use std::{collections::{HashMap, HashSet}, time::{Duration, SystemTime}};

use anyhow::Result;
use notify::{RecommendedWatcher, RecursiveMode, Watcher as _Watcher};
use parking_lot::RwLock;
use tokio::{fs, pin, sync::{mpsc::{self, UnboundedReceiver}, watch}};
use tokio_stream::{wrappers::UnboundedReceiverStream, StreamExt};
use tracing::error;
use yazi_plugin::isolate;
use yazi_proxy::WATCHER;
use yazi_shared::{fs::{File, FilesOp, Url}, RoCell};

use super::Linked;
use crate::folder::{Files, Folder};

pub(crate) static WATCHED: RoCell<RwLock<HashSet<Url>>> = RoCell::new();
pub static LINKED: RoCell<RwLock<Linked>> = RoCell::new();

pub struct Watcher {
	tx: watch::Sender<HashSet<Url>>,
}

impl Watcher {
	pub(super) fn serve() -> Self {
		let (in_tx, in_rx) = watch::channel(Default::default());
		let (out_tx, out_rx) = mpsc::unbounded_channel();

		let watcher = RecommendedWatcher::new(
			move |res: Result<notify::Event, notify::Error>| {
				let Ok(event) = res else { return };
				for path in event.paths {
					out_tx.send(Url::from(path)).ok();
				}
			},
			Default::default(),
		);

		tokio::spawn(Self::on_in(in_rx, watcher.unwrap()));
		tokio::spawn(Self::on_out(out_rx));
		Self { tx: in_tx }
	}

	pub(super) fn watch(&mut self, mut new: HashSet<&Url>) {
		new.retain(|&u| u.is_regular());
		self.tx.send(new.into_iter().cloned().collect()).ok();
	}

	pub(super) fn trigger_dirs(&self, folders: &[&Folder]) {
		let todo: Vec<_> =
			folders.iter().filter(|&f| f.cwd.is_regular()).map(|&f| (f.cwd.clone(), f.mtime)).collect();
		if todo.is_empty() {
			return;
		}

		async fn go(url: Url, mtime: Option<SystemTime>) {
			let Some(meta) = Files::assert_stale(&url, mtime).await else { return };

			if let Ok(files) = Files::from_dir_bulk(&url).await {
				FilesOp::Full(url, files, meta.modified().ok()).emit();
			}
		}

		tokio::spawn(async move {
			futures::future::join_all(todo.into_iter().map(|(url, mtime)| go(url, mtime))).await;
		});
	}

	async fn on_in(mut rx: watch::Receiver<HashSet<Url>>, mut watcher: RecommendedWatcher) {
		loop {
			let (mut to_unwatch, mut to_watch): (HashSet<_>, HashSet<_>) = {
				let (new, old) = (&*rx.borrow_and_update(), &*WATCHED.read());
				(old.difference(new).cloned().collect(), new.difference(old).cloned().collect())
			};

			to_unwatch.retain(|u| watcher.unwatch(u).is_ok());
			to_watch.retain(|u| watcher.watch(u, RecursiveMode::NonRecursive).is_ok());

			{
				let mut watched = WATCHED.write();
				watched.retain(|u| !to_unwatch.contains(u));
				watched.extend(to_watch);
			}

			if !rx.has_changed().unwrap_or(false) {
				Self::sync_linked().await;
			}

			if rx.changed().await.is_err() {
				break;
			}
		}
	}

	async fn on_out(rx: UnboundedReceiver<Url>) {
		// TODO: revert this once a new notification is implemented
		let rx = UnboundedReceiverStream::new(rx).chunks_timeout(1000, Duration::from_millis(50));
		pin!(rx);

		while let Some(urls) = rx.next().await {
			let _permit = WATCHER.acquire().await.unwrap();
			let mut reload = Vec::with_capacity(urls.len());

			for u in urls.into_iter().collect::<HashSet<_>>() {
				let Some(parent) = u.parent_url() else { continue };

				let Ok(file) = File::from(u.clone()).await else {
					FilesOp::Deleting(parent, vec![u]).emit();
					continue;
				};

				if !file.is_dir() {
					reload.push(file.clone());
				}
				FilesOp::Upserting(parent, HashMap::from_iter([(u, file)])).emit();
			}

			if reload.is_empty() {
				continue;
			}
			if let Err(e) = isolate::prefetch("mime", reload).await {
				error!("prefetch `mime` failed in watcher: {e}");
			}
		}
	}

	async fn sync_linked() {
		let mut new = WATCHED.read().clone();

		let old = {
			let mut linked = LINKED.write();
			linked.retain(|k, _| new.remove(k));
			linked.keys().cloned().collect()
		};

		async fn go(todo: HashSet<Url>) {
			for from in todo {
				let Ok(to) = fs::canonicalize(&from).await else { continue };

				if to != *from && WATCHED.read().contains(&from) {
					LINKED.write().insert(from, Url::from(to));
				}
			}
		}

		go(new).await;
		go(old).await;
	}
}