//! Attach-mode client: connect to a running pmacs daemon over a Unix
//! socket, negotiate `semantic_render + crdt_replica`, then pump
//! `InstanceMessage` frames onto the winit event loop.
//!
//! Session 3+ of the pmacs-gpu arc — see `docs/pmacs-gpu-design.md`.
//! Scope: handshake + decode the message stream + send a few
//! `FrontendEvent`s back (currently just `Viewport`; session 5+ adds
//! cursor/edit/focus). Importing the CRDT snapshot, applying live
//! ops, and reconstructing the rope happen on the main thread, where
//! the `LoroDoc` lives (it isn't trivially `Send`; cross-thread
//! shipping is the *decoded* `InstanceMessage`, not the doc state).
//!
//! The reader thread blocks on a single `read_message` per iteration;
//! every received message becomes an [`AttachEvent`] forwarded
//! through [`winit::event_loop::EventLoopProxy::send_event`], which
//! wakes the main loop so the frame logic can apply the message and
//! redraw.

use std::os::unix::net::UnixStream;
use std::path::Path;
use std::sync::mpsc;
use std::thread;

use pmacs_protocol::{
    AttachRequest, BufferId, ByteRange, CrdtOp, FrontendCapabilities, FrontendEvent, FrontendId,
    Hello, InstanceMessage, Key, KeyEvent, Modifiers, PROTOCOL_VERSION, PointerKind,
    SUPPORTED_PROTOCOL_VERSIONS, TransportError, is_supported_protocol_version, read_message,
    write_message,
};
use winit::event_loop::EventLoopProxy;

use crate::AppEvent;

/// Errors the attach client surfaces. Kept narrow on purpose: the
/// hello-world fallback is the right recovery for any of these in
/// session 3, so the caller's only job is to log + drop back to the
/// inert renderer.
#[derive(Debug)]
pub enum AttachClientError {
    /// Couldn't open the Unix socket.
    Connect(std::io::Error),
    /// Transport framing failed during the handshake.
    Handshake(TransportError),
    /// Server's `protocol_version` is outside `SUPPORTED_PROTOCOL_VERSIONS`.
    VersionMismatch { server: u32, client: u32 },
}

impl std::fmt::Display for AttachClientError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::Connect(e) => write!(f, "connect to daemon socket failed: {e}"),
            Self::Handshake(e) => write!(f, "attach handshake failed: {e}"),
            Self::VersionMismatch { server, client } => write!(
                f,
                "daemon protocol version {server} not in client's supported set (this client = \
                 {client}, supports {SUPPORTED_PROTOCOL_VERSIONS:?})"
            ),
        }
    }
}

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

/// One decoded event forwarded from the reader thread to the main
/// loop. `Message` carries the entire `InstanceMessage`; `Disconnected`
/// fires once when the reader thread exits (clean EOF or transport
/// error — both look identical from the main thread's perspective).
#[derive(Debug)]
pub enum AttachEvent {
    /// A decoded message frame from the daemon.
    Message(Box<InstanceMessage>),
    /// The reader thread exited. Includes the disconnect reason for
    /// logging on the main thread.
    Disconnected(String),
}

/// Connect, handshake, and spawn the reader thread.
///
/// Returns once the handshake has completed and the reader thread is
/// running. The reader thread owns the read half of the stream; a
/// writer thread owns the write half. The returned [`AttachClient`]
/// queues outbound `FrontendEvent`s so the winit UI thread never blocks
/// on daemon socket backpressure.
///
/// **Initial window size note** — `AttachRequest::initial_size` is
/// nominally a `CellSize` (rows × cols) anchored to the TUI. The
/// `pmacs-gpu` window isn't a cell grid; we send a placeholder of the
/// approximate cell count for the initial 800×200 window so the
/// daemon's initial render makes plausible space for content. This
/// is a small finding for session 3's audit (the wire-shape detail
/// "`AttachRequest`'s `CellSize` assumes a grid frontend"); resolution
/// classified under rule (iii) as deferred — a structural answer
/// belongs with Q#2's minimap variant or its own protocol thread,
/// not session 3's attach loop.
pub fn connect(
    socket_path: &Path,
    proxy: EventLoopProxy<AppEvent>,
) -> Result<AttachClient, AttachClientError> {
    let stream = UnixStream::connect(socket_path).map_err(AttachClientError::Connect)?;

