use std::ffi::OsStr;
use std::path::Path;

/// The final component of the path, if it is a normal file.
///
/// If the path terminates in ., .., or consists solely of a root of prefix,
/// file_name will return None.
#[cfg(unix)]
pub fn file_name<'a, P: AsRef<Path> + ?Sized>(
    path: &'a P,
) -> Option<&'a OsStr> {
    use std::os::unix::ffi::OsStrExt;
    use memchr::memrchr;

    let path = path.as_ref().as_os_str().as_bytes();
    if path.is_empty() {
        return None;
    } else if path.len() == 1 && path[0] == b'.' {
        return None;
    } else if path.last() == Some(&b'.') {
        return None;
    } else if path.len() >= 2 && &path[path.len() - 2..] == &b".."[..] {
        return None;
    }
    let last_slash = memrchr(b'/', path).map(|i| i + 1).unwrap_or(0);
    Some(OsStr::from_bytes(&path[last_slash..]))
}

/// The final component of the path, if it is a normal file.
///
/// If the path terminates in ., .., or consists solely of a root of prefix,
/// file_name will return None.
#[cfg(not(unix))]
pub fn file_name<'a, P: AsRef<Path> + ?Sized>(
    path: &'a P,
) -> Option<&'a OsStr> {
    path.as_ref().file_name()
}