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// 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.

// The os interface is intended to be uniform across all operating systems.

// Features not generally available appear in the system-specific package syscall.

package os

import (

        "io"

        "syscall"

)

// Name returns the name of the file as presented to Open.

func (f *File) Name() string { return f.name }

// Stdin, Stdout, and Stderr are open Files pointing to the standard input,

// standard output, and standard error file descriptors.

var (

        Stdin  = NewFile(syscall.Stdin, "/dev/stdin")

        Stdout = NewFile(syscall.Stdout, "/dev/stdout")

        Stderr = NewFile(syscall.Stderr, "/dev/stderr")

)

// Flags to Open 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_ASYNC    int = syscall.O_ASYNC    // generate a signal when I/O is available.

        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_NOCTTY   int = syscall.O_NOCTTY   // do not make file the controlling tty.

        O_NONBLOCK int = syscall.O_NONBLOCK // open in non-blocking mode.

        O_NDELAY   int = O_NONBLOCK         // synonym for O_NONBLOCK

        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.

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

)

// Read reads up to len(b) bytes from the File.

// It returns the number of bytes read and an error, if any.

// EOF is signaled by a zero count with err set to io.EOF.

func (f *File) Read(b []byte) (n int, err error) {

        if f == nil {

                return 0, EINVAL

        }

        n, e := f.read(b)

        if n < 0 {

                n = 0

        }

        if n == 0 && len(b) > 0 && e == nil {

                return 0, io.EOF

        }

        if e != nil {

                err = &PathError{"read", f.name, e}

        }

        return n, err

}

// 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) {

        if f == nil {

                return 0, EINVAL

        }

        for len(b) > 0 {

                m, e := f.pread(b, off)

                if m == 0 && e == nil {

                        return n, io.EOF

                }

                if e != nil {

                        err = &PathError{"read", f.name, e}

                        break

                }

                n += m

                b = b[m:]

                off += int64(m)

        }

        return

}

// 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) {

        if f == nil {

                return 0, EINVAL

        }

        n, e := f.write(b)

        if n < 0 {

                n = 0

        }

        epipecheck(f, e)

        if e != nil {

                err = &PathError{"write", f.name, e}

        }

        return n, err

}

// 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) {

        if f == nil {

                return 0, EINVAL

        }

        for len(b) > 0 {

                m, e := f.pwrite(b, off)

                if e != nil {

                        err = &PathError{"write", f.name, e}

                        break

                }

                n += m

                b = b[m:]

                off += int64(m)

        }

        return

}

// 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) {

        r, e := f.seek(offset, whence)

        if e == nil && f.dirinfo != nil && r != 0 {

                e = syscall.EISDIR

        }

        if e != nil {

                return 0, &PathError{"seek", f.name, e}

        }

        return r, nil

}

// WriteString is like Write, but writes the contents of string s rather than

// an array of bytes.

func (f *File) WriteString(s string) (ret int, err error) {

        if f == nil {

                return 0, EINVAL

        }

        return f.Write([]byte(s))

}

// Mkdir creates a new directory with the specified name and permission bits.

// It returns an error, if any.

func Mkdir(name string, perm FileMode) error {

        e := syscall.Mkdir(name, syscallMode(perm))

        if e != nil {

                return &PathError{"mkdir", name, e}

        }

        return nil

}

// Chdir changes the current working directory to the named directory.

func Chdir(dir string) error {

        if e := syscall.Chdir(dir); e != nil {

                return &PathError{"chdir", dir, e}

        }

        return nil

}

// Chdir changes the current working directory to the file,

// which must be a directory.

func (f *File) Chdir() error {

        if e := syscall.Fchdir(f.fd); e != nil {

                return &PathError{"chdir", f.name, e}

        }

        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.

// It returns the File and an error, if any.

func Open(name string) (file *File, err error) {

        return OpenFile(name, O_RDONLY, 0)

}

// Create creates the named file 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.

// It returns the File and an error, if any.

func Create(name string) (file *File, err error) {

        return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)

}