//! Repositories on disk (hub spec §4): naming, the registry of open
//! handles and their locks, and the page-ready views built from `oxy-core`.
//!
//! Every `oxy-core` call is synchronous and runs on the blocking pool under
//! the repository's lock (§16.2): pushes and other writes take the write
//! half, page reads the read half.

pub mod archive;
pub mod cache;
pub mod edits;
pub mod functions;
pub mod names;
pub mod proposals;
pub mod search;
pub mod view;

pub use cache::{Loaded, StateCache};
pub use names::RepoName;

use oxy_core::repo::Repo;
use std::collections::HashMap;
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex};
use tokio::sync::{OwnedMutexGuard, OwnedRwLockReadGuard, OwnedRwLockWriteGuard, RwLock};

/// A repository's locks (oxygenhub#249). Readers never wait for a push or
/// a gc: the store gives every handle one head and finds what a repack
/// moved (oxy-core, "readers never wait"). Writers take `writer` in turn;
/// everyone holds `life` shared, and only deleting or moving the
/// repository holds it alone.
#[derive(Default)]
struct Locks {
    life: Arc<RwLock<()>>,
    writer: Arc<tokio::sync::Mutex<()>>,
}

/// A reader's hold: the repository is not deleted or moved under it.
pub type ReadGuard = OwnedRwLockReadGuard<()>;

/// A writer's hold: no other writer runs, and the repository stays put.
/// Readers carry on.
pub struct WriteGuard {
    _writer: OwnedMutexGuard<()>,
    _life: OwnedRwLockReadGuard<()>,
}

/// Deleting or moving a repository: nothing else runs on it.
pub type ExclusiveGuard = OwnedRwLockWriteGuard<()>;

/// Where repositories live and how their access is serialised.
pub struct Repos {
    root: PathBuf,
    locks: Mutex<HashMap<String, Arc<Locks>>>,
    cache: Arc<StateCache>,
    pub searches: search::SearchCache,
}

#[derive(Debug, thiserror::Error)]
pub enum RepoError {
    #[error("no such repository")]
    NotFound,
    #[error("{0} already exists")]
    Exists(String),
    #[error("{0}")]
    Oxy(#[from] oxy_core::repo::RepoError),
    #[error("{0}")]
    Store(#[from] oxy_core::store::StoreError),
    #[error("{0}")]
    Io(#[from] std::io::Error),
}

impl Repos {
    pub fn new(root: PathBuf) -> Repos {
        // States are bounded by their estimated bytes (`cache::budget`); the
        // count only stops many tiny states piling up. At 64 it was always
        // full and evicting long before the bytes were (#145).
        let briefs = root.parent().unwrap_or(&root).join("cache").join("summaries").join(root.file_name().unwrap_or_default());
        let cache = Arc::new(StateCache::new(256).with_briefs(briefs));
        Repos { root, locks: Mutex::new(HashMap::new()), cache, searches: search::SearchCache::default() }
    }

    pub fn cache(&self) -> &Arc<StateCache> {
        &self.cache
    }

    pub fn root(&self) -> &Path {
        &self.root
    }

    /// `<root>/<owner>/<name>`, holding `.oxy/` and nothing else.
    pub fn dir(&self, name: &RepoName) -> PathBuf {
        self.root.join(&name.owner).join(&name.name)
    }

    pub fn exists(&self, name: &RepoName) -> bool {
        self.dir(name).join(oxy_core::repo::OXY_DIR).is_dir()
    }

    /// Open a hosted repository; it is always bare.
    pub fn open(&self, name: &RepoName) -> Result<Repo, RepoError> {
        if !self.exists(name) {
            return Err(RepoError::NotFound);
        }
        Ok(Repo::open(&self.dir(name))?)
    }

    /// Create an empty bare repository. With no `id` it is **unbound**: the
    /// first push binds it to the pusher's repository id, so an existing
    /// repository keeps its identity when it moves here (hub spec §4.1).
    pub fn create(&self, name: &RepoName, id: Option<[u8; 16]>) -> Result<Repo, RepoError> {
        let dir = self.dir(name);
        if dir.exists() {
            return Err(RepoError::Exists(name.to_string()));
        }
        Ok(match id {
            Some(id) => Repo::init_bare_with_id(&dir, id)?,
            None => Repo::init_bare_unbound(&dir)?,
        })
    }

