//! Hot-reload file watcher for capabilities
//!
//! Watches capability directories for changes and triggers reload
//! when files are added, modified, or removed.

use std::path::Path;
use std::sync::Arc;
use std::time::{Duration, Instant};

use notify::{Config, Event, EventKind, RecommendedWatcher, RecursiveMode, Watcher};
use parking_lot::Mutex;
use tokio::sync::mpsc;
use tracing::{debug, error, info, warn};

use super::CapabilityBackend;
use crate::Result;

/// File watcher for hot-reloading capabilities
pub struct CapabilityWatcher {
    /// The underlying watcher
    _watcher: Mutex<Option<RecommendedWatcher>>,
}

impl CapabilityWatcher {
    /// Start watching capability directories for changes
    ///
    /// This spawns a background task that watches for file changes and
    /// triggers `backend.reload()` when changes are detected.
    ///
    /// # Errors
    ///
    /// Returns an error if the file watcher cannot be created.
    pub fn start(
        backend: Arc<CapabilityBackend>,
        shutdown_rx: tokio::sync::broadcast::Receiver<()>,
    ) -> Result<Self> {
        let directories = backend.watched_directories();
        debug!(directories = ?directories, "Starting capability watcher");

        if directories.is_empty() {
            info!("No capability directories to watch");
            return Ok(Self {
                _watcher: Mutex::new(None),
            });
        }

        // Channel for file events
        let (event_tx, event_rx) = mpsc::channel(100);

        // Create watcher
        let watcher = Self::create_watcher(event_tx, &directories)?;
        debug!("File watcher created successfully");

        // Spawn debounced reload task
        Self::spawn_reload_task(backend, event_rx, shutdown_rx);
        debug!("Reload task spawned");

        Ok(Self {
            _watcher: Mutex::new(Some(watcher)),
        })
    }

    /// Create the file system watcher
    fn create_watcher(
        event_tx: mpsc::Sender<()>,
        directories: &[String],
    ) -> Result<RecommendedWatcher> {
        let mut watcher = RecommendedWatcher::new(
            move |result: std::result::Result<Event, notify::Error>| {
                match result {
                    Ok(event) => {
                        // Only react to relevant events on YAML files
                        let is_relevant = matches!(
                            event.kind,
                            EventKind::Create(_) | EventKind::Modify(_) | EventKind::Remove(_)
                        ) && event.paths.iter().any(|p| {
                            p.extension()
                                .is_some_and(|ext| ext == "yaml" || ext == "yml")
                        });

                        if is_relevant {
                            debug!(paths = ?event.paths, kind = ?event.kind, "Capability file change");
                            // Non-blocking send - if channel is full, skip this event
                            let _ = event_tx.try_send(());
                        }
                    }
                    Err(e) => {
                        error!(error = %e, "File watcher error");
                    }
                }
            },
            Config::default().with_poll_interval(Duration::from_secs(2)),
        )
        .map_err(|e| crate::Error::Internal(format!("Failed to create file watcher: {e}")))?;

        // Watch all directories
        for dir in directories {
            let path = Path::new(dir);
            if path.exists() {
                if let Err(e) = watcher.watch(path, RecursiveMode::Recursive) {
                    warn!(directory = %dir, error = %e, "Failed to watch directory");
                } else {
                    info!(directory = %dir, "Watching for capability changes");
                }
            } else {
                debug!(directory = %dir, "Directory does not exist, skipping watch");
            }
        }

        Ok(watcher)
    }

    /// Spawn the background reload task with debouncing
    fn spawn_reload_task(
        backend: Arc<CapabilityBackend>,
        mut event_rx: mpsc::Receiver<()>,
        mut shutdown_rx: tokio::sync::broadcast::Receiver<()>,
    ) {
        tokio::spawn(async move {
            // Debounce: wait 500ms after last event before reloading
            const DEBOUNCE_MS: u64 = 500;
            let mut last_event: Option<Instant> = None;
            let mut pending_reload = false;

            let mut interval = tokio::time::interval(Duration::from_millis(100));

            loop {
                tokio::select! {
                    Some(()) = event_rx.recv() => {
                        last_event = Some(Instant::now());
                        pending_reload = true;
                    }
                    _ = interval.tick() => {
                        // Check if we should trigger reload
                        if pending_reload {
                            if let Some(last) = last_event {
                                if last.elapsed() >= Duration::from_millis(DEBOUNCE_MS) {
                                    pending_reload = false;
                                    last_event = None;

                                    info!(backend = %backend.name, "Hot-reloading capabilities...");
                                    match backend.reload().await {
                                        Ok(count) => {
                                            info!(
                                                backend = %backend.name,
                                                capabilities = count,
                                                "Hot-reload complete"
                                            );
                                        }
                                        Err(e) => {
                                            error!(
                                                backend = %backend.name,
                                                error = %e,
                                                "Hot-reload failed"
                                            );
                                        }
                                    }
                                }
                            }
                        }
                    }
                    _ = shutdown_rx.recv() => {
                        info!("Capability watcher shutting down");
                        break;
                    }
                }
            }
        });
    }
}

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

    #[test]
    fn test_watcher_creation() {
        // Basic smoke test - actual file watching tested in integration tests
        let (_tx, rx) = tokio::sync::broadcast::channel(1);
        let executor = Arc::new(crate::capability::CapabilityExecutor::new());
        let backend = Arc::new(crate::capability::CapabilityBackend::new("test", executor));

        // Should not panic with empty directories
        let watcher = CapabilityWatcher::start(backend, rx);
        assert!(watcher.is_ok());
    }
}
