//! The `idea mcp-server` **bridge** — a transparent stdio↔loopback tube (M5b).
//!
//! ## Where this sits in the bind (cadrage v5 §1.3, §2)
//!
//! An MCP CLI (Claude Code, Codex) reads a `{command,args}` declaration and
//! *spawns* `<exe IdeA> mcp-server --endpoint <…> --project <…> --requester <…>`.
//! That spawned process is **this bridge**: it must **bypass Tauri/WebKit** and run
//! headless. It speaks JSON-RPC (JSON Lines) to the CLI on **stdin/stdout**, and
//! relays every line, byte-for-byte, over the project's **loopback** (the Unix
//! socket / Windows named pipe bound by [`crate::state::AppState::ensure_mcp_server`]
//! at [`crate::mcp_endpoint::mcp_endpoint`]). The real `McpServer` (which holds the
//! `OrchestratorService`) lives in the Tauri process and answers in M5c.
//!
//! **Zero business logic.** The bridge knows only *stdio + loopback + JSON lines*:
//! no `OrchestratorService`, no use case (hexagonal boundary, cadrage §5). It never
//! parses the JSON-RPC payloads it carries.
//!
//! ## Handshake format (consumed by M5c)
//!
//! Right after connecting to the loopback, **before** any JSON-RPC traffic, the
//! bridge writes a **single newline-terminated JSON line** carrying the caller's
//! identity:
//!
//! ```text
//! {"project":"<project-id>","requester":"<requester-id>"}\n
//! ```
//!
//! - It is a **distinct line** from the JSON-RPC stream that follows: the server
//!   (M5c) reads exactly one line off a fresh connection, parses it as this
//!   handshake, then hands the rest of the stream to `McpServer::serve`.
//! - `requester` is the **real agent id** (cadrage §1.4) — it lets the server tag
//!   `OrchestratorRequestProcessed.requester_id` with the actual agent instead of
//!   the frozen `"mcp"` placeholder. When `--requester` is omitted the field is the
//!   empty string.
//! - Both values are JSON strings, so any future id shape stays escape-safe.
//!
//! ## Failure posture (never hang)
//!
//! - **Endpoint absent / unreachable** ⇒ connect with a **bounded timeout**; on
//!   timeout or connect error, return a **non-zero** exit code immediately. Never
//!   block forever waiting for a listener that will never appear.
//! - **stdin EOF** (the CLI closed) ⇒ **clean exit, code 0**; the loopback
//!   connection is dropped (closed) on the way out.
//! - **Missing required args** ⇒ a clear error on stderr and a non-zero code.

use std::process::ExitCode;
use std::time::Duration;

use interprocess::local_socket::tokio::Stream as LocalSocketStream;
use interprocess::local_socket::traits::tokio::Stream as _;
use interprocess::local_socket::{GenericFilePath, ToFsName as _};
use tokio::io::{
    AsyncBufReadExt, AsyncRead, AsyncWrite, AsyncWriteExt, BufReader,
};

/// How long the bridge waits to connect to the project loopback before giving up.
/// Bounded so an absent/unreachable endpoint fails fast instead of hanging.
const CONNECT_TIMEOUT: Duration = Duration::from_secs(5);

/// Parsed `mcp-server` invocation arguments.
///
/// `--endpoint` is **required** (without it the bridge has nowhere to relay).
/// `--project` and `--requester` are optional identity hints forwarded verbatim in
/// the handshake; a missing one becomes the empty string.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct BridgeArgs {
    /// The loopback address to connect to (the `--endpoint` value, i.e.
    /// [`crate::mcp_endpoint::McpEndpoint::as_cli_arg`]).
    pub endpoint: String,
    /// The project id (`--project`), forwarded in the handshake. Empty if absent.
    pub project: String,
    /// The requesting agent id (`--requester`), forwarded in the handshake. Empty
    /// if absent.
    pub requester: String,
}

impl BridgeArgs {
    /// Parses `mcp-server`'s own arguments (i.e. `argv` **after** the `mcp-server`
    /// subcommand token). Recognises `--endpoint`, `--project`, `--requester`, each
    /// taking the following token as its value.
    ///
    /// # Errors
    /// Returns a human-readable message when `--endpoint` is missing, when a flag is
    /// given without a value, or when an unknown flag is encountered.
    pub fn parse<I, S>(args: I) -> Result<Self, String>
    where
        I: IntoIterator<Item = S>,
        S: Into<String>,
    {
        let mut endpoint: Option<String> = None;
        let mut project = String::new();
        let mut requester = String::new();

