//! WebSocket Relay Server
//!
//! Routes frames from source→receivers and inputs from receivers→source.
//!
//! ## Routing
//!
//! Connections are routed by WebSocket URI path:
//!   - `/source`       — default source (channel: "default")
//!   - `/source/{name}` — named source (channel: {name})
//!   - `/stream`       — default receiver (channel: "default")
//!   - `/stream/{name}` — named receiver (channel: {name})
//!   - `/`             — legacy: first connection = source, rest = receivers
//!
//! Each channel has its own broadcast/input channels and state cache,
//! allowing multiple independent streams through a single relay.
//!
//! ## Features
//!   - Multi-source: multiple views stream independently
//!   - Keyframe caching: late-joining receivers get current state instantly
//!   - Signal state store: caches SignalSync/Diff frames for reconstruction
//!   - Ping/pong keepalive: detects dead connections
//!   - Stats tracking: frames, bytes, latency metrics

use std::collections::HashMap;
use std::net::SocketAddr;
use std::sync::Arc;
use std::time::Instant;

use futures_util::{SinkExt, StreamExt};
use tokio::net::{TcpListener, TcpStream};
use tokio::sync::{broadcast, mpsc, RwLock};
use tokio::time::{interval, Duration};
use tokio_tungstenite::tungstenite::Message;

use crate::protocol::*;

/// Relay server configuration.
pub struct RelayConfig {
    /// Address to bind to.
    pub addr: SocketAddr,
    /// Maximum number of receivers per channel.
    pub max_receivers: usize,
    /// Frame broadcast channel capacity.
    pub frame_buffer_size: usize,
    /// Keepalive interval in seconds.
    pub keepalive_interval_secs: u64,
    /// Keepalive timeout in seconds — disconnect after this many seconds without a pong.
    pub keepalive_timeout_secs: u64,
}

impl Default for RelayConfig {
    fn default() -> Self {
        Self {
            addr: "0.0.0.0:9100".parse().unwrap(),
            max_receivers: 64,
            frame_buffer_size: 16,
            keepalive_interval_secs: 10,
            keepalive_timeout_secs: 30,
        }
    }
}

/// Stats tracked by the relay.
#[derive(Debug, Default, Clone)]
pub struct RelayStats {
    pub frames_relayed: u64,
    pub bytes_relayed: u64,
    pub inputs_relayed: u64,
    pub connected_receivers: usize,
    pub source_connected: bool,
    /// Timestamp of last frame from source (milliseconds since start).
    pub last_frame_timestamp: u32,
    /// Total keyframes sent.
    pub keyframes_sent: u64,
    /// Total signal diffs sent.
    pub signal_diffs_sent: u64,
    /// Uptime in seconds.
    pub uptime_secs: u64,
}

/// Cached state for late-joining receivers.
#[derive(Debug, Default, Clone)]
pub struct StateCache {
    /// Last pixel keyframe (full RGBA frame).
    pub last_keyframe: Option<Vec<u8>>,
    /// Last signal sync frame (full JSON state).
    pub last_signal_sync: Option<Vec<u8>>,
    /// Accumulated signal diffs since last sync.
    /// Late-joining receivers get: last_signal_sync + all diffs.
    pub pending_signal_diffs: Vec<Vec<u8>>,
}

impl StateCache {
    /// Process an incoming frame and update cache.
    fn process_frame(&mut self, msg: &[u8]) {
        if msg.len() < HEADER_SIZE {
            return;
        }
        let frame_type = msg[0];
        let flags = msg[1];

        match FrameType::from_u8(frame_type) {
            // Cache keyframes (pixel or signal sync)
            Some(FrameType::Pixels) if flags & FLAG_KEYFRAME != 0 => {
                self.last_keyframe = Some(msg.to_vec());
            }
            Some(FrameType::SignalSync) => {
                self.last_signal_sync = Some(msg.to_vec());
                self.pending_signal_diffs.clear(); // sync resets diffs
            }
            Some(FrameType::SignalDiff) => {
                self.pending_signal_diffs.push(msg.to_vec());
                // Cap accumulated diffs to prevent unbounded memory
                if self.pending_signal_diffs.len() > 1000 {
                    self.pending_signal_diffs.drain(..500);
                }
            }
            Some(FrameType::Keyframe) => {
                self.last_keyframe = Some(msg.to_vec());
            }
            _ => {}
        }
    }

