package dbx

import "sync/atomic"

// Balancer selects the next node from a list.
// It must return nil if no suitable node is available.
type Balancer interface {
	Next(nodes []*Node) *Node
}

// RoundRobinBalancer distributes load evenly across healthy nodes.
type RoundRobinBalancer struct {
	counter atomic.Uint64
}

// NewRoundRobinBalancer creates a new round-robin balancer.
func NewRoundRobinBalancer() *RoundRobinBalancer {
	return &RoundRobinBalancer{}
}

// Next returns the next healthy node, or nil if none are healthy.
func (b *RoundRobinBalancer) Next(nodes []*Node) *Node {
	n := len(nodes)
	if n == 0 {
		return nil
	}
	idx := b.counter.Add(1)
	for i := 0; i < n; i++ {
		node := nodes[(int(idx)+i)%n]
		if node.IsHealthy() {
			return node
		}
	}
	return nil
}