// Copyright 2011 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

import (
	"runtime"
	"syscall"
	"time"
)

// File represents an open file descriptor.
type File struct {
	*file
}

// file is the real representation of *File.
// The extra level of indirection ensures that no clients of os
// can overwrite this data, which could cause the finalizer
// to close the wrong file descriptor.
type file struct {
	fd      int
	name    string
	dirinfo *dirInfo // nil unless directory being read
}

// Fd returns the integer Unix file descriptor referencing the open file.
func (f *File) Fd() uintptr {
	if f == nil {
		return ^(uintptr(0))
	}
	return uintptr(f.fd)
}

// NewFile returns a new File with the given file descriptor and name.
func NewFile(fd uintptr, name string) *File {
	fdi := int(fd)
	if fdi < 0 {
		return nil
	}
	f := &File{&file{fd: fdi, name: name}}
	runtime.SetFinalizer(f.file, (*file).close)
	return f
}

// Auxiliary information if the File describes a directory
type dirInfo struct {
	buf  [syscall.STATMAX]byte // buffer for directory I/O
	nbuf int                   // length of buf; return value from Read
	bufp int                   // location of next record in buf.
}

func epipecheck(file *File, e error) {
}

// DevNull is the name of the operating system's ``null device.''
// On Unix-like systems, it is "/dev/null"; on Windows, "NUL".
const DevNull = "/dev/null"

// syscallMode returns the syscall-specific mode bits from Go's portable mode bits.
func syscallMode(i FileMode) (o uint32) {
	o |= uint32(i.Perm())
	if i&ModeAppend != 0 {
		o |= syscall.DMAPPEND
	}
	if i&ModeExclusive != 0 {
		o |= syscall.DMEXCL
	}
	if i&ModeTemporary != 0 {
		o |= syscall.DMTMP
	}
	return
}

// OpenFile is the generalized open call; most users will use Open
// or Create instead.  It opens the named file with specified flag
// (O_RDONLY etc.) and perm, (0666 etc.) if applicable.  If successful,
// methods on the returned File can be used for I/O.
// If there is an error, it will be of type *PathError.
func OpenFile(name string, flag int, perm FileMode) (file *File, err error) {
	var (
		fd     int
		e      error
		create bool
		excl   bool
		trunc  bool
		append bool
	)

	if flag&O_CREATE == O_CREATE {
		flag = flag & ^O_CREATE
		create = true
	}
	if flag&O_EXCL == O_EXCL {
		excl = true
	}
	if flag&O_TRUNC == O_TRUNC {
		trunc = true
	}
	// O_APPEND is emulated on Plan 9
	if flag&O_APPEND == O_APPEND {
		flag = flag &^ O_APPEND
		append = true
	}

	if (create && trunc) || excl {
		fd, e = syscall.Create(name, flag, syscallMode(perm))
	} else {
		fd, e = syscall.Open(name, flag)
		if e != nil && create {
			var e1 error
			fd, e1 = syscall.Create(name, flag, syscallMode(perm))
			if e1 == nil {
				e = nil
			}
		}
	}

	if e != nil {
		return nil, &PathError{"open", name, e}
	}

	if append {
		if _, e = syscall.Seek(fd, 0, SEEK_END); e != nil {
			return nil, &PathError{"seek", name, e}
		}
	}

	return NewFile(uintptr(fd), name), nil
}

// Close closes the File, rendering it unusable for I/O.
// It returns an error, if any.
func (f *File) Close() error {
	if f == nil {
		return ErrInvalid
	}
	return f.file.close()
}

func (file *file) close() error {
	if file == nil || file.fd < 0 {
		return ErrInvalid
	}
	var err error
	syscall.ForkLock.RLock()
	if e := syscall.Close(file.fd); e != nil {
		err = &PathError{"close", file.name, e}
	}
	syscall.ForkLock.RUnlock()
	file.fd = -1 // so it can't be closed again

	// no need for a finalizer anymore
	runtime.SetFinalizer(file, nil)
	return err
}

// Stat returns the FileInfo structure describing file.
// If there is an error, it will be of type *PathError.
func (f *File) Stat() (fi FileInfo, err error) {
	if f == nil {
		return nil, ErrInvalid
	}
	d, err := dirstat(f)
	if err != nil {
		return nil, err
	}
	return fileInfoFromStat(d), nil
}

