package common

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

// WriteFileAtomic creates a temporary file with data and the perm given and
// swaps it atomically with filename if successful.
func WriteFileAtomic(filename string, data []byte, perm os.FileMode) error {
	var (
		dir = filepath.Dir(filename)
		// Create in case it doesn't exist and force kernel
		// flush, which still leaves the potential of lingering disk cache.
		// Never overwrites files
		flag = os.O_WRONLY | os.O_CREATE | os.O_SYNC | os.O_TRUNC | os.O_EXCL
	)

	tempFile := filepath.Join(dir, "write-file-atomic-"+RandStr(32))
	f, err := os.OpenFile(tempFile, flag, perm)
	if err != nil {
		return err
	}
	// Clean up in any case. Defer stacking order is last-in-first-out.
	defer os.Remove(f.Name())
	defer f.Close()

	if n, err := f.Write(data); err != nil {
		return err
	} else if n < len(data) {
		return io.ErrShortWrite
	}
	// Close the file before renaming it, otherwise it will cause "The process
	// cannot access the file because it is being used by another process." on windows.
	f.Close()

	return os.Rename(f.Name(), filename)
}

//--------------------------------------------------------------------------------

func Tempfile(prefix string) (*os.File, string) {
	file, err := ioutil.TempFile("", prefix)
	if err != nil {
		PanicCrisis(err)
	}
	return file, file.Name()
}

func Tempdir(prefix string) (*os.File, string) {
	tempDir := os.TempDir() + "/" + prefix + RandStr(12)
	err := EnsureDir(tempDir, 0700)
	if err != nil {
		panic(Fmt("Error creating temp dir: %v", err))
	}
	dir, err := os.Open(tempDir)
	if err != nil {
		panic(Fmt("Error opening temp dir: %v", err))
	}
	return dir, tempDir
}