//! A UNIX socket server to run a Tower Service.

use keyfork_frame::{
    asyncext::{try_decode_from, try_encode_to},
    DecodeError, EncodeError,
};
use std::{
    io::Error,
    path::{Path, PathBuf},
};
use tokio::net::UnixListener;
use tower::{Service, ServiceExt};

#[cfg(feature = "tracing")]
use tracing::debug;

/// A UNIX Socket Server.
#[allow(clippy::module_name_repetitions)]
pub struct UnixServer {
    listener: UnixListener,
}

/// This feels like a hack, but this is a convenient way to use the same method to quickly verify
/// something across two different error types.
trait IsDisconnect {
    fn is_disconnect(&self) -> bool;
}

impl IsDisconnect for DecodeError {
    fn is_disconnect(&self) -> bool {
        if let Self::Io(e) = self {
            if let std::io::ErrorKind::UnexpectedEof = e.kind() {
                return true;
            }
        }
        false
    }
}

impl IsDisconnect for EncodeError {
    fn is_disconnect(&self) -> bool {
        if let Self::Io(e) = self {
            if let std::io::ErrorKind::UnexpectedEof = e.kind() {
                return true;
            }
        }
        false
    }
}

impl UnixServer {
    /// Bind a socket to the given `address` and create a [`UnixServer`]. This function also creates a ctrl_c handler to automatically clean up the socket file.
    ///
    /// # Errors
    /// This function may return an error if the socket can't be bound.
    pub fn bind(address: impl AsRef<Path>) -> Result<Self, Error> {
        let mut path = PathBuf::new();
        path.extend(address.as_ref().components());
        tokio::spawn(async move {
            #[cfg(feature = "tracing")]
            debug!("Binding tokio ctrl-c handler");
            let result = tokio::signal::ctrl_c().await;
            #[cfg(feature = "tracing")]
            debug!(
                ?result,
                "encountered ctrl-c, performing cleanup and exiting"
            );
            let result = tokio::fs::remove_file(&path).await;
            #[cfg(feature = "tracing")]
            if let Err(error) = result {
                debug!(%error, "unable to remove path: {}", path.display());
            }
            std::process::exit(0x80);
        });

        Ok(Self {
            listener: UnixListener::bind(address)?,
        })
    }

    /// Given a Service, accept clients and use their input to call the Service.
    ///
    /// # Errors
    /// The method may return an error if the server becomes unable to accept new connections.
    /// Errors while the server is running are logged using the `tracing` crate.
    pub async fn run<S, R>(&mut self, app: S) -> Result<(), Box<dyn std::error::Error>>
    where
        S: Service<R> + Clone + Send + 'static,
        R: From<Vec<u8>> + Send,
        <S as Service<R>>::Error: std::error::Error + Send,
        <S as Service<R>>::Response: std::convert::Into<Vec<u8>> + Send,
        <S as Service<R>>::Future: Send,
    {
        #[cfg(feature = "tracing")]
        debug!("Listening for clients");
        loop {
            let mut app = app.clone();
            let (mut socket, _) = self.listener.accept().await?;
            #[cfg(feature = "tracing")]
            debug!("new socket connected");
            tokio::spawn(async move {
                let mut has_processed_request = false;
                // Process requests until an error occurs or a client disconnects
                loop {
                    let bytes = match try_decode_from(&mut socket).await {
                        Ok(bytes) => bytes,
                        Err(e) => {
                            if e.is_disconnect() {
                                #[cfg(feature = "tracing")]
                                if !has_processed_request {
                                    debug!("client disconnected before sending any response");
                                }
                                return;
                            }
                            #[cfg(feature = "tracing")]
                            debug!(%e, "Error reading DerivationPath from socket");
                            let content = e.to_string().bytes().collect::<Vec<_>>();
                            let result = try_encode_to(&content[..], &mut socket).await;
                            #[cfg(feature = "tracing")]
                            if let Err(error) = result {
                                debug!(%error, "Error sending error to client");
                            }
                            return;
                        }
                    };

                    let app = match app.ready().await {
                        Ok(app) => app,
                        Err(e) => {
                            #[cfg(feature = "tracing")]
                            debug!(%e, "Could not poll ready");
                            let content = e.to_string().bytes().collect::<Vec<_>>();
                            let result = try_encode_to(&content[..], &mut socket).await;
                            #[cfg(feature = "tracing")]
                            if let Err(error) = result {
                                debug!(%error, "Error sending error to client");
                            }
                            return;
                        }
                    };

                    let response = match app.call(bytes.into()).await {
                        Ok(response) => response,
                        Err(e) => {
                            #[cfg(feature = "tracing")]
                            debug!(%e, "Error reading DerivationPath from socket");
                            let content = e.to_string().bytes().collect::<Vec<_>>();
                            let result = try_encode_to(&content[..], &mut socket).await;
                            #[cfg(feature = "tracing")]
                            if let Err(error) = result {
                                if error.is_disconnect() {
                                    #[cfg(feature = "tracing")]
                                    if has_processed_request {
                                        debug!("client disconnected while sending error frame");
                                    }
                                    return;
                                }
                                debug!(%error, "Error sending error to client");
                            }
                            has_processed_request = true;
                            // The error has been successfully sent, the client may perform
                            // another request.
                            continue;
                        }
                    }
                    .into();

                    if let Err(e) = try_encode_to(&response[..], &mut socket).await {
                        if e.is_disconnect() {
                            #[cfg(feature = "tracing")]
                            if has_processed_request {
                                debug!("client disconnected while sending success frame");
                            }
                            return;
                        }
                        #[cfg(feature = "tracing")]
                        debug!(%e, "Error sending response to client");
                    }

                    has_processed_request = true;
                }
            });
        }
    }
}