/// Plays audio produced by a generator closure on the host's default output device.
///
/// `AudioPlayer` owns the live [`cpal::Stream`] and exposes only playback
/// control ([`play`](Self::play), [`pause`](Self::pause)). It has no
/// knowledge of how the generator produces samples, so polyphony, pitch
/// modulation, and voice mixing all belong behind the [`Generator`] closure,
/// not here.
pub struct AudioPlayer {
    stream: Stream,
}
use crate::generators::GeneratorFn;
use cpal::{
    Device, Error, ErrorKind, FromSample, I24, OutputCallbackInfo, Sample, SampleFormat, SizedSample, Stream, StreamConfig, SupportedStreamConfig, traits::{DeviceTrait, StreamTrait},
};
use std::io::ErrorKind as IoErrorKind;

impl AudioPlayer {
    /// Builds a stream for `device`/`config` around `generator`, dispatching
    /// on `config`'s sample format to the matching CPAL sample type.
    ///
    /// The stream starts paused; call [`play`](Self::play) to produce sound.
    /// Use [`get_device_and_config`](crate::get_device_and_config) to obtain
    /// `device` and `config`.
    ///
    /// # Errors
    ///
    /// Returns an error if:
    /// - the device reports a sample format `raust` does not support, or
    /// - CPAL fails to build the output stream.
    pub fn try_new(device: &Device, config: SupportedStreamConfig, generator: GeneratorFn) -> anyhow::Result<Self> {
        let stream = match config.sample_format() {
            SampleFormat::I8 => Self::create_stream::<i8>(device, config.into(), generator),
            SampleFormat::I16 => Self::create_stream::<i16>(device, config.into(), generator),
            SampleFormat::I24 => Self::create_stream::<I24>(device, config.into(), generator),
            SampleFormat::I32 => Self::create_stream::<i32>(device, config.into(), generator),
            SampleFormat::I64 => Self::create_stream::<i64>(device, config.into(), generator),
            SampleFormat::U8 => Self::create_stream::<u8>(device, config.into(), generator),
            SampleFormat::U16 => Self::create_stream::<u16>(device, config.into(), generator),
            SampleFormat::U32 => Self::create_stream::<u32>(device, config.into(), generator),
            SampleFormat::U64 => Self::create_stream::<u64>(device, config.into(), generator),
            SampleFormat::F32 => Self::create_stream::<f32>(device, config.into(), generator),
            SampleFormat::F64 => Self::create_stream::<f64>(device, config.into(), generator),
            sample_format => Err(anyhow::Error::new(std::io::Error::new(
                IoErrorKind::InvalidData,
                format!("Unsupported sample format '{sample_format}'"),
            ))),
        }?;
        Ok(Self { stream })
    }

    /// Builds, but does not start, an output stream of sample type `T` that
    /// pulls its samples from `generator`.
    ///
    /// # Errors
    ///
    /// Returns an error if CPAL fails to build the output stream for `device`.
    pub fn create_stream<T>(
        device: &Device,
        config: StreamConfig,
        mut generator: GeneratorFn,
    ) -> Result<Stream, anyhow::Error>
    where
        T: SizedSample + FromSample<f32>,
    {
        let channels = usize::from(config.channels);
        let err_fn = |err: Error| match err.kind() {
            ErrorKind::DeviceChanged | ErrorKind::RealtimeDenied => {
                eprintln!("{err}");
            }
            _ => eprintln!("Stream error: {err}"),
        };
        let stream = device.build_output_stream(
            config,
            move |data: &mut [T], _: &OutputCallbackInfo| {
                Self::write_data(data, channels, &mut generator);
            },
            err_fn,
            None,
        )?;
        Ok(stream)
    }

    fn write_data<T>(output: &mut [T], channels: usize, next_sample: &mut dyn FnMut() -> f32)
    where
        T: Sample + FromSample<f32>,
    {
        for frame in output.chunks_mut(channels) {
            let value: T = T::from_sample(next_sample());
            for sample in frame.iter_mut() {
                *sample = value;
            }
        }
    }

    /// Resumes playback.
    ///
    /// The generator continues from exactly where [`pause`](Self::pause)
    /// left it; nothing resets.
    ///
    /// # Errors
    ///
    /// Returns an error if CPAL fails to resume the stream.
    pub fn play(&self) -> anyhow::Result<()> {
        self.stream.play()?;
        Ok(())
    }

    /// Suspends playback.
    ///
    /// The backend stops calling the generator until the next
    /// [`play`](Self::play) call, so no samples are produced while paused.
    ///
    /// # Errors
    ///
    /// Returns an error if CPAL fails to suspend the stream.
    pub fn pause(&self) -> anyhow::Result<()> {
        self.stream.pause()?;
        Ok(())
    }
}