    // Hello round-trip.
    let mut handshake_stream = stream.try_clone().map_err(AttachClientError::Connect)?;
    let hello: Hello = read_message(&mut handshake_stream).map_err(AttachClientError::Handshake)?;
    if !is_supported_protocol_version(hello.protocol_version) {
        return Err(AttachClientError::VersionMismatch {
            server: hello.protocol_version,
            client: PROTOCOL_VERSION,
        });
    }
    eprintln!(
        "pmacs-gpu: attached to daemon (protocol v{}, instance pmacs {})",
        hello.protocol_version, hello.instance_identity.pmacs_version
    );

    // AttachRequest — declare the capabilities a semantic frontend
    // needs. `multi_frontend` is included because the existing daemon
    // gates `crdt_replica` behind it (M10.x dependency).
    //
    // **Daemon requirement**: the daemon must be built with the
    // `crdt` feature (`cargo run --features crdt --bin pmacs --
    // --daemon ...`). Without it the daemon's
    // `InstanceCapabilities::default` returns `crdt_replica: false`,
    // negotiation succeeds but no `BufferSnapshot` ever arrives, and
    // the `pmacs-gpu` window sits on `(connecting...)` forever. This
    // surfaced as a session-3 finding when manually validating the
    // attach loop; classified as small under rule (iii) — recorded
    // here so the next person attaching against a non-crdt daemon
    // recognizes the symptom immediately.
    let req = AttachRequest {
        protocol_version: hello.protocol_version,
        frontend_capabilities: FrontendCapabilities {
            synchronized_output: false,
            unicode_smp: true,
            true_color: true,
            mouse: false,
            bracketed_paste: false,
            terminal_kind: Some("pmacs-gpu".to_owned()),
            multi_frontend: true,
            crdt_replica: true,
            semantic_render: true,
        },
        // Placeholder — see the doc comment above. Cell-shaped initial
        // size is awkward for a pixel frontend; for session 3 we send
        // approximate dimensions so the daemon's initial-render
        // ranging is plausible.
        initial_size: pmacs_protocol::CellSize::new(24, 80),
    };
    write_message(&mut handshake_stream, &req).map_err(AttachClientError::Handshake)?;

    // Split read/write halves for the reader thread + writer thread.
    // UnixStream clones share the underlying FD with independent
    // buffer state — safe to read on one clone while the other writes
    // (the FD is full-duplex).
    let mut read_stream = stream.try_clone().map_err(AttachClientError::Connect)?;
    let write_stream = stream;
    let (writer_tx, writer_rx) = mpsc::channel::<FrontendEvent>();

    // Reader thread. Each iteration: block on read_message, decode,
    // forward via the event-loop proxy. Exits cleanly on EOF / any
    // transport error; the main thread receives a single Disconnected
    // event and drops back to the inert renderer.
    thread::Builder::new()
        .name("pmacs-gpu attach reader".into())
        .spawn(move || {
            loop {
                match read_message::<InstanceMessage>(&mut read_stream) {
                    Ok(msg) => {
                        if proxy
                            .send_event(AppEvent::Attach(AttachEvent::Message(Box::new(msg))))
                            .is_err()
                        {
                            // Main loop torn down — quietly exit.
                            return;
                        }
                    }
                    Err(e) => {
                        let _ = proxy
                            .send_event(AppEvent::Attach(AttachEvent::Disconnected(e.to_string())));
                        return;
                    }
                }
            }
        })
        .expect("spawn attach reader thread");

    // Writer thread. Socket writes can block when the daemon falls
    // behind; doing them here keeps keyboard input, redraws, and
    // message application off that backpressure path.
    thread::Builder::new()
        .name("pmacs-gpu attach writer".into())
        .spawn(move || {
            let mut write_stream = write_stream;
            while let Ok(event) = writer_rx.recv() {
                if let Err(e) = write_message(&mut write_stream, &event) {
                    eprintln!("pmacs-gpu: attach writer stopped: {e}");
                    return;
                }
            }
        })
        .expect("spawn attach writer thread");

    Ok(AttachClient {
        writer_tx,
        frontend_id: hello.assigned_frontend_id,
        server_protocol_version: hello.protocol_version,
    })
}

