use std::io;
use std::mem;
use std::ffi::{OsString, CStr};
use std::fs::{File, read_link};
use std::os::unix::io::{AsRawFd, RawFd, FromRawFd, IntoRawFd};
use std::os::unix::ffi::{OsStringExt};
use std::path::{PathBuf};

use libc;
use crate::metadata::{self, Metadata};
use crate::list::{DirIter, open_dir, open_dirfd};

use crate::{Dir, AsPath};

#[cfg(target_os="linux")]
const BASE_OPEN_FLAGS: libc::c_int = libc::O_PATH|libc::O_CLOEXEC;
#[cfg(target_os="freebsd")]
const BASE_OPEN_FLAGS: libc::c_int = libc::O_DIRECTORY|libc::O_CLOEXEC;
#[cfg(not(any(target_os="linux", target_os="freebsd")))]
const BASE_OPEN_FLAGS: libc::c_int = libc::O_CLOEXEC;

impl Dir {
    /// Creates a directory descriptor that resolves paths relative to current
    /// working directory (AT_FDCWD)
    #[deprecated(since="0.1.15", note="\
        Use `Dir::open(\".\")` instead. \
        Dir::cwd() doesn't open actual file descriptor and uses magic value \
        instead which resolves to current dir on any syscall invocation. \
        This is usually counter-intuitive and yields a broken \
        file descriptor when using `Dir::as_raw_fd`. \
        Will be removed in version v0.2 of the library.")]
    pub fn cwd() -> Dir {
        Dir(libc::AT_FDCWD)
    }

    /// Open a directory descriptor at specified path
    // TODO(tailhook) maybe accept only absolute paths?
    pub fn open<P: AsPath>(path: P) -> io::Result<Dir> {
        Dir::_open(to_cstr(path)?.as_ref())
    }

    fn _open(path: &CStr) -> io::Result<Dir> {
        let fd = unsafe {
            libc::open(path.as_ptr(), BASE_OPEN_FLAGS)
        };
        if fd < 0 {
            Err(io::Error::last_os_error())
        } else {
            Ok(Dir(fd))
        }
    }

    /// List subdirectory of this dir
    ///
    /// You can list directory itself with `list_self`.
    pub fn list_dir<P: AsPath>(&self, path: P) -> io::Result<DirIter> {
        open_dir(self, to_cstr(path)?.as_ref())
    }

    /// List this dir
    pub fn list_self(&self) -> io::Result<DirIter> {
        unsafe {
            open_dirfd(libc::dup(self.0))
        }
    }

    /// Open subdirectory
    ///
    /// Note that this method does not resolve symlinks by default, so you may have to call
    /// [`read_link`] to resolve the real path first.
    ///
    /// [`read_link`]: #method.read_link
    pub fn sub_dir<P: AsPath>(&self, path: P) -> io::Result<Dir> {
        self._sub_dir(to_cstr(path)?.as_ref())
    }

    fn _sub_dir(&self, path: &CStr) -> io::Result<Dir> {
        let fd = unsafe {
            libc::openat(self.0,
                        path.as_ptr(),
                        BASE_OPEN_FLAGS|libc::O_NOFOLLOW)
        };
        if fd < 0 {
            Err(io::Error::last_os_error())
        } else {
            Ok(Dir(fd))
        }
    }

    /// Read link in this directory
    pub fn read_link<P: AsPath>(&self, path: P) -> io::Result<PathBuf> {
        self._read_link(to_cstr(path)?.as_ref())
    }

    fn _read_link(&self, path: &CStr) -> io::Result<PathBuf> {
        let mut buf = vec![0u8; 4096];
        let res = unsafe {
            libc::readlinkat(self.0,
                        path.as_ptr(),
                        buf.as_mut_ptr() as *mut libc::c_char, buf.len())
        };
        if res < 0 {
            Err(io::Error::last_os_error())
        } else {
            buf.truncate(res as usize);
            Ok(OsString::from_vec(buf).into())
        }
    }

