// Copyright 2015 The etcd Authors
//
// 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 fileutil

import (
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"

	"go.uber.org/zap"
)

const (
	// PrivateFileMode grants owner to read/write a file.
	PrivateFileMode = 0600
)

// IsDirWriteable checks if dir is writable by writing and removing a file
// to dir. It returns nil if dir is writable.
func IsDirWriteable(dir string) error {
	f := filepath.Join(dir, ".touch")
	if err := ioutil.WriteFile(f, []byte(""), PrivateFileMode); err != nil {
		return err
	}
	return os.Remove(f)
}

// TouchDirAll is similar to os.MkdirAll. It creates directories with 0700 permission if any directory
// does not exists. TouchDirAll also ensures the given directory is writable.
func TouchDirAll(dir string) error {
	// If path is already a directory, MkdirAll does nothing and returns nil, so,
	// first check if dir exist with an expected permission mode.
	if Exist(dir) {
		err := CheckDirPermission(dir, PrivateDirMode)
		if err != nil {
			lg, _ := zap.NewProduction()
			if lg == nil {
				lg = zap.NewExample()
			}
			lg.Warn("check file permission", zap.Error(err))
		}
	} else {
		err := os.MkdirAll(dir, PrivateDirMode)
		if err != nil {
			// if mkdirAll("a/text") and "text" is not
			// a directory, this will return syscall.ENOTDIR
			return err
		}
	}

	return IsDirWriteable(dir)
}

// CreateDirAll is similar to TouchDirAll but returns error
// if the deepest directory was not empty.
func CreateDirAll(dir string) error {
	err := TouchDirAll(dir)
	if err == nil {
		var ns []string
		ns, err = ReadDir(dir)
		if err != nil {
			return err
		}
		if len(ns) != 0 {
			err = fmt.Errorf("expected %q to be empty, got %q", dir, ns)
		}
	}
	return err
}

// Exist returns true if a file or directory exists.
func Exist(name string) bool {
	_, err := os.Stat(name)
	return err == nil
}

// DirEmpty returns true if a directory empty and can access.
func DirEmpty(name string) bool {
	ns, err := ReadDir(name)
	return len(ns) == 0 && err == nil
}

// ZeroToEnd zeros a file starting from SEEK_CUR to its SEEK_END. May temporarily
// shorten the length of the file.
func ZeroToEnd(f *os.File) error {
	// TODO: support FALLOC_FL_ZERO_RANGE
	off, err := f.Seek(0, io.SeekCurrent)
	if err != nil {
		return err
	}
	lenf, lerr := f.Seek(0, io.SeekEnd)
	if lerr != nil {
		return lerr
	}
	if err = f.Truncate(off); err != nil {
		return err
	}
	// make sure blocks remain allocated
	if err = Preallocate(f, lenf, true); err != nil {
		return err
	}
	_, err = f.Seek(off, io.SeekStart)
	return err
}

// CheckDirPermission checks permission on an existing dir.
// Returns error if dir is empty or exist with a different permission than specified.
func CheckDirPermission(dir string, perm os.FileMode) error {
	if !Exist(dir) {
		return fmt.Errorf("directory %q empty, cannot check permission.", dir)
	}
	//check the existing permission on the directory
	dirInfo, err := os.Stat(dir)
	if err != nil {
		return err
	}
	dirMode := dirInfo.Mode().Perm()
	if dirMode != perm {
		err = fmt.Errorf("directory %q exist, but the permission is %q. The recommended permission is %q to prevent possible unprivileged access to the data.", dir, dirInfo.Mode(), os.FileMode(PrivateDirMode))
		return err
	}
	return nil
}
