use std::env;
use std::ffi::OsStr;
use std::fs::{self, File, OpenOptions};
use std::io;
cfg_if::cfg_if! {
    if #[cfg(not(target_os = "wasi"))] {
        use std::os::unix::fs::{MetadataExt, OpenOptionsExt};
    } else {
        #[cfg(feature = "nightly")]
        use std::os::wasi::fs::MetadataExt;
    }
}
use crate::util;
use std::path::Path;

#[cfg(not(target_os = "redox"))]
use rustix::fs::{cwd, linkat, renameat, unlinkat, AtFlags};

pub fn create_named(path: &Path, open_options: &mut OpenOptions) -> io::Result<File> {
    open_options.read(true).write(true).create_new(true);

    #[cfg(not(target_os = "wasi"))]
    {
        open_options.mode(0o600);
    }

    open_options.open(path)
}

fn create_unlinked(path: &Path) -> io::Result<File> {
    let tmp;
    // shadow this to decrease the lifetime. It can't live longer than `tmp`.
    let mut path = path;
    if !path.is_absolute() {
        let cur_dir = env::current_dir()?;
        tmp = cur_dir.join(path);
        path = &tmp;
    }

    let f = create_named(path, &mut OpenOptions::new())?;
    // don't care whether the path has already been unlinked,
    // but perhaps there are some IO error conditions we should send up?
    let _ = fs::remove_file(path);
    Ok(f)
}

#[cfg(target_os = "linux")]
pub fn create(dir: &Path) -> io::Result<File> {
    use rustix::{fs::OFlags, io::Errno};
    OpenOptions::new()
        .read(true)
        .write(true)
        .custom_flags(OFlags::TMPFILE.bits() as i32) // do not mix with `create_new(true)`
        .open(dir)
        .or_else(|e| {
            match Errno::from_io_error(&e) {
                // These are the three "not supported" error codes for O_TMPFILE.
                Some(Errno::OPNOTSUPP) | Some(Errno::ISDIR) | Some(Errno::NOENT) => {
                    create_unix(dir)
                }
                _ => Err(e),
            }
        })
}

#[cfg(not(target_os = "linux"))]
pub fn create(dir: &Path) -> io::Result<File> {
    create_unix(dir)
}

fn create_unix(dir: &Path) -> io::Result<File> {
    util::create_helper(
        dir,
        OsStr::new(".tmp"),
        OsStr::new(""),
        crate::NUM_RAND_CHARS,
        |path| create_unlinked(&path),
    )
}

#[cfg(any(not(target_os = "wasi"), feature = "nightly"))]
pub fn reopen(file: &File, path: &Path) -> io::Result<File> {
    let new_file = OpenOptions::new().read(true).write(true).open(path)?;
    let old_meta = file.metadata()?;
    let new_meta = new_file.metadata()?;
    if old_meta.dev() != new_meta.dev() || old_meta.ino() != new_meta.ino() {
        return Err(io::Error::new(
            io::ErrorKind::NotFound,
            "original tempfile has been replaced",
        ));
    }
    Ok(new_file)
}

#[cfg(all(target_os = "wasi", not(feature = "nightly")))]
pub fn reopen(_file: &File, _path: &Path) -> io::Result<File> {
    return Err(io::Error::new(
        io::ErrorKind::Other,
        "this operation is supported on WASI only on nightly Rust (with `nightly` feature enabled)",
    ));
}

#[cfg(not(target_os = "redox"))]
pub fn persist(old_path: &Path, new_path: &Path, overwrite: bool) -> io::Result<()> {
    if overwrite {
        renameat(cwd(), old_path, cwd(), new_path)?;
    } else {
        // On Linux, use `renameat_with` to avoid overwriting an existing name,
        // if the kernel and the filesystem support it.
        #[cfg(any(target_os = "android", target_os = "linux"))]
        {
            use rustix::fs::{renameat_with, RenameFlags};
            use rustix::io::Errno;
            use std::sync::atomic::{AtomicBool, Ordering::Relaxed};

            static NOSYS: AtomicBool = AtomicBool::new(false);
            if !NOSYS.load(Relaxed) {
                match renameat_with(cwd(), old_path, cwd(), new_path, RenameFlags::NOREPLACE) {
                    Ok(()) => return Ok(()),
                    Err(Errno::NOSYS) => NOSYS.store(true, Relaxed),
                    Err(Errno::INVAL) => {}
                    Err(e) => return Err(e.into()),
                }
            }
        }

        // Otherwise use `linkat` to create the new filesystem name, which
        // will fail if the name already exists, and then `unlinkat` to remove
        // the old name.
        linkat(cwd(), old_path, cwd(), new_path, AtFlags::empty())?;
        // Ignore unlink errors. Can we do better?
        let _ = unlinkat(cwd(), old_path, AtFlags::empty());
    }
    Ok(())
}

#[cfg(target_os = "redox")]
pub fn persist(old_path: &Path, new_path: &Path, overwrite: bool) -> io::Result<()> {
    // XXX implement when possible
    Err(io::Error::from_raw_os_error(syscall::ENOSYS))
}

pub fn keep(_: &Path) -> io::Result<()> {
    Ok(())
}