// Truncate changes the size of the file.
// It does not change the I/O offset.
// If there is an error, it will be of type *PathError.
func (f *File) Truncate(size int64) error {
	if f == nil {
		return ErrInvalid
	}

	var d syscall.Dir
	d.Null()
	d.Length = size

	var buf [syscall.STATFIXLEN]byte
	n, err := d.Marshal(buf[:])
	if err != nil {
		return &PathError{"truncate", f.name, err}
	}
	if err = syscall.Fwstat(f.fd, buf[:n]); err != nil {
		return &PathError{"truncate", f.name, err}
	}
	return nil
}

const chmodMask = uint32(syscall.DMAPPEND | syscall.DMEXCL | syscall.DMTMP | ModePerm)

// Chmod changes the mode of the file to mode.
// If there is an error, it will be of type *PathError.
func (f *File) Chmod(mode FileMode) error {
	if f == nil {
		return ErrInvalid
	}
	var d syscall.Dir

	odir, e := dirstat(f)
	if e != nil {
		return &PathError{"chmod", f.name, e}
	}
	d.Null()
	d.Mode = odir.Mode&^chmodMask | syscallMode(mode)&chmodMask

	var buf [syscall.STATFIXLEN]byte
	n, err := d.Marshal(buf[:])
	if err != nil {
		return &PathError{"chmod", f.name, err}
	}
	if err = syscall.Fwstat(f.fd, buf[:n]); err != nil {
		return &PathError{"chmod", f.name, err}
	}
	return nil
}

// Sync commits the current contents of the file to stable storage.
// Typically, this means flushing the file system's in-memory copy
// of recently written data to disk.
func (f *File) Sync() (err error) {
	if f == nil {
		return ErrInvalid
	}
	var d syscall.Dir
	d.Null()

	var buf [syscall.STATFIXLEN]byte
	n, err := d.Marshal(buf[:])
	if err != nil {
		return NewSyscallError("fsync", err)
	}
	if err = syscall.Fwstat(f.fd, buf[:n]); err != nil {
		return NewSyscallError("fsync", err)
	}
	return nil
}

// read reads up to len(b) bytes from the File.
// It returns the number of bytes read and an error, if any.
func (f *File) read(b []byte) (n int, err error) {
	return syscall.Read(f.fd, b)
}

// pread reads len(b) bytes from the File starting at byte offset off.
// It returns the number of bytes read and the error, if any.
// EOF is signaled by a zero count with err set to nil.
func (f *File) pread(b []byte, off int64) (n int, err error) {
	return syscall.Pread(f.fd, b, off)
}

// write writes len(b) bytes to the File.
// It returns the number of bytes written and an error, if any.
// Since Plan 9 preserves message boundaries, never allow
// a zero-byte write.
func (f *File) write(b []byte) (n int, err error) {
	if len(b) == 0 {
		return 0, nil
	}
	return syscall.Write(f.fd, b)
}

// pwrite writes len(b) bytes to the File starting at byte offset off.
// It returns the number of bytes written and an error, if any.
// Since Plan 9 preserves message boundaries, never allow
// a zero-byte write.
func (f *File) pwrite(b []byte, off int64) (n int, err error) {
	if len(b) == 0 {
		return 0, nil
	}
	return syscall.Pwrite(f.fd, b, off)
}

// seek sets the offset for the next Read or Write on file to offset, interpreted
// according to whence: 0 means relative to the origin of the file, 1 means
// relative to the current offset, and 2 means relative to the end.
// It returns the new offset and an error, if any.
func (f *File) seek(offset int64, whence int) (ret int64, err error) {
	return syscall.Seek(f.fd, offset, whence)
}

// Truncate changes the size of the named file.
// If the file is a symbolic link, it changes the size of the link's target.
// If there is an error, it will be of type *PathError.
func Truncate(name string, size int64) error {
	var d syscall.Dir

	d.Null()
	d.Length = size

	var buf [syscall.STATFIXLEN]byte
	n, err := d.Marshal(buf[:])
	if err != nil {
		return &PathError{"truncate", name, err}
	}
	if err = syscall.Wstat(name, buf[:n]); err != nil {
		return &PathError{"truncate", name, err}
	}
	return nil
}

// Remove removes the named file or directory.
// If there is an error, it will be of type *PathError.
func Remove(name string) error {
	if e := syscall.Remove(name); e != nil {
		return &PathError{"remove", name, e}
	}
	return nil
}

// HasPrefix from the strings package.
func hasPrefix(s, prefix string) bool {
	return len(s) >= len(prefix) && s[0:len(prefix)] == prefix
}