    /// Get all messages a late-joining receiver needs to reconstruct current state.
    fn catchup_messages(&self) -> Vec<Vec<u8>> {
        let mut msgs = Vec::new();
        // Send last signal sync first (if available)
        if let Some(ref sync) = self.last_signal_sync {
            msgs.push(sync.clone());
        }
        // Then all accumulated diffs
        for diff in &self.pending_signal_diffs {
            msgs.push(diff.clone());
        }
        // Then last pixel keyframe (if available)
        if let Some(ref kf) = self.last_keyframe {
            msgs.push(kf.clone());
        }
        msgs
    }
}

/// Per-channel state — each named channel is an independent stream.
struct ChannelState {
    /// Broadcast channel: source → all receivers (frames)
    frame_tx: broadcast::Sender<Vec<u8>>,
    /// Channel: receivers → source (input events)
    input_tx: mpsc::Sender<Vec<u8>>,
    input_rx: Option<mpsc::Receiver<Vec<u8>>>,
    /// Broadcast channel for WebRTC signaling (SDP/ICE as text)
    signaling_tx: broadcast::Sender<String>,
    /// Live stats for this channel
    stats: RelayStats,
    /// Cached state for late-joining receivers
    cache: StateCache,
}

impl ChannelState {
    fn new(frame_buffer_size: usize) -> Self {
        let (frame_tx, _) = broadcast::channel(frame_buffer_size);
        let (input_tx, input_rx) = mpsc::channel(256);
        let (signaling_tx, _) = broadcast::channel(64);
        Self {
            frame_tx,
            input_tx,
            input_rx: Some(input_rx),
            signaling_tx,
            stats: RelayStats::default(),
            cache: StateCache::default(),
        }
    }
}

/// Shared relay state — holds all channels.
struct RelayState {
    /// Named channels: "default", "main", "player1", etc.
    channels: HashMap<String, Arc<RwLock<ChannelState>>>,
    /// Frame buffer size for new channels
    frame_buffer_size: usize,
    /// Server start time
    start_time: Instant,
}

impl RelayState {
    fn new(frame_buffer_size: usize) -> Self {
        Self {
            channels: HashMap::new(),
            frame_buffer_size,
            start_time: Instant::now(),
        }
    }

    /// Get or create a channel by name.
    fn get_or_create_channel(&mut self, name: &str) -> Arc<RwLock<ChannelState>> {
        self.channels
            .entry(name.to_string())
            .or_insert_with(|| Arc::new(RwLock::new(ChannelState::new(self.frame_buffer_size))))
            .clone()
    }
}

/// Parsed connection role from the WebSocket URI path.
#[derive(Debug, Clone)]
enum ConnectionRole {
    Source(String),    // channel name
    Receiver(String),  // channel name
    Signaling(String), // channel name — WebRTC signaling
}

/// Parse the WebSocket URI path to determine connection role and channel.
fn parse_path(path: &str) -> ConnectionRole {
    let parts: Vec<&str> = path.trim_start_matches('/').splitn(2, '/').collect();
    match parts.as_slice() {
        ["source"] => ConnectionRole::Source("default".to_string()),
        ["source", name] => ConnectionRole::Source(name.to_string()),
        ["stream"] => ConnectionRole::Receiver("default".to_string()),
        ["stream", name] => ConnectionRole::Receiver(name.to_string()),
        ["signal"] => ConnectionRole::Signaling("default".to_string()),
        ["signal", name] => ConnectionRole::Signaling(name.to_string()),
        _ => ConnectionRole::Receiver("default".to_string()), // legacy: `/` = receiver
    }
}

