use crate::io;
use crossbeam_channel::Sender;
use drop_bomb::DropBomb;
use notify::{DebouncedEvent, RecommendedWatcher, RecursiveMode, Watcher as NotifyWatcher};
use std::{
    path::{Path, PathBuf},
    sync::mpsc,
    thread,
    time::Duration,
};
use walkdir::{DirEntry, WalkDir};

pub(crate) struct Watcher {
    watcher: RecommendedWatcher,
    thread: thread::JoinHandle<()>,
    bomb: DropBomb,
    sender: Sender<io::Task>,
}

#[derive(Debug)]
pub enum WatcherChange {
    Create(PathBuf),
    Write(PathBuf),
    Remove(PathBuf),
    Rescan,
}

fn handle_change_event(
    ev: DebouncedEvent,
    sender: &Sender<io::Task>,
) -> Result<(), Box<std::error::Error>> {
    match ev {
        DebouncedEvent::NoticeWrite(_)
        | DebouncedEvent::NoticeRemove(_)
        | DebouncedEvent::Chmod(_) => {
            // ignore
        }
        DebouncedEvent::Rescan => {
            sender.send(io::Task::HandleChange(WatcherChange::Rescan))?;
        }
        DebouncedEvent::Create(path) => {
            sender.send(io::Task::HandleChange(WatcherChange::Create(path)))?;
        }
        DebouncedEvent::Write(path) => {
            sender.send(io::Task::HandleChange(WatcherChange::Write(path)))?;
        }
        DebouncedEvent::Remove(path) => {
            sender.send(io::Task::HandleChange(WatcherChange::Remove(path)))?;
        }
        DebouncedEvent::Rename(src, dst) => {
            sender.send(io::Task::HandleChange(WatcherChange::Remove(src)))?;
            sender.send(io::Task::HandleChange(WatcherChange::Create(dst)))?;
        }
        DebouncedEvent::Error(err, path) => {
            // TODO should we reload the file contents?
            log::warn!("watcher error \"{}\", {:?}", err, path);
        }
    }
    Ok(())
}

const WATCHER_DELAY: Duration = Duration::from_millis(250);

impl Watcher {
    pub(crate) fn start(
        output_sender: Sender<io::Task>,
    ) -> Result<Watcher, Box<std::error::Error>> {
        let (input_sender, input_receiver) = mpsc::channel();
        let watcher = notify::watcher(input_sender, WATCHER_DELAY)?;
        let sender = output_sender.clone();
        let thread = thread::spawn(move || {
            input_receiver
                .into_iter()
                // forward relevant events only
                .try_for_each(|change| handle_change_event(change, &output_sender))
                .unwrap()
        });
        Ok(Watcher {
            watcher,
            thread,
            sender,
            bomb: DropBomb::new(format!("Watcher was not shutdown")),
        })
    }

    pub fn watch_recursive(
        &mut self,
        dir: &Path,
        filter_entry: impl Fn(&DirEntry) -> bool,
        emit_for_existing: bool,
    ) {
        for res in WalkDir::new(dir).into_iter().filter_entry(filter_entry) {
            match res {
                Ok(entry) => {
                    if entry.path().is_dir() {
                        match self.watcher.watch(dir, RecursiveMode::NonRecursive) {
                            Ok(()) => log::debug!("watching \"{}\"", dir.display()),
                            Err(e) => log::warn!("could not watch \"{}\": {}", dir.display(), e),
                        }
                    }
                    if emit_for_existing {
                        // emit as create because we haven't seen it yet
                        if let Err(e) =
                            self.sender
                                .send(io::Task::HandleChange(WatcherChange::Create(
                                    entry.path().to_path_buf(),
                                )))
                        {
                            log::warn!("watcher error: {}", e)
                        }
                    }
                }
                Err(e) => log::warn!("watcher error: {}", e),
            }
        }
    }

    pub fn shutdown(mut self) -> thread::Result<()> {
        self.bomb.defuse();
        drop(self.watcher);
        let res = self.thread.join();
        match &res {
            Ok(()) => log::info!("... Watcher terminated with ok"),
            Err(_) => log::error!("... Watcher terminated with err"),
        }
        res
    }
}