package raffle import ( "crypto/rand" "encoding/binary" mathRand "math/rand" "github.com/pkg/errors" ) type ( cryptRandSrc struct{} ) var errNoCandidatesLeft = errors.New("no candidates left") func pickWinnerFromRaffle(r raffle) (winner raffleEntry, err error) { var maxScore float64 for _, re := range r.Entries { if re.WasPicked { // We skip previously picked winners and pretend they // don't exist continue } maxScore += re.Multiplier } if maxScore == 0 { return winner, errNoCandidatesLeft } winnerPoint := mathRand.New(cryptRandSrc{}).Float64() * maxScore //#nosec:G404 - RNG is using a secure source for i := range r.Entries { re := r.Entries[i] if re.WasPicked { // We skip previously picked winners and pretend they // don't exist continue } winnerPoint -= re.Multiplier if winnerPoint < 0 { winner = re break } } return winner, nil } func (cryptRandSrc) Int63() int64 { var b [8]byte if _, err := rand.Read(b[:]); err != nil { return -1 } // mask off sign bit to ensure positive number return int64(binary.LittleEndian.Uint64(b[:]) & (1<<63 - 1)) } // We're using a non-seedable source func (cryptRandSrc) Seed(int64) {}