//! Android's pinned std lacks file locks; retain identical advisory-lock semantics.
use std::{fs::File, io};

pub(crate) fn lock(file: &File) -> io::Result<()> {
    #[cfg(target_os = "android")]
    return rustix::fs::flock(file, rustix::fs::FlockOperation::LockExclusive).map_err(Into::into);
    #[cfg(not(target_os = "android"))]
    file.lock()
}

pub(crate) fn try_lock(file: &File) -> io::Result<()> {
    #[cfg(target_os = "android")]
    return rustix::fs::flock(file, rustix::fs::FlockOperation::NonBlockingLockExclusive)
        .map_err(Into::into);
    #[cfg(not(target_os = "android"))]
    file.try_lock().map_err(|error| match error {
        std::fs::TryLockError::WouldBlock => io::ErrorKind::WouldBlock.into(),
        std::fs::TryLockError::Error(error) => error,
    })
}

#[cfg(unix)]
pub(crate) fn directory(directory: &cap_std::fs::Dir) -> io::Result<File> {
    let file = directory.open(".")?.into_std();
    lock(&file)?;
    Ok(file)
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn independent_owners_contend_until_the_lock_is_dropped() {
        let temp = tempfile::tempdir().unwrap();
        let path = temp.path().join("owner.lock");
        let first = File::create(&path).unwrap();
        let second = File::open(&path).unwrap();
        lock(&first).unwrap();
        assert_eq!(
            try_lock(&second).unwrap_err().kind(),
            io::ErrorKind::WouldBlock
        );
        drop(first);
        try_lock(&second).unwrap();
    }
    #[cfg(unix)]
    #[test]
    fn directory_gate_covers_file_creation_before_its_owner_lock() {
        let root = tempfile::tempdir().unwrap();
        let dir =
            cap_std::fs::Dir::open_ambient_dir(root.path(), cap_std::ambient_authority()).unwrap();
        let first = directory(&dir).unwrap();
        let second = dir.open(".").unwrap().into_std();
        assert_eq!(
            try_lock(&second).unwrap_err().kind(),
            io::ErrorKind::WouldBlock
        );
        drop(first);
        try_lock(&second).unwrap();
    }
}