    /// Open file for reading in this directory
    ///
    /// Note that this method does not resolve symlinks by default, so you may have to call
    /// [`read_link`] to resolve the real path first.
    ///
    /// [`read_link`]: #method.read_link
    pub fn open_file<P: AsPath>(&self, path: P) -> io::Result<File> {
        self._open_file(to_cstr(path)?.as_ref(),
            libc::O_RDONLY, 0)
    }

    /// Open file for writing, create if necessary, truncate on open
    ///
    /// If there exists a symlink at the destination path, this method will fail. In that case, you
    /// will need to remove the symlink before calling this method. If you are on Linux, you can
    /// alternatively create an unnamed file with [`new_unnamed_file`] and then rename it,
    /// clobbering the symlink at the destination.
    ///
    /// [`new_unnamed_file`]: #method.new_unnamed_file
    pub fn write_file<P: AsPath>(&self, path: P, mode: libc::mode_t)
        -> io::Result<File>
    {
        self._open_file(to_cstr(path)?.as_ref(),
            libc::O_CREAT|libc::O_WRONLY|libc::O_TRUNC,
            mode)
    }

    /// Open file for append, create if necessary
    ///
    /// If there exists a symlink at the destination path, this method will fail. In that case, you
    /// will need to call [`read_link`] to resolve the real path first.
    ///
    /// [`read_link`]: #method.read_link
    pub fn append_file<P: AsPath>(&self, path: P, mode: libc::mode_t)
        -> io::Result<File>
    {
        self._open_file(to_cstr(path)?.as_ref(),
            libc::O_CREAT|libc::O_WRONLY|libc::O_APPEND,
            mode)
    }

    /// Create file for writing (and truncate) in this directory
    ///
    /// Deprecated alias for `write_file`
    ///
    /// If there exists a symlink at the destination path, this method will fail. In that case, you
    /// will need to remove the symlink before calling this method. If you are on Linux, you can
    /// alternatively create an unnamed file with [`new_unnamed_file`] and then rename it,
    /// clobbering the symlink at the destination.
    ///
    /// [`new_unnamed_file`]: #method.new_unnamed_file
    #[deprecated(since="0.1.7", note="please use `write_file` instead")]
    pub fn create_file<P: AsPath>(&self, path: P, mode: libc::mode_t)
        -> io::Result<File>
    {
        self._open_file(to_cstr(path)?.as_ref(),
            libc::O_CREAT|libc::O_WRONLY|libc::O_TRUNC,
            mode)
    }

    /// Create a tmpfile in this directory which isn't linked to any filename
    ///
    /// This works by passing `O_TMPFILE` into the openat call. The flag is
    /// supported only on linux. So this function always returns error on
    /// such systems.
    ///
    /// **WARNING!** On glibc < 2.22 file permissions of the newly created file
    /// may be arbitrary. Consider chowning after creating a file.
    ///
    /// Note: It may be unclear why creating unnamed file requires a dir. There
    /// are two reasons:
    ///
    /// 1. It's created (and occupies space) on a real filesystem, so the
    ///    directory is a way to find out which filesystem to attach file to
    /// 2. This method is mostly needed to initialize the file then link it
    ///    using ``link_file_at`` to the real directory entry. When linking
    ///    it must be linked into the same filesystem. But because for most
    ///    programs finding out filesystem layout is an overkill the rule of
    ///    thumb is to create a file in the the target directory.
    ///
    /// Currently, we recommend to fallback on any error if this operation
    /// can't be accomplished rather than relying on specific error codes,
    /// because semantics of errors are very ugly.
    #[cfg(target_os="linux")]
    pub fn new_unnamed_file(&self, mode: libc::mode_t)
        -> io::Result<File>
    {
        self._open_file(unsafe { CStr::from_bytes_with_nul_unchecked(b".\0") },
            libc::O_TMPFILE|libc::O_WRONLY,
            mode)
    }

