// Select selects the up host with the least number of connections in the
// pool. If more than one host has the same least number of connections,
// one of the hosts is chosen at random.
func (LeastConnSelection) Select(pool UpstreamPool, _ *http.Request, _ http.ResponseWriter) *Upstream {
	var bestHost *Upstream
	var count int
	leastReqs := -1

	for _, host := range pool {
		if !host.Available() {
			continue
		}
		numReqs := host.NumRequests()
		if leastReqs == -1 || numReqs < leastReqs {
			leastReqs = numReqs
			count = 0
		}

		// among hosts with same least connections, perform a reservoir
		// sample: https://en.wikipedia.org/wiki/Reservoir_sampling
		if numReqs == leastReqs {
			count++
			if count > 1 || (weakrand.Int()%count) == 0 { //nolint:gosec
				bestHost = host
			}
		}
	}

	return bestHost
}