use crate::config::ClientConfig;
use crate::config::DnsResolver;
use crate::config::DnsResolverExt;
use crate::config::Ipv6DualStackConfig;
use crate::config::ServerConfig;
use crate::connection::Connection;
use crate::driver::streams::session::StreamSession;
use crate::driver::streams::ProtoReadError;
use crate::driver::streams::ProtoWriteError;
use crate::driver::utils::varint_w2q;
use crate::driver::Driver;
use crate::error::ConnectingError;
use crate::error::ConnectionError;
use crate::VarInt;
use quinn::TokioRuntime;
use socket2::Domain as SocketDomain;
use socket2::Protocol as SocketProtocol;
use socket2::Socket;
use socket2::Type as SocketType;
use std::collections::HashMap;
use std::future::Future;
use std::marker::PhantomData;
use std::net::SocketAddr;
use std::net::SocketAddrV4;
use std::net::SocketAddrV6;
use std::pin::Pin;
use std::sync::Arc;
use std::task::Context;
use std::task::Poll;
use tokio::sync::Mutex;
use tracing::debug;
use url::Host;
use url::Url;
use wtransport_proto::error::ErrorCode;
use wtransport_proto::frame::FrameKind;
use wtransport_proto::headers::Headers;
use wtransport_proto::session::ReservedHeader;
use wtransport_proto::session::SessionRequest as SessionRequestProto;
use wtransport_proto::session::SessionResponse as SessionResponseProto;

/// Helper structure for Endpoint types.
pub mod endpoint_side {
    use super::*;

    /// Type of endpoint accepting multiple WebTransport connections.
    ///
    /// Use [`Endpoint::server`] to create and server-endpoint.
    pub struct Server {
        pub(super) _marker: PhantomData<()>,
    }

    /// Type of endpoint opening a WebTransport connection.
    ///
    /// Use [`Endpoint::client`] to create and client-endpoint.
    pub struct Client {
        pub(super) dns_resolver: Mutex<Box<dyn DnsResolver + Send + Sync + Unpin>>,
    }
}

/// Entrypoint for creating client or server connections.
///
/// A single endpoint can be used to accept or connect multiple connections.
/// Each endpoint internally binds an UDP socket.
///
/// # Server
/// Use [`Endpoint::server`] for creating a server-side endpoint.
/// Afterwards use the method [`Endpoint::accept`] for awaiting on incoming session request.
///
/// ```no_run
/// # use anyhow::Result;
/// # use wtransport::ServerConfig;
/// # use wtransport::Identity;
/// use wtransport::Endpoint;
///
/// # async fn run() -> Result<()> {
/// # let config = ServerConfig::builder()
/// #       .with_bind_default(4433)
/// #       .with_identity(&Identity::self_signed(["doc"]).unwrap())
/// #       .build();
/// let server = Endpoint::server(config)?;
/// loop {
///     let incoming_session = server.accept().await;
///     // Spawn task that handles client incoming session...
/// }
/// # Ok(())
/// # }
/// ```
///
/// # Client
/// Use [`Endpoint::client`] for creating a client-side endpoint and use [`Endpoint::connect`]
/// to connect to a server specifying the URL.
///
/// ```no_run
/// # use anyhow::Result;
/// use wtransport::ClientConfig;
/// use wtransport::Endpoint;
///
/// # async fn run() -> Result<()> {
/// let connection = Endpoint::client(ClientConfig::default())?
///     .connect("https://localhost:4433")
///     .await?;
/// # Ok(())
/// # }
/// ```
pub struct Endpoint<Side> {
    endpoint: quinn::Endpoint,
    side: Side,
}

impl<Side> Endpoint<Side> {
    fn bind_socket(
        bind_address: SocketAddr,
        dual_stack_config: Ipv6DualStackConfig,
    ) -> std::io::Result<Socket> {
        let domain = match bind_address {
            SocketAddr::V4(_) => SocketDomain::IPV4,
            SocketAddr::V6(_) => SocketDomain::IPV6,
        };

        let socket = Socket::new(domain, SocketType::DGRAM, Some(SocketProtocol::UDP))?;

        match dual_stack_config {
            Ipv6DualStackConfig::OsDefault => {}
            Ipv6DualStackConfig::Deny => socket.set_only_v6(true)?,
            Ipv6DualStackConfig::Allow => socket.set_only_v6(false)?,
        }

        socket.bind(&bind_address.into())?;