/// Run the WebSocket relay server.
pub async fn run_relay(config: RelayConfig) -> Result<(), Box<dyn std::error::Error>> {
    let listener = TcpListener::bind(&config.addr).await?;
    eprintln!("╔══════════════════════════════════════════════════╗");
    eprintln!("║   DreamStack Bitstream Relay v0.4.0             ║");
    eprintln!("║                                                  ║");
    eprintln!("║   Source:   ws://{}/source/{{name}}  ║", config.addr);
    eprintln!("║   Receiver: ws://{}/stream/{{name}}  ║", config.addr);
    eprintln!("║   Signal:   ws://{}/signal/{{name}}  ║", config.addr);
    eprintln!("║                                                  ║");
    eprintln!("║   Multi-source, WebRTC signaling, keyframe cache ║");
    eprintln!("╚══════════════════════════════════════════════════╝");

    let state = Arc::new(RwLock::new(RelayState::new(config.frame_buffer_size)));

    // Background: periodic stats logging
    {
        let state = state.clone();
        tokio::spawn(async move {
            let mut tick = interval(Duration::from_secs(30));
            loop {
                tick.tick().await;
                let s = state.read().await;
                let uptime = s.start_time.elapsed().as_secs();
                for (name, channel) in &s.channels {
                    let cs = channel.read().await;
                    if cs.stats.source_connected || cs.stats.connected_receivers > 0 {
                        eprintln!(
                            "[relay:{name}] up={uptime}s frames={} bytes={} inputs={} receivers={} signal_diffs={} cached={}",
                            cs.stats.frames_relayed,
                            cs.stats.bytes_relayed,
                            cs.stats.inputs_relayed,
                            cs.stats.connected_receivers,
                            cs.stats.signal_diffs_sent,
                            cs.cache.last_signal_sync.is_some(),
                        );
                    }
                }
            }
        });
    }

    while let Ok((stream, addr)) = listener.accept().await {
        let state = state.clone();
        let keepalive_interval = config.keepalive_interval_secs;
        let keepalive_timeout = config.keepalive_timeout_secs;
        tokio::spawn(handle_connection(stream, addr, state, keepalive_interval, keepalive_timeout));
    }
    Ok(())
}

async fn handle_connection(
    stream: TcpStream,
    addr: SocketAddr,
    state: Arc<RwLock<RelayState>>,
    keepalive_interval: u64,
    _keepalive_timeout: u64,
) {
    // Extract the URI path during handshake to determine role
    let mut role = ConnectionRole::Receiver("default".to_string());

    let ws_stream = match tokio_tungstenite::accept_hdr_async(
        stream,
        |req: &tokio_tungstenite::tungstenite::handshake::server::Request,
         res: tokio_tungstenite::tungstenite::handshake::server::Response| {
            role = parse_path(req.uri().path());
            Ok(res)
        },
    )
    .await
    {
        Ok(ws) => ws,
        Err(e) => {
            eprintln!("[relay] WebSocket handshake failed from {}: {}", addr, e);
            return;
        }
    };

    // Get or create the channel
    let (channel, channel_name) = {
        let mut s = state.write().await;
        let name = match &role {
            ConnectionRole::Source(n) | ConnectionRole::Receiver(n) | ConnectionRole::Signaling(n) => n.clone(),
        };
        let ch = s.get_or_create_channel(&name);
        (ch, name)
    };

    // Legacy fallback: if path was `/` and no source exists, treat as source
    let role = match role {
        ConnectionRole::Receiver(ref name) if name == "default" => {
            let cs = channel.read().await;
            if !cs.stats.source_connected {
                ConnectionRole::Source("default".to_string())
            } else {
                role
            }
        }
        _ => role,
    };

    match role {
        ConnectionRole::Source(ref _name) => {
            eprintln!("[relay:{channel_name}] Source connected: {addr}");
            handle_source(ws_stream, addr, channel, &channel_name, keepalive_interval).await;
        }
        ConnectionRole::Receiver(ref _name) => {
            eprintln!("[relay:{channel_name}] Receiver connected: {addr}");
            handle_receiver(ws_stream, addr, channel, &channel_name).await;
        }
        ConnectionRole::Signaling(ref _name) => {
            eprintln!("[relay:{channel_name}] Signaling peer connected: {addr}");
            handle_signaling(ws_stream, addr, channel, &channel_name).await;
        }
    }
}

async fn handle_source(
    ws_stream: tokio_tungstenite::WebSocketStream<TcpStream>,
    addr: SocketAddr,
    channel: Arc<RwLock<ChannelState>>,
    channel_name: &str,
    keepalive_interval: u64,
) {
    let (mut ws_sink, mut ws_source) = ws_stream.split();

