feat(server): multi-channel monitor notifications

server/internal/notify/dispatch.go

@@ -0,0 +1,64 @@
+// Package notify formats and delivers monitor state-change alerts to
+// notification channels. It depends only on models so services can call it
+// without an import cycle.
+package notify
+
+import (
+	"fmt"
+	"time"
+
+	"github.com/mrhid6/vantage/server/internal/models"
+)
+
+// Event describes a monitor state transition worth alerting on.
+type Event struct {
+	MonitorName string
+	Type        string
+	OldStatus   string
+	NewStatus   string
+	Message     string
+	Time        time.Time
+}
+
+// title is a short one-line summary used by the text-based channels.
+func (e Event) title() string {
+	verb := "recovered"
+	if e.NewStatus == models.StatusDown {
+		verb = "is DOWN"
+	}
+	s := fmt.Sprintf("[Vantage] %s (%s) %s", e.MonitorName, e.Type, verb)
+	if e.Message != "" {
+		s += ": " + e.Message
+	}
+	return s
+}
+
+// Dispatch delivers ev to a single channel, formatting per channel type.
+func Dispatch(ch models.NotificationChannel, ev Event) error {
+	switch ch.Type {
+	case models.ChannelWebhook:
+		return dispatchWebhook(ch, ev)
+	case models.ChannelDiscord:
+		return dispatchDiscord(ch, ev)
+	case models.ChannelSlack:
+		return dispatchSlack(ch, ev)
+	case models.ChannelTelegram:
+		return dispatchTelegram(ch, ev)
+	case models.ChannelSMTP:
+		return dispatchSMTP(ch, ev)
+	default:
+		return fmt.Errorf("unknown channel type: %s", ch.Type)
+	}
+}
+
+// Test delivers a synthetic event so users can verify a channel's configuration.
+func Test(ch models.NotificationChannel) error {
+	return Dispatch(ch, Event{
+		MonitorName: "Test monitor",
+		Type:        "http",
+		OldStatus:   models.StatusUp,
+		NewStatus:   models.StatusDown,
+		Message:     "this is a test alert from Vantage",
+		Time:        time.Now(),
+	})
+}

server/internal/notify/http.go

@@ -0,0 +1,71 @@
+package notify
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/mrhid6/vantage/server/internal/models"
+)
+
+var httpClient = &http.Client{Timeout: 10 * time.Second}
+
+func postJSON(target string, payload any) error {
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return err
+	}
+	resp, err := httpClient.Post(target, "application/json", bytes.NewReader(body))
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode >= 300 {
+		return fmt.Errorf("HTTP %d from %s", resp.StatusCode, target)
+	}
+	return nil
+}
+
+// dispatchWebhook posts the full event as JSON to a user-supplied URL.
+func dispatchWebhook(ch models.NotificationChannel, ev Event) error {
+	target := ch.Config["url"]
+	if target == "" {
+		return fmt.Errorf("webhook: missing url")
+	}
+	return postJSON(target, map[string]any{
+		"monitor":    ev.MonitorName,
+		"type":       ev.Type,
+		"old_status": ev.OldStatus,
+		"new_status": ev.NewStatus,
+		"message":    ev.Message,
+		"time":       ev.Time.Format(time.RFC3339),
+	})
+}
+
+func dispatchDiscord(ch models.NotificationChannel, ev Event) error {
+	target := ch.Config["url"]
+	if target == "" {
+		return fmt.Errorf("discord: missing url")
+	}
+	return postJSON(target, map[string]string{"content": ev.title()})
+}
+
+func dispatchSlack(ch models.NotificationChannel, ev Event) error {
+	target := ch.Config["url"]
+	if target == "" {
+		return fmt.Errorf("slack: missing url")
+	}
+	return postJSON(target, map[string]string{"text": ev.title()})
+}
+
+func dispatchTelegram(ch models.NotificationChannel, ev Event) error {
+	token := ch.Config["token"]
+	chatID := ch.Config["chat_id"]
+	if token == "" || chatID == "" {
+		return fmt.Errorf("telegram: missing token or chat_id")
+	}
+	api := fmt.Sprintf("https://api.telegram.org/bot%s/sendMessage", token)
+	return postJSON(api, map[string]string{"chat_id": chatID, "text": ev.title()})
+}

server/internal/notify/smtp.go

@@ -0,0 +1,45 @@
+package notify
+
+import (
+	"fmt"
+	"net/smtp"
+	"strings"
+
+	"github.com/mrhid6/vantage/server/internal/models"
+)
+
+// dispatchSMTP sends the alert as a plain-text email. Config keys: host, port,
+// username, password, from, to. Auth is skipped when username is empty.
+func dispatchSMTP(ch models.NotificationChannel, ev Event) error {
+	host := ch.Config["host"]
+	port := ch.Config["port"]
+	from := ch.Config["from"]
+	to := ch.Config["to"]
+	if host == "" || port == "" || from == "" || to == "" {
+		return fmt.Errorf("smtp: missing host/port/from/to")
+	}
+
+	title := ev.title()
+	msg := strings.Join([]string{
+		"From: " + from,
+		"To: " + to,
+		"Subject: " + title,
+		"",
+		title,
+		"",
+		"Monitor: " + ev.MonitorName,
+		"Status: " + ev.OldStatus + " -> " + ev.NewStatus,
+		"Time: " + ev.Time.String(),
+	}, "\r\n")
+
+	var auth smtp.Auth
+	if user := ch.Config["username"]; user != "" {
+		auth = smtp.PlainAuth("", user, ch.Config["password"], host)
+	}
+	addr := host + ":" + port
+	recipients := strings.Split(to, ",")
+	for i := range recipients {
+		recipients[i] = strings.TrimSpace(recipients[i])
+	}
+	return smtp.SendMail(addr, auth, from, recipients, []byte(msg))
+}