        Ok(socket)
    }

    /// Closes all of this endpoint's connections immediately and cease accepting new connections.
    pub fn close(&self, error_code: VarInt, reason: &[u8]) {
        self.endpoint.close(varint_w2q(error_code), reason);
    }

    /// Waits for all connections on the endpoint to be cleanly shut down.
    pub async fn wait_idle(&self) {
        self.endpoint.wait_idle().await;
    }

    /// Gets the local [`SocketAddr`] the underlying socket is bound to.
    pub fn local_addr(&self) -> std::io::Result<SocketAddr> {
        self.endpoint.local_addr()
    }
}

impl Endpoint<endpoint_side::Server> {
    /// Constructs a *server* endpoint.
    pub fn server(server_config: ServerConfig) -> std::io::Result<Self> {
        let quic_config = server_config.quic_config;
        let socket =
            Self::bind_socket(server_config.bind_address, server_config.dual_stack_config)?;
        let runtime = Arc::new(TokioRuntime);

        let endpoint = quinn::Endpoint::new(
            quinn::EndpointConfig::default(),
            Some(quic_config),
            socket.into(),
            runtime,
        )?;

        Ok(Self {
            endpoint,
            side: endpoint_side::Server {
                _marker: PhantomData,
            },
        })
    }

    /// Get the next incoming connection attempt from a client.
    pub async fn accept(&self) -> IncomingSession {
        let quic_connecting = self
            .endpoint
            .accept()
            .await
            .expect("Endpoint cannot be closed");

        debug!("New incoming QUIC connection");

        IncomingSession::new(quic_connecting)
    }

    /// Reloads the server configuration.
    ///
    /// Useful for e.g. refreshing TLS certificates without disrupting existing connections.
    ///
    /// # Arguments
    ///
    /// * `server_config` - The new configuration for the server.
    /// * `rebind` - A boolean indicating whether the server should rebind its socket.
    ///              If `true`, the server will bind to a new socket with the provided configuration.
    ///              If `false`, the bind address configuration will be ignored.
    pub fn reload_config(&self, server_config: ServerConfig, rebind: bool) -> std::io::Result<()> {
        if rebind {
            let socket =
                Self::bind_socket(server_config.bind_address, server_config.dual_stack_config)?;
            self.endpoint.rebind(socket.into())?;
        }

        let quic_config = server_config.quic_config;
        self.endpoint.set_server_config(Some(quic_config));

        Ok(())
    }

    /// Rejects new incoming connections without affecting existing connections
    pub fn reject_new_connections(&self) {
        self.endpoint.reject_new_connections();
    }
}

impl Endpoint<endpoint_side::Client> {
    /// Constructs a *client* endpoint.
    pub fn client(client_config: ClientConfig) -> std::io::Result<Self> {
        let quic_config = client_config.quic_config;
        let socket =
            Self::bind_socket(client_config.bind_address, client_config.dual_stack_config)?;
        let runtime = Arc::new(TokioRuntime);

        let mut endpoint = quinn::Endpoint::new(
            quinn::EndpointConfig::default(),
            None,
            socket.into(),
            runtime,
        )?;

        endpoint.set_default_client_config(quic_config);

        Ok(Self {
            endpoint,
            side: endpoint_side::Client {
                dns_resolver: Mutex::new(client_config.dns_resolver),
            },
        })
    }