/// Handle the main loop keeps after `connect` returns. It queues
/// `FrontendEvent`s for the attach writer thread.
pub struct AttachClient {
    writer_tx: mpsc::Sender<FrontendEvent>,
    /// Assigned by the daemon in the `Hello` response. Every
    /// `FrontendEvent` carries this so the daemon can route input back
    /// to the per-session `SemanticRenderState`.
    frontend_id: FrontendId,
    /// The daemon's `Hello.protocol_version`. Wire variants newer
    /// than the daemon (e.g. `Pointer`, v5) must be gated on this —
    /// an older daemon hard-errors decoding an unknown variant.
    server_protocol_version: u32,
}

impl AttachClient {
    /// Frontend id assigned by the daemon in the initial `Hello`.
    pub fn frontend_id(&self) -> FrontendId {
        self.frontend_id
    }

    /// Send a `FrontendEvent::Viewport` to the daemon. The daemon's
    /// `SemanticRenderState::set_viewport` feeds the spans producer;
    /// without this call the daemon ships no `StyleSpans` for the
    /// buffer (no declared viewport ⇒ no scoped styling).
    pub fn send_viewport(
        &self,
        buffer_id: BufferId,
        visible: ByteRange,
        generation: u64,
    ) -> Result<(), TransportError> {
        self.send_event(FrontendEvent::Viewport {
            frontend_id: self.frontend_id,
            buffer_id,
            visible,
            generation,
        })
    }

    /// Send a `FrontendEvent::Key` to the daemon (session B1). The
    /// daemon routes it through `dispatch_key` — the same keymap +
    /// command + Lua stack the TUI drives — so cursor motion and (in
    /// later sessions) edits are produced entirely instance-side; the
    /// resulting `CursorByte` / `CrdtOp` come back over the attach
    /// stream. `timestamp_ns` is 0 (no capture clock plumbed yet; the
    /// daemon does not depend on it).
    pub fn send_key(&self, key: Key, mods: Modifiers) -> Result<(), TransportError> {
        self.send_event(FrontendEvent::Key(KeyEvent {
            frontend_id: self.frontend_id,
            key,
            mods,
            timestamp_ns: 0,
        }))
    }

    /// Send a `FrontendEvent::Pointer` (session M-2): a locally
    /// hit-tested gesture in source bytes. Callers gate on
    /// [`Self::server_protocol_version`] `>= 5`.
    pub fn send_pointer(
        &self,
        buffer_id: BufferId,
        byte: u64,
        kind: PointerKind,
        mods: Modifiers,
    ) -> Result<(), TransportError> {
        self.send_event(FrontendEvent::Pointer {
            frontend_id: self.frontend_id,
            buffer_id,
            byte,
            kind,
            mods,
        })
    }

    /// Send a `FrontendEvent::Paste` (Q#CM6) carrying OS-clipboard
    /// bytes read locally via `arboard` on Ctrl-V. The daemon inserts it
    /// at the cursor (replacing any region) and refreshes its clipboard
    /// slot, exactly as it handles the TUI's bracketed paste.
    pub fn send_paste(&self, data: Vec<u8>) -> Result<(), TransportError> {
        self.send_event(FrontendEvent::Paste {
            frontend_id: self.frontend_id,
            data,
        })
    }

    /// Send a `FrontendEvent::MenuPointer` (Q#CM1) — open-menu
    /// navigation hit-tested locally against the popup we drew. `index`
    /// is the row the pointer is over (`None` = off the menu); `invoke`
    /// marks a click (invoke the row, or dismiss when `index` is `None`).
    pub fn send_menu_pointer(
        &self,
        index: Option<u32>,
        invoke: bool,
    ) -> Result<(), TransportError> {
        self.send_event(FrontendEvent::MenuPointer {
            frontend_id: self.frontend_id,
            index,
            invoke,
        })
    }

    /// The daemon's negotiated wire version from `Hello`.
    pub fn server_protocol_version(&self) -> u32 {
        self.server_protocol_version
    }

    /// Send a locally-authored CRDT operation to the daemon. The GPU
    /// uses this for idle plain-text insertion after applying the same
    /// op to its local Loro replica, avoiding a Key round trip on the
    /// hot typing path.
    pub fn send_crdt_op(&self, buffer_id: BufferId, op: CrdtOp) -> Result<(), TransportError> {
        self.send_event(FrontendEvent::CrdtOp {
            frontend_id: self.frontend_id,
            buffer_id,
            op,
        })
    }

    fn send_event(&self, event: FrontendEvent) -> Result<(), TransportError> {
        self.writer_tx.send(event).map_err(|_| {
            TransportError::Io(std::io::Error::new(
                std::io::ErrorKind::BrokenPipe,
                "attach writer thread stopped",
            ))
        })
    }
}