        let mut it = args.into_iter().map(Into::into);
        while let Some(flag) = it.next() {
            match flag.as_str() {
                "--endpoint" => {
                    endpoint = Some(
                        it.next()
                            .ok_or_else(|| "--endpoint requires a value".to_string())?,
                    );
                }
                "--project" => {
                    project = it
                        .next()
                        .ok_or_else(|| "--project requires a value".to_string())?;
                }
                "--requester" => {
                    requester = it
                        .next()
                        .ok_or_else(|| "--requester requires a value".to_string())?;
                }
                other => {
                    return Err(format!("unknown argument: {other}"));
                }
            }
        }

        let endpoint = endpoint.ok_or_else(|| "--endpoint is required".to_string())?;
        Ok(Self {
            endpoint,
            project,
            requester,
        })
    }

    /// The first handshake line the bridge writes on the loopback (newline
    /// included). See the module docs for the format consumed by M5c.
    fn handshake_line(&self) -> Vec<u8> {
        let line = serde_json::json!({
            "project": self.project,
            "requester": self.requester,
        })
        .to_string();
        let mut bytes = line.into_bytes();
        bytes.push(b'\n');
        bytes
    }
}

/// Synchronous entry point called from `main`/`lib::run` when `argv[1] ==
/// "mcp-server"`. Parses the args, stands up a Tokio runtime, and runs the bridge.
///
/// Returns the process [`ExitCode`]: `0` on a clean stdin-EOF shutdown, non-zero on
/// any argument/connection/relay failure. Never blocks indefinitely (connect is
/// time-bounded).
#[must_use]
pub fn run_mcp_bridge<I, S>(args: I) -> ExitCode
where
    I: IntoIterator<Item = S>,
    S: Into<String>,
{
    let args = match BridgeArgs::parse(args) {
        Ok(a) => a,
        Err(e) => {
            eprintln!("idea mcp-server: {e}");
            return ExitCode::FAILURE;
        }
    };

    // A current-thread runtime is enough: the bridge is two coupled I/O loops, no
    // CPU work. Keeps the headless process lean (no Tauri, no webview).
    let runtime = match tokio::runtime::Builder::new_current_thread()
        .enable_io()
        .enable_time()
        .build()
    {
        Ok(rt) => rt,
        Err(e) => {
            eprintln!("idea mcp-server: failed to start runtime: {e}");
            return ExitCode::FAILURE;
        }
    };

    runtime.block_on(async move {
        match bridge_over_loopback(&args).await {
            Ok(()) => ExitCode::SUCCESS,
            Err(e) => {
                eprintln!("idea mcp-server: {e}");
                ExitCode::FAILURE
            }
        }
    })
}

/// Connects to the project loopback at `args.endpoint` (time-bounded) and relays
/// between the **real stdio** of this process and that connection.
async fn bridge_over_loopback(args: &BridgeArgs) -> Result<(), String> {
    let conn = connect_loopback(&args.endpoint).await?;
    // Split the duplex loopback into independent owned halves so the two relay
    // directions can run without sharing a lock.
    let (lp_read, lp_write) = tokio::io::split(conn);
    relay(
        args,
        tokio::io::stdin(),
        tokio::io::stdout(),
        lp_read,
        lp_write,
    )
    .await
}

/// Connects to the loopback endpoint with a bounded timeout. An absent or
/// unreachable endpoint surfaces as an `Err` (⇒ non-zero exit), **never a hang**.
async fn connect_loopback(endpoint: &str) -> Result<LocalSocketStream, String> {
    let name = endpoint
        .to_fs_name::<GenericFilePath>()
        .map_err(|e| format!("invalid endpoint {endpoint:?}: {e}"))?;

    match tokio::time::timeout(CONNECT_TIMEOUT, LocalSocketStream::connect(name)).await {
        Ok(Ok(stream)) => Ok(stream),
        Ok(Err(e)) => Err(format!("cannot connect to endpoint {endpoint:?}: {e}")),
        Err(_) => Err(format!(
            "timed out connecting to endpoint {endpoint:?} after {}s",
            CONNECT_TIMEOUT.as_secs()
        )),
    }
}