    /// Establishes a WebTransport connection to a specified URL.
    ///
    /// This method initiates a WebTransport connection to the specified URL.
    /// It validates the URL, and performs necessary steps to establish a secure connection.
    ///
    /// # Arguments
    ///
    /// * `options` - Connection options specifying the URL and additional headers.
    ///               It can be simply an [URL](https://en.wikipedia.org/wiki/URL) string representing
    ///               the WebTransport endpoint to connect to. It must have an `https` scheme.
    ///               The URL can specify either an IP address or a hostname.
    ///               When specifying a hostname, the method will internally perform DNS resolution,
    ///               configured with
    ///               [`ClientConfigBuilder::dns_resolver`](crate::config::ClientConfigBuilder::dns_resolver).
    ///
    /// # Examples
    ///
    /// Connect using a URL with a hostname (DNS resolution is performed):
    ///
    /// ```no_run
    /// # use anyhow::Result;
    /// # use wtransport::endpoint::endpoint_side::Client;
    /// # async fn example(endpoint: wtransport::Endpoint<Client>) -> Result<()> {
    /// let url = "https://example.com:4433/webtransport";
    /// let connection = endpoint.connect(url).await?;
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Connect using a URL with an IP address:
    ///
    /// ```no_run
    /// # use anyhow::Result;
    /// # use wtransport::endpoint::endpoint_side::Client;
    /// # async fn example(endpoint: wtransport::Endpoint<Client>) -> Result<()> {
    /// let url = "https://127.0.0.1:4343/webtransport";
    /// let connection = endpoint.connect(url).await?;
    /// # Ok(())
    /// # }
    /// ```
    ///
    /// Connect adding an additional header:
    ///
    /// ```no_run
    /// # use anyhow::Result;
    /// # use wtransport::endpoint::endpoint_side::Client;
    /// # use wtransport::endpoint::ConnectOptions;
    /// # async fn example(endpoint: wtransport::Endpoint<Client>) -> Result<()> {
    /// let options = ConnectOptions::builder("https://example.com:4433/webtransport")
    ///     .add_header("Authorization", "AuthToken")
    ///     .build();
    /// let connection = endpoint.connect(options).await?;
    /// # Ok(())
    /// # }
    /// ```
    pub async fn connect<O>(&self, options: O) -> Result<Connection, ConnectingError>
    where
        O: IntoConnectOptions,
    {
        let options = options.into_options();

        let url = Url::parse(&options.url)
            .map_err(|parse_error| ConnectingError::InvalidUrl(parse_error.to_string()))?;

        if url.scheme() != "https" {
            return Err(ConnectingError::InvalidUrl(
                "WebTransport URL scheme must be 'https'".to_string(),
            ));
        }

        let host = url.host().expect("https scheme must have an host");
        let port = url.port().unwrap_or(443);

        let (socket_address, server_name) = match host {
            Host::Domain(domain) => {
                let socket_address = self
                    .side
                    .dns_resolver
                    .lock()
                    .await
                    .resolve(&format!("{domain}:{port}"))
                    .await
                    .map_err(ConnectingError::DnsLookup)?
                    .ok_or(ConnectingError::DnsNotFound)?;

                (socket_address, domain.to_string())
            }
            Host::Ipv4(address) => {
                let socket_address = SocketAddr::V4(SocketAddrV4::new(address, port));
                (socket_address, address.to_string())
            }
            Host::Ipv6(address) => {
                let socket_address = SocketAddr::V6(SocketAddrV6::new(address, port, 0, 0));
                (socket_address, address.to_string())
            }
        };

        let quic_connection = self
            .endpoint
            .connect(socket_address, &server_name)
            .map_err(ConnectingError::with_connect_error)?
            .await
            .map_err(|connection_error| {
                ConnectingError::ConnectionError(connection_error.into())
            })?;

        let driver = Driver::init(quic_connection.clone());

        let _settings = driver.accept_settings().await.map_err(|driver_error| {
            ConnectingError::ConnectionError(ConnectionError::with_driver_error(
                driver_error,
                &quic_connection,
            ))
        })?;