    /// `create` off the async workers (#335): a bare init makes about
    /// sixteen fsyncs, and on a busy disk each waits behind every other
    /// write, so a create once held a worker for 26 s and stalled the
    /// requests queued behind it.
    pub async fn create_async(self: &Arc<Self>, name: &RepoName, id: Option<[u8; 16]>) -> Result<(), RepoError> {
        let (repos, name) = (self.clone(), name.clone());
        tokio::task::spawn_blocking(move || repos.create(&name, id).map(drop))
            .await
            .map_err(|e| RepoError::Io(std::io::Error::other(e.to_string())))?
    }

    /// Create an empty, unbound bare repository whose objects and
    /// operation log are kept in the store at `url` (oxygenhub#96); the
    /// store's credentials must already be known to the opener.
    pub fn create_on(&self, name: &RepoName, url: &str) -> Result<Repo, RepoError> {
        let dir = self.dir(name);
        if dir.exists() {
            return Err(RepoError::Exists(name.to_string()));
        }
        let made = (|| -> Result<Repo, RepoError> {
            drop(Repo::init_bare_on(&dir, [0; 16], Some(url))?);
            // Unbound as `create` makes them: oxy-core's marker file in
            // place of the id, so the first push gives the id.
            let oxy = dir.join(oxy_core::repo::OXY_DIR);
            std::fs::remove_file(oxy.join("id"))?;
            std::fs::write(oxy.join("unbound"), b"")?;
            Ok(Repo::open(&dir)?)
        })();
        if made.is_err() {
            let _ = std::fs::remove_dir_all(&dir);
        }
        made
    }

    /// Fork `src` into `dest` (hub spec §4): a new bare repository with its
    /// own id, the source's objects hard-linked where the file system allows
    /// (copied otherwise; objects are immutable, so sharing them is safe),
    /// and the source's bookmarks. The trust policy is not copied: the
    /// fork's owner sets their own. Runs under the source's writer lock, so
    /// no push lands while its files are linked.
    pub async fn fork(&self, src: &RepoName, dest: &RepoName) -> Result<(), RepoError> {
        let guard = self.write_guard(src).await;
        let (from, to) = (self.dir(src), self.dir(dest));
        if !self.exists(src) {
            return Err(RepoError::NotFound);
        }
        if to.exists() {
            return Err(RepoError::Exists(dest.to_string()));
        }
        if Repo::open(&from).is_ok_and(|r| r.config.storage_url.is_some()) {
            return Err(RepoError::Io(std::io::Error::other(
                "a repository kept in a bucket cannot be forked yet: clone it and push the clone to a new repository",
            )));
        }
        tokio::task::spawn_blocking(move || {
            let _guard = guard;
            let made = (|| -> Result<(), RepoError> {
                drop(Repo::init_bare(&to)?);
                let objects = |d: &Path| d.join(oxy_core::repo::OXY_DIR).join("objects");
                link_tree(&objects(&from), &objects(&to))?;
                let source = Repo::open(&from)?;
                let fork = Repo::open(&to)?;
                let existing: Vec<String> = fork.bookmarks()?.into_iter().map(|b| b.name).collect();
                for b in source.bookmarks()? {
                    if existing.contains(&b.name) {
                        fork.bookmark_set(&b.name, &b.heads)?;
                    } else {
                        fork.bookmark_create(&b.name, Some(&b.heads))?;
                    }
                }
                Ok(())
            })();
            if made.is_err() {
                let _ = std::fs::remove_dir_all(&to);
            }
            made
        })
        .await
        .map_err(|e| RepoError::Io(std::io::Error::other(e.to_string())))?
    }

    /// Move a repository to another name (a transfer, #108): the directory,
    /// and the lock the old name held.
    pub fn rename(&self, from: &RepoName, to: &RepoName) -> Result<(), RepoError> {
        let (src, dest) = (self.dir(from), self.dir(to));
        if !src.exists() {
            return Err(RepoError::NotFound);
        }
        if dest.exists() {
            return Err(RepoError::Exists(to.to_string()));
        }
        if let Some(parent) = dest.parent() {
            std::fs::create_dir_all(parent)?;
        }
        std::fs::rename(&src, &dest)?;
        let mut locks = self.locks.lock().unwrap();
        if let Some(l) = locks.remove(&from.to_string()) {
            locks.insert(to.to_string(), l);
        }
        Ok(())
    }

