package balancer

import "math/rand/v2"

type weightedRandom struct{}

// WeightedRandom returns a strategy that selects endpoints randomly,
// weighted by each endpoint's Weight field. Endpoints with Weight <= 0
// are treated as having a weight of 1.
func WeightedRandom() Strategy {
	return &weightedRandom{}
}

func (w *weightedRandom) Next(healthy []Endpoint) (Endpoint, error) {
	if len(healthy) == 0 {
		return Endpoint{}, ErrNoHealthy
	}

	totalWeight := 0
	for _, ep := range healthy {
		weight := ep.Weight
		if weight <= 0 {
			weight = 1
		}
		totalWeight += weight
	}

	r := rand.IntN(totalWeight)
	for _, ep := range healthy {
		weight := ep.Weight
		if weight <= 0 {
			weight = 1
		}
		r -= weight
		if r < 0 {
			return ep, nil
		}
	}

	// Should never reach here, but return last endpoint as a safeguard.
	return healthy[len(healthy)-1], nil
}