refactor: IndexNow request batches and answer outcome as functions

No behaviour change: NotifyIndexNow splits through indexNowBatches and
SendIndexNow maps the answer through indexNowOutcome, so both can be unit
tested without a queue or the network.

classes/indexnow.go

@@ -142,15 +142,24 @@ func NotifyIndexNow(ctx context.Context, app *backpack.App, db *gorm.DB, res Reb
 	if err != nil {
 		return err
 	}
-	for start := 0; start < len(urls); start += MaxIndexNowURLs {
-		end := min(start+MaxIndexNowURLs, len(urls))
-		if err := m.Enqueue(ctx, db, IndexNowArgs{URLs: urls[start:end]}, conga.EnqueueOpts{}); err != nil {
+	for _, batch := range indexNowBatches(urls) {
+		if err := m.Enqueue(ctx, db, IndexNowArgs{URLs: batch}, conga.EnqueueOpts{}); err != nil {
 			return err
 		}
 	}
 	return nil
 }
 
+// indexNowBatches splits urls into requests of at most MaxIndexNowURLs, in
+// order.
+func indexNowBatches(urls []string) [][]string {
+	var out [][]string
+	for start := 0; start < len(urls); start += MaxIndexNowURLs {
+		out = append(out, urls[start:min(start+MaxIndexNowURLs, len(urls))])
+	}
+	return out
+}
+
 // indexNowBody is the JSON of an IndexNow request. keyLocation is not sent:
 // the key file is served at the site root, which covers every address of
 // the host (P33-14).
@@ -214,11 +223,11 @@ func SendIndexNow(ctx context.Context, app *backpack.App, args IndexNowArgs) err
 		time.Now().UTC(), len(urls), status).Error; err != nil {
 		return err
 	}
-	switch {
-	case status == http.StatusOK || status == http.StatusAccepted:
+	switch indexNowOutcome(status) {
+	case indexNowSent:
 		pluginLog.Info("golem15.sitemap: indexnow notified", "urls", len(urls), "status", status)
 		return nil
-	case status == http.StatusTooManyRequests || status >= 500:
+	case indexNowRetry:
 		pluginLog.Warn("golem15.sitemap: indexnow will retry", "urls", len(urls), "status", status)
 		return errIndexNowRetry{status: status}
 	default:
@@ -227,6 +236,26 @@ func SendIndexNow(ctx context.Context, app *backpack.App, args IndexNowArgs) err
 	}
 }
 
+// The outcomes of an IndexNow answer.
+const (
+	indexNowSent = iota
+	indexNowRetry
+	indexNowRefused
+)
+
+// indexNowOutcome maps an IndexNow answer's status: 200 and 202 are sent,
+// 429 and 5xx are retried, everything else (400, 403, 422) is refused and
+// not retried.
+func indexNowOutcome(status int) int {
+	switch {
+	case status == http.StatusOK || status == http.StatusAccepted:
+		return indexNowSent
+	case status == http.StatusTooManyRequests || status >= 500:
+		return indexNowRetry
+	}
+	return indexNowRefused
+}
+
 // EnsureKey gives settings row 1 an IndexNow key on save: while enabled,
 // a new key is generated when none is stored or rotate is set (the
 // indexnow_new_key checkbox), so the old key file answers 404 at once. It