    /// Create a tmpfile in this directory which isn't linked to any filename
    ///
    /// This works by passing `O_TMPFILE` into the openat call. The flag is
    /// supported only on linux. So this function always returns error on
    /// such systems.
    ///
    /// Note: It may be unclear why creating unnamed file requires a dir. There
    /// are two reasons:
    ///
    /// 1. It's created (and occupies space) on a real filesystem, so the
    ///    directory is a way to find out which filesystem to attach file to
    /// 2. This method is mostly needed to initialize the file then link it
    ///    using ``link_file_at`` to the real directory entry. When linking
    ///    it must be linked into the same filesystem. But because for most
    ///    programs finding out filesystem layout is an overkill the rule of
    ///    thumb is to create a file in the the target directory.
    ///
    /// Currently, we recommend to fallback on any error if this operation
    /// can't be accomplished rather than relying on specific error codes,
    /// because semantics of errors are very ugly.
    #[cfg(not(target_os="linux"))]
    pub fn new_unnamed_file<P: AsPath>(&self, _mode: libc::mode_t)
        -> io::Result<File>
    {
        Err(io::Error::new(io::ErrorKind::Other,
            "creating unnamed tmpfiles is only supported on linux"))
    }

    /// Link open file to a specified path
    ///
    /// This is used with ``new_unnamed_file()`` to create and initialize the
    /// file before linking it into a filesystem. This requires `/proc` to be
    /// mounted and works **only on linux**.
    ///
    /// On systems other than linux this always returns error. It's expected
    /// that in most cases this methos is not called if ``new_unnamed_file``
    /// fails. But in obscure scenarios where `/proc` is not mounted this
    /// method may fail even on linux. So your code should be able to fallback
    /// to a named file if this method fails too.
    #[cfg(target_os="linux")]
    pub fn link_file_at<F: AsRawFd, P: AsPath>(&self, file: &F, path: P)
        -> io::Result<()>
    {
        let fd_path = format!("/proc/self/fd/{}", file.as_raw_fd());
        _hardlink(&Dir(libc::AT_FDCWD), to_cstr(fd_path)?.as_ref(),
            &self, to_cstr(path)?.as_ref(),
            libc::AT_SYMLINK_FOLLOW)
    }

    /// Link open file to a specified path
    ///
    /// This is used with ``new_unnamed_file()`` to create and initialize the
    /// file before linking it into a filesystem. This requires `/proc` to be
    /// mounted and works **only on linux**.
    ///
    /// On systems other than linux this always returns error. It's expected
    /// that in most cases this methos is not called if ``new_unnamed_file``
    /// fails. But in obscure scenarios where `/proc` is not mounted this
    /// method may fail even on linux. So your code should be able to fallback
    /// to a named file if this method fails too.
    #[cfg(not(target_os="linux"))]
    pub fn link_file_at<F: AsRawFd, P: AsPath>(&self, _file: F, _path: P)
        -> io::Result<()>
    {
        Err(io::Error::new(io::ErrorKind::Other,
            "linking unnamed fd to directories is only supported on linux"))
    }

    /// Create file if not exists, fail if exists
    ///
    /// This function checks existence and creates file atomically with
    /// respect to other threads and processes.
    ///
    /// Technically it means passing `O_EXCL` flag to open.
    pub fn new_file<P: AsPath>(&self, path: P, mode: libc::mode_t)
        -> io::Result<File>
    {
        self._open_file(to_cstr(path)?.as_ref(),
            libc::O_CREAT|libc::O_EXCL|libc::O_WRONLY,
            mode)
    }

    /// Open file for reading and writing without truncation, create if needed
    ///
    /// If there exists a symlink at the destination path, this method will fail. In that case, you
    /// will need to call [`read_link`] to resolve the real path first.
    ///
    /// [`read_link`]: #method.read_link
    pub fn update_file<P: AsPath>(&self, path: P, mode: libc::mode_t)
        -> io::Result<File>
    {
        self._open_file(to_cstr(path)?.as_ref(),
            libc::O_CREAT|libc::O_RDWR,
            mode)
    }

    fn _open_file(&self, path: &CStr, flags: libc::c_int, mode: libc::mode_t)
        -> io::Result<File>
    {
        unsafe {
            // Note: In below call to `openat`, *mode* must be cast to
            // `unsigned` because the optional `mode` argument to `openat` is
            // variadic in the signature. Since integers are not implicitly
            // promoted as they are in C this would break on Freebsd where
            // *mode_t* is an alias for `uint16_t`.
            let res = libc::openat(self.0, path.as_ptr(),
                            flags|libc::O_CLOEXEC|libc::O_NOFOLLOW,
                            mode as libc::c_uint);
            if res < 0 {
                Err(io::Error::last_os_error())
            } else {
                Ok(File::from_raw_fd(res))
            }
        }
    }

