// Copyright © 2014 Steve Francia <spf@spf13.com>.
// Copyright 2013 tsuru authors. All rights reserved.
//
// 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 afero provides types and methods for interacting with the filesystem,
// as an abstraction layer.

// Afero also provides a few implementations that are mostly interoperable. One that
// uses the operating system filesystem, one that uses memory to store files
// (cross platform) and an interface that should be implemented if you want to
// provide your own filesystem.

package afero

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

// File represents a file in the filesystem.
type File interface {
	io.Closer
	io.Reader
	io.ReaderAt
	io.Seeker
	io.Writer
	io.WriterAt

	Name() string
	Readdir(count int) ([]os.FileInfo, error)
	Readdirnames(n int) ([]string, error)
	Stat() (os.FileInfo, error)
	Sync() error
	Truncate(size int64) error
	WriteString(s string) (ret int, err error)
}

// Fs is the filesystem interface.
//
// Any simulated or real filesystem should implement this interface.
type Fs interface {
	// Create creates a file in the filesystem, returning the file and an
	// error, if any happens.
	Create(name string) (File, error)

	// Mkdir creates a directory in the filesystem, return an error if any
	// happens.
	Mkdir(name string, perm os.FileMode) error

	// MkdirAll creates a directory path and all parents that does not exist
	// yet.
	MkdirAll(path string, perm os.FileMode) error

	// Open opens a file, returning it or an error, if any happens.
	Open(name string) (File, error)

	// OpenFile opens a file using the given flags and the given mode.
	OpenFile(name string, flag int, perm os.FileMode) (File, error)

	// Remove removes a file identified by name, returning an error, if any
	// happens.
	Remove(name string) error

	// RemoveAll removes a directory path and all any children it contains. It
	// does not fail if the path does not exist (return nil).
	RemoveAll(path string) error

	// Rename renames a file.
	Rename(oldname, newname string) error

	// Stat returns a FileInfo describing the named file, or an error, if any
	// happens.
	Stat(name string) (os.FileInfo, error)

	// The name of this FileSystem
	Name() string

	//Chmod changes the mode of the named file to mode.
	Chmod(name string, mode os.FileMode) error

	//Chtimes changes the access and modification times of the named file
	Chtimes(name string, atime time.Time, mtime time.Time) error
}

var (
	ErrFileClosed        = errors.New("File is closed")
	ErrOutOfRange        = errors.New("Out of range")
	ErrTooLarge          = errors.New("Too large")
	ErrFileNotFound      = os.ErrNotExist
	ErrFileExists        = os.ErrExist
	ErrDestinationExists = os.ErrExist
)

// ReadDir reads the directory named by dirname and returns
// a list of sorted directory entries.
func ReadDir(dirname string, fs Fs) ([]os.FileInfo, error) {
	f, err := fs.Open(dirname)
	if err != nil {
		return nil, err
	}
	list, err := f.Readdir(-1)
	f.Close()
	if err != nil {
		return nil, err
	}
	sort.Sort(byName(list))
	return list, nil
}

// readDirNames reads the directory named by dirname and returns
// a sorted list of directory entries.
// adapted from https://golang.org/src/path/filepath/path.go
func readDirNames(dirname string, fs Fs) ([]string, error) {
	f, err := fs.Open(dirname)
	if err != nil {
		return nil, err
	}
	names, err := f.Readdirnames(-1)
	f.Close()
	if err != nil {
		return nil, err
	}
	sort.Strings(names)
	return names, nil
}

// walk recursively descends path, calling walkFn
// adapted from https://golang.org/src/path/filepath/path.go
func walk(path string, info os.FileInfo, walkFn filepath.WalkFunc, fs Fs) error {
	err := walkFn(path, info, nil)
	if err != nil {
		if info.IsDir() && err == filepath.SkipDir {
			return nil
		}
		return err
	}

	if !info.IsDir() {
		return nil
	}

	names, err := readDirNames(path, fs)
	if err != nil {
		return walkFn(path, info, err)
	}

	for _, name := range names {
		filename := filepath.Join(path, name)
		fileInfo, err := lstatIfOs(filename, fs)
		if err != nil {
			if err := walkFn(filename, fileInfo, err); err != nil && err != filepath.SkipDir {
				return err
			}
		} else {
			err = walk(filename, fileInfo, walkFn, fs)
			if err != nil {
				if !fileInfo.IsDir() || err != filepath.SkipDir {
					return err
				}
			}
		}
	}
	return nil
}

// if the filesystem is OsFs use Lstat, else use fs.Stat
func lstatIfOs(path string, fs Fs) (info os.FileInfo, err error) {
	_, ok := fs.(*OsFs)
	if ok {
		info, err = os.Lstat(path)
	} else {
		info, err = fs.Stat(path)
	}
	return
}

// Walk walks the file tree rooted at root, calling walkFn for each file or
// directory in the tree, including root. All errors that arise visiting files
// and directories are filtered by walkFn. The files are walked in lexical
// order, which makes the output deterministic but means that for very
// large directories Walk can be inefficient.
// Walk does not follow symbolic links.
func Walk(root string, walkFn filepath.WalkFunc, fs Fs) error {
	info, err := lstatIfOs(root, fs)
	if err != nil {
		return walkFn(root, nil, err)
	}
	return walk(root, info, walkFn, fs)
}

// byName implements sort.Interface.
type byName []os.FileInfo

func (f byName) Len() int           { return len(f) }
func (f byName) Less(i, j int) bool { return f[i].Name() < f[j].Name() }
func (f byName) Swap(i, j int)      { f[i], f[j] = f[j], f[i] }