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//! Functions to interact with Mercurial command server.

use std::io;
use std::path::Path;
use std::process::Stdio;
use tokio::process::Command;

use crate::codec::ChannelMessage;
use crate::connection::{Connection, PipeConnection};
use crate::message::{self, ServerSpec};
use crate::protocol::Protocol;
use crate::runcommand::{self, UiHandler};

/// Command-server client holding active connection.
#[derive(Debug)]
pub struct Client<C> {
    proto: Protocol<C>,
    spec: ServerSpec,
}

impl<C> Client<C> {
    fn new(proto: Protocol<C>, spec: ServerSpec) -> Self {
        Self { proto, spec }
    }

    /// Server capabilities, encoding, etc.
    pub fn server_spec(&self) -> &ServerSpec {
        &self.spec
    }

    /// Mutably borrows the underlying protocol.
    ///
    /// This is a low-level interface to implement new command handler.
    pub fn borrow_protocol_mut(&mut self) -> &mut Protocol<C> {
        &mut self.proto
    }
}

impl<C> Client<C>
where
    C: Connection,
{
    /// Runs the Mercurial command specified in bytes.
    ///
    /// # Panics
    ///
    /// Panics if argument contains `\0` character.
    pub async fn run_command(
        &mut self,
        handler: &mut impl UiHandler,
        args: impl IntoIterator<Item = impl AsRef<[u8]>>,
    ) -> io::Result<i32> {
        runcommand::run_command(
            self.borrow_protocol_mut(),
            handler,
            message::pack_args(args),
        )
        .await
    }
}

/// Command-server client which spawns new server process and interacts via pipe.
pub type PipeClient = Client<PipeConnection>;

impl PipeClient {
    /// Spawns a server process at the specified directory with the default configuration.
    pub async fn spawn_at(dir: impl AsRef<Path>) -> io::Result<Self> {
        let mut command = Command::new("hg");
        command
            .args(&[
                "serve",
                "--cmdserver",
                "pipe",
                "--config",
                "ui.interactive=True",
            ])
            .current_dir(dir)
            .env("HGPLAIN", "1");
        PipeClient::spawn_with(&mut command).await
    }

    /// Spawns a server process by the given process builder.
    pub async fn spawn_with(command: &mut Command) -> io::Result<Self> {
        let child = command
            .stdin(Stdio::piped())
            .stdout(Stdio::piped())
            .spawn()?;
        let mut proto = Protocol::new(PipeConnection::new(child));
        let spec = read_hello(&mut proto).await?;
        Ok(Self::new(proto, spec))
    }

    // TODO: shuts down the process cleanly?
}

#[cfg(unix)]
pub use self::unix::UnixClient;

#[cfg(unix)]
mod unix {
    use std::ffi::OsStr;
    use std::os::unix::io::{AsRawFd, RawFd};
    use tokio::net::UnixStream;

    use super::*;
    use crate::connection::UnixConnection;

    impl<C> Client<C>
    where
        C: Connection,
    {
        /// Runs the Mercurial command specified in platform string.
        pub async fn run_command_os(
            &mut self,
            handler: &mut impl UiHandler,
            args: impl IntoIterator<Item = impl AsRef<OsStr>>,
        ) -> io::Result<i32> {
            runcommand::run_command(
                self.borrow_protocol_mut(),
                handler,
                message::pack_args_os(args),
            )
            .await
        }
    }

    impl<C> AsRawFd for Client<C>
    where
        C: AsRawFd,
    {
        fn as_raw_fd(&self) -> RawFd {
            self.proto.as_raw_fd()
        }
    }

    /// Command-server client which interacts via Unix domain socket.
    pub type UnixClient = Client<UnixConnection>;

    impl UnixClient {
        /// Connects to a command server listening at the specified socket path.
        pub async fn connect(path: impl AsRef<Path>) -> io::Result<Self> {
            let stream = UnixStream::connect(path).await?;
            let mut proto = Protocol::new(UnixConnection::new(stream));
            let spec = read_hello(&mut proto).await?;
            Ok(Self::new(proto, spec))
        }
    }
}

async fn read_hello(proto: &mut Protocol<impl Connection>) -> io::Result<ServerSpec> {
    match proto.fetch_response().await? {
        ChannelMessage::Data(b'o', data) => message::parse_hello(data),
        _ => Err(io::Error::new(
            io::ErrorKind::InvalidData,
            "no hello message received",
        )),
    }
}