//! TCP transport — the production control-plane transport.
//!
//! Blocking model: every blocking point parks the **calling actor** on fd
//! readiness ([`crate::scheduler::wait_readable`] / `wait_writable`); the
//! scheduler thread is never blocked. All conn/listener methods must
//! therefore run inside an actor. `listen` itself only binds (no waiting)
//! and is callable anywhere.
//!
//! Addresses are pre-resolved `ip:port` strings (`SocketAddr` syntax, IPv4
//! or IPv6). Hostnames are rejected with `InvalidInput`: name resolution is
//! the single c9 seam, not something each transport does on the side.
//!
//! Writes use `send(2)` with `MSG_NOSIGNAL` — a peer reset must surface as
//! `BrokenPipe`/`ConnectionReset`, not `SIGPIPE`.

use std::io;
use std::net::{SocketAddr, TcpListener as StdListener, TcpStream};
use std::os::fd::{AsRawFd, RawFd};

use crate::scheduler::{wait_readable, wait_writable};

use super::{Conn, Listener, Transport};

// ---------------------------------------------------------------------------
// sockaddr plumbing
// ---------------------------------------------------------------------------

/// A `sockaddr_in`/`sockaddr_in6` built from a parsed `SocketAddr`, plus its
/// length, ready for `connect(2)`.
union SockAddrUnion {
    v4: libc::sockaddr_in,
    v6: libc::sockaddr_in6,
}

fn to_sockaddr(sa: &SocketAddr) -> (SockAddrUnion, libc::socklen_t) {
    match sa {
        SocketAddr::V4(v4) => {
            let raw = libc::sockaddr_in {
                sin_family: libc::AF_INET as libc::sa_family_t,
                sin_port: v4.port().to_be(),
                sin_addr: libc::in_addr {
                    s_addr: u32::from_be_bytes(v4.ip().octets()).to_be(),
                },
                sin_zero: [0; 8],
            };
            (
                SockAddrUnion { v4: raw },
                std::mem::size_of::<libc::sockaddr_in>() as libc::socklen_t,
            )
        }
        SocketAddr::V6(v6) => {
            let raw = libc::sockaddr_in6 {
                sin6_family: libc::AF_INET6 as libc::sa_family_t,
                sin6_port: v6.port().to_be(),
                sin6_flowinfo: v6.flowinfo(),
                sin6_addr: libc::in6_addr {
                    s6_addr: v6.ip().octets(),
                },
                sin6_scope_id: v6.scope_id(),
            };
            (
                SockAddrUnion { v6: raw },
                std::mem::size_of::<libc::sockaddr_in6>() as libc::socklen_t,
            )
        }
    }
}

fn parse_addr(addr: &str) -> io::Result<SocketAddr> {
    addr.parse().map_err(|_| {
        io::Error::new(
            io::ErrorKind::InvalidInput,
            format!("{addr:?} is not a resolved ip:port — resolution is the c9 seam"),
        )
    })
}

fn so_error(fd: RawFd) -> io::Result<()> {
    let mut err: libc::c_int = 0;
    let mut len = std::mem::size_of::<libc::c_int>() as libc::socklen_t;
    let rc = unsafe {
        libc::getsockopt(
            fd,
            libc::SOL_SOCKET,
            libc::SO_ERROR,
            (&mut err) as *mut _ as *mut libc::c_void,
            &mut len,
        )
    };
    if rc != 0 {
        return Err(io::Error::last_os_error());
    }
    if err != 0 {
        return Err(io::Error::from_raw_os_error(err));
    }
    Ok(())
}

// ---------------------------------------------------------------------------
// Conn
// ---------------------------------------------------------------------------

/// One established TCP control connection. Owns the socket; drop closes it.
pub struct TcpConn {
    stream: TcpStream,
    closed: bool,
}

impl TcpConn {
    fn fd(&self) -> RawFd {
        self.stream.as_raw_fd()
    }
}

impl Conn for TcpConn {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        if self.closed {
            return Ok(0);
        }
        if buf.is_empty() {
            return Ok(0);
        }
        loop {
            wait_readable(self.fd())?;
            let n = unsafe { libc::read(self.fd(), buf.as_mut_ptr() as *mut _, buf.len()) };
            if n >= 0 {
                return Ok(n as usize);
            }
            let e = io::Error::last_os_error();
            match e.kind() {
                // Spurious readiness or signal: park again.
                io::ErrorKind::WouldBlock | io::ErrorKind::Interrupted => continue,
                _ => return Err(e),
            }
        }
    }

