// HTTP/3 Transport Implementation for Cap'n Web Protocol
// Provides HTTP/3 support with QUIC multiplexing for high-performance RPC

use crate::{RpcTransport, TransportError};
use async_trait::async_trait;
use capnweb_core::{decode_message, encode_message, Message};
use quinn::{Connection, Endpoint, RecvStream, SendStream};
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::sync::Arc;
use tokio::sync::{mpsc, Mutex, RwLock};

/// HTTP/3 transport configuration
#[derive(Debug, Clone)]
pub struct Http3Config {
    /// Maximum concurrent streams per connection
    pub max_concurrent_streams: u32,
    /// Stream idle timeout in seconds
    pub stream_idle_timeout: u64,
    /// Connection idle timeout in seconds
    pub connection_idle_timeout: u64,
    /// Enable stream multiplexing
    pub enable_multiplexing: bool,
    /// Request compression
    pub enable_compression: bool,
}

impl Default for Http3Config {
    fn default() -> Self {
        Self {
            max_concurrent_streams: 1000,
            stream_idle_timeout: 30,
            connection_idle_timeout: 300,
            enable_multiplexing: true,
            enable_compression: false, // Disabled by default for simplicity
        }
    }
}

/// HTTP/3 request/response headers
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Http3Headers {
    pub method: String,
    pub path: String,
    pub authority: String,
    pub scheme: String,
    pub content_type: String,
    pub user_agent: String,
    pub custom_headers: HashMap<String, String>,
}

impl Default for Http3Headers {
    fn default() -> Self {
        Self {
            method: "POST".to_string(),
            path: "/rpc".to_string(),
            authority: "localhost".to_string(),
            scheme: "https".to_string(),
            content_type: "application/json".to_string(),
            user_agent: "CapnWeb-Rust/1.0".to_string(),
            custom_headers: HashMap::new(),
        }
    }
}

/// HTTP/3 stream handler for individual RPC streams
#[derive(Debug)]
struct Http3Stream {
    stream_id: u64,
    send_stream: SendStream,
    recv_stream: RecvStream,
    headers: Http3Headers,
}

impl Http3Stream {
    /// Create a new HTTP/3 stream
    fn new(stream_id: u64, send_stream: SendStream, recv_stream: RecvStream) -> Self {
        Self {
            stream_id,
            send_stream,
            recv_stream,
            headers: Http3Headers::default(),
        }
    }

    /// Send an HTTP/3 request with RPC payload
    async fn send_request(&mut self, message: &Message) -> Result<(), TransportError> {
        // Encode the message
        let payload = encode_message(message).map_err(|e| TransportError::Codec(e.to_string()))?;

        // Create HTTP/3 pseudo-headers (simplified version)
        let headers_frame = self.create_headers_frame(&payload)?;

        // Send headers frame
        self.send_stream
            .write_all(&headers_frame)
            .await
            .map_err(|e| TransportError::Io(std::io::Error::new(std::io::ErrorKind::Other, e)))?;

        // Send data frame
        let data_frame = self.create_data_frame(&payload)?;
        self.send_stream
            .write_all(&data_frame)
            .await
            .map_err(|e| TransportError::Io(std::io::Error::new(std::io::ErrorKind::Other, e)))?;

        self.send_stream
            .finish()
            .await
            .map_err(|e| TransportError::Io(std::io::Error::new(std::io::ErrorKind::Other, e)))?;

        tracing::trace!(
            stream_id = self.stream_id,
            payload_size = payload.len(),
            "HTTP/3 request sent"
        );
        Ok(())
    }

    /// Receive an HTTP/3 response
    async fn receive_response(&mut self) -> Result<Message, TransportError> {
        // Read HTTP/3 frames (simplified implementation)
        // In a full HTTP/3 implementation, we would parse actual HTTP/3 frames

        // For now, we'll read a length-prefixed message similar to our other transports
        let mut len_bytes = [0u8; 4];
        self.recv_stream
            .read_exact(&mut len_bytes)
            .await
            .map_err(|e| TransportError::Protocol(format!("Failed to read length: {}", e)))?;

        let len = u32::from_be_bytes(len_bytes) as usize;

        let mut payload = vec![0u8; len];
        self.recv_stream
            .read_exact(&mut payload)
            .await
            .map_err(|e| TransportError::Protocol(format!("Failed to read payload: {}", e)))?;

        let message = decode_message(&payload).map_err(|e| TransportError::Codec(e.to_string()))?;

        tracing::trace!(
            stream_id = self.stream_id,
            payload_size = payload.len(),
            "HTTP/3 response received"
        );
        Ok(message)
    }

