// Copyright ©2015 The Go Authors
// Copyright ©2015 Steve Francia <spf@spf13.com>
//
// 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

import (
	"bytes"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strconv"
	"sync"
	"time"
)

// 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] }

// ReadDir reads the directory named by dirname and returns
// a list of sorted directory entries.
func (a Afero) ReadDir(dirname string) ([]os.FileInfo, error) {
	return ReadDir(dirname, a.fs)
}

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
}

// ReadFile reads the file named by filename and returns the contents.
// A successful call returns err == nil, not err == EOF. Because ReadFile
// reads the whole file, it does not treat an EOF from Read as an error
// to be reported.
func (a Afero) ReadFile(filename string) ([]byte, error) {
	return ReadFile(filename, a.fs)
}

func ReadFile(filename string, fs Fs) ([]byte, error) {
	f, err := fs.Open(filename)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	// It's a good but not certain bet that FileInfo will tell us exactly how much to
	// read, so let's try it but be prepared for the answer to be wrong.
	var n int64

	if fi, err := f.Stat(); err == nil {
		// Don't preallocate a huge buffer, just in case.
		if size := fi.Size(); size < 1e9 {
			n = size
		}
	}
	// As initial capacity for readAll, use n + a little extra in case Size is zero,
	// and to avoid another allocation after Read has filled the buffer.  The readAll
	// call will read into its allocated internal buffer cheaply.  If the size was
	// wrong, we'll either waste some space off the end or reallocate as needed, but
	// in the overwhelmingly common case we'll get it just right.
	return readAll(f, n+bytes.MinRead)
}

// readAll reads from r until an error or EOF and returns the data it read
// from the internal buffer allocated with a specified capacity.
func readAll(r io.Reader, capacity int64) (b []byte, err error) {
	buf := bytes.NewBuffer(make([]byte, 0, capacity))
	// If the buffer overflows, we will get bytes.ErrTooLarge.
	// Return that as an error. Any other panic remains.
	defer func() {
		e := recover()
		if e == nil {
			return
		}
		if panicErr, ok := e.(error); ok && panicErr == bytes.ErrTooLarge {
			err = panicErr
		} else {
			panic(e)
		}
	}()
	_, err = buf.ReadFrom(r)
	return buf.Bytes(), err
}

// ReadAll reads from r until an error or EOF and returns the data it read.
// A successful call returns err == nil, not err == EOF. Because ReadAll is
// defined to read from src until EOF, it does not treat an EOF from Read
// as an error to be reported.
func ReadAll(r io.Reader) ([]byte, error) {
	return readAll(r, bytes.MinRead)
}

// WriteFile writes data to a file named by filename.
// If the file does not exist, WriteFile creates it with permissions perm;
// otherwise WriteFile truncates it before writing.
func (a Afero) WriteFile(filename string, data []byte, perm os.FileMode) error {
	return WriteFile(filename, data, perm, a.fs)
}

func WriteFile(filename string, data []byte, perm os.FileMode, fs Fs) error {
	f, err := fs.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
	if err != nil {
		return err
	}
	n, err := f.Write(data)
	if err == nil && n < len(data) {
		err = io.ErrShortWrite
	}
	if err1 := f.Close(); err == nil {
		err = err1
	}
	return err
}

// Random number state.
// We generate random temporary file names so that there's a good
// chance the file doesn't exist yet - keeps the number of tries in
// TempFile to a minimum.
var rand uint32
var randmu sync.Mutex

func reseed() uint32 {
	return uint32(time.Now().UnixNano() + int64(os.Getpid()))
}

func nextSuffix() string {
	randmu.Lock()
	r := rand
	if r == 0 {
		r = reseed()
	}
	r = r*1664525 + 1013904223 // constants from Numerical Recipes
	rand = r
	randmu.Unlock()
	return strconv.Itoa(int(1e9 + r%1e9))[1:]
}

// TempFile creates a new temporary file in the directory dir
// with a name beginning with prefix, opens the file for reading
// and writing, and returns the resulting *File.
// If dir is the empty string, TempFile uses the default directory
// for temporary files (see os.TempDir).
// Multiple programs calling TempFile simultaneously
// will not choose the same file.  The caller can use f.Name()
// to find the pathname of the file.  It is the caller's responsibility
// to remove the file when no longer needed.
func (a Afero) TempFile(dir, prefix string) (f File, err error) {
	return TempFile(dir, prefix, a.fs)
}

func TempFile(dir, prefix string, fs Fs) (f File, err error) {
	if dir == "" {
		dir = os.TempDir()
	}

	nconflict := 0
	for i := 0; i < 10000; i++ {
		name := filepath.Join(dir, prefix+nextSuffix())
		f, err = fs.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0600)
		if os.IsExist(err) {
			if nconflict++; nconflict > 10 {
				randmu.Lock()
				rand = reseed()
				randmu.Unlock()
			}
			continue
		}
		break
	}
	return
}

// TempDir creates a new temporary directory in the directory dir
// with a name beginning with prefix and returns the path of the
// new directory.  If dir is the empty string, TempDir uses the
// default directory for temporary files (see os.TempDir).
// Multiple programs calling TempDir simultaneously
// will not choose the same directory.  It is the caller's responsibility
// to remove the directory when no longer needed.
func (a Afero) TempDir(dir, prefix string) (name string, err error) {
	return TempDir(dir, prefix, a.fs)
}
func TempDir(dir, prefix string, fs Fs) (name string, err error) {
	if dir == "" {
		dir = os.TempDir()
	}

	nconflict := 0
	for i := 0; i < 10000; i++ {
		try := filepath.Join(dir, prefix+nextSuffix())
		err = fs.Mkdir(try, 0700)
		if os.IsExist(err) {
			if nconflict++; nconflict > 10 {
				randmu.Lock()
				rand = reseed()
				randmu.Unlock()
			}
			continue
		}
		if err == nil {
			name = try
		}
		break
	}
	return
}