// 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 provides a platform-independent interface to operating system
// functionality. The design is Unix-like, although the error handling is
// Go-like; failing calls return values of type error rather than error numbers.
// Often, more information is available within the error. For example,
// if a call that takes a file name fails, such as Open or Stat, the error
// will include the failing file name when printed and will be of type
// *PathError, which may be unpacked for more information.
//
// The os interface is intended to be uniform across all operating systems.
// Features not generally available appear in the system-specific package syscall.
//
// Here is a simple example, opening a file and reading some of it.
//
//	file, err := os.Open("file.go") // For read access.
//	if err != nil {
//		log.Fatal(err)
//	}
//
// If the open fails, the error string will be self-explanatory, like
//
//	open file.go: no such file or directory
//
// The file's data can then be read into a slice of bytes. Read and
// Write take their byte counts from the length of the argument slice.
//
//	data := make([]byte, 100)
//	count, err := file.Read(data)
//	if err != nil {
//		log.Fatal(err)
//	}
//	fmt.Printf("read %d bytes: %q\n", count, data[:count])
package os

import (
	"errors"
	"syscall"
	"time"
)

// Name returns the name of the file as presented to Open.
func (f *File) Name() string { return "" }

// Stdin, Stdout, and Stderr are open Files pointing to the standard input,
// standard output, and standard error file descriptors.
//
// Note that the Go runtime writes to standard error for panics and crashes;
// closing Stderr may cause those messages to go elsewhere, perhaps
// to a file opened later.
var (
	Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
	Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
	Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
)

// Flags to OpenFile wrapping those of the underlying system. Not all
// flags may be implemented on a given system.
const (
	O_RDONLY int = syscall.O_RDONLY // open the file read-only.
	O_WRONLY int = syscall.O_WRONLY // open the file write-only.
	O_RDWR   int = syscall.O_RDWR   // open the file read-write.
	O_APPEND int = syscall.O_APPEND // append data to the file when writing.
	O_CREATE int = syscall.O_CREAT  // create a new file if none exists.
	O_EXCL   int = syscall.O_EXCL   // used with O_CREATE, file must not exist
	O_SYNC   int = syscall.O_SYNC   // open for synchronous I/O.
	O_TRUNC  int = syscall.O_TRUNC  // if possible, truncate file when opened.
)

// Seek whence values.
//
// Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd.
const (
	SEEK_SET int = 0 // seek relative to the origin of the file
	SEEK_CUR int = 1 // seek relative to the current offset
	SEEK_END int = 2 // seek relative to the end
)

// LinkError records an error during a link or symlink or rename
// system call and the paths that caused it.
type LinkError struct {
	Op  string
	Old string
	New string
	Err error
}

func (e *LinkError) Error() string {
	return ""
}

// Read reads up to len(b) bytes from the File.
// It returns the number of bytes read and any error encountered.
// At end of file, Read returns 0, io.EOF.
func (f *File) Read(b []byte) (n int, err error) {
	return 0, nil
}

// ReadAt reads len(b) bytes from the File starting at byte offset off.
// It returns the number of bytes read and the error, if any.
// ReadAt always returns a non-nil error when n < len(b).
// At end of file, that error is io.EOF.
func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
	return 0, nil
}

// Write writes len(b) bytes to the File.
// It returns the number of bytes written and an error, if any.
// Write returns a non-nil error when n != len(b).
func (f *File) Write(b []byte) (n int, err error) {
	return 0, nil
}

// WriteAt writes len(b) bytes to the File starting at byte offset off.
// It returns the number of bytes written and an error, if any.
// WriteAt returns a non-nil error when n != len(b).
func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
	return 0, nil
}

// 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.
// The behavior of Seek on a file opened with O_APPEND is not specified.
func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
	return 0, nil
}

// WriteString is like Write, but writes the contents of string s rather than
// a slice of bytes.
func (f *File) WriteString(s string) (n int, err error) {
	return 0, nil
}

// Mkdir creates a new directory with the specified name and permission bits.
// If there is an error, it will be of type *PathError.
func Mkdir(name string, perm FileMode) error {
	return nil
}

// Chdir changes the current working directory to the named directory.
// If there is an error, it will be of type *PathError.
func Chdir(dir string) error {
	return nil
}

// Open opens the named file for reading. If successful, methods on
// the returned file can be used for reading; the associated file
// descriptor has mode O_RDONLY.
// If there is an error, it will be of type *PathError.
func Open(name string) (*File, error) {
	return nil, nil
}