    /// Create HTTP/3 HEADERS frame (simplified)
    fn create_headers_frame(&self, payload: &[u8]) -> Result<Vec<u8>, TransportError> {
        // Simplified HTTP/3 HEADERS frame
        // In a real implementation, this would use QPACK compression
        let mut frame = Vec::new();

        // Frame type (HEADERS = 0x01)
        frame.push(0x01);

        // Frame length (placeholder - would be calculated properly)
        frame.extend_from_slice(&(200u32.to_be_bytes())); // Placeholder length

        // Pseudo-headers (simplified encoding)
        frame.extend_from_slice(format!(":method {}\n", self.headers.method).as_bytes());
        frame.extend_from_slice(format!(":path {}\n", self.headers.path).as_bytes());
        frame.extend_from_slice(format!(":authority {}\n", self.headers.authority).as_bytes());
        frame.extend_from_slice(format!(":scheme {}\n", self.headers.scheme).as_bytes());
        frame.extend_from_slice(format!("content-type {}\n", self.headers.content_type).as_bytes());
        frame.extend_from_slice(format!("content-length {}\n", payload.len()).as_bytes());
        frame.extend_from_slice(format!("user-agent {}\n", self.headers.user_agent).as_bytes());

        // Add custom headers
        for (name, value) in &self.headers.custom_headers {
            frame.extend_from_slice(format!("{} {}\n", name, value).as_bytes());
        }

        Ok(frame)
    }

    /// Create HTTP/3 DATA frame (simplified)
    fn create_data_frame(&self, payload: &[u8]) -> Result<Vec<u8>, TransportError> {
        let mut frame = Vec::new();

        // Frame type (DATA = 0x00)
        frame.push(0x00);

        // Frame length
        frame.extend_from_slice(&(payload.len() as u32).to_be_bytes());

        // Payload
        frame.extend_from_slice(payload);

        Ok(frame)
    }
}

/// HTTP/3 transport implementation
pub struct Http3Transport {
    /// QUIC connection
    connection: Arc<Connection>,
    /// Active streams
    streams: Arc<RwLock<HashMap<u64, Http3Stream>>>,
    /// Stream counter
    next_stream_id: Arc<Mutex<u64>>,
    /// Configuration
    config: Http3Config,
    /// Message queues for multiplexing
    outgoing_queue: Arc<Mutex<mpsc::UnboundedReceiver<Message>>>,
    incoming_queue: Arc<Mutex<mpsc::UnboundedSender<Message>>>,
    /// Queue senders/receivers
    queue_tx: mpsc::UnboundedSender<Message>,
    queue_rx: mpsc::UnboundedReceiver<Message>,
}

impl Http3Transport {
    /// Create a new HTTP/3 transport
    pub fn new(connection: Connection, config: Http3Config) -> Self {
        let (queue_tx, queue_rx) = mpsc::unbounded_channel();
        let (incoming_tx, incoming_rx) = mpsc::unbounded_channel();

        Self {
            connection: Arc::new(connection),
            streams: Arc::new(RwLock::new(HashMap::new())),
            next_stream_id: Arc::new(Mutex::new(0)),
            config,
            outgoing_queue: Arc::new(Mutex::new(queue_rx)),
            incoming_queue: Arc::new(Mutex::new(incoming_tx)),
            queue_tx,
            queue_rx: incoming_rx,
        }
    }

    /// Create a new stream for HTTP/3 communication
    async fn create_stream(&self) -> Result<u64, TransportError> {
        let (send_stream, recv_stream) = self.connection.open_bi().await.map_err(|e| {
            TransportError::Protocol(format!("Failed to open bidirectional stream: {}", e))
        })?;

        let mut stream_id_guard = self.next_stream_id.lock().await;
        let stream_id = *stream_id_guard;
        *stream_id_guard += 1;

        let stream = Http3Stream::new(stream_id, send_stream, recv_stream);
        self.streams.write().await.insert(stream_id, stream);

        tracing::debug!(stream_id = stream_id, "HTTP/3 stream created");
        Ok(stream_id)
    }

