at-container-registry/pkg/appview/jetstream/endpoint_rotator.go

package jetstream

import "sync"

// EndpointRotator cycles through a list of endpoint URLs for failover.
// Thread-safe via sync.Mutex.
type EndpointRotator struct {
	mu        sync.Mutex
	endpoints []string
	index     int
}

// NewEndpointRotator creates a rotator from a list of endpoints.
// Panics if endpoints is empty.
func NewEndpointRotator(endpoints []string) *EndpointRotator {
	if len(endpoints) == 0 {
		panic("EndpointRotator requires at least one endpoint")
	}
	return &EndpointRotator{
		endpoints: endpoints,
	}
}

// Current returns the current endpoint without advancing.
func (r *EndpointRotator) Current() string {
	r.mu.Lock()
	defer r.mu.Unlock()
	return r.endpoints[r.index]
}

// Next advances to the next endpoint (wrapping around) and returns it.
func (r *EndpointRotator) Next() string {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.index = (r.index + 1) % len(r.endpoints)
	return r.endpoints[r.index]
}

// Reset returns to the first endpoint.
func (r *EndpointRotator) Reset() {
	r.mu.Lock()
	defer r.mu.Unlock()
	r.index = 0
}

// Len returns the number of endpoints.
func (r *EndpointRotator) Len() int {
	return len(r.endpoints)
}