use std::{ffi::OsStr, io, os::unix::fs::MetadataExt, path::Path, sync::Arc};

use ::users::os::unix::UserExt;
use moka::future::{Cache, CacheBuilder};
use tokio::{fs::File, io::AsyncReadExt};

use crate::{
    consts,
    server::caches::{mime::Mime, users::UsersCache},
};

pub mod mime;
pub mod users;

const MIME_IMAGE_PREFIX: &str = "image/";

pub struct MimeWithBytes {
    pub mime: Box<str>,
    pub bytes: Box<[u8]>,
}

pub type Image = Arc<MimeWithBytes>;

// TODO: most of the cache methods here block the executor, if we wanna commit to async we'd have
// to consider that
pub struct AppCache<'a> {
    only_groups: &'a [crate::serdes::Group],
    // FIXME: blocks
    user_cache: UsersCache,
    // FIXME: blocks
    magic_mime_cookie: Mime,

    /// MUST only contain users from an accepted group, we do not want to cache arbitrary usernames
    /// and blow memory up.
    ///
    /// [`Option<Image>`] because users may not have a pfp.
    pfp_cache: Cache<String, Option<Image>>,
}

impl<'a> AppCache<'a> {
    /// # Errors
    ///
    /// Errors if anything failed opening the magic cookie.
    ///
    /// # Panics
    ///
    /// If weighter's usize doesn't fit in its u32
    #[must_use]
    pub fn new(
        magic_dbs: magic::cookie::DatabasePaths,
        only_groups: &'a [crate::serdes::Group],
    ) -> Self {
        Self {
            only_groups,

            user_cache: UsersCache::new(),

            magic_mime_cookie: Mime::new(magic_dbs),

            pfp_cache: CacheBuilder::new(consts::MAX_PFP_CACHE_CAPACITY)
                .time_to_live(consts::USER_CACHES_TTL)
                .weigher(|_, v: &Option<Image>| {
                    v.as_ref()
                        .map_or(1, |v| v.bytes.len())
                        .try_into()
                        .expect("size of image to fit in weigher's size")
                })
                .build(),
        }
    }

    fn is_member_groups(&self, groups: Option<impl AsRef<[::users::Group]>>) -> bool {
        groups.is_some_and(|groups| {
            groups.as_ref().iter().any(|group| {
                let gid = group.gid();

                self.only_groups.iter().any(|from_gr| from_gr.0 == gid)
            })
        })
    }

    pub async fn get_member_user_by_name<S: AsRef<OsStr> + ?Sized>(
        &self,
        username: &S,
    ) -> Option<Arc<::users::User>> {
        let user = self.user_cache.get_user_by_name(username).await?;

        // FIXME: `user.groups()` is not cached and could be a DoS point. But I don't think caching
        // if a user is member of any group is the proper way for this lmfao
        if self.is_member_groups(user.groups()) {
            Some(user)
        } else {
            None
        }
    }

    async fn read_logo_from_home(&self, home: &Path) -> Option<Image> {
        async fn read_limited_path<const MAXSIZE: u64>(path: &Path) -> io::Result<Vec<u8>> {
            let f = File::open(path).await?;
            let size = f.metadata().await?.size();

            if size > MAXSIZE {
                return Err(io::Error::new(
                    io::ErrorKind::FileTooLarge,
                    "filesize is bigger than MAXSIZE",
                ));
            }
            let mut buf = Vec::with_capacity(size.try_into().expect("u64 to fit in usize"));
            // `.take()` just in case an open fd happens to grow, `.metadata()` SHOULD take
            // properties from the fd and lock the read fd until its closed but still
            f.take(MAXSIZE).read_to_end(&mut buf).await?;
            Ok(buf)
        }

        for subpath in consts::USER_PFP_PATHS {
            let path = home.join(subpath);

            if let Ok(img_buf) = read_limited_path::<{ consts::MAX_PFP_SIZE }>(&path).await
                && let Ok(Ok(mime)) = self.magic_mime_cookie.buffer(&img_buf) // TODO: first layer
                                                                              // error is actually
                                                                              // relevant
                && mime.starts_with(MIME_IMAGE_PREFIX)
            {
                return Some(Arc::new(MimeWithBytes {
                    mime: mime.into_boxed_str(),
                    bytes: img_buf.into_boxed_slice(),
                }));
            }
        }

        None
    }

    /// Doesn't differenciate users without pfp and nonexistent ones
    ///
    /// So ig a feature not a bug? Less scraping? As in, scraping a user without pfp will just
    /// default to default pfp.
    ///
    /// # Performance
    ///
    /// `T` is very generic, usually just takes the path of [`AsRef<str>`], but rarely it can take
    /// the [`ToOwned<Owned = String>`] path. That means, if you only have access to a type like
    /// [`str`], use it. But if by any chance you have a [`String`] of the value and it's not going
    /// to be used anymore, that might be more performant.
    ///
    /// The loss is mainly just the allocation time, just a username, should be small enough but
    /// still, just giving it flexibility. Also maybe a [`std::borrow::Cow<str>`] will work
    /// perfectly too.
    ///
    /// # Security
    ///
    /// Images ultimately come from users home directories, so they could be anything, not only
    /// images (though there's a MIME check, but not designed to be relied upon), make sure to
    /// provide the mime type and `X-Content-Type-Options: nosniff` when serving it via http/s.
    pub async fn get_pfp<T>(&self, username: T) -> Option<Image>
    where
        T: AsRef<str> + ToOwned<Owned = String>,
    {
        // If caching is done properly, it will take advantage of async.
        if let Some(cached_pfp) = self.pfp_cache.get(username.as_ref()).await {
            return cached_pfp;
        }

        // This blocks for now, so if we win with caching better. Non-member username requests
        // won't cache, we win with actual user-cache and not pushing those away, but will make
        // DDoS miss cache constantly.
        let user = self.get_member_user_by_name(username.as_ref()).await?;
        let img = self.read_logo_from_home(user.home_dir()).await?;

        self.pfp_cache
            .insert(username.to_owned(), Some(img.clone()))
            .await;

        Some(img)
    }
}