//! HTTP/2 Server Connections

use std::error::Error as StdError;
use std::fmt;
use std::future::Future;
use std::pin::Pin;
use std::sync::Arc;
use std::task::{Context, Poll};
use std::time::Duration;

use crate::rt::{Read, Write};
use futures_util::ready;
use pin_project_lite::pin_project;

use crate::body::{Body, Incoming as IncomingBody};
use crate::proto;
use crate::rt::bounds::Http2ServerConnExec;
use crate::service::HttpService;
use crate::{common::time::Time, rt::Timer};

pin_project! {
    /// A [`Future`](core::future::Future) representing an HTTP/2 connection, bound to a
    /// [`Service`](crate::service::Service), returned from
    /// [`Builder::serve_connection`](struct.Builder.html#method.serve_connection).
    ///
    /// To drive HTTP on this connection this future **must be polled**, typically with
    /// `.await`. If it isn't polled, no progress will be made on this connection.
    #[must_use = "futures do nothing unless polled"]
    pub struct Connection<T, S, E>
    where
        S: HttpService<IncomingBody>,
    {
        conn: proto::h2::Server<T, S, S::ResBody, E>,
    }
}

/// A configuration builder for HTTP/2 server connections.
///
/// **Note**: The default values of options are *not considered stable*. They
/// are subject to change at any time.
#[derive(Clone, Debug)]
pub struct Builder<E> {
    exec: E,
    timer: Time,
    h2_builder: proto::h2::server::Config,
}

// ===== impl Connection =====

impl<I, S, E> fmt::Debug for Connection<I, S, E>
where
    S: HttpService<IncomingBody>,
{
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Connection").finish()
    }
}

impl<I, B, S, E> Connection<I, S, E>
where
    S: HttpService<IncomingBody, ResBody = B>,
    S::Error: Into<Box<dyn StdError + Send + Sync>>,
    I: Read + Write + Unpin,
    B: Body + 'static,
    B::Error: Into<Box<dyn StdError + Send + Sync>>,
    E: Http2ServerConnExec<S::Future, B>,
{
    /// Start a graceful shutdown process for this connection.
    ///
    /// This `Connection` should continue to be polled until shutdown
    /// can finish.
    ///
    /// # Note
    ///
    /// This should only be called while the `Connection` future is still
    /// pending. If called after `Connection::poll` has resolved, this does
    /// nothing.
    pub fn graceful_shutdown(mut self: Pin<&mut Self>) {
        self.conn.graceful_shutdown();
    }
}

impl<I, B, S, E> Future for Connection<I, S, E>
where
    S: HttpService<IncomingBody, ResBody = B>,
    S::Error: Into<Box<dyn StdError + Send + Sync>>,
    I: Read + Write + Unpin,
    B: Body + 'static,
    B::Error: Into<Box<dyn StdError + Send + Sync>>,
    E: Http2ServerConnExec<S::Future, B>,
{
    type Output = crate::Result<()>;

    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
        match ready!(Pin::new(&mut self.conn).poll(cx)) {
            Ok(_done) => {
                //TODO: the proto::h2::Server no longer needs to return
                //the Dispatched enum
                Poll::Ready(Ok(()))
            }
            Err(e) => Poll::Ready(Err(e)),
        }
    }
}

// ===== impl Builder =====

impl<E> Builder<E> {
    /// Create a new connection builder.
    ///
    /// This starts with the default options, and an executor which is a type
    /// that implements [`Http2ServerConnExec`] trait.
    ///
    /// [`Http2ServerConnExec`]: crate::rt::bounds::Http2ServerConnExec
    pub fn new(exec: E) -> Self {
        Self {
            exec,
            timer: Time::Empty,
            h2_builder: Default::default(),
        }
    }

    /// Configures the maximum number of pending reset streams allowed before a GOAWAY will be sent.
    ///
    /// This will default to the default value set by the [`h2` crate](https://crates.io/crates/h2).
    /// As of v0.4.0, it is 20.
    ///
    /// See <https://github.com/hyperium/hyper/issues/2877> for more information.
    pub fn max_pending_accept_reset_streams(&mut self, max: impl Into<Option<usize>>) -> &mut Self {
        self.h2_builder.max_pending_accept_reset_streams = max.into();
        self
    }

    /// Configures the maximum number of local reset streams allowed before a GOAWAY will be sent.
    ///
    /// If not set, hyper will use a default, currently of 1024.
    ///
    /// If `None` is supplied, hyper will not apply any limit.
    /// This is not advised, as it can potentially expose servers to DOS vulnerabilities.
    ///
    /// See <https://rustsec.org/advisories/RUSTSEC-2024-0003.html> for more information.
    #[cfg(feature = "http2")]
    #[cfg_attr(docsrs, doc(cfg(feature = "http2")))]
    pub fn max_local_error_reset_streams(mut self, max: impl Into<Option<usize>>) -> Self {
        self.h2_builder.max_local_error_reset_streams = max.into();
        self
    }