    // Mark source as connected and take the input_rx
    let input_rx = {
        let mut cs = channel.write().await;
        cs.stats.source_connected = true;
        cs.input_rx.take()
    };

    let frame_tx = {
        let cs = channel.read().await;
        cs.frame_tx.clone()
    };

    // Forward input events from receivers → source
    if let Some(mut input_rx) = input_rx {
        let channel_clone = channel.clone();
        tokio::spawn(async move {
            while let Some(input_bytes) = input_rx.recv().await {
                let msg = Message::Binary(input_bytes.into());
                if ws_sink.send(msg).await.is_err() {
                    break;
                }
                let mut cs = channel_clone.write().await;
                cs.stats.inputs_relayed += 1;
            }
        });
    }

    // Keepalive: periodic pings
    let channel_ping = channel.clone();
    let ping_task = tokio::spawn(async move {
        let mut tick = interval(Duration::from_secs(keepalive_interval));
        let mut seq = 0u16;
        loop {
            tick.tick().await;
            let cs = channel_ping.read().await;
            if !cs.stats.source_connected {
                break;
            }
            let _ = cs.frame_tx.send(crate::codec::ping(seq, 0));
            drop(cs);
            seq = seq.wrapping_add(1);
        }
    });

    // Receive frames from source → broadcast to receivers
    let channel_name_owned = channel_name.to_string();
    while let Some(Ok(msg)) = ws_source.next().await {
        if let Message::Binary(data) = msg {
            let data_vec: Vec<u8> = data.into();
            {
                let mut cs = channel.write().await;
                cs.stats.frames_relayed += 1;
                cs.stats.bytes_relayed += data_vec.len() as u64;

                // Update state cache
                cs.cache.process_frame(&data_vec);

                // Track frame-type-specific stats
                if data_vec.len() >= HEADER_SIZE {
                    match FrameType::from_u8(data_vec[0]) {
                        Some(FrameType::SignalDiff) => cs.stats.signal_diffs_sent += 1,
                        Some(FrameType::Pixels) | Some(FrameType::Keyframe) |
                        Some(FrameType::SignalSync) => cs.stats.keyframes_sent += 1,
                        _ => {}
                    }
                    let ts = u32::from_le_bytes([
                        data_vec[4], data_vec[5], data_vec[6], data_vec[7],
                    ]);
                    cs.stats.last_frame_timestamp = ts;
                }
            }
            // Broadcast to all receivers on this channel
            let _ = frame_tx.send(data_vec);
        }
    }

    // Source disconnected
    ping_task.abort();
    eprintln!("[relay:{channel_name_owned}] Source disconnected: {addr}");
    let mut cs = channel.write().await;
    cs.stats.source_connected = false;
}

async fn handle_receiver(
    ws_stream: tokio_tungstenite::WebSocketStream<TcpStream>,
    addr: SocketAddr,
    channel: Arc<RwLock<ChannelState>>,
    channel_name: &str,
) {
    let (mut ws_sink, mut ws_source) = ws_stream.split();

    // Subscribe to frame broadcast and get catchup messages
    let (mut frame_rx, catchup_msgs) = {
        let mut cs = channel.write().await;
        cs.stats.connected_receivers += 1;
        let rx = cs.frame_tx.subscribe();
        let catchup = cs.cache.catchup_messages();
        (rx, catchup)
    };

    let input_tx = {
        let cs = channel.read().await;
        cs.input_tx.clone()
    };

    // Send cached state to late-joining receiver
    let channel_name_owned = channel_name.to_string();
    if !catchup_msgs.is_empty() {
        eprintln!(
            "[relay:{channel_name_owned}] Sending {} catchup messages to {addr}",
            catchup_msgs.len(),
        );
        for msg_bytes in catchup_msgs {
            let msg = Message::Binary(msg_bytes.into());
            if ws_sink.send(msg).await.is_err() {
                eprintln!("[relay:{channel_name_owned}] Failed to send catchup to {addr}");
                let mut cs = channel.write().await;
                cs.stats.connected_receivers = cs.stats.connected_receivers.saturating_sub(1);
                return;
            }
        }
    }