    /// Make a symlink in this directory
    ///
    /// Note: the order of arguments differ from `symlinkat`
    pub fn symlink<P: AsPath, R: AsPath>(&self, path: P, value: R)
        -> io::Result<()>
    {
        self._symlink(to_cstr(path)?.as_ref(), to_cstr(value)?.as_ref())
    }
    fn _symlink(&self, path: &CStr, link: &CStr) -> io::Result<()> {
        unsafe {
            let res = libc::symlinkat(link.as_ptr(),
                self.0, path.as_ptr());
            if res < 0 {
                Err(io::Error::last_os_error())
            } else {
                Ok(())
            }
        }
    }

    /// Create a subdirectory in this directory
    pub fn create_dir<P: AsPath>(&self, path: P, mode: libc::mode_t)
        -> io::Result<()>
    {
        self._create_dir(to_cstr(path)?.as_ref(), mode)
    }
    fn _create_dir(&self, path: &CStr, mode: libc::mode_t) -> io::Result<()> {
        unsafe {
            let res = libc::mkdirat(self.0, path.as_ptr(), mode);
            if res < 0 {
                Err(io::Error::last_os_error())
            } else {
                Ok(())
            }
        }
    }

    /// Rename a file in this directory to another name (keeping same dir)
    pub fn local_rename<P: AsPath, R: AsPath>(&self, old: P, new: R)
        -> io::Result<()>
    {
        rename(self, to_cstr(old)?.as_ref(), self, to_cstr(new)?.as_ref())
    }

    /// Similar to `local_rename` but atomically swaps both paths
    ///
    /// Only supported on Linux.
    #[cfg(target_os="linux")]
    pub fn local_exchange<P: AsPath, R: AsPath>(&self, old: P, new: R)
        -> io::Result<()>
    {
        // Workaround https://github.com/tailhook/openat/issues/35
        // AKA https://github.com/rust-lang/libc/pull/2116
        // Unfortunately since we made this libc::c_int in our
        // public API, we can't easily change it right now.
        let flags = libc::RENAME_EXCHANGE as libc::c_int;
        rename_flags(self, to_cstr(old)?.as_ref(),
            self, to_cstr(new)?.as_ref(),
            flags)
    }

    /// Remove a subdirectory in this directory
    ///
    /// Note only empty directory may be removed
    pub fn remove_dir<P: AsPath>(&self, path: P)
        -> io::Result<()>
    {
        self._unlink(to_cstr(path)?.as_ref(), libc::AT_REMOVEDIR)
    }
    /// Remove a file in this directory
    pub fn remove_file<P: AsPath>(&self, path: P)
        -> io::Result<()>
    {
        self._unlink(to_cstr(path)?.as_ref(), 0)
    }
    fn _unlink(&self, path: &CStr, flags: libc::c_int) -> io::Result<()> {
        unsafe {
            let res = libc::unlinkat(self.0, path.as_ptr(), flags);
            if res < 0 {
                Err(io::Error::last_os_error())
            } else {
                Ok(())
            }
        }
    }

    /// Get the path of this directory (if possible)
    ///
    /// This uses symlinks in `/proc/self`, they sometimes may not be
    /// available so use with care.
    pub fn recover_path(&self) -> io::Result<PathBuf> {
        let fd = self.0;
        if fd != libc::AT_FDCWD {
            read_link(format!("/proc/self/fd/{}", fd))
        } else {
            read_link("/proc/self/cwd")
        }
    }

    /// Returns metadata of an entry in this directory
    ///
    /// If the destination path is a symlink, this will return the metadata of the symlink itself.
    /// If you would like to follow the symlink and return the metadata of the target, you will
    /// have to call [`read_link`] to resolve the real path first.
    ///
    /// [`read_link`]: #method.read_link
    pub fn metadata<P: AsPath>(&self, path: P) -> io::Result<Metadata> {
        self._stat(to_cstr(path)?.as_ref(), libc::AT_SYMLINK_NOFOLLOW)
    }
    fn _stat(&self, path: &CStr, flags: libc::c_int) -> io::Result<Metadata> {
        unsafe {
            let mut stat = mem::zeroed();
            let res = libc::fstatat(self.0, path.as_ptr(),
                &mut stat, flags);
            if res < 0 {
                Err(io::Error::last_os_error())
            } else {
                Ok(metadata::new(stat))
            }
        }
    }

