//! Leg I/O task spawners.
//!
//! Each SIP leg gets two tasks:
//! - Inbound: recv_from on RTP socket → strip header → send RtpPacket to mixer channel
//! - Outbound: recv encoded RTP from mixer channel → send_to remote media endpoint
//!
//! WebRTC leg I/O is handled inside webrtc_engine.rs (on_track + track.write).

use crate::mixer::RtpPacket;
use std::net::SocketAddr;
use std::sync::Arc;
use tokio::net::UdpSocket;
use tokio::sync::mpsc;

/// Channel pair for connecting a leg to the mixer.
pub struct LegChannels {
    /// Mixer receives decoded packets from this leg.
    pub inbound_tx: mpsc::Sender<RtpPacket>,
    pub inbound_rx: mpsc::Receiver<RtpPacket>,
    /// Mixer sends encoded RTP to this leg.
    pub outbound_tx: mpsc::Sender<Vec<u8>>,
    pub outbound_rx: mpsc::Receiver<Vec<u8>>,
}

/// Create a channel pair for a leg.
pub fn create_leg_channels() -> LegChannels {
    let (inbound_tx, inbound_rx) = mpsc::channel::<RtpPacket>(64);
    let (outbound_tx, outbound_rx) = mpsc::channel::<Vec<u8>>(8);
    LegChannels {
        inbound_tx,
        inbound_rx,
        outbound_tx,
        outbound_rx,
    }
}

/// Spawn the inbound I/O task for a SIP leg.
/// Reads RTP from the socket, parses the variable-length header (RFC 3550),
/// and sends the payload to the mixer.
/// Returns the JoinHandle (exits when the inbound_tx channel is dropped).
pub fn spawn_sip_inbound(
    rtp_socket: Arc<UdpSocket>,
    inbound_tx: mpsc::Sender<RtpPacket>,
) -> tokio::task::JoinHandle<()> {
    tokio::spawn(async move {
        let mut buf = vec![0u8; 1500];
        loop {
            match rtp_socket.recv_from(&mut buf).await {
                Ok((n, _from)) => {
                    if n < 12 {
                        continue; // Too small for RTP header.
                    }
                    let pt = buf[1] & 0x7F;
                    let marker = (buf[1] & 0x80) != 0;
                    let seq = u16::from_be_bytes([buf[2], buf[3]]);
                    let timestamp = u32::from_be_bytes([buf[4], buf[5], buf[6], buf[7]]);

                    // RFC 3550: header length = 12 + (CC * 4) + optional extension.
                    let cc = (buf[0] & 0x0F) as usize;
                    let has_extension = (buf[0] & 0x10) != 0;
                    let mut offset = 12 + cc * 4;
                    if has_extension {
                        if offset + 4 > n {
                            continue; // Malformed: extension header truncated.
                        }
                        let ext_len =
                            u16::from_be_bytes([buf[offset + 2], buf[offset + 3]]) as usize;
                        offset += 4 + ext_len * 4;
                    }
                    if offset >= n {
                        continue; // No payload after header.
                    }

                    let payload = buf[offset..n].to_vec();
                    if payload.is_empty() {
                        continue;
                    }
                    if inbound_tx
                        .send(RtpPacket {
                            payload,
                            payload_type: pt,
                            marker,
                            seq,
                            timestamp,
                        })
                        .await
                        .is_err()
                    {
                        break; // Channel closed — leg removed.
                    }
                }
                Err(_) => break, // Socket error.
            }
        }
    })
}

/// Spawn the outbound I/O task for a SIP leg.
/// Reads encoded RTP packets from the mixer and sends them to the remote media endpoint.
/// Returns the JoinHandle (exits when the outbound_rx channel is closed).
pub fn spawn_sip_outbound(
    rtp_socket: Arc<UdpSocket>,
    remote_media: SocketAddr,
    mut outbound_rx: mpsc::Receiver<Vec<u8>>,
) -> tokio::task::JoinHandle<()> {
    tokio::spawn(async move {
        while let Some(rtp_data) = outbound_rx.recv().await {
            let _ = rtp_socket.send_to(&rtp_data, remote_media).await;
        }
    })
}