    // Forward frames from broadcast → this receiver
    let send_task = tokio::spawn(async move {
        loop {
            match frame_rx.recv().await {
                Ok(frame_bytes) => {
                    let msg = Message::Binary(frame_bytes.into());
                    if ws_sink.send(msg).await.is_err() {
                        break;
                    }
                }
                Err(broadcast::error::RecvError::Lagged(n)) => {
                    eprintln!("[relay] Receiver {addr} lagged by {n} frames");
                }
                Err(_) => break,
            }
        }
    });

    // Forward input events from this receiver → source
    while let Some(Ok(msg)) = ws_source.next().await {
        if let Message::Binary(data) = msg {
            let _ = input_tx.send(data.into()).await;
        }
    }

    // Receiver disconnected
    send_task.abort();
    eprintln!("[relay:{channel_name_owned}] Receiver disconnected: {addr}");
    let mut cs = channel.write().await;
    cs.stats.connected_receivers = cs.stats.connected_receivers.saturating_sub(1);
}

/// Handle a WebRTC signaling connection.
///
/// Signaling peers exchange JSON messages (SDP offers/answers, ICE candidates)
/// over WebSocket. The relay broadcasts all text messages to all other peers
/// on the same channel, enabling peer-to-peer WebRTC setup.
async fn handle_signaling(
    ws_stream: tokio_tungstenite::WebSocketStream<TcpStream>,
    addr: SocketAddr,
    channel: Arc<RwLock<ChannelState>>,
    channel_name: &str,
) {
    let (mut ws_sink, mut ws_source) = ws_stream.split();

    // Subscribe to signaling broadcast
    let mut sig_rx = {
        let cs = channel.read().await;
        cs.signaling_tx.subscribe()
    };

    let sig_tx = {
        let cs = channel.read().await;
        cs.signaling_tx.clone()
    };

    // Forward signaling messages from broadcast → this peer
    let channel_name_owned = channel_name.to_string();
    let send_task = tokio::spawn(async move {
        loop {
            match sig_rx.recv().await {
                Ok(msg_text) => {
                    let msg = Message::Text(msg_text.into());
                    if ws_sink.send(msg).await.is_err() {
                        break;
                    }
                }
                Err(broadcast::error::RecvError::Lagged(n)) => {
                    eprintln!("[relay:{channel_name_owned}] Signaling peer lagged by {n} messages");
                }
                Err(_) => break,
            }
        }
    });

    // Forward signaling messages from this peer → broadcast to others
    while let Some(Ok(msg)) = ws_source.next().await {
        if let Message::Text(text) = msg {
            let text_str: String = text.into();
            let _ = sig_tx.send(text_str);
        }
    }

    send_task.abort();
    eprintln!("[relay:{channel_name}] Signaling peer disconnected: {addr}");
}

// ─── Tests ───

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

    #[test]
    fn default_config() {
        let config = RelayConfig::default();
        assert_eq!(config.addr, "0.0.0.0:9100".parse::<SocketAddr>().unwrap());
        assert_eq!(config.max_receivers, 64);
        assert_eq!(config.frame_buffer_size, 16);
        assert_eq!(config.keepalive_interval_secs, 10);
    }

    #[test]
    fn stats_default() {
        let stats = RelayStats::default();
        assert_eq!(stats.frames_relayed, 0);
        assert_eq!(stats.bytes_relayed, 0);
        assert!(!stats.source_connected);
        assert_eq!(stats.keyframes_sent, 0);
        assert_eq!(stats.signal_diffs_sent, 0);
    }

    #[test]
    fn state_cache_signal_sync() {
        let mut cache = StateCache::default();

        // Simulate a SignalSync frame
        let sync_json = br#"{"count":0}"#;
        let sync_msg = crate::codec::signal_sync_frame(0, 100, sync_json);
        cache.process_frame(&sync_msg);

        assert!(cache.last_signal_sync.is_some());
        assert_eq!(cache.pending_signal_diffs.len(), 0);

