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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.

// +build darwin freebsd linux netbsd openbsd

package os

import (
        "runtime"
        "syscall"
)

// 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
        nepipe  int      // number of consecutive EPIPE in Write
}

// Fd returns the integer Unix file descriptor referencing the open file.
func (f *File) Fd() int {
        if f == nil {
                return -1
        }
        return f.fd
}

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

// Auxiliary information if the File describes a directory
type dirInfo struct {
        buf []byte       // buffer for directory I/O
        dir *syscall.DIR // from opendir
}

// 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.
// It returns the File and an error, if any.
func OpenFile(name string, flag int, perm FileMode) (file *File, err error) {
        r, e := syscall.Open(name, flag|syscall.O_CLOEXEC, syscallMode(perm))
        if e != nil {
                return nil, &PathError{"open", name, e}
        }

        // There's a race here with fork/exec, which we are
        // content to live with.  See ../syscall/exec_unix.go.
        // On OS X 10.6, the O_CLOEXEC flag is not respected.
        // On OS X 10.7, the O_CLOEXEC flag works.
        // Without a cheap & reliable way to detect 10.6 vs 10.7 at
        // runtime, we just always call syscall.CloseOnExec on Darwin.
        // Once >=10.7 is prevalent, this extra call can removed.
        if syscall.O_CLOEXEC == 0 || runtime.GOOS == "darwin" { // O_CLOEXEC not supported
                syscall.CloseOnExec(r)
        }

        return NewFile(r, name), nil
}

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

func (file *file) close() error {
        if file == nil || file.fd < 0 {
                return EINVAL
        }
        var err error
        if e := syscall.Close(file.fd); e != nil {
                err = &PathError{"close", file.name, e}
        }

        if file.dirinfo != nil {
                if libc_closedir(file.dirinfo.dir) < 0 && err == nil {
                        err = &PathError{"closedir", file.name, syscall.GetErrno()}
                }
        }

        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.
// It returns the FileInfo and an error, if any.
func (f *File) Stat() (fi FileInfo, err error) {
        var stat syscall.Stat_t
        err = syscall.Fstat(f.fd, &stat)
        if err != nil {
                return nil, &PathError{"stat", f.name, err}
        }
        return fileInfoFromStat(&stat, f.name), nil
}

// Stat returns a FileInfo describing the named file and an error, if any.
// If name names a valid symbolic link, the returned FileInfo describes
// the file pointed at by the link and has fi.FollowedSymlink set to true.
// If name names an invalid symbolic link, the returned FileInfo describes
// the link itself and has fi.FollowedSymlink set to false.
func Stat(name string) (fi FileInfo, err error) {
        var stat syscall.Stat_t
        err = syscall.Stat(name, &stat)
        if err != nil {
                return nil, &PathError{"stat", name, err}
        }
        return fileInfoFromStat(&stat, name), nil
}

// Lstat returns a FileInfo describing the named file and an
// error, if any.  If the file is a symbolic link, the returned FileInfo
// describes the symbolic link.  Lstat makes no attempt to follow the link.
func Lstat(name string) (fi FileInfo, err error) {
        var stat syscall.Stat_t
        err = syscall.Lstat(name, &stat)
        if err != nil {
                return nil, &PathError{"lstat", name, err}
        }
        return fileInfoFromStat(&stat, name), nil
}

func (f *File) readdir(n int) (fi []FileInfo, err error) {
        dirname := f.name
        if dirname == "" {
                dirname = "."
        }
        dirname += "/"
        names, err := f.Readdirnames(n)
        fi = make([]FileInfo, len(names))
        for i, filename := range names {
                fip, err := Lstat(dirname + filename)
                if err == nil {
                        fi[i] = fip
                } else {
                        fi[i] = &fileStat{name: filename}
                }
        }
        return fi, err
}

// 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 0.
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.
func (f *File) write(b []byte) (n int, err error) {
        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.
func (f *File) pwrite(b []byte, off int64) (n int, err error) {
        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.
func Truncate(name string, size int64) error {
        if e := syscall.Truncate(name, size); e != nil {
                return &PathError{"truncate", name, e}
        }
        return nil
}

// Remove removes the named file or directory.
func Remove(name string) error {
        // System call interface forces us to know
        // whether name is a file or directory.
        // Try both: it is cheaper on average than
        // doing a Stat plus the right one.
        e := syscall.Unlink(name)
        if e == nil {
                return nil
        }
        e1 := syscall.Rmdir(name)
        if e1 == nil {
                return nil
        }

        // Both failed: figure out which error to return.
        // OS X and Linux differ on whether unlink(dir)
        // returns EISDIR, so can't use that.  However,
        // both agree that rmdir(file) returns ENOTDIR,
        // so we can use that to decide which error is real.
        // Rmdir might also return ENOTDIR if given a bad
        // file path, like /etc/passwd/foo, but in that case,
        // both errors will be ENOTDIR, so it's okay to
        // use the error from unlink.
        if e1 != syscall.ENOTDIR {
                e = e1
        }
        return &PathError{"remove", name, e}
}

// basename removes trailing slashes and the leading directory name from path name
func basename(name string) string {
        i := len(name) - 1
        // Remove trailing slashes
        for ; i > 0 && name[i] == '/'; i-- {
                name = name[:i]
        }
        // Remove leading directory name
        for i--; i >= 0; i-- {
                if name[i] == '/' {
                        name = name[i+1:]
                        break
                }
        }

        return name
}

// 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

        // See ../syscall/exec.go for description of lock.
        syscall.ForkLock.RLock()
        e := syscall.Pipe(p[0:])
        if e != nil {
                syscall.ForkLock.RUnlock()
                return nil, nil, NewSyscallError("pipe", e)
        }
        syscall.CloseOnExec(p[0])
        syscall.CloseOnExec(p[1])
        syscall.ForkLock.RUnlock()

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

// TempDir returns the default directory to use for temporary files.
func TempDir() string {
        dir := Getenv("TMPDIR")
        if dir == "" {
                dir = "/tmp"
        }
        return dir
}