        // TODO(biagio): validate settings

        let mut session_request_proto =
            SessionRequestProto::new(url.as_ref()).expect("Url has been already validate");

        for (k, v) in options.additional_headers {
            session_request_proto
                .insert(k.clone(), v)
                .map_err(|ReservedHeader| ConnectingError::ReservedHeader(k))?;
        }

        let mut stream_session = match driver.open_session(session_request_proto).await {
            Ok(stream_session) => stream_session,
            Err(driver_error) => {
                return Err(ConnectingError::ConnectionError(
                    ConnectionError::with_driver_error(driver_error, &quic_connection),
                ))
            }
        };

        let session_id = stream_session.session_id();

        match stream_session
            .write_frame(stream_session.request().headers().generate_frame())
            .await
        {
            Ok(()) => {}
            Err(ProtoWriteError::Stopped) => {
                return Err(ConnectingError::SessionRejected);
            }
            Err(ProtoWriteError::NotConnected) => {
                return Err(ConnectingError::with_no_connection(&quic_connection));
            }
        }

        let frame = loop {
            let frame = match stream_session.read_frame().await {
                Ok(frame) => frame,
                Err(ProtoReadError::H3(error_code)) => {
                    quic_connection.close(varint_w2q(error_code.to_code()), b"");
                    return Err(ConnectingError::ConnectionError(
                        ConnectionError::local_h3_error(error_code),
                    ));
                }
                Err(ProtoReadError::IO(_io_error)) => {
                    return Err(ConnectingError::with_no_connection(&quic_connection));
                }
            };

            if let FrameKind::Exercise(_) = frame.kind() {
                continue;
            }
            break frame;
        };

        if !matches!(frame.kind(), FrameKind::Headers) {
            quic_connection.close(varint_w2q(ErrorCode::FrameUnexpected.to_code()), b"");
            return Err(ConnectingError::ConnectionError(
                ConnectionError::local_h3_error(ErrorCode::FrameUnexpected),
            ));
        }

        let headers = match Headers::with_frame(&frame) {
            Ok(headers) => headers,
            Err(error_code) => {
                quic_connection.close(varint_w2q(error_code.to_code()), b"");
                return Err(ConnectingError::ConnectionError(
                    ConnectionError::local_h3_error(error_code),
                ));
            }
        };

        let session_response = match SessionResponseProto::try_from(headers) {
            Ok(session_response) => session_response,
            Err(_) => {
                quic_connection.close(varint_w2q(ErrorCode::Message.to_code()), b"");
                return Err(ConnectingError::ConnectionError(
                    ConnectionError::local_h3_error(ErrorCode::Message),
                ));
            }
        };

        if session_response.code().is_successful() {
            match driver.register_session(stream_session).await {
                Ok(()) => {}
                Err(driver_error) => {
                    return Err(ConnectingError::ConnectionError(
                        ConnectionError::with_driver_error(driver_error, &quic_connection),
                    ))
                }
            }
        } else {
            return Err(ConnectingError::SessionRejected);
        }

        Ok(Connection::new(quic_connection, driver, session_id))
    }
}

/// Options for establishing a client WebTransport connection.
///
/// Used in [`Endpoint::connect`].
///
/// # Examples
///
/// ```no_run
/// # use anyhow::Result;
/// # use wtransport::endpoint::endpoint_side::Client;
/// # use wtransport::endpoint::ConnectOptions;
/// # async fn example(endpoint: wtransport::Endpoint<Client>) -> Result<()> {
/// let options = ConnectOptions::builder("https://example.com:4433/webtransport")
///     .add_header("Authorization", "AuthToken")
///     .build();
/// let connection = endpoint.connect(options).await?;
/// # Ok(())
/// # }
/// ```
pub struct ConnectOptions {
    url: String,
    additional_headers: HashMap<String, String>,
}