    fn write_all(&mut self, mut buf: &[u8]) -> io::Result<()> {
        if self.closed {
            return Err(io::Error::new(
                io::ErrorKind::NotConnected,
                "tcp conn closed locally",
            ));
        }
        while !buf.is_empty() {
            wait_writable(self.fd())?;
            let n = unsafe {
                libc::send(
                    self.fd(),
                    buf.as_ptr() as *const _,
                    buf.len(),
                    libc::MSG_NOSIGNAL,
                )
            };
            if n >= 0 {
                buf = &buf[n as usize..];
                continue;
            }
            let e = io::Error::last_os_error();
            match e.kind() {
                io::ErrorKind::WouldBlock | io::ErrorKind::Interrupted => continue,
                _ => return Err(e),
            }
        }
        Ok(())
    }

    fn close(&mut self) {
        if !self.closed {
            self.closed = true;
            // Best-effort: the peer sees EOF after draining. The fd itself
            // is released when the owning stream drops.
            let _ = self.stream.shutdown(std::net::Shutdown::Both);
        }
    }

    fn peer_addr(&self) -> String {
        match self.stream.peer_addr() {
            Ok(sa) => sa.to_string(),
            Err(_) => "<disconnected>".to_string(),
        }
    }

    fn readable_arm(&self) -> Option<crate::scheduler::FdArm> {
        Some(crate::scheduler::FdArm::readable(self.fd()))
    }
}

// ---------------------------------------------------------------------------
// Listener
// ---------------------------------------------------------------------------

/// A bound TCP listen point (non-blocking socket; accept parks the actor).
pub struct TcpListener {
    inner: StdListener,
    local: SocketAddr,
}

impl Listener for TcpListener {
    fn readable_arm(&self) -> Option<crate::scheduler::FdArm> {
        Some(crate::scheduler::FdArm::readable(self.inner.as_raw_fd()))
    }

    fn accept(&mut self) -> io::Result<Box<dyn Conn>> {
        loop {
            wait_readable(self.inner.as_raw_fd())?;
            match self.inner.accept() {
                Ok((stream, _peer)) => {
                    stream.set_nonblocking(true)?;
                    return Ok(Box::new(TcpConn {
                        stream,
                        closed: false,
                    }));
                }
                Err(e)
                    if e.kind() == io::ErrorKind::WouldBlock
                        || e.kind() == io::ErrorKind::Interrupted =>
                {
                    continue;
                }
                Err(e) => return Err(e),
            }
        }
    }

    fn local_addr(&self) -> String {
        self.local.to_string()
    }
}

// ---------------------------------------------------------------------------
// Transport
// ---------------------------------------------------------------------------

/// The TCP transport. Stateless; every call stands alone.
pub struct TcpTransport;

impl Transport for TcpTransport {
    fn dial(&self, addr: &str) -> io::Result<Box<dyn Conn>> {
        let sa = parse_addr(addr)?;
        let family = match sa {
            SocketAddr::V4(_) => libc::AF_INET,
            SocketAddr::V6(_) => libc::AF_INET6,
        };
        let fd = unsafe {
            libc::socket(
                family,
                libc::SOCK_STREAM | libc::SOCK_NONBLOCK | libc::SOCK_CLOEXEC,
                0,
            )
        };
        if fd < 0 {
            return Err(io::Error::last_os_error());
        }
        // From here the fd is owned by `stream`; any early return drops it.
        let stream = unsafe {
            use std::os::fd::FromRawFd;
            TcpStream::from_raw_fd(fd)
        };
        let (raw, len) = to_sockaddr(&sa);
        let rc = unsafe { libc::connect(fd, (&raw) as *const _ as *const libc::sockaddr, len) };
        if rc != 0 {
            let e = io::Error::last_os_error();
            if e.raw_os_error() != Some(libc::EINPROGRESS) {
                return Err(e);
            }
            // Connect in flight: park until the socket is writable, then the
            // verdict is in SO_ERROR.
            wait_writable(fd)?;
            so_error(fd)?;
        }
        Ok(Box::new(TcpConn {
            stream,
            closed: false,
        }))
    }

    fn listen(&self, addr: &str) -> io::Result<Box<dyn Listener>> {
        let sa = parse_addr(addr)?;
        let inner = StdListener::bind(sa)?;
        inner.set_nonblocking(true)?;
        let local = inner.local_addr()?;
        Ok(Box::new(TcpListener { inner, local }))
    }
}