/// The transparent relay, generic over its four streams so tests drive it with
/// in-memory pipes (no real stdio, no real socket).
///
/// Sequence:
/// 1. Write the **handshake line** (`project`+`requester`) to the loopback.
/// 2. Loop: read one **line** from the CLI (`cli_in`) → write it to the loopback;
///    read one **line** from the loopback → write it to the CLI (`cli_out`).
/// 3. **CLI stdin EOF** ⇒ stop, return `Ok(())` (clean code 0). Dropping the
///    loopback writer closes that direction of the connection.
///
/// The loop is request/response paced (one CLI line in, one loopback line back),
/// matching the JSON Lines `StdioTransport` the server speaks. A loopback that
/// closes mid-exchange surfaces as an error (non-zero exit).
async fn relay<CIn, COut, LIn, LOut>(
    args: &BridgeArgs,
    cli_in: CIn,
    mut cli_out: COut,
    lp_read: LIn,
    mut lp_write: LOut,
) -> Result<(), String>
where
    CIn: AsyncRead + Unpin,
    COut: AsyncWrite + Unpin,
    LIn: AsyncRead + Unpin,
    LOut: AsyncWrite + Unpin,
{
    // 1. Handshake (identity) before any JSON-RPC byte.
    lp_write
        .write_all(&args.handshake_line())
        .await
        .map_err(|e| format!("handshake write failed: {e}"))?;
    lp_write
        .flush()
        .await
        .map_err(|e| format!("handshake flush failed: {e}"))?;

    let mut cli_reader = BufReader::new(cli_in);
    let mut lp_reader = BufReader::new(lp_read);
    let mut cli_line = String::new();
    let mut lp_line = String::new();

    loop {
        // 2a. CLI → loopback (one line). EOF ⇒ clean shutdown.
        cli_line.clear();
        let n = cli_reader
            .read_line(&mut cli_line)
            .await
            .map_err(|e| format!("stdin read failed: {e}"))?;
        if n == 0 {
            // CLI closed stdin: nothing more to forward. Clean exit.
            return Ok(());
        }
        lp_write
            .write_all(cli_line.as_bytes())
            .await
            .map_err(|e| format!("loopback write failed: {e}"))?;
        lp_write
            .flush()
            .await
            .map_err(|e| format!("loopback flush failed: {e}"))?;

        // 2b. loopback → CLI (one line). EOF here is a server hangup mid-exchange.
        lp_line.clear();
        let m = lp_reader
            .read_line(&mut lp_line)
            .await
            .map_err(|e| format!("loopback read failed: {e}"))?;
        if m == 0 {
            return Err("loopback closed before answering".to_string());
        }
        cli_out
            .write_all(lp_line.as_bytes())
            .await
            .map_err(|e| format!("stdout write failed: {e}"))?;
        cli_out
            .flush()
            .await
            .map_err(|e| format!("stdout flush failed: {e}"))?;
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::sync::Arc;

    use interprocess::local_socket::tokio::Listener as LocalSocketListener;
    use interprocess::local_socket::traits::tokio::Listener as _;
    use interprocess::local_socket::{GenericFilePath, ListenerOptions};
    use tokio::io::AsyncReadExt as _;

    // ---- argument parsing -------------------------------------------------

    #[test]
    fn parses_all_three_flags() {
        let a = BridgeArgs::parse([
            "--endpoint", "/tmp/x.sock", "--project", "p1", "--requester", "agent-7",
        ])
        .unwrap();
        assert_eq!(a.endpoint, "/tmp/x.sock");
        assert_eq!(a.project, "p1");
        assert_eq!(a.requester, "agent-7");
    }

    #[test]
    fn endpoint_is_required() {
        let err = BridgeArgs::parse(["--project", "p1"]).unwrap_err();
        assert!(err.contains("--endpoint"), "got: {err}");
    }

    #[test]
    fn project_and_requester_default_to_empty() {
        let a = BridgeArgs::parse(["--endpoint", "/tmp/x.sock"]).unwrap();
        assert_eq!(a.project, "");
        assert_eq!(a.requester, "");
    }

    #[test]
    fn flag_without_value_is_an_error() {
        assert!(BridgeArgs::parse(["--endpoint"]).is_err());
        assert!(BridgeArgs::parse(["--endpoint", "/x", "--project"]).is_err());
    }

