Set ntfy priority depending on Prometheus labels

It is possible to configure a priority for an arbitrary label.
Furthermore a priority/order of those arbitrary labels should be
defined. The Alertmanager payload is checked for these and the
priority will be selected from the highest valued label that has one
set in the configuration file.

config.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"strings"
 
 	"git.sr.ht/~emersion/go-scfg"
 )
@@ -12,6 +13,7 @@ type config struct {
 	User        string
 	Password    string
 	ntfy        ntfyConfig
+	labels      labels
 }
 
 type ntfyConfig struct {
@@ -20,6 +22,15 @@ type ntfyConfig struct {
 	Password string
 }
 
+type labels struct {
+	Order []string
+	Label map[string]labelConfig
+}
+
+type labelConfig struct {
+	Priority string
+}
+
 func readConfig(path string) (*config, error) {
 	cfg, err := scfg.Load(path)
 	if err != nil {
@@ -59,6 +70,44 @@ func readConfig(path string) (*config, error) {
 		}
 	}
 
+	labelsDir := cfg.Get("labels")
+	if labelsDir != nil {
+		d = labelsDir.Children.Get("order")
+		if d != nil {
+			var order string
+			if err := d.ParseParams(&order); err != nil {
+				return nil, err
+			}
+
+			config.labels.Order = strings.Split(order, ",")
+		}
+
+		labels := make(map[string]labelConfig)
+		for _, labelName := range config.labels.Order {
+			labelDir := labelsDir.Children.Get(labelName)
+
+			if labelDir != nil {
+				labelConfig := new(labelConfig)
+				var name string
+
+				if err := labelDir.ParseParams(&name); err != nil {
+					return nil, err
+				}
+
+				d = labelDir.Children.Get("priority")
+				if d != nil {
+					if err := d.ParseParams(&labelConfig.Priority); err != nil {
+						return nil, err
+					}
+				}
+
+				labels[fmt.Sprintf("%s:%s", labelName, name)] = *labelConfig
+			}
+		}
+
+		config.labels.Label = labels
+	}
+
 	ntfyDir := cfg.Get("ntfy")
 	if ntfyDir == nil {
 		return nil, fmt.Errorf("%q directive missing", "ntfy")

main.go

@@ -98,6 +98,28 @@ func (rcv *receiver) handleWebhooks(w http.ResponseWriter, r *http.Request) {
 	}
 
 	req.Header.Set("X-Title", title)
+
+	var priority string
+	for _, labelName := range rcv.cfg.labels.Order {
+		val, ok := event.CommonLabels[labelName]
+		if !ok {
+			continue
+		}
+
+		labelConfig, ok := rcv.cfg.labels.Label[fmt.Sprintf("%s:%s", labelName, val)]
+		if !ok {
+			continue
+		}
+
+		if priority == "" {
+			priority = labelConfig.Priority
+		}
+	}
+
+	if priority != "" {
+		req.Header.Set("X-Priority", priority)
+	}
+
 	resp, err := client.Do(req)
 	if err != nil {
 		rcv.logger.Error(err)