//! FFmpeg-based progressive streaming decoder/encoder
//!
//! This module provides progressive audio streaming using FFmpeg,
//! allowing for much lower latency than the claxon/flacenc approach.
//!
//! Key advantages:
//! - Start streaming immediately (< 1 second latency)
//! - Progressive decoding and encoding in a pipeline
//! - Better performance (C code vs Rust)
//! - Support for multiple output formats

use anyhow::{anyhow, Context, Result};
use bytes::Bytes;
use ffmpeg_next as ffmpeg;
use std::io::{Read, Write};
use std::sync::mpsc::{sync_channel, Receiver, SyncSender};
use tokio::task;
use tracing::{debug, error, trace};

/// Initialize FFmpeg (must be called once at startup)
pub fn init() -> Result<()> {
    ffmpeg::init().context("Failed to initialize FFmpeg")?;
    Ok(())
}

/// PCM chunk with decoded audio data
#[derive(Debug, Clone)]
pub struct PCMChunk {
    pub samples: Vec<i16>,  // Interleaved 16-bit samples
    pub sample_rate: u32,
    pub channels: u32,
    pub position_ms: u64,
}

/// Progressive decoder that decodes FLAC data as it arrives
pub struct ProgressiveDecoder {
    input_rx: Receiver<Result<Bytes, String>>,
    buffer: Vec<u8>,
    decoder_ctx: Option<ffmpeg::codec::context::Context>,
    sample_rate: u32,
    channels: u32,
    total_samples_decoded: u64,
}

impl ProgressiveDecoder {
    /// Create a new progressive decoder from a byte stream
    pub fn new(mut stream: impl Read + Send + 'static) -> Result<Self> {
        let (tx, rx) = sync_channel(64);

        // Spawn a thread to read from the stream and feed chunks
        std::thread::spawn(move || {
            let mut buffer = vec![0u8; 8192];
            loop {
                match stream.read(&mut buffer) {
                    Ok(0) => break,  // EOF
                    Ok(n) => {
                        let chunk = Bytes::copy_from_slice(&buffer[..n]);
                        if tx.send(Ok(chunk)).is_err() {
                            break;
                        }
                    }
                    Err(e) => {
                        let _ = tx.send(Err(e.to_string()));
                        break;
                    }
                }
            }
        });

        Ok(Self {
            input_rx: rx,
            buffer: Vec::with_capacity(65536),
            decoder_ctx: None,
            sample_rate: 0,
            channels: 0,
            total_samples_decoded: 0,
        })
    }

    /// Decode the next chunk of PCM data
    pub fn decode_chunk(&mut self) -> Result<Option<PCMChunk>> {
        // Receive more data from the stream
        while self.buffer.len() < 4096 {
            match self.input_rx.try_recv() {
                Ok(Ok(bytes)) => {
                    self.buffer.extend_from_slice(&bytes);
                }
                Ok(Err(e)) => {
                    return Err(anyhow!("Stream error: {}", e));
                }
                Err(std::sync::mpsc::TryRecvError::Empty) => {
                    // No more data available right now
                    break;
                }
                Err(std::sync::mpsc::TryRecvError::Disconnected) => {
                    // Stream ended
                    if self.buffer.is_empty() {
                        return Ok(None);
                    }
                    break;
                }
            }
        }

        if self.buffer.is_empty() {
            return Ok(None);
        }

        // Initialize decoder on first call
        if self.decoder_ctx.is_none() {
            self.init_decoder()?;
        }

        // Decode a frame
        // TODO: Implement actual FFmpeg decoding
        // For now, return a placeholder

        Ok(None)
    }

    fn init_decoder(&mut self) -> Result<()> {
        // TODO: Initialize FFmpeg decoder from buffer
        // Parse FLAC header, create decoder context
        Ok(())
    }
}

/// Progressive encoder that encodes PCM to FLAC as data arrives
pub struct ProgressiveEncoder {
    output_tx: SyncSender<Bytes>,
    encoder_ctx: Option<ffmpeg::codec::context::Context>,
    sample_rate: u32,
    channels: u32,
}

impl ProgressiveEncoder {
    /// Create a new progressive encoder
    pub fn new(sample_rate: u32, channels: u32) -> Result<(Self, Receiver<Bytes>)> {
        let (tx, rx) = sync_channel(64);

        let encoder = Self {
            output_tx: tx,
            encoder_ctx: None,
            sample_rate,
            channels,
        };

        Ok((encoder, rx))
    }

    /// Encode a chunk of PCM data
    pub fn encode_chunk(&mut self, pcm: &PCMChunk) -> Result<()> {
        // TODO: Implement FFmpeg encoding
        Ok(())
    }

    /// Flush any remaining encoded data
    pub fn flush(&mut self) -> Result<()> {
        // TODO: Flush encoder
        Ok(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_ffmpeg_init() {
        assert!(init().is_ok());
    }
}