    /// Sets the [`SETTINGS_INITIAL_WINDOW_SIZE`][spec] option for HTTP2
    /// stream-level flow control.
    ///
    /// Passing `None` will do nothing.
    ///
    /// If not set, hyper will use a default.
    ///
    /// [spec]: https://httpwg.org/specs/rfc9113.html#SETTINGS_INITIAL_WINDOW_SIZE
    pub fn initial_stream_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
        if let Some(sz) = sz.into() {
            self.h2_builder.adaptive_window = false;
            self.h2_builder.initial_stream_window_size = sz;
        }
        self
    }

    /// Sets the max connection-level flow control for HTTP2.
    ///
    /// Passing `None` will do nothing.
    ///
    /// If not set, hyper will use a default.
    pub fn initial_connection_window_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
        if let Some(sz) = sz.into() {
            self.h2_builder.adaptive_window = false;
            self.h2_builder.initial_conn_window_size = sz;
        }
        self
    }

    /// Sets whether to use an adaptive flow control.
    ///
    /// Enabling this will override the limits set in
    /// `initial_stream_window_size` and
    /// `initial_connection_window_size`.
    pub fn adaptive_window(&mut self, enabled: bool) -> &mut Self {
        use proto::h2::SPEC_WINDOW_SIZE;

        self.h2_builder.adaptive_window = enabled;
        if enabled {
            self.h2_builder.initial_conn_window_size = SPEC_WINDOW_SIZE;
            self.h2_builder.initial_stream_window_size = SPEC_WINDOW_SIZE;
        }
        self
    }

    /// Sets the maximum frame size to use for HTTP2.
    ///
    /// Passing `None` will do nothing.
    ///
    /// If not set, hyper will use a default.
    pub fn max_frame_size(&mut self, sz: impl Into<Option<u32>>) -> &mut Self {
        if let Some(sz) = sz.into() {
            self.h2_builder.max_frame_size = sz;
        }
        self
    }

    /// Sets the [`SETTINGS_MAX_CONCURRENT_STREAMS`][spec] option for HTTP2
    /// connections.
    ///
    /// Default is 200, but not part of the stability of hyper. It could change
    /// in a future release. You are encouraged to set your own limit.
    ///
    /// Passing `None` will remove any limit.
    ///
    /// [spec]: https://httpwg.org/specs/rfc9113.html#SETTINGS_MAX_CONCURRENT_STREAMS
    pub fn max_concurrent_streams(&mut self, max: impl Into<Option<u32>>) -> &mut Self {
        self.h2_builder.max_concurrent_streams = max.into();
        self
    }

    /// Sets an interval for HTTP2 Ping frames should be sent to keep a
    /// connection alive.
    ///
    /// Pass `None` to disable HTTP2 keep-alive.
    ///
    /// Default is currently disabled.
    pub fn keep_alive_interval(&mut self, interval: impl Into<Option<Duration>>) -> &mut Self {
        self.h2_builder.keep_alive_interval = interval.into();
        self
    }

    /// Sets a timeout for receiving an acknowledgement of the keep-alive ping.
    ///
    /// If the ping is not acknowledged within the timeout, the connection will
    /// be closed. Does nothing if `keep_alive_interval` is disabled.
    ///
    /// Default is 20 seconds.
    pub fn keep_alive_timeout(&mut self, timeout: Duration) -> &mut Self {
        self.h2_builder.keep_alive_timeout = timeout;
        self
    }

    /// Set the maximum write buffer size for each HTTP/2 stream.
    ///
    /// Default is currently ~400KB, but may change.
    ///
    /// # Panics
    ///
    /// The value must be no larger than `u32::MAX`.
    pub fn max_send_buf_size(&mut self, max: usize) -> &mut Self {
        assert!(max <= std::u32::MAX as usize);
        self.h2_builder.max_send_buffer_size = max;
        self
    }

    /// Enables the [extended CONNECT protocol].
    ///
    /// [extended CONNECT protocol]: https://datatracker.ietf.org/doc/html/rfc8441#section-4
    pub fn enable_connect_protocol(&mut self) -> &mut Self {
        self.h2_builder.enable_connect_protocol = true;
        self
    }

    /// Sets the max size of received header frames.
    ///
    /// Default is currently 16KB, but can change.
    pub fn max_header_list_size(&mut self, max: u32) -> &mut Self {
        self.h2_builder.max_header_list_size = max;
        self
    }

    /// Set the timer used in background tasks.
    pub fn timer<M>(&mut self, timer: M) -> &mut Self
    where
        M: Timer + Send + Sync + 'static,
    {
        self.timer = Time::Timer(Arc::new(timer));
        self
    }

    /// Bind a connection together with a [`Service`](crate::service::Service).
    ///
    /// This returns a Future that must be polled in order for HTTP to be
    /// driven on the connection.
    pub fn serve_connection<S, I, Bd>(&self, io: I, service: S) -> Connection<I, S, E>
    where
        S: HttpService<IncomingBody, ResBody = Bd>,
        S::Error: Into<Box<dyn StdError + Send + Sync>>,
        Bd: Body + 'static,
        Bd::Error: Into<Box<dyn StdError + Send + Sync>>,
        I: Read + Write + Unpin,
        E: Http2ServerConnExec<S::Future, Bd>,
    {
        let proto = proto::h2::Server::new(
            io,
            service,
            &self.h2_builder,
            self.exec.clone(),
            self.timer.clone(),
        );
        Connection { conn: proto }
    }
}