use std::io::Write as _;
use std::net::SocketAddr;
use tokio::io;
use tokio::io::AsyncRead;
use tokio::io::AsyncWrite;
use tokio::net::TcpListener;
use tokio_tungstenite::accept_async;
use tracing::warn;

use crate::ExecServerRuntimePaths;
use crate::connection::JsonRpcConnection;
use crate::server::processor::ConnectionProcessor;

pub const DEFAULT_LISTEN_URL: &str = "ws://127.0.0.1:0";

#[derive(Debug, Clone, Eq, PartialEq)]
pub(crate) enum ExecServerListenTransport {
    WebSocket(SocketAddr),
    Stdio,
}

#[derive(Debug, Clone, Eq, PartialEq)]
pub enum ExecServerListenUrlParseError {
    UnsupportedListenUrl(String),
    InvalidWebSocketListenUrl(String),
}

impl std::fmt::Display for ExecServerListenUrlParseError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            ExecServerListenUrlParseError::UnsupportedListenUrl(listen_url) => write!(
                f,
                "unsupported --listen URL `{listen_url}`; expected `ws://IP:PORT` or `stdio`"
            ),
            ExecServerListenUrlParseError::InvalidWebSocketListenUrl(listen_url) => write!(
                f,
                "invalid websocket --listen URL `{listen_url}`; expected `ws://IP:PORT`"
            ),
        }
    }
}

impl std::error::Error for ExecServerListenUrlParseError {}

pub(crate) fn parse_listen_url(
    listen_url: &str,
) -> Result<ExecServerListenTransport, ExecServerListenUrlParseError> {
    if matches!(listen_url, "stdio" | "stdio://") {
        return Ok(ExecServerListenTransport::Stdio);
    }

    if let Some(socket_addr) = listen_url.strip_prefix("ws://") {
        return socket_addr
            .parse::<SocketAddr>()
            .map(ExecServerListenTransport::WebSocket)
            .map_err(|_| {
                ExecServerListenUrlParseError::InvalidWebSocketListenUrl(listen_url.to_string())
            });
    }

    Err(ExecServerListenUrlParseError::UnsupportedListenUrl(
        listen_url.to_string(),
    ))
}

pub(crate) async fn run_transport(
    listen_url: &str,
    runtime_paths: ExecServerRuntimePaths,
) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
    match parse_listen_url(listen_url)? {
        ExecServerListenTransport::WebSocket(bind_address) => {
            run_websocket_listener(bind_address, runtime_paths).await
        }
        ExecServerListenTransport::Stdio => run_stdio_connection(runtime_paths).await,
    }
}

async fn run_stdio_connection(
    runtime_paths: ExecServerRuntimePaths,
) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
    run_stdio_connection_with_io(io::stdin(), io::stdout(), runtime_paths).await
}

async fn run_stdio_connection_with_io<R, W>(
    reader: R,
    writer: W,
    runtime_paths: ExecServerRuntimePaths,
) -> Result<(), Box<dyn std::error::Error + Send + Sync>>
where
    R: AsyncRead + Unpin + Send + 'static,
    W: AsyncWrite + Unpin + Send + 'static,
{
    let processor = ConnectionProcessor::new(runtime_paths);
    tracing::info!("codex-exec-server listening on stdio");
    processor
        .run_connection(JsonRpcConnection::from_stdio(
            reader,
            writer,
            "exec-server stdio".to_string(),
        ))
        .await;
    Ok(())
}

async fn run_websocket_listener(
    bind_address: SocketAddr,
    runtime_paths: ExecServerRuntimePaths,
) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
    let listener = TcpListener::bind(bind_address).await?;
    let local_addr = listener.local_addr()?;
    let processor = ConnectionProcessor::new(runtime_paths);
    tracing::info!("codex-exec-server listening on ws://{local_addr}");
    println!("ws://{local_addr}");
    std::io::stdout().flush()?;

    loop {
        let (stream, peer_addr) = listener.accept().await?;
        let processor = processor.clone();
        tokio::spawn(async move {
            match accept_async(stream).await {
                Ok(websocket) => {
                    processor
                        .run_connection(JsonRpcConnection::from_websocket(
                            websocket,
                            format!("exec-server websocket {peer_addr}"),
                        ))
                        .await;
                }
                Err(err) => {
                    warn!(
                        "failed to accept exec-server websocket connection from {peer_addr}: {err}"
                    );
                }
            }
        });
    }
}

#[cfg(test)]
#[path = "transport_tests.rs"]
mod transport_tests;