// Create creates the named file with mode 0666 (before umask), truncating
// it if it already exists. If successful, methods on the returned
// File can be used for I/O; the associated file descriptor has mode
// O_RDWR.
// If there is an error, it will be of type *PathError.
func Create(name string) (*File, error) {
	return nil, nil
}

// Rename renames (moves) oldpath to newpath.
// If newpath already exists and is not a directory, Rename replaces it.
// OS-specific restrictions may apply when oldpath and newpath are in different directories.
// If there is an error, it will be of type *LinkError.
func Rename(oldpath, newpath string) error {
	return nil
}

// TempDir returns the default directory to use for temporary files.
//
// On Unix systems, it returns $TMPDIR if non-empty, else /tmp.
// On Windows, it uses GetTempPath, returning the first non-empty
// value from %TMP%, %TEMP%, %USERPROFILE%, or the Windows directory.
// On Plan 9, it returns /tmp.
//
// The directory is neither guaranteed to exist nor have accessible
// permissions.
func TempDir() string {
	return ""
}

// 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.
//
// A different subset of the mode bits are used, depending on the
// operating system.
//
// On Unix, the mode's permission bits, ModeSetuid, ModeSetgid, and
// ModeSticky are used.
//
// On Windows, the mode must be non-zero but otherwise only the 0200
// bit (owner writable) of mode is used; it controls whether the
// file's read-only attribute is set or cleared. attribute. The other
// bits are currently unused. Use mode 0400 for a read-only file and
// 0600 for a readable+writable file.
//
// On Plan 9, the mode's permission bits, ModeAppend, ModeExclusive,
// and ModeTemporary are used.
func Chmod(name string, mode FileMode) error { return nil }

// 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 { return nil }

// 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 "", nil
}

// 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.
//
// On Windows, it always returns the syscall.EWINDOWS error, wrapped
// in *PathError.
func Chown(name string, uid, gid int) error {
	return nil
}

// 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.
//
// On Windows, it always returns the syscall.EWINDOWS error, wrapped
// in *PathError.
func Lchown(name string, uid, gid int) error {
	return nil
}

// Chown changes the numeric uid and gid of the named file.
// If there is an error, it will be of type *PathError.
//
// On Windows, it always returns the syscall.EWINDOWS error, wrapped
// in *PathError.
func (f *File) Chown(uid, gid int) error {
	return 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 {
	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() error {
	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 {
	return nil
}

// Chdir changes the current working directory to the file,
// which must be a directory.
// If there is an error, it will be of type *PathError.
func (f *File) Chdir() error {
	return nil
}

// Fd returns the integer Unix file descriptor referencing the open file.
// The file descriptor is valid only until f.Close is called or f is garbage collected.
func (f *File) Fd() uintptr {
	return 0
}

// NewFile returns a new File with the given file descriptor and
// name. The returned value will be nil if fd is not a valid file
// descriptor.
func NewFile(fd uintptr, name string) *File {
	return nil
}

// 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"

// 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, error) {
	return nil, nil
}

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

// 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 {
	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 {
	return nil
}

// 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 nil
}

// 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 nil
}

// Executable returns the path name for the executable that started
// the current process. There is no guarantee that the path is still
// pointing to the correct executable. If a symlink was used to start
// the process, depending on the operating system, the result might
// be the symlink or the path it pointed to. If a stable result is
// needed, path/filepath.EvalSymlinks might help.
//
// Executable returns an absolute path unless an error occurred.
//
// The main use case is finding resources located relative to an
// executable.
//
// Executable is not supported on nacl.
func Executable() (string, error) {
	return "", nil
}

// The only signal values guaranteed to be present on all systems
// are Interrupt (send the process an interrupt) and Kill (force
// the process to exit).
var (
	Interrupt Signal = syscall.SIGINT
	Kill      Signal = syscall.SIGKILL
)

// ProcessState stores information about a process, as reported by Wait.
type ProcessState struct {
	unexported struct{}
}

// Pid returns the process id of the exited process.
func (p *ProcessState) Pid() int {
	return 0
}

func (p *ProcessState) String() string {
	return ""
}

// Process stores the information about a process created by StartProcess.
type Process struct {
	Pid        int
	unexported struct{}
}