// Variant of LastIndex from the strings package.
func lastIndex(s string, sep byte) int {
	for i := len(s) - 1; i >= 0; i-- {
		if s[i] == sep {
			return i
		}
	}
	return -1
}

func rename(oldname, newname string) error {
	dirname := oldname[:lastIndex(oldname, '/')+1]
	if hasPrefix(newname, dirname) {
		newname = newname[len(dirname):]
	} else {
		return &LinkError{"rename", oldname, newname, ErrInvalid}
	}

	// If newname still contains slashes after removing the oldname
	// prefix, the rename is cross-directory and must be rejected.
	// This case is caught by d.Marshal below.

	var d syscall.Dir

	d.Null()
	d.Name = newname

	buf := make([]byte, syscall.STATFIXLEN+len(d.Name))
	n, err := d.Marshal(buf[:])
	if err != nil {
		return &LinkError{"rename", oldname, newname, err}
	}
	if err = syscall.Wstat(oldname, buf[:n]); err != nil {
		return &LinkError{"rename", oldname, newname, err}
	}
	return nil
}

// Chmod changes the mode of the named file to mode.
// If the file is a symbolic link, it changes the mode of the link's target.
// If there is an error, it will be of type *PathError.
func Chmod(name string, mode FileMode) error {
	var d syscall.Dir

	odir, e := dirstat(name)
	if e != nil {
		return &PathError{"chmod", name, e}
	}
	d.Null()
	d.Mode = odir.Mode&^chmodMask | syscallMode(mode)&chmodMask

	var buf [syscall.STATFIXLEN]byte
	n, err := d.Marshal(buf[:])
	if err != nil {
		return &PathError{"chmod", name, err}
	}
	if err = syscall.Wstat(name, buf[:n]); err != nil {
		return &PathError{"chmod", name, err}
	}
	return nil
}

// Chtimes changes the access and modification times of the named
// file, similar to the Unix utime() or utimes() functions.
//
// The underlying filesystem may truncate or round the values to a
// less precise time unit.
// If there is an error, it will be of type *PathError.
func Chtimes(name string, atime time.Time, mtime time.Time) error {
	var d syscall.Dir

	d.Null()
	d.Atime = uint32(atime.Unix())
	d.Mtime = uint32(mtime.Unix())

	var buf [syscall.STATFIXLEN]byte
	n, err := d.Marshal(buf[:])
	if err != nil {
		return &PathError{"chtimes", name, err}
	}
	if err = syscall.Wstat(name, buf[:n]); err != nil {
		return &PathError{"chtimes", name, err}
	}
	return nil
}

// Pipe returns a connected pair of Files; reads from r return bytes
// written to w. It returns the files and an error, if any.
func Pipe() (r *File, w *File, err error) {
	var p [2]int

	syscall.ForkLock.RLock()
	if e := syscall.Pipe(p[0:]); e != nil {
		syscall.ForkLock.RUnlock()
		return nil, nil, NewSyscallError("pipe", e)
	}
	syscall.ForkLock.RUnlock()

	return NewFile(uintptr(p[0]), "|0"), NewFile(uintptr(p[1]), "|1"), nil
}

// not supported on Plan 9

// Link creates newname as a hard link to the oldname file.
// If there is an error, it will be of type *LinkError.
func Link(oldname, newname string) error {
	return &LinkError{"link", oldname, newname, syscall.EPLAN9}
}

// Symlink creates newname as a symbolic link to oldname.
// If there is an error, it will be of type *LinkError.
func Symlink(oldname, newname string) error {
	return &LinkError{"symlink", oldname, newname, syscall.EPLAN9}
}

// Readlink returns the destination of the named symbolic link.
// If there is an error, it will be of type *PathError.
func Readlink(name string) (string, error) {
	return "", &PathError{"readlink", name, syscall.EPLAN9}
}

// Chown changes the numeric uid and gid of the named file.
// If the file is a symbolic link, it changes the uid and gid of the link's target.
// If there is an error, it will be of type *PathError.
func Chown(name string, uid, gid int) error {
	return &PathError{"chown", name, syscall.EPLAN9}
}

// Lchown changes the numeric uid and gid of the named file.
// If the file is a symbolic link, it changes the uid and gid of the link itself.
// If there is an error, it will be of type *PathError.
func Lchown(name string, uid, gid int) error {
	return &PathError{"lchown", name, syscall.EPLAN9}
}

// Chown changes the numeric uid and gid of the named file.
// If there is an error, it will be of type *PathError.
func (f *File) Chown(uid, gid int) error {
	if f == nil {
		return ErrInvalid
	}
	return &PathError{"chown", f.name, syscall.EPLAN9}
}

// TempDir returns the default directory to use for temporary files.
func TempDir() string {
	return "/tmp"
}