32Buffer,
                        Endian::Big,
                        |a, _| a
                    );
                }
                _ => println!("unsupported format {:?}", stream_type),
            }
        });
        // Create the stream paused
        self.cpal_streams
            .lock()
            .unwrap()
            .push(Some(Stream { driver: driver.clone(), playing: false }));

        // Give the ID based on the stream count
        Ok(StreamId(count))
    }

    /// Play the cpal stream for the given ID.
    ///
    /// TODO: This will also play all other paused streams... need a nicer way of addressing ASIO's
    /// limitation of only being able to start/stop the entire driver.
    pub fn play_stream(&self, stream_id: StreamId) -> Result<(), PlayStreamError> {
        let mut streams = self.cpal_streams.lock().unwrap();
        if let Some(s) = streams.get_mut(stream_id.0).expect("Bad play stream index") {
            s.playing = true;
            // Calling play when already playing is a no-op
            s.driver.start().map_err(play_stream_err)?;
        }
        Ok(())
    }

    /// Pause the cpal stream for the given ID.
    ///
    /// Pause the ASIO streams if there are no other CPAL streams playing, as ASIO only allows
    /// stopping the entire driver.
    ///
    /// TODO: Come up with a nicer solution for this.
    pub fn pause_stream(&self, stream_id: StreamId) -> Result<(), PauseStreamError> {
        let mut streams = self.cpal_streams.lock().unwrap();
        let streams_playing = streams.iter()
            .filter(|s| s.map(|s| s.playing).unwrap_or(false))
            .count();
        if let Some(s) = streams.get_mut(stream_id.0).expect("Bad pause stream index") {
            if streams_playing <= 1 {
                s.driver.stop().map_err(pause_stream_err)?;
                s.playing = false;
            }
        }
        Ok(())
    }

    /// Destroy the cpal stream based on the ID.
    pub fn destroy_stream(&self, stream_id: StreamId) {
        // TODO: Should we not also remove an ASIO stream here?
        let mut streams = self.cpal_streams.lock().unwrap();
        streams.get_mut(stream_id.0).take();
    }

    /// Run the cpal callbacks
    pub fn run<F>(&self, mut callback: F) -> !
    where
        F: FnMut(StreamId, StreamDataResult) + Send,
    {
        let callback: &mut (FnMut(StreamId, StreamDataResult) + Send) = &mut callback;
        // Transmute needed to convince the compiler that the callback has a static lifetime
        *self.callbacks.lock().unwrap() = Some(unsafe { mem::transmute(callback) });
        loop {
            // A sleep here to prevent the loop being
            // removed in --release
            thread::sleep(Duration::new(1u64, 0u32));
        }
    }
}

/// Clean up if event loop is dropped.
/// Currently event loop is never dropped.
impl Drop for EventLoop {
    fn drop(&mut self) {
        *self.asio_streams.lock().unwrap() = sys::AsioStreams {
            output: None,
            input: None,
        };
    }
}

/// Helper function to convert to system endianness
fn convert_endian_to<T: PrimInt>(sample: T, endian: Endian) -> T {
    match endian {
        Endian::Big => sample.to_be(),
        Endian::Little => sample.to_le(),
    }
}

/// Helper function to convert from system endianness
fn convert_endian_from<T: PrimInt>(sample: T, endian: Endian) -> T {
    match endian {
        Endian::Big => T::from_be(sample),
        Endian::Little => T::from_le(sample),
    }
}

fn build_stream_err(e: sys::AsioError) -> BuildStreamError {
    match e {
        sys::AsioError::NoDrivers |
        sys::AsioError::HardwareMalfunction => BuildStreamError::DeviceNotAvailable,
        sys::AsioError::InvalidInput |
        sys::AsioError::BadMode => BuildStreamError::InvalidArgument,
        err => {
            let description = format!("{}", err);
            BackendSpecificError { description }.into()
        }
    }
}

fn pause_stream_err(e: sys::AsioError) -> PauseStreamError {
    match e {
        sys::AsioError::NoDrivers |
        sys::AsioError::HardwareMalfunction => PauseStreamError::DeviceNotAvailable,
        err => {
            let description = format!("{}", err);
            BackendSpecificError { description }.into()
        }
    }
}

fn play_stream_err(e: sys::AsioError) -> PlayStreamError {
    match e {
        sys::AsioError::NoDrivers |
        sys::AsioError::HardwareMalfunction => PlayStreamError::DeviceNotAvailable,
        err => {
            let description = format!("{}", err);
            BackendSpecificError { description }.into()
        }
    }
}