extern crate sdl2;

use sdl2::audio::{AudioCallback, AudioSpecDesired};
use std::time::Duration;

struct SquareWave {
    phase_inc: f32,
    phase: f32,
    volume: f32
}

impl AudioCallback for SquareWave {
    type Channel = f32;

    fn callback(&mut self, out: &mut [f32]) {
        // Generate a square wave
        for x in out.iter_mut() {
            *x = if self.phase <= 0.5 { self.volume } else { -self.volume };
            self.phase = (self.phase + self.phase_inc) % 1.0;
        }
    }
}

fn main() -> Result<(), String> {
    let sdl_context = sdl2::init()?;
    let audio_subsystem = sdl_context.audio()?;

    let desired_spec = AudioSpecDesired {
        freq: Some(44_100),
        channels: Some(1),  // mono
        samples: None       // default sample size
    };

    let device = audio_subsystem.open_playback(None, &desired_spec, |spec| {
        // Show obtained AudioSpec
        println!("{:?}", spec);

        // initialize the audio callback
        SquareWave {
            phase_inc: 440.0 / spec.freq as f32,
            phase: 0.0,
            volume: 0.25
        }
    })?;

    // Start playback
    device.resume();

    // Play for 2 seconds
    std::thread::sleep(Duration::from_millis(2_000));

    // Device is automatically closed when dropped
    
    Ok(())
}