absfs

type File interface {
	// Name returns the name of the file as presented to Open.
	Name() string

	// 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.
	Read(p []byte) (int, error)

	// 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.
	ReadAt(b []byte, off int64) (n int, err error)

	// 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.
	ReadDir(int) ([]fs.DirEntry, error)

	// 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).
	Write(p []byte) (int, error)

	// 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).
	WriteAt(b []byte, off int64) (n int, err error)

	// WriteString is like Write, but writes the contents of string s rather than
	// a slice of bytes.
	WriteString(s string) (n int, err error)

	// Stat returns the FileInfo structure describing file. If there is an error,
	// it will be of type *PathError.
	Stat() (fs.FileInfo, error)

	// 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.
	Seek(offset int64, whence int) (ret int64, err error)

	// 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.
	Sync() error

	// 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 *fs.PathError.
	Truncate(size int64) error

	// Close closes the File, rendering it unusable for I/O. It returns an error,
	// if any.
	Close() error
}

type FileSystem interface {
	FS() fs.FS

	// 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 *fs.PathError.
	Open(name string) (File, error)

	// OpenFile is the generalized open call; most users will use Open or
	// Create instead. It opens the named file with specified flag (os.O_RDONLY etc.).
	// If the file does not exist, and the os.O_CREATE flag is passed, it is created
	// with mode perm (before umask). If successful, methods on the returned File
	// can be used for I/O. If there is an error, it will be of type *fs.PathError.
	OpenFile(name string, flag int, perm fs.FileMode) (File, error)

	// Create creates or truncates the named file. If the file already exists,
	// it is truncated. If the file does not exist, it is created with mode 0666
	// (before umask). If successful, methods on the returned File can be used for
	// I/O; the associated file descriptor has mode os.O_RDWR. If there is an error,
	// it will be of type *fs.PathError.
	Create(name string) (File, error)

	// ReadFile reads the named file and returns its contents.
	// A successful call returns a nil error, not io.EOF.
	// (Because ReadFile reads the whole file, the expected EOF
	// from the final Read is not treated as an error to be reported.)
	ReadFile(name string) ([]byte, error)

	// ReadDir reads the named directory
	// and returns a list of directory entries sorted by filename.
	ReadDir(name string) ([]fs.DirEntry, error)

	// WriteFile writes data to the named file, creating it if necessary. If the
	// file does not exist, WriteFile creates it with permissions perm (before umask);
	// otherwise WriteFile truncates it before writing, without changing permissions.
	WriteFile(name string, data []byte, perm fs.FileMode) error

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

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

	// Stat returns the FileInfo structure describing file. If there is an error,
	// it will be of type *fs.PathError.
	Stat(name string) (fs.FileInfo, error)

	// 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 *fs.PathError.
	Lstat(name string) (fs.FileInfo, error)

	// 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 *os.LinkError.
	Rename(oldpath, newpath string) error

	// Remove removes the named file or (empty) directory. If there is an error,
	// it will be of type *fs.PathError.
	Remove(name string) error

	// 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). If there is an error, it will be of type
	// *fs.PathError.
	RemoveAll(path string) error

	// 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 *fs.PathError.
	Truncate(name string, size int64) error

	// WalkDir walks the file tree rooted at root, calling fn for each file or directory
	// in the tree, including root. All errors that arise visiting files and directories
	// are filtered by fn: see the fs.WalkDirFunc documentation for details. The files may
	// or may not be walked in lexical order.
	WalkDir(root string, fn fs.WalkDirFunc) error

	// Abs returns an absolute representation of path.
	// If the path is not absolute it will be joined with the current
	// working directory to turn it into an absolute path. The absolute
	// path name for a given file is not guaranteed to be unique.
	// Abs calls pandorasbox.Clean on the result.
	Abs(path string) (string, error)

	Separator() uint8
	ListSeparator() uint8

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

	// 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.
	Getwd() (dir string, err error)

	// TempDir returns the default directory to use for temporary files.
	// The directory is neither guaranteed to exist nor have accessible
	// permissions.
	TempDir() string
}