    #[test]
    fn unknown_flag_is_an_error() {
        let err = BridgeArgs::parse(["--endpoint", "/x", "--bogus"]).unwrap_err();
        assert!(err.contains("unknown"), "got: {err}");
    }

    #[test]
    fn handshake_line_carries_identity_as_json() {
        let a = BridgeArgs {
            endpoint: "/tmp/x.sock".into(),
            project: "proj".into(),
            requester: "rq".into(),
        };
        let line = a.handshake_line();
        assert_eq!(*line.last().unwrap(), b'\n');
        let v: serde_json::Value =
            serde_json::from_slice(&line[..line.len() - 1]).unwrap();
        assert_eq!(v["project"], "proj");
        assert_eq!(v["requester"], "rq");
    }

    // ---- relay (in-memory streams, no socket) -----------------------------

    /// Nominal relay over in-memory duplex pipes: handshake reaches the fake
    /// server, a scripted request is forwarded, and the canned response comes back
    /// on the CLI stdout.
    #[tokio::test]
    async fn relay_forwards_handshake_request_and_response() {
        // CLI stdin: one JSON-RPC request line, then EOF.
        let cli_in = b"{\"method\":\"tools/call\",\"id\":1}\n".to_vec();
        let mut cli_out: Vec<u8> = Vec::new();

        // The "loopback" is a duplex pipe: the bridge writes to `lp_write`/reads
        // from `lp_read`; the fake server reads from `srv_read`/writes to
        // `srv_write`.
        let (lp_read, srv_write) = tokio::io::duplex(4096); // server → bridge
        let (srv_read, lp_write) = tokio::io::duplex(4096); // bridge → server

        let args = BridgeArgs {
            endpoint: "unused".into(),
            project: "proj-1".into(),
            requester: "agent-9".into(),
        };

        // Fake server: read handshake line, then read the request line, then answer.
        let server = tokio::spawn(async move {
            let mut reader = BufReader::new(srv_read);
            let mut handshake = String::new();
            reader.read_line(&mut handshake).await.unwrap();
            let mut request = String::new();
            reader.read_line(&mut request).await.unwrap();

            let mut w = srv_write;
            w.write_all(b"{\"result\":\"ok\",\"id\":1}\n").await.unwrap();
            w.flush().await.unwrap();
            (handshake, request)
        });

        relay(
            &args,
            &cli_in[..],
            &mut cli_out,
            lp_read,
            lp_write,
        )
        .await
        .unwrap();

        let (handshake, request) = server.await.unwrap();
        let hs: serde_json::Value =
            serde_json::from_str(handshake.trim_end()).unwrap();
        assert_eq!(hs["project"], "proj-1");
        assert_eq!(hs["requester"], "agent-9");
        assert_eq!(request.trim_end(), "{\"method\":\"tools/call\",\"id\":1}");
        assert_eq!(
            String::from_utf8(cli_out).unwrap(),
            "{\"result\":\"ok\",\"id\":1}\n"
        );
    }

    /// stdin EOF with no request ⇒ relay returns `Ok` (code 0), having still sent
    /// the handshake.
    #[tokio::test]
    async fn relay_clean_exit_on_immediate_eof() {
        let cli_in: &[u8] = b""; // immediate EOF
        let mut cli_out: Vec<u8> = Vec::new();

        let (lp_read, srv_write) = tokio::io::duplex(4096);
        let (srv_read, lp_write) = tokio::io::duplex(4096);

        let args = BridgeArgs {
            endpoint: "unused".into(),
            project: "p".into(),
            requester: String::new(),
        };

        let server = tokio::spawn(async move {
            let mut reader = BufReader::new(srv_read);
            let mut handshake = String::new();
            reader.read_line(&mut handshake).await.unwrap();
            // Keep srv_write alive until the bridge drops its writer (EOF).
            let mut buf = Vec::new();
            let _ = reader.read_to_end(&mut buf).await;
            drop(srv_write);
            handshake
        });

        relay(&args, cli_in, &mut cli_out, lp_read, lp_write)
            .await
            .expect("clean EOF exit");

        let handshake = server.await.unwrap();
        assert!(handshake.contains("\"project\":\"p\""));
        assert!(cli_out.is_empty(), "no response expected on immediate EOF");
    }