// ProcAttr holds the attributes that will be applied to a new process
// started by StartProcess.
type ProcAttr struct {
	// If Dir is non-empty, the child changes into the directory before
	// creating the process.
	Dir string
	// If Env is non-nil, it gives the environment variables for the
	// new process in the form returned by Environ.
	// If it is nil, the result of Environ will be used.
	Env []string
	// Files specifies the open files inherited by the new process. The
	// first three entries correspond to standard input, standard output, and
	// standard error. An implementation may support additional entries,
	// depending on the underlying operating system. A nil entry corresponds
	// to that file being closed when the process starts.
	Files []*File

	// Operating system-specific process creation attributes.
	// Note that setting this field means that your program
	// may not execute properly or even compile on some
	// operating systems.
	Sys *syscall.SysProcAttr
}

// A Signal represents an operating system signal.
// The usual underlying implementation is operating system-dependent:
// on Unix it is syscall.Signal.
type Signal interface {
	String() string
	Signal() // to distinguish from other Stringers
}

// Getpid returns the process id of the caller.
func Getpid() int { return 0 }

// Getppid returns the process id of the caller's parent.
func Getppid() int { return 0 }

// FindProcess looks for a running process by its pid.
//
// The Process it returns can be used to obtain information
// about the underlying operating system process.
//
// On Unix systems, FindProcess always succeeds and returns a Process
// for the given pid, regardless of whether the process exists.
func FindProcess(pid int) (*Process, error) {
	return nil, nil
}

// StartProcess starts a new process with the program, arguments and attributes
// specified by name, argv and attr.
//
// StartProcess is a low-level interface. The os/exec package provides
// higher-level interfaces.
//
// If there is an error, it will be of type *PathError.
func StartProcess(name string, argv []string, attr *ProcAttr) (*Process, error) {
	return nil, nil
}

// Release releases any resources associated with the Process p,
// rendering it unusable in the future.
// Release only needs to be called if Wait is not.
func (p *Process) Release() error {
	return nil
}

// Kill causes the Process to exit immediately.
func (p *Process) Kill() error {
	return nil
}

// Wait waits for the Process to exit, and then returns a
// ProcessState describing its status and an error, if any.
// Wait releases any resources associated with the Process.
// On most operating systems, the Process must be a child
// of the current process or an error will be returned.
func (p *Process) Wait() (*ProcessState, error) {
	return nil, nil
}

// Signal sends a signal to the Process.
// Sending Interrupt on Windows is not implemented.
func (p *Process) Signal(sig Signal) error {
	return nil
}

// UserTime returns the user CPU time of the exited process and its children.
func (p *ProcessState) UserTime() time.Duration {
	return 0
}

// SystemTime returns the system CPU time of the exited process and its children.
func (p *ProcessState) SystemTime() time.Duration {
	return 0
}

// Exited reports whether the program has exited.
func (p *ProcessState) Exited() bool {
	return false
}

// Success reports whether the program exited successfully,
// such as with exit status 0 on Unix.
func (p *ProcessState) Success() bool {
	return false
}

// Sys returns system-dependent exit information about
// the process. Convert it to the appropriate underlying
// type, such as syscall.WaitStatus on Unix, to access its contents.
func (p *ProcessState) Sys() any {
	return nil
}

// SysUsage returns system-dependent resource usage information about
// the exited process. Convert it to the appropriate underlying
// type, such as *syscall.Rusage on Unix, to access its contents.
// (On Unix, *syscall.Rusage matches struct rusage as defined in the
// getrusage(2) manual page.)
func (p *ProcessState) SysUsage() any {
	return nil
}

// Portable analogs of some common system call errors.
var (
	ErrInvalid    = errors.New("invalid argument") // methods on File will return this error when the receiver is nil
	ErrPermission = errors.New("permission denied")
	ErrExist      = errors.New("file already exists")
	ErrNotExist   = errors.New("file does not exist")
	ErrClosed     = errors.New("file already closed")
)

// PathError records an error and the operation and file path that caused it.
type PathError struct {
	Op   string
	Path string
	Err  error
}

func (e *PathError) Error() string { return "" }

// SyscallError records an error from a specific system call.
type SyscallError struct {
	Syscall string
	Err     error
}

func (e *SyscallError) Error() string { return "" }

// NewSyscallError returns, as an error, a new SyscallError
// with the given system call name and error details.
// As a convenience, if err is nil, NewSyscallError returns nil.
func NewSyscallError(syscall string, err error) error {
	return nil
}

