/*
 * Minio Cloud Storage, (C) 2015 Minio, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package fs

import (
	"errors"
	"os"
	"path/filepath"
	"sort"
)

// RemoveAllDirs - removes only itself and all subdirectories
func RemoveAllDirs(path string) error {
	allFiles := func(fp string, fl os.FileInfo, err error) error {
		if fp == path {
			return nil
		}
		if fl.Mode().IsRegular() || fl.Mode()&os.ModeSymlink == os.ModeSymlink {
			return ErrDirNotEmpty
		}
		if fl.Mode().IsDir() {
			if err := os.Remove(fp); err != nil {
				if os.IsNotExist(err) {
					return nil
				}
				return err
			}
		}
		return nil
	}
	err := WalkUnsorted(path, allFiles)
	if err != nil {
		if os.IsNotExist(err) {
			return nil
		}
		return err
	}
	return nil
}

// Walk walks the file tree rooted at root, calling walkFn for each file or
// directory in the tree, including root.
func Walk(root string, walkFn WalkFunc) error {
	info, err := os.Lstat(root)
	if err != nil {
		return walkFn(root, nil, err)
	}
	return walk(root, info, walkFn)
}

// WalkUnsorted walks the file tree rooted at root, calling walkFn for each file or
// directory in the tree, including root.
func WalkUnsorted(root string, walkFn WalkFunc) error {
	info, err := os.Lstat(root)
	if err != nil {
		return walkFn(root, nil, err)
	}
	return walk(root, info, walkFn)
}

// readDirNames reads the directory named by dirname and returns
// a sorted list of directory entries.
func readDirNames(dirname string) ([]string, error) {
	names, err := readDirUnsortedNames(dirname)
	if err != nil {
		return nil, err
	}
	sort.Strings(names)
	return names, nil
}

func readDirUnsortedNames(dirname string) ([]string, error) {
	f, err := os.Open(dirname)
	if err != nil {
		return nil, err
	}
	names, err := f.Readdirnames(-1)
	f.Close()
	if err != nil {
		return nil, err
	}
	return names, nil
}

// WalkFunc is the type of the function called for each file or directory
// visited by Walk. The path argument contains the argument to Walk as a
// prefix; that is, if Walk is called with "dir", which is a directory
// containing the file "a", the walk function will be called with argument
// "dir/a". The info argument is the os.FileInfo for the named path.
type WalkFunc func(path string, info os.FileInfo, err error) error

// ErrSkipDir is used as a return value from WalkFuncs to indicate that
// the directory named in the call is to be skipped. It is not returned
// as an error by any function.
var ErrSkipDir = errors.New("skip this directory")

// ErrSkipFile is used as a return value from WalkFuncs to indicate that
// the file named in the call is to be skipped. It is not returned
// as an error by any function.
var ErrSkipFile = errors.New("skip this file")

// ErrDirNotEmpty is used to throw error on directories which have atleast one regular
// file or a symlink left
var ErrDirNotEmpty = errors.New("directory not empty")

func walkUnsorted(path string, info os.FileInfo, walkFn WalkFunc) error {
	err := walkFn(path, info, nil)
	if err != nil {
		if info.Mode().IsDir() && err == ErrSkipDir {
			return nil
		}
		if info.Mode().IsRegular() && err == ErrSkipFile {
			return nil
		}
		return err
	}

	if !info.IsDir() {
		return nil
	}

	names, err := readDirUnsortedNames(path)
	if err != nil {
		return walkFn(path, info, err)
	}
	for _, name := range names {
		filename := filepath.Join(path, name)
		fileInfo, err := os.Lstat(filename)
		if err != nil {
			if err := walkFn(filename, fileInfo, err); err != nil && err != ErrSkipDir && err != ErrSkipFile {
				return err
			}
		} else {
			err = walk(filename, fileInfo, walkFn)
			if err != nil {
				if err == ErrSkipDir || err == ErrSkipFile {
					return nil
				}
				return err
			}
		}
	}
	return nil
}

// walk recursively descends path, calling w.
func walk(path string, info os.FileInfo, walkFn WalkFunc) error {
	err := walkFn(path, info, nil)
	if err != nil {
		if info.Mode().IsDir() && err == ErrSkipDir {
			return nil
		}
		if info.Mode().IsRegular() && err == ErrSkipFile {
			return nil
		}
		return err
	}

	if !info.IsDir() {
		return nil
	}

	names, err := readDirNames(path)
	if err != nil {
		return walkFn(path, info, err)
	}
	for _, name := range names {
		filename := filepath.Join(path, name)
		fileInfo, err := os.Lstat(filename)
		if err != nil {
			if err := walkFn(filename, fileInfo, err); err != nil && err != ErrSkipDir && err != ErrSkipFile {
				return err
			}
		} else {
			err = walk(filename, fileInfo, walkFn)
			if err != nil {
				if err == ErrSkipDir || err == ErrSkipFile {
					return nil
				}
				return err
			}
		}
	}
	return nil
}