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use std::ffi::CString;
use std::fs;
use std::io;
use std::path::{Path, PathBuf};

// Unfortunately, on windows, it looks like msvcrt.dll is silently translating
// verbatim paths under the hood to non-verbatim paths! This manifests itself as
// gcc looking like it cannot accept paths of the form `\\?\C:\...`, but the
// real bug seems to lie in msvcrt.dll.
//
// Verbatim paths are generally pretty rare, but the implementation of
// `fs::canonicalize` currently generates paths of this form, meaning that we're
// going to be passing quite a few of these down to gcc, so we need to deal with
// this case.
//
// For now we just strip the "verbatim prefix" of `\\?\` from the path. This
// will probably lose information in some cases, but there's not a whole lot
// more we can do with a buggy msvcrt...
//
// For some more information, see this comment:
//   https://github.com/rust-lang/rust/issues/25505#issuecomment-102876737
#[cfg(windows)]
pub fn fix_windows_verbatim_for_gcc(p: &Path) -> PathBuf {
    use std::ffi::OsString;
    use std::path;
    let mut components = p.components();
    let prefix = match components.next() {
        Some(path::Component::Prefix(p)) => p,
        _ => return p.to_path_buf(),
    };
    match prefix.kind() {
        path::Prefix::VerbatimDisk(disk) => {
            let mut base = OsString::from(format!("{}:", disk as char));
            base.push(components.as_path());
            PathBuf::from(base)
        }
        path::Prefix::VerbatimUNC(server, share) => {
            let mut base = OsString::from(r"\\");
            base.push(server);
            base.push(r"\");
            base.push(share);
            base.push(components.as_path());
            PathBuf::from(base)
        }
        _ => p.to_path_buf(),
    }
}

#[cfg(not(windows))]
pub fn fix_windows_verbatim_for_gcc(p: &Path) -> PathBuf {
    p.to_path_buf()
}

pub enum LinkOrCopy {
    Link,
    Copy,
}

/// Copies `p` into `q`, preferring to use hard-linking if possible. If
/// `q` already exists, it is removed first.
/// The result indicates which of the two operations has been performed.
pub fn link_or_copy<P: AsRef<Path>, Q: AsRef<Path>>(p: P, q: Q) -> io::Result<LinkOrCopy> {
    let p = p.as_ref();
    let q = q.as_ref();
    match fs::remove_file(&q) {
        Ok(()) => (),
        Err(err) if err.kind() == io::ErrorKind::NotFound => (),
        Err(err) => return Err(err),
    }

    match fs::hard_link(p, q) {
        Ok(()) => Ok(LinkOrCopy::Link),
        Err(_) => match fs::copy(p, q) {
            Ok(_) => Ok(LinkOrCopy::Copy),
            Err(e) => Err(e),
        },
    }
}

#[cfg(unix)]
pub fn path_to_c_string(p: &Path) -> CString {
    use std::ffi::OsStr;
    use std::os::unix::ffi::OsStrExt;
    let p: &OsStr = p.as_ref();
    CString::new(p.as_bytes()).unwrap()
}
#[cfg(windows)]
pub fn path_to_c_string(p: &Path) -> CString {
    CString::new(p.to_str().unwrap()).unwrap()
}