// IsExist returns a boolean indicating whether the error is known to report
// that a file or directory already exists. It is satisfied by ErrExist as
// well as some syscall errors.
func IsExist(err error) bool {
	return false
}

// IsNotExist returns a boolean indicating whether the error is known to
// report that a file or directory does not exist. It is satisfied by
// ErrNotExist as well as some syscall errors.
func IsNotExist(err error) bool {
	return false
}

// IsPermission returns a boolean indicating whether the error is known to
// report that permission is denied. It is satisfied by ErrPermission as well
// as some syscall errors.
func IsPermission(err error) bool {
	return false
}

// Expand replaces ${var} or $var in the string based on the mapping function.
// For example, os.ExpandEnv(s) is equivalent to os.Expand(s, os.Getenv).
func Expand(s string, mapping func(string) string) string {
	return ""
}

// ExpandEnv replaces ${var} or $var in the string according to the values
// of the current environment variables. References to undefined
// variables are replaced by the empty string.
func ExpandEnv(s string) string {
	return ""
}

// Getenv retrieves the value of the environment variable named by the key.
// It returns the value, which will be empty if the variable is not present.
// To distinguish between an empty value and an unset value, use LookupEnv.
func Getenv(key string) string {
	return ""
}

// LookupEnv retrieves the value of the environment variable named
// by the key. If the variable is present in the environment the
// value (which may be empty) is returned and the boolean is true.
// Otherwise the returned value will be empty and the boolean will
// be false.
func LookupEnv(key string) (string, bool) {
	return "", false
}

// Setenv sets the value of the environment variable named by the key.
// It returns an error, if any.
func Setenv(key, value string) error {
	return nil
}

// Unsetenv unsets a single environment variable.
func Unsetenv(key string) error {
	return nil
}

// Clearenv deletes all environment variables.
func Clearenv() {
	return
}

// Environ returns a copy of strings representing the environment,
// in the form "key=value".
func Environ() []string {
	return nil
}

// Readdir reads the contents of the directory associated with file and
// returns a slice of up to n FileInfo values, as would be returned
// by Lstat, in directory order. Subsequent calls on the same file will yield
// further FileInfos.
//
// If n > 0, Readdir returns at most n FileInfo structures. In this case, if
// Readdir returns an empty slice, it will return a non-nil error
// explaining why. At the end of a directory, the error is io.EOF.
//
// If n <= 0, Readdir returns all the FileInfo from the directory in
// a single slice. In this case, if Readdir succeeds (reads all
// the way to the end of the directory), it returns the slice and a
// nil error. If it encounters an error before the end of the
// directory, Readdir returns the FileInfo read until that point
// and a non-nil error.
func (f *File) Readdir(n int) ([]FileInfo, error) {
	return nil, nil
}

// Readdirnames reads and returns a slice of names from the directory f.
//
// If n > 0, Readdirnames returns at most n names. In this case, if
// Readdirnames returns an empty slice, it will return a non-nil error
// explaining why. At the end of a directory, the error is io.EOF.
//
// If n <= 0, Readdirnames returns all the names from the directory in
// a single slice. In this case, if Readdirnames succeeds (reads all
// the way to the end of the directory), it returns the slice and a
// nil error. If it encounters an error before the end of the
// directory, Readdirnames returns the names read until that point and
// a non-nil error.
func (f *File) Readdirnames(n int) (names []string, err error) {
	return nil, nil
}

// Getwd returns a rooted path name corresponding to the
// current directory. If the current directory can be
// reached via multiple paths (due to symbolic links),
// Getwd may return any one of them.
func Getwd() (dir string, err error) {
	return "", nil
}

// MkdirAll creates a directory named path,
// along with any necessary parents, and returns nil,
// or else returns an error.
// The permission bits perm are used for all
// directories that MkdirAll creates.
// If path is already a directory, MkdirAll does nothing
// and returns nil.
func MkdirAll(path string, perm FileMode) error {
	return nil
}

// RemoveAll removes path and any children it contains.
// It removes everything it can but returns the first error
// it encounters. If the path does not exist, RemoveAll
// returns nil (no error).
func RemoveAll(path string) error {
	return nil
}

const (
	PathSeparator     = '/' // OS-specific path separator
	PathListSeparator = ':' // OS-specific path list separator
)

// IsPathSeparator reports whether c is a directory separator character.
func IsPathSeparator(c uint8) bool {
	return false
}

// 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) {
	return nil, nil, nil
}

