//! CWD tracking via a SEPARATE SSH exec channel.
//!
//! This module opens an independent exec channel on the same SSH connection and
//! periodically runs `pwd` to determine the remote shell's current working
//! directory. The terminal data stream is NEVER touched — CWD is tracked
//! entirely out of band.
//!
//! When the CWD changes, an `ssh:cwd:{session_id}` event is emitted to the
//! frontend.

use std::sync::Arc;

use log::{debug, error, warn};
use russh::client::Handle;
use russh::ChannelMsg;
use tauri::{AppHandle, Emitter};
use tokio::sync::watch;
use tokio::sync::Mutex as TokioMutex;

use crate::ssh::session::SshClient;

/// Tracks the current working directory of a remote shell by periodically
/// running `pwd` over a separate exec channel.
pub struct CwdTracker {
    _sender: watch::Sender<String>,
    pub receiver: watch::Receiver<String>,
}

impl CwdTracker {
    /// Create a new CWD tracker with an empty initial directory.
    pub fn new() -> Self {
        let (sender, receiver) = watch::channel(String::new());
        Self {
            _sender: sender,
            receiver,
        }
    }

    /// Spawn a background tokio task that polls `pwd` every 2 seconds on a
    /// separate exec channel.
    ///
    /// The task runs until the SSH connection is closed or the channel cannot
    /// be opened. CWD changes are emitted as `ssh:cwd:{session_id}` events.
    pub fn start(
        &self,
        handle: Arc<TokioMutex<Handle<SshClient>>>,
        app_handle: AppHandle,
        session_id: String,
    ) {
        let sender = self._sender.clone();

        tokio::spawn(async move {
            // Brief initial delay to let the shell start up.
            tokio::time::sleep(tokio::time::Duration::from_millis(500)).await;

            let mut previous_cwd = String::new();

            loop {
                // Open a fresh exec channel for each `pwd` invocation.
                // Some SSH servers do not allow multiple exec requests on a
                // single channel, so we open a new one each time.
                let result = {
                    let handle_guard = handle.lock().await;
                    handle_guard.channel_open_session().await
                };

                let mut exec_channel = match result {
                    Ok(ch) => ch,
                    Err(e) => {
                        debug!(
                            "CWD tracker for session {} could not open exec channel: {} — stopping",
                            session_id, e
                        );
                        break;
                    }
                };

                // Execute `pwd` on the exec channel.
                if let Err(e) = exec_channel.exec(true, "pwd").await {
                    warn!(
                        "CWD tracker for session {}: failed to exec pwd: {}",
                        session_id, e
                    );
                    break;
                }

                // Read the output.
                let mut output = String::new();
                loop {
                    match exec_channel.wait().await {
                        Some(ChannelMsg::Data { ref data }) => {
                            if let Ok(text) = std::str::from_utf8(data.as_ref()) {
                                output.push_str(text);
                            }
                        }
                        Some(ChannelMsg::Eof) | Some(ChannelMsg::Close) | None => break,
                        Some(ChannelMsg::ExitStatus { .. }) => {
                            // pwd exited — we may still get data, keep reading
                        }
                        _ => {}
                    }
                }

                let cwd = output.trim().to_string();

                if !cwd.is_empty() && cwd != previous_cwd {
                    previous_cwd = cwd.clone();

                    // Update the watch channel.
                    let _ = sender.send(cwd.clone());

                    // Emit event to frontend.
                    let event_name = format!("ssh:cwd:{}", session_id);
                    if let Err(e) = app_handle.emit(&event_name, &cwd) {
                        error!(
                            "CWD tracker for session {}: failed to emit event: {}",
                            session_id, e
                        );
                    }
                }

                // Wait 2 seconds before the next poll.
                tokio::time::sleep(tokio::time::Duration::from_secs(2)).await;
            }

            debug!("CWD tracker for session {} stopped", session_id);
        });
    }
}