Initial structure

internal/alerts/message.go

@@ -0,0 +1,53 @@
+// Package alerts dispatches state-transition notifications to the
+// configured channels (SMTP, Discord). The aggregator owns hysteresis
+// so this package fires exactly one message per UP↔DOWN flip.
+package alerts
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/jasper/quptime/internal/checks"
+	"github.com/jasper/quptime/internal/config"
+)
+
+// Message is the rendered notification ready to ship across any
+// channel. Channels may format Subject + Body differently (SMTP uses
+// both; Discord renders a single string).
+type Message struct {
+	Subject string
+	Body    string
+}
+
+// Render produces a human-readable message from one state transition.
+func Render(nodeID string, check *config.Check, from, to checks.State, snap checks.Snapshot) Message {
+	now := time.Now().UTC().Format(time.RFC3339)
+	verb := transitionVerb(from, to)
+	subject := fmt.Sprintf("[quptime] %s %s — %s", check.Name, verb, check.Target)
+
+	var b strings.Builder
+	fmt.Fprintf(&b, "Check %q is now %s.\n", check.Name, strings.ToUpper(string(to)))
+	fmt.Fprintf(&b, "Previous state: %s\n", from)
+	fmt.Fprintf(&b, "Target:         %s (%s)\n", check.Target, check.Type)
+	fmt.Fprintf(&b, "Reports:        %d (ok=%d, fail=%d)\n", snap.Reports, snap.OKCount, snap.NotOK)
+	if snap.Detail != "" {
+		fmt.Fprintf(&b, "Detail:         %s\n", snap.Detail)
+	}
+	fmt.Fprintf(&b, "Master:         %s\n", nodeID)
+	fmt.Fprintf(&b, "When:           %s\n", now)
+	return Message{Subject: subject, Body: b.String()}
+}
+
+func transitionVerb(from, to checks.State) string {
+	switch to {
+	case checks.StateDown:
+		return "DOWN"
+	case checks.StateUp:
+		if from == checks.StateDown {
+			return "RECOVERED"
+		}
+		return "UP"
+	}
+	return strings.ToUpper(string(to))
+}