    /// Get or create a stream for sending
    async fn get_send_stream(&self) -> Result<u64, TransportError> {
        if self.config.enable_multiplexing {
            // Create a new stream for each message when multiplexing
            self.create_stream().await
        } else {
            // Reuse the first stream when not multiplexing
            let streams = self.streams.read().await;
            if let Some(&stream_id) = streams.keys().next() {
                Ok(stream_id)
            } else {
                drop(streams);
                self.create_stream().await
            }
        }
    }

    /// Process outgoing messages in the background
    pub async fn start_background_processing(&self) {
        let streams = self.streams.clone();
        let config = self.config.clone();
        let connection = self.connection.clone();

        tokio::spawn(async move {
            tracing::info!("HTTP/3 background processing started");

            // This would handle connection management, stream cleanup, etc.
            loop {
                tokio::time::sleep(tokio::time::Duration::from_secs(1)).await;

                // Clean up idle streams
                let mut streams_lock = streams.write().await;
                let initial_count = streams_lock.len();

                // Remove streams that have been idle (simplified logic)
                streams_lock.retain(|&stream_id, _stream| {
                    // In a real implementation, track stream activity timestamps
                    true // Keep all streams for now
                });

                if streams_lock.len() != initial_count {
                    tracing::debug!(
                        cleaned_streams = initial_count - streams_lock.len(),
                        remaining_streams = streams_lock.len(),
                        "Cleaned up idle HTTP/3 streams"
                    );
                }
            }
        });
    }

    /// Get connection statistics
    pub async fn get_stats(&self) -> Http3Stats {
        let streams = self.streams.read().await;
        let connection_stats = self.connection.stats();

        Http3Stats {
            active_streams: streams.len(),
            max_concurrent_streams: self.config.max_concurrent_streams,
            bytes_sent: connection_stats.udp_tx.bytes,
            bytes_received: connection_stats.udp_rx.bytes,
            packets_sent: connection_stats.udp_tx.datagrams,
            packets_received: connection_stats.udp_rx.datagrams,
            connection_errors: 0, // Would track errors in real implementation
            stream_errors: 0,     // Would track errors in real implementation
        }
    }
}

#[async_trait]
impl RpcTransport for Http3Transport {
    async fn send(&mut self, message: Message) -> Result<(), TransportError> {
        let stream_id = self.get_send_stream().await?;

        let mut streams = self.streams.write().await;
        let stream = streams
            .get_mut(&stream_id)
            .ok_or_else(|| TransportError::Protocol("Stream not found".to_string()))?;

        stream.send_request(&message).await?;

        tracing::trace!(stream_id = stream_id, "Message sent via HTTP/3");
        Ok(())
    }

    async fn recv(&mut self) -> Result<Option<Message>, TransportError> {
        // In a real implementation, this would coordinate with background tasks
        // that handle incoming streams and populate the incoming queue

        match self.queue_rx.try_recv() {
            Ok(message) => {
                tracing::trace!("Message received via HTTP/3");
                Ok(Some(message))
            }
            Err(mpsc::error::TryRecvError::Empty) => Ok(None),
            Err(mpsc::error::TryRecvError::Disconnected) => Err(TransportError::ConnectionClosed),
        }
    }

    async fn close(&mut self) -> Result<(), TransportError> {
        tracing::info!("Closing HTTP/3 transport");

        // Close all streams
        let mut streams = self.streams.write().await;
        streams.clear();

        // Close the QUIC connection
        self.connection.close(0u32.into(), b"transport closed");

        tracing::info!("HTTP/3 transport closed");
        Ok(())
    }
}

/// HTTP/3 client for establishing connections
pub struct Http3Client {
    endpoint: Endpoint,
    config: Http3Config,
}

impl Http3Client {
    /// Create a new HTTP/3 client
    pub fn new(endpoint: Endpoint, config: Http3Config) -> Self {
        Self { endpoint, config }
    }

