// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// This is a copy of `tempfile.go` from the Go 1.14 standard library.
// It has been modified to make TempFile() respect the process' umask
// instead of creating files with 0600 permissions. This is used to
// ensure files uploaded to Shaman storage will be usable by other
// processes (like Flamenco Worker running as a different user).

package filestore

import (
	"os"
	"path/filepath"
	"strconv"
	"strings"
	"sync"
	"time"
)

// 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 nextRandom() 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,
// opens the file for reading and writing, and returns the resulting *os.File.
// The filename is generated by taking pattern and adding a random
// string to the end. If pattern includes a "*", the random string
// replaces the last "*".
// 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 TempFile(dir, pattern string) (f *os.File, err error) {
	if dir == "" {
		dir = os.TempDir()
	}

	prefix, suffix := prefixAndSuffix(pattern)

	nconflict := 0
	for i := 0; i < 10000; i++ {
		name := filepath.Join(dir, prefix+nextRandom()+suffix)
		f, err = os.OpenFile(name, os.O_RDWR|os.O_CREATE|os.O_EXCL, 0666) // Changed from 0600 in the standard Go code.
		if os.IsExist(err) {
			if nconflict++; nconflict > 10 {
				randmu.Lock()
				rand = reseed()
				randmu.Unlock()
			}
			continue
		}
		break
	}
	return
}

// prefixAndSuffix splits pattern by the last wildcard "*", if applicable,
// returning prefix as the part before "*" and suffix as the part after "*".
func prefixAndSuffix(pattern string) (prefix, suffix string) {
	if pos := strings.LastIndex(pattern, "*"); pos != -1 {
		prefix, suffix = pattern[:pos], pattern[pos+1:]
	} else {
		prefix = pattern
	}
	return
}