Initial structure

internal/alerts/dispatcher.go

@@ -0,0 +1,69 @@
+package alerts
+
+import (
+	"fmt"
+	"log"
+
+	"github.com/jasper/quptime/internal/checks"
+	"github.com/jasper/quptime/internal/config"
+)
+
+// Dispatcher fans an aggregator transition out to every alert listed
+// on the check. Errors are logged but never propagated: alerting must
+// not block the aggregation pipeline.
+type Dispatcher struct {
+	cluster *config.ClusterConfig
+	selfID  string
+	logger  *log.Logger
+}
+
+// New constructs a Dispatcher.
+func New(cluster *config.ClusterConfig, selfID string, logger *log.Logger) *Dispatcher {
+	if logger == nil {
+		logger = log.Default()
+	}
+	return &Dispatcher{cluster: cluster, selfID: selfID, logger: logger}
+}
+
+// OnTransition is wired as checks.TransitionFn.
+func (d *Dispatcher) OnTransition(check *config.Check, from, to checks.State, snap checks.Snapshot) {
+	if to == checks.StateUnknown {
+		return
+	}
+	msg := Render(d.selfID, check, from, to, snap)
+	for _, alertID := range check.AlertIDs {
+		alert, _ := d.cluster.FindAlert(alertID)
+		if alert == nil {
+			d.logger.Printf("alerts: check %q references unknown alert %q", check.Name, alertID)
+			continue
+		}
+		if err := d.dispatchOne(alert, msg); err != nil {
+			d.logger.Printf("alerts: %q via %s: %v", alert.Name, alert.Type, err)
+		}
+	}
+}
+
+// Test sends a one-shot test message to the named alert. Returns an
+// error so the CLI can surface failures interactively.
+func (d *Dispatcher) Test(alertID string) error {
+	alert, _ := d.cluster.FindAlert(alertID)
+	if alert == nil {
+		return fmt.Errorf("alert %q not found", alertID)
+	}
+	msg := Message{
+		Subject: "[quptime] test alert",
+		Body:    fmt.Sprintf("This is a test of alert %q from node %s.\nIf you see this, the alert channel is wired correctly.\n", alert.Name, d.selfID),
+	}
+	return d.dispatchOne(alert, msg)
+}
+
+func (d *Dispatcher) dispatchOne(a *config.Alert, msg Message) error {
+	switch a.Type {
+	case config.AlertSMTP:
+		return sendSMTP(a, msg)
+	case config.AlertDiscord:
+		return sendDiscord(a, msg)
+	default:
+		return fmt.Errorf("unknown alert type %q", a.Type)
+	}
+}