use std::{
	io::Cursor,
	sync::{
		Arc,
		Condvar,
		Mutex,
	},
	thread,
};

use anyhow::{
	anyhow,
	//bail,
	Result,
};

use byteorder::{
	LittleEndian,
	ReadBytesExt,
};

use cpal::traits::{
	DeviceTrait,
	HostTrait,
	StreamTrait,
};

const SAMPLE_RATE: u32 = 48000;

#[derive (Default)]
struct PcmBuffers {
	buffers: Vec <Vec <f32>>,
	
	// Always points into the first buffer, if any
	consumer_cursor: usize,
}

impl PcmBuffers {
	fn samples_available (&self) -> usize {
		self.buffers.iter ().map (|b| b.len ()).sum::<usize> () - self.consumer_cursor
	}
	
	#[warn(unused_must_use)]
	fn consume_exact (&mut self, data: &mut [f32]) -> bool {
		if data.len () > self.samples_available () {
			return false;
		}
		
		for x in data {
			if self.consumer_cursor >= self.buffers [0].len () {
				self.buffers.remove (0);
				self.consumer_cursor = 0;
			}
			
			*x = self.buffers [0][self.consumer_cursor];
			self.consumer_cursor += 1;
		}
		
		true
	}
	
	fn produce (&mut self, new_buffer: Vec <f32>) {
		self.buffers.push (new_buffer);
	}
}

fn main () -> Result <()> {
	let host = cpal::default_host ();
	let device = host.default_output_device ().ok_or_else (|| anyhow! ("can't open cpal device"))?;
	
	let mut supported_configs_range = device.supported_output_configs ()?
	.filter (|c| c.channels () == 2 && c.sample_format () == cpal::SampleFormat::F32);
	
	let config = supported_configs_range.next ()
	.ok_or_else (|| anyhow! ("can't get stereo f32 audio output"))?
	.with_sample_rate (cpal::SampleRate (SAMPLE_RATE))
	.config ();
	
	let pair = Arc::new ((Mutex::new (PcmBuffers::default ()), Condvar::new ()));
	let pair2 = Arc::clone (&pair);
	
	let thread_decoder = thread::spawn (move|| {
		/*
		Pipeline:
		- demuxer
		- decoder
		- resampler
		- cpal
		*/
		
		let (lock, cvar) = &*pair2;
		
		let mut input_ctx = ffmpeg_next::format::input (&"test.m4a")?;
		let stream = input_ctx
		.streams ()
		.best (ffmpeg_next::media::Type::Audio)
		.ok_or_else (|| anyhow! ("can't find good audio stream"))?;
		let best_stream_idx = stream.index ();
		
		let mut decoder = stream.codec ().decoder ().audio ()?;
		let mut resampler = decoder.resampler (
			ffmpeg_next::util::format::sample::Sample::F32 (
				ffmpeg_next::util::format::sample::Type::Packed,
			),
			ffmpeg_next::util::channel_layout::ChannelLayout::STEREO,
			48000,
		)?;
		let mut frame = ffmpeg_next::util::frame::Audio::empty ();
		let mut packets = input_ctx.packets ();
		
		loop {
			// eprintln! ("decode thread parking");
			
			let mut pcm_buffers = cvar.wait_while (lock.lock ().unwrap (), |pcm_buffers| {
				// eprintln! ("checking cvar...");
				pcm_buffers.samples_available () >= 48_000
			}).unwrap ();
			
			let mut did_anything = false;
			
			
			
			while decoder.receive_frame (&mut frame).is_ok () {
				did_anything = true;
				let mut buffer = vec! [0.0f32; frame.plane::<f32> (0).len () * 2];
				
				let mut rdr_left = frame.plane::<f32> (0).iter ();
				let mut rdr_right = frame.plane::<f32> (1).iter ();
				
				for x in buffer.chunks_mut (2) {
					x [0] = *rdr_left.next ().unwrap ();
					x [1] = *rdr_right.next ().unwrap ();
				}
				
				pcm_buffers.produce (buffer);
			}
			
			match packets.next () {
				None => {},
				Some ((stream, packet)) => {
					did_anything = true;
					if stream.index () == best_stream_idx {
						decoder.send_packet (&packet)?;
					}
				},
			}
			
			if ! did_anything {
				break;
			}
		}
		
		Ok::<_, anyhow::Error> (())
	});
	
	let stream = device.build_output_stream (
		&config,
		move |data: &mut [f32], _: &cpal::OutputCallbackInfo| {
			let (lock, cvar) = &*pair;
			
			let mut pcm_buffers = match lock.lock () {
				Ok (x) => x,
				Err (_) => return,
			};
			
			if ! pcm_buffers.consume_exact (data) {
				eprintln! ("PCM buffer underflow");
			}
			
			if pcm_buffers.samples_available () < 24_000 {
				cvar.notify_one ();
			}
		},
		move |err| {
			// react to errors here.
		},
	);
	
	std::thread::sleep (std::time::Duration::from_millis (1_000));
	
	thread_decoder.join ().unwrap ()?;
	
	Ok (())
}

#[cfg (test)]
mod test {
	use super::*;
	
	#[test]
	fn decode () -> Result <()> {
		ffmpeg_next::init ()?;
		
		let mut input_ctx = ffmpeg_next::format::input (&"test.opus")?;
		let stream = input_ctx
		.streams ()
		.best (ffmpeg_next::media::Type::Audio)
		.ok_or_else (|| anyhow! ("can't find good audio stream"))?;
		let best_stream_idx = stream.index ();
		
		let mut decoder = stream.codec ().decoder ().audio ()?;
		
		let mut packet_count = 0;
		let mut frame_count = 0;
		let mut frame = ffmpeg_next::util::frame::Audio::empty ();
		
		let mut packets = input_ctx.packets ();
		
		loop {
			let mut did_anything = false;
			
			while decoder.receive_frame (&mut frame).is_ok () {
				frame_count += 1;
				did_anything = true;
			}
			
			match packets.next () {
				None => {},
				Some ((stream, packet)) => {
					did_anything = true;
					if stream.index () == best_stream_idx {
						packet_count += 1;
						decoder.send_packet (&packet)?;
					}
				},
			}
			
			if ! did_anything {
				break;
			}
		}
		
		assert_eq! (packet_count, 5496);
		assert_eq! (frame_count, 5496);
		
		Ok (())
	}
}