    // ---- end-to-end over a real loopback ----------------------------------

    fn temp_endpoint(tag: &str) -> String {
        let dir = std::env::temp_dir();
        let pid = std::process::id();
        let nanos = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap()
            .as_nanos();
        dir.join(format!("idea-mcp-bridge-test-{tag}-{pid}-{nanos}.sock"))
            .to_string_lossy()
            .into_owned()
    }

    fn bind(endpoint: &str) -> LocalSocketListener {
        let name = endpoint.to_fs_name::<GenericFilePath>().unwrap();
        ListenerOptions::new()
            .name(name)
            .reclaim_name(true)
            .create_tokio()
            .expect("bind test listener")
    }

    /// Endpoint absent ⇒ `connect_loopback` fails fast (no hang), so the bridge
    /// would exit non-zero. Bounded by a test timeout well under CONNECT_TIMEOUT
    /// for the "connect error" path (a non-existent socket errors immediately).
    #[tokio::test]
    async fn connect_to_absent_endpoint_errors_fast() {
        let endpoint = temp_endpoint("absent");
        let res = tokio::time::timeout(
            Duration::from_secs(10),
            connect_loopback(&endpoint),
        )
        .await
        .expect("connect_loopback must not hang");
        assert!(res.is_err(), "absent endpoint must yield an error");
    }

    /// `run_mcp_bridge` with a missing `--endpoint` returns a non-zero code.
    #[test]
    fn run_bridge_missing_endpoint_is_non_zero() {
        let code = run_mcp_bridge(["--project", "p"]);
        assert_eq!(code, ExitCode::FAILURE);
    }

    /// Full end-to-end over a **real** interprocess loopback: a test listener plays
    /// the server (reads the handshake, echoes a canned response); the relay drives
    /// it over an actual connection. Verifies the handshake crosses the real socket
    /// and the response returns on the CLI stdout.
    #[tokio::test]
    async fn end_to_end_over_real_loopback() {
        let endpoint = temp_endpoint("e2e");
        let listener = bind(&endpoint);

        let captured = Arc::new(tokio::sync::Mutex::new((String::new(), String::new())));
        let captured_srv = Arc::clone(&captured);

        // Fake server accepts one connection, reads handshake + request, answers.
        let server = tokio::spawn(async move {
            let conn = listener.accept().await.unwrap();
            let (r, w) = tokio::io::split(conn);
            let mut reader = BufReader::new(r);
            let mut handshake = String::new();
            reader.read_line(&mut handshake).await.unwrap();
            let mut request = String::new();
            reader.read_line(&mut request).await.unwrap();
            *captured_srv.lock().await = (handshake, request);

            let mut w = w;
            w.write_all(b"{\"result\":\"pong\",\"id\":42}\n")
                .await
                .unwrap();
            w.flush().await.unwrap();
            // Hold until the bridge finishes (its stdin EOF will end it).
            let mut rest = Vec::new();
            let _ = reader.read_to_end(&mut rest).await;
        });

        let args = BridgeArgs {
            endpoint: endpoint.clone(),
            project: "proj-e2e".into(),
            requester: "agent-e2e".into(),
        };

        let cli_in = b"{\"method\":\"ping\",\"id\":42}\n".to_vec();
        let mut cli_out: Vec<u8> = Vec::new();

        // Drive the whole bridge_over_loopback path (real connect + split + relay),
        // but feed our own stdio streams via `relay` to avoid touching process std.
        let conn = tokio::time::timeout(
            Duration::from_secs(10),
            connect_loopback(&endpoint),
        )
        .await
        .expect("no hang")
        .expect("connect to live endpoint");
        let (lp_read, lp_write) = tokio::io::split(conn);

        tokio::time::timeout(
            Duration::from_secs(10),
            relay(&args, &cli_in[..], &mut cli_out, lp_read, lp_write),
        )
        .await
        .expect("relay must not hang")
        .expect("relay ok");

        server.await.unwrap();

        let (handshake, request) = captured.lock().await.clone();
        let hs: serde_json::Value =
            serde_json::from_str(handshake.trim_end()).unwrap();
        assert_eq!(hs["project"], "proj-e2e");
        assert_eq!(hs["requester"], "agent-e2e");
        assert_eq!(request.trim_end(), "{\"method\":\"ping\",\"id\":42}");
        assert_eq!(
            String::from_utf8(cli_out).unwrap(),
            "{\"result\":\"pong\",\"id\":42}\n"
        );
    }
}