    /// Connect to an HTTP/3 server
    pub async fn connect(&self, server_addr: &str) -> Result<Http3Transport, TransportError> {
        tracing::info!(server_addr = server_addr, "Connecting to HTTP/3 server");

        let connection = self
            .endpoint
            .connect(
                server_addr.parse().map_err(|e| {
                    TransportError::Protocol(format!("Invalid server address: {}", e))
                })?,
                "localhost",
            )
            .map_err(|e| TransportError::Protocol(format!("Connection failed: {}", e)))?
            .await
            .map_err(|e| TransportError::Protocol(format!("Connection failed: {}", e)))?;

        let transport = Http3Transport::new(connection, self.config.clone());
        transport.start_background_processing().await;

        tracing::info!(server_addr = server_addr, "HTTP/3 connection established");
        Ok(transport)
    }
}

/// HTTP/3 transport statistics
#[derive(Debug, Clone)]
pub struct Http3Stats {
    pub active_streams: usize,
    pub max_concurrent_streams: u32,
    pub bytes_sent: u64,
    pub bytes_received: u64,
    pub packets_sent: u64,
    pub packets_received: u64,
    pub connection_errors: u64,
    pub stream_errors: u64,
}

/// Create a client endpoint with HTTP/3 configuration
pub fn make_http3_client_endpoint(config: Http3Config) -> Result<Endpoint, TransportError> {
    let mut client_cfg = configure_http3_client(config);
    let endpoint = Endpoint::client("0.0.0.0:0".parse().unwrap())
        .map_err(|e| TransportError::Protocol(format!("Failed to create endpoint: {}", e)))?;

    Ok(endpoint)
}

fn configure_http3_client(config: Http3Config) -> quinn::ClientConfig {
    let mut transport_config = quinn::TransportConfig::default();

    // Configure HTTP/3 specific settings
    transport_config.max_concurrent_bidi_streams(config.max_concurrent_streams.into());
    transport_config.max_idle_timeout(Some(
        std::time::Duration::from_secs(config.connection_idle_timeout)
            .try_into()
            .unwrap(),
    ));

    let crypto = rustls::ClientConfig::builder()
        .dangerous()
        .with_custom_certificate_verifier(SkipServerVerification::new())
        .with_no_client_auth();

    let mut client_config = quinn::ClientConfig::new(Arc::new(
        quinn::crypto::rustls::QuicClientConfig::try_from(crypto).unwrap(),
    ));
    client_config.transport_config(Arc::new(transport_config));

    client_config
}

/// Skip certificate verification for testing
/// WARNING: Only use this for testing!
#[derive(Debug)]
struct SkipServerVerification;

impl SkipServerVerification {
    fn new() -> Arc<Self> {
        Arc::new(Self)
    }
}

impl rustls::client::danger::ServerCertVerifier for SkipServerVerification {
    fn verify_server_cert(
        &self,
        _end_entity: &rustls::pki_types::CertificateDer<'_>,
        _intermediates: &[rustls::pki_types::CertificateDer<'_>],
        _server_name: &rustls::pki_types::ServerName<'_>,
        _ocsp_response: &[u8],
        _now: rustls::pki_types::UnixTime,
    ) -> Result<rustls::client::danger::ServerCertVerified, rustls::Error> {
        Ok(rustls::client::danger::ServerCertVerified::assertion())
    }

    fn verify_tls12_signature(
        &self,
        _message: &[u8],
        _cert: &rustls::pki_types::CertificateDer<'_>,
        _dss: &rustls::DigitallySignedStruct,
    ) -> Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error> {
        Ok(rustls::client::danger::HandshakeSignatureValid::assertion())
    }

    fn verify_tls13_signature(
        &self,
        _message: &[u8],
        _cert: &rustls::pki_types::CertificateDer<'_>,
        _dss: &rustls::DigitallySignedStruct,
    ) -> Result<rustls::client::danger::HandshakeSignatureValid, rustls::Error> {
        Ok(rustls::client::danger::HandshakeSignatureValid::assertion())
    }

    fn supported_verify_schemes(&self) -> Vec<rustls::SignatureScheme> {
        vec![
            rustls::SignatureScheme::RSA_PKCS1_SHA256,
            rustls::SignatureScheme::ECDSA_NISTP256_SHA256,
            rustls::SignatureScheme::RSA_PKCS1_SHA384,
            rustls::SignatureScheme::ECDSA_NISTP384_SHA384,
            rustls::SignatureScheme::RSA_PKCS1_SHA512,
            rustls::SignatureScheme::RSA_PSS_SHA256,
            rustls::SignatureScheme::RSA_PSS_SHA384,
            rustls::SignatureScheme::RSA_PSS_SHA512,
            rustls::SignatureScheme::ED25519,
        ]
    }
}

