package router

import (
	cryptorand "crypto/rand"
	"math/big"
)

// CryptoRandom is the production source for weighted selection. Returning the
// upper bound on a rare entropy failure makes SelectCandidates reject the
// value rather than silently biasing traffic to a route member.
type CryptoRandom struct{}

func (CryptoRandom) Uint64n(limit uint64) uint64 {
	if limit == 0 {
		return 0
	}
	value, err := cryptorand.Int(cryptorand.Reader, new(big.Int).SetUint64(limit))
	if err != nil {
		return limit
	}
	return value.Uint64()
}

var _ RandomSource = CryptoRandom{}