        // Simulate a SignalDiff
        let diff_json = br#"{"count":1}"#;
        let diff_msg = crate::codec::signal_diff_frame(1, 200, diff_json);
        cache.process_frame(&diff_msg);

        assert_eq!(cache.pending_signal_diffs.len(), 1);

        // Catchup should contain sync + diff
        let catchup = cache.catchup_messages();
        assert_eq!(catchup.len(), 2);
    }

    #[test]
    fn state_cache_signal_sync_resets_diffs() {
        let mut cache = StateCache::default();

        // Add some diffs
        for i in 0..5 {
            let json = format!(r#"{{"count":{}}}"#, i);
            let msg = crate::codec::signal_diff_frame(i, i as u32 * 100, json.as_bytes());
            cache.process_frame(&msg);
        }
        assert_eq!(cache.pending_signal_diffs.len(), 5);

        // A new sync should clear diffs
        let sync = crate::codec::signal_sync_frame(10, 1000, b"{}");
        cache.process_frame(&sync);
        assert_eq!(cache.pending_signal_diffs.len(), 0);
        assert!(cache.last_signal_sync.is_some());
    }

    #[test]
    fn state_cache_keyframe() {
        let mut cache = StateCache::default();

        // Simulate a keyframe pixel frame
        let kf = crate::codec::pixel_frame(0, 100, 10, 10, &vec![0xFF; 400]);
        cache.process_frame(&kf);

        assert!(cache.last_keyframe.is_some());
        let catchup = cache.catchup_messages();
        assert_eq!(catchup.len(), 1);
    }

    #[test]
    fn state_cache_diff_cap() {
        let mut cache = StateCache::default();

        // Add more than 1000 diffs — should auto-trim
        for i in 0..1100u16 {
            let json = format!(r#"{{"n":{}}}"#, i);
            let msg = crate::codec::signal_diff_frame(i, i as u32, json.as_bytes());
            cache.process_frame(&msg);
        }
        // Should have been trimmed: 1100 - 500 = 600 remaining after first trim at 1001
        assert!(cache.pending_signal_diffs.len() <= 600);
    }

    // ─── Path Routing Tests ───

    #[test]
    fn parse_path_source_default() {
        match parse_path("/source") {
            ConnectionRole::Source(name) => assert_eq!(name, "default"),
            _ => panic!("Expected Source"),
        }
    }

    #[test]
    fn parse_path_source_named() {
        match parse_path("/source/main") {
            ConnectionRole::Source(name) => assert_eq!(name, "main"),
            _ => panic!("Expected Source"),
        }
    }

    #[test]
    fn parse_path_stream_default() {
        match parse_path("/stream") {
            ConnectionRole::Receiver(name) => assert_eq!(name, "default"),
            _ => panic!("Expected Receiver"),
        }
    }

    #[test]
    fn parse_path_stream_named() {
        match parse_path("/stream/player1") {
            ConnectionRole::Receiver(name) => assert_eq!(name, "player1"),
            _ => panic!("Expected Receiver"),
        }
    }

    #[test]
    fn parse_path_signal_default() {
        match parse_path("/signal") {
            ConnectionRole::Signaling(name) => assert_eq!(name, "default"),
            _ => panic!("Expected Signaling"),
        }
    }

    #[test]
    fn parse_path_signal_named() {
        match parse_path("/signal/main") {
            ConnectionRole::Signaling(name) => assert_eq!(name, "main"),
            _ => panic!("Expected Signaling"),
        }
    }

    #[test]
    fn parse_path_legacy_root() {
        match parse_path("/") {
            ConnectionRole::Receiver(name) => assert_eq!(name, "default"),
            _ => panic!("Expected Receiver for legacy path"),
        }
    }

    #[test]
    fn channel_state_creation() {
        let mut state = RelayState::new(16);
        let ch1 = state.get_or_create_channel("main");
        let ch2 = state.get_or_create_channel("player1");
        let ch1_again = state.get_or_create_channel("main");

        assert_eq!(state.channels.len(), 2);
        assert!(Arc::ptr_eq(&ch1, &ch1_again));
        assert!(!Arc::ptr_eq(&ch1, &ch2));
    }
}