use notify::{Config, EventKind, PollWatcher, RecommendedWatcher, RecursiveMode, Watcher};
use std::path::Path;
use std::sync::mpsc;
use std::time::Duration;
use tauri::{AppHandle, Emitter, Manager};

use crate::state::AppState;
use crate::types::FileEvent;
use crate::vault::operations::helixnotes_dir;

const IOS_POLL_INTERVAL: Duration = Duration::from_secs(10);
const NATIVE_POLL_INTERVAL: Duration = Duration::from_secs(1);

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
enum WatcherBackend {
    Recommended,
    Poll,
}

const fn watcher_backend_for_target(is_ios: bool) -> WatcherBackend {
    if is_ios {
        WatcherBackend::Poll
    } else {
        WatcherBackend::Recommended
    }
}

const fn poll_interval_for_backend(backend: WatcherBackend) -> Duration {
    match backend {
        WatcherBackend::Recommended => NATIVE_POLL_INTERVAL,
        WatcherBackend::Poll => IOS_POLL_INTERVAL,
    }
}

pub enum VaultWatcher {
    Recommended(RecommendedWatcher),
    Poll(PollWatcher),
}

impl VaultWatcher {
    fn watch(&mut self, path: &Path, recursive_mode: RecursiveMode) -> notify::Result<()> {
        match self {
            Self::Recommended(watcher) => watcher.watch(path, recursive_mode),
            Self::Poll(watcher) => watcher.watch(path, recursive_mode),
        }
    }
}

pub fn start_watcher(app: AppHandle, vault_path: String) -> Result<VaultWatcher, String> {
    let (tx, rx) = mpsc::channel();

    let backend = watcher_backend_for_target(cfg!(target_os = "ios"));
    let config = Config::default().with_poll_interval(poll_interval_for_backend(backend));
    let mut watcher = match backend {
        WatcherBackend::Recommended => VaultWatcher::Recommended(
            RecommendedWatcher::new(tx, config).map_err(|e| e.to_string())?,
        ),
        WatcherBackend::Poll => {
            VaultWatcher::Poll(PollWatcher::new(tx, config).map_err(|e| e.to_string())?)
        }
    };

    watcher
        .watch(Path::new(&vault_path), RecursiveMode::Recursive)
        .map_err(|e| e.to_string())?;

    let hn_dir = helixnotes_dir(&vault_path);

    std::thread::spawn(move || {
        while let Ok(result) = rx.recv() {
            match result {
                Ok(event) => {
                    // Skip all file events while importing
                    let state = app.state::<AppState>();
                    if state.importing.load(std::sync::atomic::Ordering::Relaxed) {
                        continue;
                    }
                    // Skip .helixnotes directory events
                    let dominated_by_hn = event.paths.iter().all(|p| p.starts_with(&hn_dir));
                    if dominated_by_hn {
                        continue;
                    }

                    // Only care about .md file events
                    let has_md = event.paths.iter().any(|p| {
                        p.extension().and_then(|x| x.to_str()) == Some("md") || p.is_dir()
                    });

                    if !has_md {
                        continue;
                    }

                    let event_type = match event.kind {
                        EventKind::Create(_) => "create",
                        EventKind::Modify(_) => "modify",
                        EventKind::Remove(_) => "remove",
                        _ => continue,
                    };

                    for path in &event.paths {
                        let fe = FileEvent {
                            event_type: event_type.to_string(),
                            path: path.to_string_lossy().to_string(),
                        };
                        let _ = app.emit("file-changed", &fe);
                    }

                    // On mobile, throttle event emission to prevent IPC flooding
                    // on FUSE filesystems where Syncthing/other apps generate
                    // constant file activity that blocks the Tauri command channel.
                    #[cfg(mobile)]
                    {
                        std::thread::sleep(Duration::from_secs(2));
                        while rx.try_recv().is_ok() {}
                    }
                }
                Err(e) => {
                    log::error!("File watcher error: {}", e);
                }
            }
        }
    });

    Ok(watcher)
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn ios_uses_polling_backend() {
        assert_eq!(watcher_backend_for_target(true), WatcherBackend::Poll);
    }

    #[test]
    fn other_platforms_keep_recommended_backend() {
        assert_eq!(
            watcher_backend_for_target(false),
            WatcherBackend::Recommended
        );
    }

    #[test]
    fn watcher_backends_use_the_expected_intervals() {
        assert_eq!(
            poll_interval_for_backend(WatcherBackend::Poll),
            Duration::from_secs(10)
        );
        assert_eq!(
            poll_interval_for_backend(WatcherBackend::Recommended),
            Duration::from_secs(1)
        );
    }
}