    /// Returns the metadata of the directory itself.
    pub fn self_metadata(&self) -> io::Result<Metadata> {
        unsafe {
            let mut stat = mem::zeroed();
            let res = libc::fstat(self.0, &mut stat);
            if res < 0 {
                Err(io::Error::last_os_error())
            } else {
                Ok(metadata::new(stat))
            }
        }
    }

    /// Constructs a new `Dir` from a given raw file descriptor,
    /// ensuring it is a directory file descriptor first.
    ///
    /// This function **consumes ownership** of the specified file
    /// descriptor. The returned `Dir` will take responsibility for
    /// closing it when it goes out of scope.
    pub unsafe fn from_raw_fd_checked(fd: RawFd) -> io::Result<Self> {
        let mut stat = mem::zeroed();
        let res = libc::fstat(fd, &mut stat);
        if res < 0 {
            Err(io::Error::last_os_error())
        } else {
            match stat.st_mode & libc::S_IFMT {
                libc::S_IFDIR => Ok(Dir(fd)),
                _ => Err(io::Error::from_raw_os_error(libc::ENOTDIR))
            }
        }
    }

    /// Creates a new independently owned handle to the underlying directory.
    pub fn try_clone(&self) -> io::Result<Self> {
        let fd = unsafe { libc::dup(self.0) };
        if fd == -1 {
            Err(io::Error::last_os_error())
        } else {
            unsafe { Self::from_raw_fd_checked(fd) }
        }
    }
}

/// Rename (move) a file between directories
///
/// Files must be on a single filesystem anyway. This funtion does **not**
/// fallback to copying if needed.
pub fn rename<P, R>(old_dir: &Dir, old: P, new_dir: &Dir, new: R)
    -> io::Result<()>
    where P: AsPath, R: AsPath,
{
    _rename(old_dir, to_cstr(old)?.as_ref(), new_dir, to_cstr(new)?.as_ref())
}

fn _rename(old_dir: &Dir, old: &CStr, new_dir: &Dir, new: &CStr)
    -> io::Result<()>
{
    unsafe {
        let res = libc::renameat(old_dir.0, old.as_ptr(),
            new_dir.0, new.as_ptr());
        if res < 0 {
            Err(io::Error::last_os_error())
        } else {
            Ok(())
        }
    }
}

/// Create a hardlink to a file
///
/// Files must be on a single filesystem even if they are in different
/// directories.
///
/// Note: by default ``linkat`` syscall doesn't resolve symbolic links, and
/// it's also behavior of this function. It's recommended to resolve symlinks
/// manually if needed.
pub fn hardlink<P, R>(old_dir: &Dir, old: P, new_dir: &Dir, new: R)
    -> io::Result<()>
    where P: AsPath, R: AsPath,
{
    _hardlink(old_dir, to_cstr(old)?.as_ref(),
              new_dir, to_cstr(new)?.as_ref(),
              0)
}

fn _hardlink(old_dir: &Dir, old: &CStr, new_dir: &Dir, new: &CStr,
             flags: libc::c_int)
    -> io::Result<()>
{
    unsafe {
        let res = libc::linkat(old_dir.0, old.as_ptr(),
            new_dir.0, new.as_ptr(), flags);
        if res < 0 {
            Err(io::Error::last_os_error())
        } else {
            Ok(())
        }
    }
}

/// Rename (move) a file between directories with flags
///
/// Files must be on a single filesystem anyway. This funtion does **not**
/// fallback to copying if needed.
///
/// Only supported on Linux.
#[cfg(target_os="linux")]
pub fn rename_flags<P, R>(old_dir: &Dir, old: P, new_dir: &Dir, new: R,
    flags: libc::c_int)
    -> io::Result<()>
    where P: AsPath, R: AsPath,
{
    _rename_flags(old_dir, to_cstr(old)?.as_ref(),
        new_dir, to_cstr(new)?.as_ref(),
        flags)
}

