package nfs

import (
	"crypto/rand"
	"encoding/binary"
	"fmt"
)

func generateRandomFSID() (uint32, error) {
	var b [4]byte
	if _, err := rand.Read(b[:]); err != nil {
		return 0, fmt.Errorf("crypto/rand read: %w", err)
	}
	n := binary.BigEndian.Uint32(b[:])
	if n == 0 {
		n = 1
	}
	return n, nil
}

func UniqueFSID(used map[uint32]struct{}) (uint32, error) {
	for i := 0; i < 64; i++ {
		n, err := generateRandomFSID()
		if err != nil {
			return 0, err
		}
		if _, dup := used[n]; !dup {
			return n, nil
		}
	}
	return 0, fmt.Errorf("fsid space exhausted after 64 attempts")
}