use failure::Error;
use inotify::{Inotify, WatchMask, EventMask};
use serde::de::DeserializeOwned;
use std::fs::File;
use std::io::BufReader;
use std::path::Path;
use std::path::PathBuf;

/// Reloadable config file
pub struct ConfigFile<T> {
    is_dummy : bool,
    config: T,
    path: PathBuf,
    inotify: Option<Inotify>,
    inotify_buffer: [u8; 1024],
}

impl<T> ConfigFile<T>
where
    T: Default + std::fmt::Debug + DeserializeOwned,
{
    pub fn borrow(&self) -> &T {
        &self.config
    }

    /// Create a new reloadable config file
    /// If loading fails, an error is printed and default values are be used
    pub fn new<P: AsRef<Path>>(path: P) -> Result<Self, Error> {
        let loaded = Self::load(&path);
        if let Err(e) = &loaded {
            eprintln!("Config file failed to load/parse: {}", e);
        }

        Ok(Self {
            is_dummy: false,
            config: loaded.unwrap_or(T::default()),
            path: path.as_ref().to_owned(),
            inotify: Self::setup_inotify(&path),
            inotify_buffer: [0; 1024],
        })
    }

    /// New without a backing file
    #[allow(dead_code)]
    pub fn new_from_defaults() -> Self {
        Self {
            is_dummy: true,
            config: T::default(),
            path: "".into(),
            inotify: None,
            inotify_buffer: [0; 1024]
        }
    }

    /// Try to install inotify
    fn setup_inotify<P: AsRef<Path>>(path: P) -> Option<Inotify> {
        let inotify = Inotify::init();
        if let Err(e) = inotify {
            eprintln!("Failed to set up inotify for config file reload!\n{}", e);
            return None;
        }

        let mut inotify = inotify.unwrap();
        let rv = inotify.add_watch(&path, WatchMask::MODIFY | WatchMask::CLOSE);

        match rv {
            Err(e) => {
                eprintln!("Failed to add inotify watch for config!\n{}", e);
                None
            }
            Ok(_) => Some(inotify),
        }
    }

    /// Update the config file if needed (there are inotify events)
    /// - if inotify failed to init, or an error occurs trying to get events from it,
    ///   the 'def' value is used (true = reload if unsure)
    pub fn update_if_needed(&mut self, def: bool) -> Result<bool, Error> {
        if self.is_dummy {
            debug!("Config is dummy, no path to reload.");
            return Ok(false);
        }

        let needed = match self.inotify.as_mut() {
            Some(ino) => {
                let rv = ino.read_events(&mut self.inotify_buffer);
                match rv {
                    Ok(evs) => {
                        let mut changed = false;
                        let mut need_reinstall = false;
                        for ev in evs {
                            if ev.mask.contains(EventMask::IGNORED) {
                                debug!("Inotify watcher got removed by OS??");
                                changed = true;
                                need_reinstall = true;
                            }
                            if ev.mask.contains(EventMask::MODIFY) {
                                changed = true;
                            }
                        }
                        if changed {
                            info!("Config file changes detected, reloading");
                        }
                        if need_reinstall {
                            debug!("Reinstalling inotify");
                            self.inotify = Self::setup_inotify(&self.path);
                        }
                        changed
                    }
                    _ => {
                        error!("Failed to get inotify events.");
                        def
                    }
                }
            }
            None => def,
        };

        if needed {
            self.update()?;
        } else {
            debug!("Config update not needed.");
        }

        Ok(needed)
    }

    /// load and parse the config file
    fn load<P: AsRef<Path>>(path: P) -> Result<T, Error> {
        info!("Loading config file @ {}", path.as_ref().to_str().unwrap_or("???"));
        let file = File::open(&path)?;
        let reader = BufReader::new(file);
        let val : T = serde_json::from_reader(reader)?;

        debug!("Loaded config:\n{:#?}", val);

        Ok(val)
    }

    /// Reload unconditionally
    pub fn update(&mut self) -> Result<(), Error> {
        if self.is_dummy {
            debug!("Config is dummy, no path to reload.");
            return Ok(());
        }

        self.config = Self::load(&self.path)?;
        Ok(())
    }
}