nightshade 0.56.0

A cross-platform data-oriented game engine.
Documentation 
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use notify::{Event, EventKind, RecursiveMode, Watcher};
use std::collections::{HashMap, HashSet};
use std::path::PathBuf;
use std::sync::mpsc;

pub struct FileWatcher {
    watcher: Option<notify::RecommendedWatcher>,
    receiver: std::sync::Mutex<mpsc::Receiver<Result<Event, notify::Error>>>,
    sender: mpsc::Sender<Result<Event, notify::Error>>,
    path_to_key: HashMap<PathBuf, String>,
    key_to_path: HashMap<String, PathBuf>,
    changed_keys: HashSet<String>,
}

impl Default for FileWatcher {
    fn default() -> Self {
        let (sender, receiver) = mpsc::channel();
        let watcher_sender = sender.clone();
        let watcher = notify::recommended_watcher(watcher_sender).ok();
        Self {
            watcher,
            receiver: std::sync::Mutex::new(receiver),
            sender,
            path_to_key: HashMap::new(),
            key_to_path: HashMap::new(),
            changed_keys: HashSet::new(),
        }
    }
}

impl FileWatcher {
    pub fn watch(&mut self, key: String, path: PathBuf) {
        if self.key_to_path.contains_key(&key) {
            return;
        }
        let canonical = path.canonicalize().unwrap_or(path);
        tracing::info!("Watching file [{}]: {}", key, canonical.display());
        self.path_to_key.insert(canonical.clone(), key.clone());
        self.key_to_path.insert(key, canonical.clone());
        if let Some(watcher) = &mut self.watcher {
            let _ = watcher.watch(&canonical, RecursiveMode::NonRecursive);
        }
    }

    pub fn poll(&mut self) {
        let mut events = Vec::new();
        while let Ok(event_result) = self.receiver.lock().unwrap().try_recv() {
            if let Ok(event) = event_result {
                events.push(event);
            }
        }
        for event in events {
            if !matches!(event.kind, EventKind::Modify(_) | EventKind::Create(_)) {
                continue;
            }
            for path in event.paths {
                let canonical = path.canonicalize().unwrap_or(path);
                if let Some(key) = self.path_to_key.get(&canonical) {
                    self.changed_keys.insert(key.clone());
                }
            }
        }

        if self.watcher.is_none() {
            let watcher_sender = self.sender.clone();
            if let Ok(mut new_watcher) = notify::recommended_watcher(watcher_sender) {
                for path in self.key_to_path.values() {
                    let _ = new_watcher.watch(path, RecursiveMode::NonRecursive);
                }
                self.watcher = Some(new_watcher);
            }
        }
    }

    pub fn take_change(&mut self, key: &str) -> bool {
        self.changed_keys.remove(key)
    }
}

pub fn poll_file_watcher_system(world: &mut crate::ecs::world::World) {
    world.plugin_resource_mut::<FileWatcher>().poll();
}

/// Installs hot-reload file watching: the file and asset watcher polls run
/// at the end of the frame, alongside the other housekeeping passes. Watch
/// a file with `world.plugin_resource_mut::<FileWatcher>().watch(key, path)`
/// and consume changes with `take_change(key)`.
pub struct FileWatcherPlugin;

impl crate::app::Plugin for FileWatcherPlugin {
    fn build(&self, app: &mut crate::app::App) {
        use crate::app::Stage;
        app.add_system(Stage::Last, poll_file_watcher_system);
        #[cfg(feature = "assets")]
        app.add_system(
            Stage::Last,
            crate::ecs::asset_watcher::poll_asset_watcher_system,
        );
    }
}