// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package os_overloads

import (
	"os"
	"syscall"

	"golang.org/x/sys/windows"
)

func isAbs(path string) (b bool) {
	v := volumeName(path)
	if v == "" {
		return false
	}
	path = path[len(v):]
	if path == "" {
		return false
	}
	return os.IsPathSeparator(path[0])
}

func volumeName(path string) (v string) {
	if len(path) < 2 {
		return ""
	}
	// with drive letter
	c := path[0]
	if path[1] == ':' &&
		('0' <= c && c <= '9' || 'a' <= c && c <= 'z' ||
			'A' <= c && c <= 'Z') {
		return path[:2]
	}
	// is it UNC
	if l := len(path); l >= 5 && os.IsPathSeparator(path[0]) && os.IsPathSeparator(path[1]) &&
		!os.IsPathSeparator(path[2]) && path[2] != '.' {
		// first, leading `\\` and next shouldn't be `\`. its server name.
		for n := 3; n < l-1; n++ {
			// second, next '\' shouldn't be repeated.
			if os.IsPathSeparator(path[n]) {
				n++
				// third, following something characters. its share name.
				if !os.IsPathSeparator(path[n]) {
					if path[n] == '.' {
						break
					}
					for ; n < l; n++ {
						if os.IsPathSeparator(path[n]) {
							break
						}
					}
					return path[:n]
				}
				break
			}
		}
	}
	return ""
}

// fixLongPath returns the extended-length (\\?\-prefixed) form of
// path when needed, in order to avoid the default 260 character file
// path limit imposed by Windows. If path is not easily converted to
// the extended-length form (for example, if path is a relative path
// or contains .. elements), or is short enough, fixLongPath returns
// path unmodified.
//
// See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx#maxpath
func fixLongPath(path string) string {
	// Do nothing (and don't allocate) if the path is "short".
	// Empirically (at least on the Windows Server 2013 builder),
	// the kernel is arbitrarily okay with < 248 bytes. That
	// matches what the docs above say:
	// "When using an API to create a directory, the specified
	// path cannot be so long that you cannot append an 8.3 file
	// name (that is, the directory name cannot exceed MAX_PATH
	// minus 12)." Since MAX_PATH is 260, 260 - 12 = 248.
	//
	// The MSDN docs appear to say that a normal path that is 248 bytes long
	// will work; empirically the path must be less then 248 bytes long.
	if len(path) < 248 {
		// Don't fix. (This is how Go 1.7 and earlier worked,
		// not automatically generating the \\?\ form)
		return path
	}

	// The extended form begins with \\?\, as in
	// \\?\c:\windows\foo.txt or \\?\UNC\server\share\foo.txt.
	// The extended form disables evaluation of . and .. path
	// elements and disables the interpretation of / as equivalent
	// to \. The conversion here rewrites / to \ and elides
	// . elements as well as trailing or duplicate separators. For
	// simplicity it avoids the conversion entirely for relative
	// paths or paths containing .. elements. For now,
	// \\server\share paths are not converted to
	// \\?\UNC\server\share paths because the rules for doing so
	// are less well-specified.
	if len(path) >= 2 && path[:2] == `\\` {
		// Don't canonicalize UNC paths.
		return path
	}
	if !isAbs(path) {
		// Relative path
		return path
	}

	const prefix = `\\?`

	pathbuf := make([]byte, len(prefix)+len(path)+len(`\`))
	copy(pathbuf, prefix)
	n := len(path)
	r, w := 0, len(prefix)
	for r < n {
		switch {
		case os.IsPathSeparator(path[r]):
			// empty block
			r++
		case path[r] == '.' && (r+1 == n || os.IsPathSeparator(path[r+1])):
			// /./
			r++
		case r+1 < n && path[r] == '.' && path[r+1] == '.' && (r+2 == n || os.IsPathSeparator(path[r+2])):
			// /../ is currently unhandled
			return path
		default:
			pathbuf[w] = '\\'
			w++
			for ; r < n && !os.IsPathSeparator(path[r]); r++ {
				pathbuf[w] = path[r]
				w++
			}
		}
	}
	// A drive's root directory needs a trailing \
	if w == len(`\\?\c:`) {
		pathbuf[w] = '\\'
		w++
	}
	return string(pathbuf[:w])
}

// syscallMode returns the syscall-specific mode bits from Go's portable mode bits.
func syscallMode(i os.FileMode) (o uint32) {
	o |= uint32(i.Perm())
	if i&os.ModeSetuid != 0 {
		o |= syscall.S_ISUID
	}
	if i&os.ModeSetgid != 0 {
		o |= syscall.S_ISGID
	}
	if i&os.ModeSticky != 0 {
		o |= syscall.S_ISVTX
	}
	// No mapping for Go's ModeTemporary (plan9 only).
	return
}

//If the bool is set to true then the file is opened with the parameters FILE_ATTRIBUTE_TEMPORARY and
// FILE_FLAG_DELETE_ON_CLOSE
func OpenFile(name string, flag int, perm os.FileMode, setToTempAndDelete bool) (file *os.File, err error) {
	r, e := Open(fixLongPath(name), flag|windows.O_CLOEXEC, syscallMode(perm), setToTempAndDelete)
	if e != nil {
		return nil, e
	}
	return os.NewFile(uintptr(r), name), nil
}