/// Advanced HTTP/3 features
pub mod advanced {
    use super::*;

    /// HTTP/3 connection pool for managing multiple connections
    #[derive(Debug)]
    pub struct Http3ConnectionPool {
        connections: Arc<RwLock<HashMap<String, Arc<Http3Transport>>>>,
        config: Http3Config,
        max_connections_per_host: usize,
    }

    impl Http3ConnectionPool {
        /// Create a new connection pool
        pub fn new(config: Http3Config) -> Self {
            Self {
                connections: Arc::new(RwLock::new(HashMap::new())),
                config,
                max_connections_per_host: 10,
            }
        }

        /// Get or create a connection to the specified host
        pub async fn get_connection(
            &self,
            host: &str,
        ) -> Result<Arc<Http3Transport>, TransportError> {
            let connections = self.connections.read().await;
            if let Some(transport) = connections.get(host) {
                return Ok(transport.clone());
            }
            drop(connections);

            // Create new connection
            let endpoint = make_http3_client_endpoint(self.config.clone())?;
            let client = Http3Client::new(endpoint, self.config.clone());
            let transport = client.connect(host).await?;
            let transport_arc = Arc::new(transport);

            // Store in pool
            let mut connections = self.connections.write().await;
            connections.insert(host.to_string(), transport_arc.clone());

            tracing::info!(host = host, "New HTTP/3 connection added to pool");
            Ok(transport_arc)
        }

        /// Get pool statistics
        pub async fn get_pool_stats(&self) -> HashMap<String, Http3Stats> {
            let connections = self.connections.read().await;
            let mut stats = HashMap::new();

            for (host, transport) in connections.iter() {
                stats.insert(host.clone(), transport.get_stats().await);
            }

            stats
        }
    }

    /// HTTP/3 load balancer for distributing requests
    #[derive(Debug)]
    pub struct Http3LoadBalancer {
        servers: Vec<String>,
        pool: Http3ConnectionPool,
        current_index: Arc<Mutex<usize>>,
    }

    impl Http3LoadBalancer {
        /// Create a new load balancer
        pub fn new(servers: Vec<String>, config: Http3Config) -> Self {
            Self {
                servers,
                pool: Http3ConnectionPool::new(config),
                current_index: Arc::new(Mutex::new(0)),
            }
        }

        /// Get the next server using round-robin
        pub async fn get_next_connection(&self) -> Result<Arc<Http3Transport>, TransportError> {
            if self.servers.is_empty() {
                return Err(TransportError::Protocol(
                    "No servers configured".to_string(),
                ));
            }

            let mut index = self.current_index.lock().await;
            let server = &self.servers[*index];
            *index = (*index + 1) % self.servers.len();
            drop(index);

            self.pool.get_connection(server).await
        }
    }
}

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

    #[test]
    fn test_http3_config_default() {
        let config = Http3Config::default();
        assert_eq!(config.max_concurrent_streams, 1000);
        assert!(config.enable_multiplexing);
        assert!(!config.enable_compression);
    }

    #[test]
    fn test_http3_headers_default() {
        let headers = Http3Headers::default();
        assert_eq!(headers.method, "POST");
        assert_eq!(headers.path, "/rpc");
        assert_eq!(headers.content_type, "application/json");
    }

    #[tokio::test]
    async fn test_http3_transport_creation() {
        // This test would require a mock QUIC connection
        // For now, we just test that the structures compile
        let config = Http3Config::default();
        assert!(config.max_concurrent_streams > 0);
    }

    #[tokio::test]
    async fn test_http3_connection_pool() {
        let config = Http3Config::default();
        let pool = advanced::Http3ConnectionPool::new(config);

        // Test that the pool can be created
        assert_eq!(pool.max_connections_per_host, 10);
    }
}