#[cfg(target_os="linux")]
fn _rename_flags(old_dir: &Dir, old: &CStr, new_dir: &Dir, new: &CStr,
    flags: libc::c_int)
    -> io::Result<()>
{
    unsafe {
        let res = libc::syscall(
            libc::SYS_renameat2,
            old_dir.0, old.as_ptr(),
            new_dir.0, new.as_ptr(), flags);
        if res < 0 {
            Err(io::Error::last_os_error())
        } else {
            Ok(())
        }
    }
}

impl AsRawFd for Dir {
    #[inline]
    fn as_raw_fd(&self) -> RawFd {
        self.0
    }
}

impl FromRawFd for Dir {
    /// The user must guarantee that the passed in `RawFd` is in fact
    /// a directory file descriptor.
    #[inline]
    unsafe fn from_raw_fd(fd: RawFd) -> Dir {
        Dir(fd)
    }
}

impl IntoRawFd for Dir {
    #[inline]
    fn into_raw_fd(self) -> RawFd {
        let result = self.0;
        mem::forget(self);
        return result;
    }
}

impl Drop for Dir {
    fn drop(&mut self) {
        let fd = self.0;
        if fd != libc::AT_FDCWD {
            unsafe {
                libc::close(fd);
            }
        }
    }
}

fn to_cstr<P: AsPath>(path: P) -> io::Result<P::Buffer> {
    path.to_path()
    .ok_or_else(|| {
        io::Error::new(io::ErrorKind::InvalidInput,
                       "nul byte in file name")
    })
}

#[cfg(test)]
mod test {
    use std::io::{Read};
    use std::path::Path;
    use std::os::unix::io::{FromRawFd, IntoRawFd};
    use crate::{Dir};

    #[test]
    fn test_open_ok() {
        assert!(Dir::open("src").is_ok());
    }

    #[test]
    #[cfg_attr(target_os="freebsd", should_panic(expected="Not a directory"))]
    fn test_open_file() {
        Dir::open("src/lib.rs").unwrap();
    }

    #[test]
    fn test_read_file() {
        let dir = Dir::open("src").unwrap();
        let mut buf = String::new();
        dir.open_file("lib.rs").unwrap()
            .read_to_string(&mut buf).unwrap();
        assert!(buf.find("extern crate libc;").is_some());
    }

    #[test]
    fn test_from_into() {
        let dir = Dir::open("src").unwrap();
        let dir = unsafe { Dir::from_raw_fd(dir.into_raw_fd()) };
        let mut buf = String::new();
        dir.open_file("lib.rs").unwrap()
            .read_to_string(&mut buf).unwrap();
        assert!(buf.find("extern crate libc;").is_some());
    }

    #[test]
    #[should_panic(expected="No such file or directory")]
    fn test_open_no_dir() {
        Dir::open("src/some-non-existent-file").unwrap();
    }

    #[test]
    fn test_list() {
        let dir = Dir::open("src").unwrap();
        let me = dir.list_dir(".").unwrap();
        assert!(me.collect::<Result<Vec<_>, _>>().unwrap()
                .iter().find(|x| {
                    x.file_name() == Path::new("lib.rs").as_os_str()
                })
                .is_some());
    }

    #[test]
    fn test_from_raw_fd_checked() {
        let fd = Dir::open(".").unwrap().into_raw_fd();
        let dir = unsafe { Dir::from_raw_fd_checked(fd) }.unwrap();
        let filefd = dir.open_file("src/lib.rs").unwrap().into_raw_fd();
        match unsafe { Dir::from_raw_fd_checked(filefd) } {
            Ok(_) => assert!(false, "from_raw_fd_checked succeeded on a non-directory fd!"),
            Err(e) => assert_eq!(e.raw_os_error().unwrap(), libc::ENOTDIR)
        }
    }

    #[test]
    fn test_try_clone() {
        let d = Dir::open(".").unwrap();
        let d2 = d.try_clone().unwrap();
        drop(d);
        let _file = d2.open_file("src/lib.rs").unwrap();
    }
}