Format the alert message

For now the format is similar to the email receiver. Maybe switch to
template usage in the future.

go.mod

@@ -3,3 +3,5 @@ module git.xenrox.net/~xenrox/ntfy-alertmanager
 go 1.19
 
 require git.xenrox.net/~xenrox/go-log v0.0.0-20221009121411-e93f4223b622
+
+require golang.org/x/text v0.3.7

go.sum

@@ -1,2 +1,4 @@
 git.xenrox.net/~xenrox/go-log v0.0.0-20221009121411-e93f4223b622 h1:XxHbaQOQllWEMoeSLocFWPyqMPWCDUDatDEtIdYIXhI=
 git.xenrox.net/~xenrox/go-log v0.0.0-20221009121411-e93f4223b622/go.mod h1:d98WFDHGpxaEThKue5CfGtr9OrWgbaApprt3GH+OM4s=
+golang.org/x/text v0.3.7 h1:olpwvP2KacW1ZWvsR7uQhoyTYvKAupfQrRGBFM352Gk=
+golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=

main.go

@@ -1,20 +1,98 @@
 package main
 
 import (
+	"encoding/json"
+	"fmt"
 	"net/http"
 	"strings"
+	"time"
 
 	"git.xenrox.net/~xenrox/go-log"
+	"golang.org/x/text/cases"
+	"golang.org/x/text/language"
 )
 
-func handleWebhooks(w http.ResponseWriter, r *http.Request) {
-	http.Post("https://ntfy.sh/alertmanager_test", "text/plain",
-		strings.NewReader("Payload received"))
+type receiver struct {
+	logger *log.Logger
+}
+
+type payload struct {
+	Status            string                 `json:"status"`
+	Alerts            []alert                `json:"alerts"`
+	GroupLabels       map[string]interface{} `json:"groupLabels"`
+	CommonLabels      map[string]interface{} `json:"commonLabels"`
+	CommonAnnotations map[string]interface{} `json:"commonAnnotations"`
+}
+
+type alert struct {
+	Status      string                 `json:"status"`
+	Labels      map[string]interface{} `json:"labels"`
+	Annotations map[string]interface{} `json:"annotations"`
+}
+
+func (rcv *receiver) handleWebhooks(w http.ResponseWriter, r *http.Request) {
+	defer r.Body.Close()
+
+	var event payload
+	if err := json.NewDecoder(r.Body).Decode(&event); err != nil {
+		rcv.logger.Error(err)
+		return
+	}
+
+	count := len(event.Alerts)
+	title := fmt.Sprintf("[%s", strings.ToUpper(event.Status))
+	if event.Status == "firing" {
+		title = fmt.Sprintf("%s:%d", title, count)
+	}
+
+	title += "]"
+	for _, value := range event.GroupLabels {
+		title = fmt.Sprintf("%s %s", title, value)
+	}
+
+	var body string
+	c := cases.Title(language.English)
+
+	for _, alert := range event.Alerts {
+		alertBody := fmt.Sprintf("%s\nLabels:\n", c.String(alert.Status))
+		for key, value := range alert.Labels {
+			alertBody = fmt.Sprintf("%s%s = %s\n", alertBody, key, value)
+		}
+
+		alertBody += "Annotations:\n"
+		for key, value := range alert.Annotations {
+			alertBody = fmt.Sprintf("%s%s = %s\n", alertBody, key, value)
+		}
+
+		alertBody += "\n"
+
+		body += alertBody
+	}
+
+	client := &http.Client{Timeout: time.Second * 3}
+	url := "https://ntfy.sh/alertmanager_test"
+	req, err := http.NewRequest(http.MethodPost, url, strings.NewReader(body))
+	if err != nil {
+		rcv.logger.Error(err)
+	}
+
+	req.Header.Set("X-Title", title)
+	resp, err := client.Do(req)
+	if err != nil {
+		rcv.logger.Error(err)
+	}
+
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		rcv.logger.Error("ntfy: received status code %d", resp.StatusCode)
+	}
 }
 
 func main() {
 	logger := log.NewDefaultLogger()
 
-	http.HandleFunc("/", handleWebhooks)
+	receiver := &receiver{logger: logger}
+
+	http.HandleFunc("/", receiver.handleWebhooks)
 	logger.Fatal(http.ListenAndServe("127.0.0.1:8080", nil))
 }