package writeBytesFuzz

import (
	"crypto/rand"
	"fmt"
	"os"

	"git.thisco.de/vbatts/fuzz-walker/walker"
	"github.com/hashicorp/errwrap"
)

func init() {
	walker.RegisterFuzzFunc(Name, FuzzFunc)
	// malloc early
	for _, size := range sizes {
		bufs[size] = make([]byte, size)
	}
}

var bufs = map[int][]byte{}
var sizes = []int{1, 9, 33, 65, 129, 257} // going with common int sizes + 1
var randomized = false

// this need only be run once
func randomize(b map[int][]byte) error {
	for size := range b {
		_, err := rand.Read(b[size])
		if err != nil {
			return err
		}
	}
	return nil
}

const Name = "writeBytesFuzz"

func FuzzFunc(path string, info os.FileInfo) error {
	if !info.Mode().IsRegular() {
		return nil
	}
	if !randomized {
		if err := randomize(bufs); err != nil {
			return err
		}
	}
	fd, err := os.OpenFile(path, os.O_WRONLY, os.ModePerm)
	if err != nil {
		return err
	}
	defer fd.Close()

	for size, buf := range bufs {
		_, err := fd.Write(buf)
		if err != nil {
			return errwrap.Wrapf(fmt.Sprintf("failed writing %d random bytes to %q: {{err}}", size, path), err)
		}
	}
	return nil
}