// Args hold the command-line arguments, starting with the program name.
var Args []string

// Getuid returns the numeric user id of the caller.
//
// On Windows, it returns -1.
func Getuid() int { return 0 }

// Geteuid returns the numeric effective user id of the caller.
//
// On Windows, it returns -1.
func Geteuid() int { return 0 }

// Getgid returns the numeric group id of the caller.
//
// On Windows, it returns -1.
func Getgid() int { return 0 }

// Getegid returns the numeric effective group id of the caller.
//
// On Windows, it returns -1.
func Getegid() int { return 0 }

// Getgroups returns a list of the numeric ids of groups that the caller belongs to.
//
// On Windows, it returns syscall.EWINDOWS. See the os/user package
// for a possible alternative.
func Getgroups() ([]int, error) {
	return nil, nil
}

// Exit causes the current program to exit with the given status code.
// Conventionally, code zero indicates success, non-zero an error.
// The program terminates immediately; deferred functions are not run.
func Exit(code int) {
	return
}

// Stat returns the FileInfo structure describing file.
// If there is an error, it will be of type *PathError.
func (f *File) Stat() (FileInfo, error) {
	return nil, nil
}

// Stat returns a FileInfo describing the named file.
// If there is an error, it will be of type *PathError.
func Stat(name string) (FileInfo, error) {
	return nil, nil
}

// Lstat returns a FileInfo describing the named file.
// If the file is a symbolic link, the returned FileInfo
// describes the symbolic link. Lstat makes no attempt to follow the link.
// If there is an error, it will be of type *PathError.
func Lstat(name string) (FileInfo, error) {
	return nil, nil
}

// Getpagesize returns the underlying system's memory page size.
func Getpagesize() int { return 0 }

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

// A FileInfo describes a file and is returned by Stat and Lstat.
type FileInfo interface {
	Name() string       // base name of the file
	Size() int64        // length in bytes for regular files; system-dependent for others
	Mode() FileMode     // file mode bits
	ModTime() time.Time // modification time
	IsDir() bool        // abbreviation for Mode().IsDir()
	Sys() interface{}   // underlying data source (can return nil)
}

// A FileMode represents a file's mode and permission bits.
// The bits have the same definition on all systems, so that
// information about files can be moved from one system
// to another portably. Not all bits apply to all systems.
// The only required bit is ModeDir for directories.
type FileMode uint32

// The defined file mode bits are the most significant bits of the FileMode.
// The nine least-significant bits are the standard Unix rwxrwxrwx permissions.
// The values of these bits should be considered part of the public API and
// may be used in wire protocols or disk representations: they must not be
// changed, although new bits might be added.
const (
	// The single letters are the abbreviations
	// used by the String method's formatting.
	ModeDir        FileMode = 1 << (32 - 1 - iota) // d: is a directory
	ModeAppend                                     // a: append-only
	ModeExclusive                                  // l: exclusive use
	ModeTemporary                                  // T: temporary file; Plan 9 only
	ModeSymlink                                    // L: symbolic link
	ModeDevice                                     // D: device file
	ModeNamedPipe                                  // p: named pipe (FIFO)
	ModeSocket                                     // S: Unix domain socket
	ModeSetuid                                     // u: setuid
	ModeSetgid                                     // g: setgid
	ModeCharDevice                                 // c: Unix character device, when ModeDevice is set
	ModeSticky                                     // t: sticky

	// Mask for the type bits. For regular files, none will be set.
	ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice

	ModePerm FileMode = 0777 // Unix permission bits
)

func (m FileMode) String() string {
	return ""
}

// IsDir reports whether m describes a directory.
// That is, it tests for the ModeDir bit being set in m.
func (m FileMode) IsDir() bool {
	return false
}

// IsRegular reports whether m describes a regular file.
// That is, it tests that no mode type bits are set.
func (m FileMode) IsRegular() bool {
	return false
}

// Perm returns the Unix permission bits in m.
func (m FileMode) Perm() FileMode {
	return 0
}

// SameFile reports whether fi1 and fi2 describe the same file.
// For example, on Unix this means that the device and inode fields
// of the two underlying structures are identical; on other systems
// the decision may be based on the path names.
// SameFile only applies to results returned by this package's Stat.
// It returns false in other cases.
func SameFile(fi1, fi2 FileInfo) bool {
	return false
}

// Hostname returns the host name reported by the kernel.
func Hostname() (name string, err error) {
	return "", nil
}