//! An implementation of `loader::Handle`, based on `walkdir` and `notify`.
//!
//! The file watching bits here are untested and quite probably buggy. For this
//! reason, by default we don't watch files and rely on editor's file watching
//! capabilities.
//!
//! Hopefully, one day a reliable file watching/walking crate appears on
//! crates.io, and we can reduce this to trivial glue code.
use std::fs;

use crossbeam_channel::{never, select, unbounded, Receiver, Sender};
use notify::{RecommendedWatcher, RecursiveMode, Watcher};
use paths::{AbsPath, AbsPathBuf};
use vfs::loader;
use walkdir::WalkDir;

#[derive(Debug)]
pub struct NotifyHandle {
    // Relative order of fields below is significant.
    sender: Sender<Message>,
    _thread: jod_thread::JoinHandle,
}

#[derive(Debug)]
enum Message {
    Config(loader::Config),
    Invalidate(AbsPathBuf),
}

impl loader::Handle for NotifyHandle {
    fn spawn(sender: loader::Sender) -> NotifyHandle {
        let actor = NotifyActor::new(sender);
        let (sender, receiver) = unbounded::<Message>();
        let thread = jod_thread::Builder::new()
            .name("VfsLoader".to_owned())
            .spawn(move || actor.run(receiver))
            .expect("failed to spawn thread");
        NotifyHandle { sender, _thread: thread }
    }
    fn set_config(&mut self, config: loader::Config) {
        self.sender.send(Message::Config(config)).unwrap();
    }
    fn invalidate(&mut self, path: AbsPathBuf) {
        self.sender.send(Message::Invalidate(path)).unwrap();
    }
    fn load_sync(&mut self, path: &AbsPath) -> Option<Vec<u8>> {
        read(path)
    }
}

type NotifyEvent = notify::Result<notify::Event>;

struct NotifyActor {
    sender: loader::Sender,
    watched_entries: Vec<loader::Entry>,
    // Drop order is significant.
    watcher: Option<(RecommendedWatcher, Receiver<NotifyEvent>)>,
}

#[derive(Debug)]
enum Event {
    Message(Message),
    NotifyEvent(NotifyEvent),
}

impl NotifyActor {
    fn new(sender: loader::Sender) -> NotifyActor {
        NotifyActor { sender, watched_entries: Vec::new(), watcher: None }
    }
    fn next_event(&self, receiver: &Receiver<Message>) -> Option<Event> {
        let watcher_receiver = self.watcher.as_ref().map(|(_, receiver)| receiver);
        select! {
            recv(receiver) -> it => it.ok().map(Event::Message),
            recv(watcher_receiver.unwrap_or(&never())) -> it => Some(Event::NotifyEvent(it.unwrap())),
        }
    }
    fn run(mut self, inbox: Receiver<Message>) {
        while let Some(event) = self.next_event(&inbox) {
            tracing::debug!("vfs-notify event: {:?}", event);
            match event {
                Event::Message(msg) => match msg {
                    Message::Config(config) => {
                        self.watcher = None;
                        if !config.watch.is_empty() {
                            let (watcher_sender, watcher_receiver) = unbounded();
                            let watcher = log_notify_error(RecommendedWatcher::new(move |event| {
                                watcher_sender.send(event).unwrap();
                            }));
                            self.watcher = watcher.map(|it| (it, watcher_receiver));
                        }

                        let config_version = config.version;

                        let n_total = config.load.len();
                        self.send(loader::Message::Progress { n_total, n_done: 0, config_version });

                        self.watched_entries.clear();

                        for (i, entry) in config.load.into_iter().enumerate() {
                            let watch = config.watch.contains(&i);
                            if watch {
                                self.watched_entries.push(entry.clone());
                            }
                            let files = self.load_entry(entry, watch);
                            self.send(loader::Message::Loaded { files });
                            self.send(loader::Message::Progress {
                                n_total,
                                n_done: i + 1,
                                config_version,
                            });
                        }
                    }
                    Message::Invalidate(path) => {
                        let contents = read(path.as_path());
                        let files = vec![(path, contents)];
                        self.send(loader::Message::Loaded { files });
                    }
                },
                Event::NotifyEvent(event) => {
                    if let Some(event) = log_notify_error(event) {
                        let files = event
                            .paths
                            .into_iter()
                            .map(|path| AbsPathBuf::try_from(path).unwrap())
                            .filter_map(|path| {
                                let meta = fs::metadata(&path).ok()?;
                                if meta.file_type().is_dir()
                                    && self
                                        .watched_entries
                                        .iter()
                                        .any(|entry| entry.contains_dir(&path))
                                {
                                    self.watch(path);
                                    return None;
                                }

                                if !meta.file_type().is_file() {
                                    return None;
                                }
                                if !self
                                    .watched_entries
                                    .iter()
                                    .any(|entry| entry.contains_file(&path))
                                {
                                    return None;
                                }

                                let contents = read(&path);
                                Some((path, contents))
                            })
                            .collect();
                        self.send(loader::Message::Loaded { files });
                    }
                }
            }
        }
    }
    fn load_entry(
        &mut self,
        entry: loader::Entry,
        watch: bool,
    ) -> Vec<(AbsPathBuf, Option<Vec<u8>>)> {
        match entry {
            loader::Entry::Files(files) => files
                .into_iter()
                .map(|file| {
                    if watch {
                        self.watch(file.clone());
                    }
                    let contents = read(file.as_path());
                    (file, contents)
                })
                .collect::<Vec<_>>(),
            loader::Entry::Directories(dirs) => {
                let mut res = Vec::new();

                for root in &dirs.include {
                    let walkdir =
                        WalkDir::new(root).follow_links(true).into_iter().filter_entry(|entry| {
                            if !entry.file_type().is_dir() {
                                return true;
                            }
                            let path = AbsPath::assert(entry.path());
                            root == path
                                || dirs.exclude.iter().chain(&dirs.include).all(|it| it != path)
                        });

                    let files = walkdir.filter_map(|it| it.ok()).filter_map(|entry| {
                        let is_dir = entry.file_type().is_dir();
                        let is_file = entry.file_type().is_file();
                        let abs_path = AbsPathBuf::assert(entry.into_path());
                        if is_dir && watch {
                            self.watch(abs_path.clone());
                        }
                        if !is_file {
                            return None;
                        }
                        let ext = abs_path.extension().unwrap_or_default();
                        if dirs.extensions.iter().all(|it| it.as_str() != ext) {
                            return None;
                        }
                        Some(abs_path)
                    });

                    res.extend(files.map(|file| {
                        let contents = read(file.as_path());
                        (file, contents)
                    }));
                }
                res
            }
        }
    }

    fn watch(&mut self, path: AbsPathBuf) {
        if let Some((watcher, _)) = &mut self.watcher {
            log_notify_error(watcher.watch(path.as_ref(), RecursiveMode::NonRecursive));
        }
    }
    fn send(&mut self, msg: loader::Message) {
        (self.sender)(msg);
    }
}

fn read(path: &AbsPath) -> Option<Vec<u8>> {
    std::fs::read(path).ok()
}

fn log_notify_error<T>(res: notify::Result<T>) -> Option<T> {
    res.map_err(|err| tracing::warn!("notify error: {}", err)).ok()
}