//! Agent service — async message bus between TUI and Sol gRPC session.
//!
//! The TUI sends `AgentRequest`s and receives `AgentEvent`s through
//! crossbeam channels. The gRPC session runs on a background tokio task,
//! so the UI thread never blocks on network I/O.
//!
//! This module is designed to be usable as a library — nothing here
//! depends on ratatui or terminal state.

use crossbeam_channel::{Receiver, Sender, TrySendError};

use super::client::{self, CodeSession};

// ── Requests (TUI → Agent) ──────────────────────────────────────────────

/// A request from the UI to the agent backend.
pub enum AgentRequest {
    /// Send a chat message to Sol.
    Chat { text: String },
    /// End the session gracefully.
    End,
}

// ── Events (Agent → TUI) ───────────────────────────────────────────────

/// An event from the agent backend to the UI.
#[derive(Clone, Debug)]
pub enum AgentEvent {
    /// Sol started generating a response.
    Generating,
    /// A tool started executing.
    ToolStart { name: String, detail: String },
    /// A tool finished executing.
    ToolDone { name: String, success: bool },
    /// Sol's full response text.
    Response { text: String },
    /// A non-fatal error from Sol.
    Error { message: String },
    /// Status update (shown in title bar).
    Status { message: String },
    /// Session ended.
    SessionEnded,
}

// ── Agent handle (owned by TUI) ────────────────────────────────────────

/// Handle for the TUI to communicate with the background agent task.
pub struct AgentHandle {
    tx: Sender<AgentRequest>,
    pub rx: Receiver<AgentEvent>,
}

impl AgentHandle {
    /// Send a chat message. Non-blocking.
    pub fn chat(&self, text: &str) {
        let _ = self.tx.try_send(AgentRequest::Chat {
            text: text.to_string(),
        });
    }

    /// Request session end. Non-blocking.
    pub fn end(&self) {
        let _ = self.tx.try_send(AgentRequest::End);
    }

    /// Drain all pending events. Non-blocking.
    pub fn poll_events(&self) -> Vec<AgentEvent> {
        let mut events = Vec::new();
        while let Ok(event) = self.rx.try_recv() {
            events.push(event);
        }
        events
    }
}

// ── Spawn ──────────────────────────────────────────────────────────────

/// Spawn the agent background task. Returns a handle for the TUI.
pub fn spawn(session: CodeSession) -> AgentHandle {
    let (req_tx, req_rx) = crossbeam_channel::bounded::<AgentRequest>(32);
    let (evt_tx, evt_rx) = crossbeam_channel::bounded::<AgentEvent>(256);

    tokio::spawn(agent_loop(session, req_rx, evt_tx));

    AgentHandle {
        tx: req_tx,
        rx: evt_rx,
    }
}

/// The background agent loop. Reads requests, calls gRPC, emits events.
async fn agent_loop(
    mut session: CodeSession,
    req_rx: Receiver<AgentRequest>,
    evt_tx: Sender<AgentEvent>,
) {
    loop {
        // Block on the crossbeam channel from a tokio context
        let req = match tokio::task::block_in_place(|| req_rx.recv()) {
            Ok(req) => req,
            Err(_) => break, // TUI dropped the handle
        };

        match req {
            AgentRequest::Chat { text } => {
                let _ = evt_tx.try_send(AgentEvent::Generating);

                match session.chat(&text).await {
                    Ok(resp) => {
                        // Emit tool events
                        for event in &resp.events {
                            let agent_event = match event {
                                client::ChatEvent::ToolStart { name, detail } => {
                                    AgentEvent::ToolStart {
                                        name: name.clone(),
                                        detail: detail.clone(),
                                    }
                                }
                                client::ChatEvent::ToolDone { name, success } => {
                                    AgentEvent::ToolDone {
                                        name: name.clone(),
                                        success: *success,
                                    }
                                }
                                client::ChatEvent::Status(msg) => AgentEvent::Status {
                                    message: msg.clone(),
                                },
                                client::ChatEvent::Error(msg) => AgentEvent::Error {
                                    message: msg.clone(),
                                },
                            };
                            let _ = evt_tx.try_send(agent_event);
                        }

                        let _ = evt_tx.try_send(AgentEvent::Response { text: resp.text });
                    }
                    Err(e) => {
                        let _ = evt_tx.try_send(AgentEvent::Error {
                            message: e.to_string(),
                        });
                    }
                }
            }
            AgentRequest::End => {
                let _ = session.end().await;
                let _ = evt_tx.try_send(AgentEvent::SessionEnded);
                break;
            }
        }
    }
}