//! Folder monitor — watches a directory for new files and emits
//! `folder-monitor-new-files` with absolute paths to the renderer.
//!
//! Reflects the v1 `lib/folder-monitor.js` design: debounced notify events,
//! extension include/exclude filter, skip-duplicates against a seen-set,
//! optional recursive watch, initial scan on start.

use notify::{EventKind, RecursiveMode, Watcher};
use notify_debouncer_full::{new_debouncer, DebouncedEvent, DebounceEventResult};
use parking_lot::Mutex;
use serde::{Deserialize, Serialize};
use std::collections::HashSet;
use std::path::{Path, PathBuf};
use std::sync::Arc;
use std::time::Duration;
use tauri::{AppHandle, Emitter};
use tokio::sync::mpsc;

#[derive(Debug, Clone, Serialize, Deserialize, Default)]
#[serde(rename_all = "camelCase")]
pub struct FolderMonitorSettings {
    pub enabled: bool,
    pub folder_path: String,
    #[serde(default)]
    pub recursive: bool,
    #[serde(default = "default_filter_mode")]
    pub filter_mode: String,
    #[serde(default)]
    pub extensions: String,
    #[serde(default = "truthy")]
    pub skip_duplicates: bool,
    #[serde(default = "default_delay")]
    pub delay_sec: u64,
}
fn default_filter_mode() -> String { "include".into() }
fn truthy() -> bool { true }
fn default_delay() -> u64 { 3 }

pub struct FolderMonitor {
    app: AppHandle,
    stop_tx: Mutex<Option<mpsc::Sender<()>>>,
    current: Mutex<Option<FolderMonitorSettings>>,
    seen: Arc<Mutex<HashSet<PathBuf>>>,
}

impl FolderMonitor {
    pub fn new(app: AppHandle) -> Self {
        Self {
            app,
            stop_tx: Mutex::new(None),
            current: Mutex::new(None),
            seen: Arc::new(Mutex::new(HashSet::new())),
        }
    }

    pub fn is_running(&self) -> bool {
        self.stop_tx.lock().is_some()
    }

    pub fn current(&self) -> Option<FolderMonitorSettings> {
        self.current.lock().clone()
    }

    pub async fn start(&self, settings: FolderMonitorSettings) -> Result<(), String> {
        self.stop().await;
        if !settings.enabled || settings.folder_path.is_empty() {
            return Ok(());
        }
        let root = PathBuf::from(&settings.folder_path);
        if !root.exists() {
            return Err(format!("Ordner existiert nicht: {}", root.display()));
        }
        let recursive = if settings.recursive { RecursiveMode::Recursive } else { RecursiveMode::NonRecursive };
        let extensions = parse_extensions(&settings.extensions);
        let filter_include = settings.filter_mode == "include";
        let skip_dup = settings.skip_duplicates;
        let delay = Duration::from_secs(settings.delay_sec.max(1));

        let seen = self.seen.clone();

        // Seed baseline so existing files don't get queued on startup.
        if skip_dup {
            let mut s = seen.lock();
            s.clear();
            walk_collect(&root, settings.recursive, &mut s);
        }

        let (stop_tx, mut stop_rx) = mpsc::channel::<()>(1);
        let (event_tx, mut event_rx) = mpsc::channel::<Vec<PathBuf>>(32);

        let app = self.app.clone();
        tokio::spawn(async move {
            while let Some(paths) = event_rx.recv().await {
                if paths.is_empty() { continue; }
                let filtered: Vec<String> = paths.into_iter()
                    .filter(|p| path_matches(p, &extensions, filter_include))
                    .filter_map(|p| p.to_str().map(|s| s.to_string()))
                    .collect();
                if filtered.is_empty() { continue; }
                let _ = app.emit("folder-monitor-new-files", filtered);
            }
        });

        let event_tx_cloned = event_tx.clone();
        let seen_cloned = seen.clone();
        tokio::task::spawn_blocking(move || {
            let (debounce_tx, debounce_rx) = std::sync::mpsc::channel::<DebounceEventResult>();
            let mut debouncer = match new_debouncer(
                delay,
                None,
                move |res: DebounceEventResult| { let _ = debounce_tx.send(res); },
            ) {
                Ok(d) => d,
                Err(e) => { tracing::error!("folder-monitor debouncer: {e}"); return; }
            };
            if let Err(e) = debouncer.watch(&root, recursive) {
                tracing::error!("folder-monitor watch: {e}");
                return;
            }
            loop {
                match debounce_rx.recv_timeout(Duration::from_millis(250)) {
                    Ok(Ok(events)) => {
                        let mut new_paths = Vec::new();
                        for ev in events {
                            if matches!(ev.event.kind, EventKind::Create(_) | EventKind::Modify(_)) {
                                for p in &ev.paths {
                                    if p.is_file() {
                                        let mut s = seen_cloned.lock();
                                        if skip_dup && !s.insert(p.clone()) { continue; }
                                        new_paths.push(p.clone());
                                    }
                                }
                            }
                        }
                        if !new_paths.is_empty() {
                            let _ = event_tx_cloned.blocking_send(new_paths);
                        }
                    }
                    Ok(Err(_)) => {}
                    Err(std::sync::mpsc::RecvTimeoutError::Timeout) => {
                        if stop_rx.try_recv().is_ok() { break; }
                    }
                    Err(_) => break,
                }
            }
        });

        *self.stop_tx.lock() = Some(stop_tx);
        *self.current.lock() = Some(settings);
        Ok(())
    }

    pub async fn stop(&self) {
        let tx = self.stop_tx.lock().take();
        if let Some(tx) = tx { let _ = tx.send(()).await; }
        *self.current.lock() = None;
    }
}

fn parse_extensions(s: &str) -> Vec<String> {
    s.split(',')
        .map(|x| x.trim().trim_start_matches('.').to_lowercase())
        .filter(|x| !x.is_empty())
        .collect()
}

fn path_matches(p: &Path, extensions: &[String], include: bool) -> bool {
    if extensions.is_empty() { return true; }
    let ext = p.extension().and_then(|e| e.to_str()).map(|e| e.to_lowercase()).unwrap_or_default();
    let listed = extensions.iter().any(|e| *e == ext);
    if include { listed } else { !listed }
}

fn walk_collect(dir: &Path, recursive: bool, out: &mut HashSet<PathBuf>) {
    let Ok(rd) = std::fs::read_dir(dir) else { return };
    for entry in rd.flatten() {
        let p = entry.path();
        if p.is_file() { out.insert(p); }
        else if p.is_dir() && recursive { walk_collect(&p, recursive, out); }
    }
}