impl ConnectOptions {
    /// Creates a new `ConnectOptions` using a builder pattern.
    ///
    /// # Arguments
    ///
    /// * `url` - A [URL](https://en.wikipedia.org/wiki/URL) string representing the WebTransport
    ///           endpoint to connect to. It must have an `https` scheme.
    ///           The URL can specify either an IP address or a hostname.
    ///           When specifying a hostname, the method will internally perform DNS resolution,
    ///           configured with
    ///           [`ClientConfigBuilder::dns_resolver`](crate::config::ClientConfigBuilder::dns_resolver).
    pub fn builder<S>(url: S) -> ConnectRequestBuilder
    where
        S: ToString,
    {
        ConnectRequestBuilder {
            url: url.to_string(),
            additional_headers: Default::default(),
        }
    }
}

/// A trait for converting types into `ConnectOptions`.
pub trait IntoConnectOptions {
    /// Perform value-to-value conversion into [`ConnectOptions`].
    fn into_options(self) -> ConnectOptions;
}

/// A builder for [`ConnectOptions`].
///
/// See [`ConnectOptions::builder`].
pub struct ConnectRequestBuilder {
    url: String,
    additional_headers: HashMap<String, String>,
}

impl ConnectRequestBuilder {
    /// Adds a header to the connection options.
    ///
    /// # Examples
    ///
    /// ```rust
    /// use wtransport::endpoint::ConnectOptions;
    ///
    /// let options = ConnectOptions::builder("https://example.com:4433/webtransport")
    ///     .add_header("Authorization", "AuthToken")
    ///     .build();
    /// ```
    pub fn add_header<K, V>(mut self, key: K, value: V) -> Self
    where
        K: ToString,
        V: ToString,
    {
        self.additional_headers
            .insert(key.to_string(), value.to_string());
        self
    }

    /// Constructs the [`ConnectOptions`] from the builder configuration.
    pub fn build(self) -> ConnectOptions {
        ConnectOptions {
            url: self.url,
            additional_headers: self.additional_headers,
        }
    }
}

impl IntoConnectOptions for ConnectRequestBuilder {
    fn into_options(self) -> ConnectOptions {
        self.build()
    }
}

impl IntoConnectOptions for ConnectOptions {
    fn into_options(self) -> ConnectOptions {
        self
    }
}

impl<S> IntoConnectOptions for S
where
    S: ToString,
{
    fn into_options(self) -> ConnectOptions {
        ConnectOptions::builder(self).build()
    }
}

type DynFutureIncomingSession =
    dyn Future<Output = Result<SessionRequest, ConnectionError>> + Send + Sync;

/// [`Future`] for an in-progress incoming connection attempt.
///
/// Created by [`Endpoint::accept`].
pub struct IncomingSession(Pin<Box<DynFutureIncomingSession>>);

impl IncomingSession {
    fn new(quic_connecting: quinn::Connecting) -> Self {
        Self(Box::pin(Self::accept(quic_connecting)))
    }

    async fn accept(quic_connecting: quinn::Connecting) -> Result<SessionRequest, ConnectionError> {
        let quic_connection = quic_connecting.await?;

        let driver = Driver::init(quic_connection.clone());

        let _settings = driver.accept_settings().await.map_err(|driver_error| {
            ConnectionError::with_driver_error(driver_error, &quic_connection)
        })?;

        // TODO(biagio): validate settings

        let stream_session = driver.accept_session().await.map_err(|driver_error| {
            ConnectionError::with_driver_error(driver_error, &quic_connection)
        })?;

        Ok(SessionRequest::new(quic_connection, driver, stream_session))
    }
}

impl Future for IncomingSession {
    type Output = Result<SessionRequest, ConnectionError>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        Future::poll(self.0.as_mut(), cx)
    }
}