    /// Move a repository to the trash (hub spec §4.1); a job empties it later.
    pub fn trash(&self, name: &RepoName) -> Result<PathBuf, RepoError> {
        let dir = self.dir(name);
        if !dir.exists() {
            return Err(RepoError::NotFound);
        }
        let trash = self.root.parent().unwrap_or(&self.root).join("trash").join(&name.owner);
        // A drop's name is `drops/ID`: its own directory under the owner's.
        let dest = trash.join(format!("{}-{}", name.name, crate::db::now_ms()));
        std::fs::create_dir_all(dest.parent().unwrap_or(&trash))?;
        std::fs::rename(&dir, &dest)?;
        Ok(dest)
    }

    fn lock(&self, name: &RepoName) -> Arc<Locks> {
        self.locks.lock().unwrap().entry(name.to_string()).or_default().clone()
    }

    /// Read while `f` runs on the blocking pool: never waiting for a
    /// writer, only for the repository being deleted or moved.
    pub async fn read<T: Send + 'static>(
        &self,
        name: &RepoName,
        f: impl FnOnce(&Repo, &StateCache) -> Result<T, RepoError> + Send + 'static,
    ) -> Result<T, RepoError> {
        let guard = self.read_guard(name).await;
        let dir = self.dir(name);
        let exists = self.exists(name);
        let cache = self.cache.clone();
        tokio::task::spawn_blocking(move || {
            let _guard = guard;
            if !exists {
                return Err(RepoError::NotFound);
            }
            let repo = Repo::open(&dir)?;
            f(&repo, &cache)
        })
        .await
        .map_err(|e| RepoError::Io(std::io::Error::other(e)))?
    }

    /// Write while `f` runs on the blocking pool, after the writers ahead.
    pub async fn write<T: Send + 'static>(
        &self,
        name: &RepoName,
        f: impl FnOnce(&Repo, &StateCache) -> Result<T, RepoError> + Send + 'static,
    ) -> Result<T, RepoError> {
        let guard = self.write_guard(name).await;
        let dir = self.dir(name);
        let exists = self.exists(name);
        let cache = self.cache.clone();
        tokio::task::spawn_blocking(move || {
            let _guard = guard;
            if !exists {
                return Err(RepoError::NotFound);
            }
            let repo = Repo::open(&dir)?;
            f(&repo, &cache)
        })
        .await
        .map_err(|e| RepoError::Io(std::io::Error::other(e)))?
    }

    /// The writer's hold alone, for callers that open the repository
    /// themselves (the protocol server's push, a backup's last pass). The
    /// writer lock first, so a writer queued behind others holds nothing a
    /// delete would wait for.
    pub async fn write_guard(&self, name: &RepoName) -> WriteGuard {
        let locks = self.lock(name);
        let writer = locks.writer.clone().lock_owned().await;
        WriteGuard { _writer: writer, _life: locks.life.clone().read_owned().await }
    }

    pub async fn read_guard(&self, name: &RepoName) -> ReadGuard {
        self.lock(name).life.clone().read_owned().await
    }

    /// Deleting or moving the repository: waits for every reader and
    /// writer, and holds off new ones.
    pub async fn exclusive_guard(&self, name: &RepoName) -> ExclusiveGuard {
        self.lock(name).life.clone().write_owned().await
    }
}

/// Hard-link every file under `from` into the same place under `to`,
/// copying when a link is not possible (another file system). Temporary
/// files of writers in progress are skipped.
fn link_tree(from: &Path, to: &Path) -> std::io::Result<()> {
    std::fs::create_dir_all(to)?;
    for e in std::fs::read_dir(from)? {
        let e = e?;
        let name = e.file_name();
        let n = name.to_string_lossy();
        if n.starts_with("tmp-") || n.starts_with("sigs-tmp-") || n.contains(".tmp") {
            continue;
        }
        let (src, dst) = (e.path(), to.join(&name));
        if e.file_type()?.is_dir() {
            link_tree(&src, &dst)?;
        } else if !dst.exists() && std::fs::hard_link(&src, &dst).is_err() {
            std::fs::copy(&src, &dst)?;
        }
    }
    Ok(())
}