// Copyright 2014 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 webdav

import (
	"io"
	"net/http"
	"os"
	"path"
	"path/filepath"
	"strings"
)

// A FileSystem implements access to a collection of named files. The elements
// in a file path are separated by slash ('/', U+002F) characters, regardless
// of host operating system convention.
//
// Each method has the same semantics as the os package's function of the same
// name.
type FileSystem interface {
	Mkdir(name string, perm os.FileMode) error
	OpenFile(name string, flag int, perm os.FileMode) (File, error)
	RemoveAll(name string) error
	Stat(name string) (os.FileInfo, error)
}

// A File is returned by a FileSystem's OpenFile method and can be served by a
// Handler.
type File interface {
	http.File
	io.Writer
}

// A Dir implements FileSystem using the native file system restricted to a
// specific directory tree.
//
// While the FileSystem.OpenFile method takes '/'-separated paths, a Dir's
// string value is a filename on the native file system, not a URL, so it is
// separated by filepath.Separator, which isn't necessarily '/'.
//
// An empty Dir is treated as ".".
type Dir string

func (d Dir) resolve(name string) string {
	// This implementation is based on Dir.Open's code in the standard net/http package.
	if filepath.Separator != '/' && strings.IndexRune(name, filepath.Separator) >= 0 ||
		strings.Contains(name, "\x00") {
		return ""
	}
	dir := string(d)
	if dir == "" {
		dir = "."
	}
	return filepath.Join(dir, filepath.FromSlash(path.Clean("/"+name)))
}

func (d Dir) Mkdir(name string, perm os.FileMode) error {
	if name = d.resolve(name); name == "" {
		return os.ErrNotExist
	}
	return os.Mkdir(name, perm)
}

func (d Dir) OpenFile(name string, flag int, perm os.FileMode) (File, error) {
	if name = d.resolve(name); name == "" {
		return nil, os.ErrNotExist
	}
	return os.OpenFile(name, flag, perm)
}

func (d Dir) RemoveAll(name string) error {
	if name = d.resolve(name); name == "" {
		return os.ErrNotExist
	}
	if name == filepath.Clean(string(d)) {
		// Prohibit removing the virtual root directory.
		return os.ErrInvalid
	}
	return os.RemoveAll(name)
}

func (d Dir) Stat(name string) (os.FileInfo, error) {
	if name = d.resolve(name); name == "" {
		return nil, os.ErrNotExist
	}
	return os.Stat(name)
}

// TODO: a MemFS implementation.