//! Per-agent socket listener. Each socket file's existence on disk
//! authenticates the caller: connecting to `<.../agents/foo/mcp.sock>` means
//! you are `foo`.

use std::path::{Path, PathBuf};
use std::sync::Arc;

use anyhow::{Context, Result};
use hive_sh4re::{AgentRequest, AgentResponse, Message};
use tokio::io::{AsyncBufReadExt, AsyncWriteExt, BufReader};
use tokio::net::{UnixListener, UnixStream};
use tokio::task::JoinHandle;

use crate::broker::Broker;

pub struct AgentSocket {
    pub path: PathBuf,
    pub handle: JoinHandle<()>,
}

pub fn start(agent: &str, socket_path: &Path, broker: Arc<Broker>) -> Result<AgentSocket> {
    let agent = agent.to_owned();
    if let Some(parent) = socket_path.parent() {
        std::fs::create_dir_all(parent)
            .with_context(|| format!("create agent socket dir {}", parent.display()))?;
    }
    if socket_path.exists() {
        std::fs::remove_file(socket_path).context("remove stale agent socket")?;
    }
    let listener = UnixListener::bind(socket_path)
        .with_context(|| format!("bind agent socket {}", socket_path.display()))?;
    tracing::info!(%agent, socket = %socket_path.display(), "agent socket listening");

    let path = socket_path.to_path_buf();
    let handle = tokio::spawn(async move {
        loop {
            match listener.accept().await {
                Ok((stream, _)) => {
                    let agent = agent.clone();
                    let broker = broker.clone();
                    tokio::spawn(async move {
                        if let Err(e) = serve(stream, agent, broker).await {
                            tracing::warn!(error = ?e, "agent connection failed");
                        }
                    });
                }
                Err(e) => {
                    tracing::warn!(error = ?e, "agent listener accept failed; exiting");
                    return;
                }
            }
        }
    });
    Ok(AgentSocket { path, handle })
}

async fn serve(stream: UnixStream, agent: String, broker: Arc<Broker>) -> Result<()> {
    let (read, mut write) = stream.into_split();
    let mut reader = BufReader::new(read);
    let mut line = String::new();
    loop {
        line.clear();
        let n = reader.read_line(&mut line).await?;
        if n == 0 {
            return Ok(());
        }
        let resp = match serde_json::from_str::<AgentRequest>(line.trim()) {
            Ok(req) => dispatch(&req, &agent, &broker),
            Err(e) => AgentResponse::Err {
                message: format!("parse error: {e}"),
            },
        };
        let mut payload = serde_json::to_string(&resp)?;
        payload.push('\n');
        write.write_all(payload.as_bytes()).await?;
        write.flush().await?;
    }
}

fn dispatch(req: &AgentRequest, agent: &str, broker: &Broker) -> AgentResponse {
    match req {
        AgentRequest::Send { to, body } => {
            match broker.send(&Message {
                from: agent.to_owned(),
                to: to.clone(),
                body: body.clone(),
            }) {
                Ok(()) => AgentResponse::Ok,
                Err(e) => AgentResponse::Err {
                    message: format!("{e:#}"),
                },
            }
        }
        AgentRequest::Recv => match broker.recv(agent) {
            Ok(Some(msg)) => AgentResponse::Message {
                from: msg.from,
                body: msg.body,
            },
            Ok(None) => AgentResponse::Empty,
            Err(e) => AgentResponse::Err {
                message: format!("{e:#}"),
            },
        },
    }
}