/// A incoming client session request.
///
/// Server should use methods [`accept`](Self::accept), [`forbidden`](Self::forbidden),
/// or [`not_found`](Self::not_found) in order to validate or reject the client request.
pub struct SessionRequest {
    quic_connection: quinn::Connection,
    driver: Driver,
    stream_session: StreamSession,
}

impl SessionRequest {
    pub(crate) fn new(
        quic_connection: quinn::Connection,
        driver: Driver,
        stream_session: StreamSession,
    ) -> Self {
        Self {
            quic_connection,
            driver,
            stream_session,
        }
    }

    /// Returns the peer's UDP address.
    ///
    /// **Note**: as QUIC supports migration, remote address may change
    /// during connection. Furthermore, when IPv6 support is enabled, IPv4
    /// addresses may be mapped to IPv6.
    #[inline(always)]
    pub fn remote_address(&self) -> SocketAddr {
        self.quic_connection.remote_address()
    }

    /// Returns the `:authority` field of the request.
    pub fn authority(&self) -> &str {
        self.stream_session.request().authority()
    }

    /// Returns the `:path` field of the request.
    pub fn path(&self) -> &str {
        self.stream_session.request().path()
    }

    /// Returns the `origin` field of the request if present.
    pub fn origin(&self) -> Option<&str> {
        self.stream_session.request().origin()
    }

    /// Returns the `user-agent` field of the request if present.
    pub fn user_agent(&self) -> Option<&str> {
        self.stream_session.request().user_agent()
    }

    /// Returns all header fields associated with the request.
    pub fn headers(&self) -> &HashMap<String, String> {
        self.stream_session.request().headers().as_ref()
    }

    /// Accepts the client request and it establishes the WebTransport session.
    pub async fn accept(mut self) -> Result<Connection, ConnectionError> {
        let user_agent = self.user_agent().unwrap_or_default();

        let mut response = SessionResponseProto::ok();

        // Chrome support
        if !user_agent.contains("firefox") {
            response.add("sec-webtransport-http3-draft", "draft02");
        }

        self.send_response(response).await?;

        let session_id = self.stream_session.session_id();

        self.driver
            .register_session(self.stream_session)
            .await
            .map_err(|driver_error| {
                ConnectionError::with_driver_error(driver_error, &self.quic_connection)
            })?;

        Ok(Connection::new(
            self.quic_connection,
            self.driver,
            session_id,
        ))
    }

    /// Rejects the client request by replying with `403` status code.
    pub async fn forbidden(self) {
        self.reject(SessionResponseProto::forbidden()).await;
    }

    /// Rejects the client request by replying with `404` status code.
    pub async fn not_found(self) {
        self.reject(SessionResponseProto::not_found()).await;
    }

    /// Rejects the client request by replying with `429` status code.
    pub async fn too_many_requests(self) {
        self.reject(SessionResponseProto::too_many_requests()).await;
    }

    async fn reject(mut self, mut response: SessionResponseProto) {
        let user_agent = self.user_agent().unwrap_or_default();

        // Chrome support
        if !user_agent.contains("firefox") {
            response.add("sec-webtransport-http3-draft", "draft02");
        }

        let _ = self.send_response(response).await;
        self.stream_session.finish().await;
    }

    async fn send_response(
        &mut self,
        response: SessionResponseProto,
    ) -> Result<(), ConnectionError> {
        let frame = response.headers().generate_frame();

        match self.stream_session.write_frame(frame).await {
            Ok(()) => Ok(()),
            Err(ProtoWriteError::NotConnected) => {
                Err(ConnectionError::no_connect(&self.quic_connection))
            }
            Err(ProtoWriteError::Stopped) => {
                self.quic_connection
                    .close(varint_w2q(ErrorCode::ClosedCriticalStream.to_code()), b"");

                Err(ConnectionError::local_h3_error(
                    ErrorCode::ClosedCriticalStream,
                ))
            }
        }
    }
}