display notifications

internal/alerts/aod.go

@@ -0,0 +1,93 @@
+package alerts
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// AlwaysOnDisplay sends each alert to the session API used by the wall
+// display. A session is created for the alert and then given a status and log
+// entry so the display can show both the current incident and its details.
+type AlwaysOnDisplay struct {
+	URL    string
+	Client *http.Client
+}
+
+func (a *AlwaysOnDisplay) Name() string { return "always-on-display" }
+
+type aodSession struct {
+	ID string `json:"id"`
+}
+
+func (a *AlwaysOnDisplay) Send(ctx context.Context, alert Alert) error {
+	client := a.Client
+	if client == nil {
+		client = &http.Client{Timeout: 15 * time.Second}
+	}
+	base := strings.TrimRight(a.URL, "/")
+
+	var session aodSession
+	name := fmt.Sprintf("%s alert: %s", strings.ToUpper(string(alert.Priority())), alert.Spike.Service)
+	if alert.Test {
+		name = "TEST alert: " + alert.Spike.Service
+	}
+	if err := postJSONDecode(ctx, client, base+"/api/sessions", nil, map[string]string{"name": name}, &session); err != nil {
+		return err
+	}
+	if session.ID == "" {
+		return fmt.Errorf("always-on-display: session response did not include an id")
+	}
+
+	status := firstLine(alert.Text(""))
+	if err := postJSON(ctx, client, base+"/api/sessions/"+session.ID+"/status", nil, map[string]string{"status": status}); err != nil {
+		return err
+	}
+	level := "info"
+	if alert.Priority() == PriorityHigh {
+		level = "error"
+	} else if alert.Priority() == PriorityMedium {
+		level = "warning"
+	}
+	return postJSON(ctx, client, base+"/api/sessions/"+session.ID+"/log", nil, map[string]string{
+		"level":   level,
+		"message": alert.Text(""),
+	})
+}
+
+func firstLine(s string) string {
+	if i := strings.IndexByte(s, '\n'); i >= 0 {
+		return s[:i]
+	}
+	return s
+}
+
+func postJSONDecode(ctx context.Context, client *http.Client, target string, headers map[string]string, body any, out any) error {
+	raw, err := json.Marshal(body)
+	if err != nil {
+		return err
+	}
+	req, err := http.NewRequestWithContext(ctx, http.MethodPost, target, strings.NewReader(string(raw)))
+	if err != nil {
+		return fmt.Errorf("always-on-display: invalid request")
+	}
+	req.Header.Set("Content-Type", "application/json")
+	for k, v := range headers {
+		req.Header.Set(k, v)
+	}
+	resp, err := client.Do(req)
+	if err != nil {
+		return fmt.Errorf("always-on-display: request failed: %w", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode/100 != 2 {
+		return fmt.Errorf("always-on-display: HTTP %d", resp.StatusCode)
+	}
+	if err := json.NewDecoder(resp.Body).Decode(out); err != nil {
+		return fmt.Errorf("always-on-display: invalid session response: %w", err)
+	}
+	return nil
+}