Add Telegram Alerting (#102)

alerting/provider/telegram/telegram.go

@@ -0,0 +1,52 @@
+package telegram
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/TwinProduction/gatus/alerting/provider/custom"
+	"github.com/TwinProduction/gatus/core"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Telegram
+type AlertProvider struct {
+	Token string `yaml:"token"`
+	ID    string `yaml:"id"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.Token) > 0 && len(provider.ID) > 0
+}
+
+// ToCustomAlertProvider converts the provider into a custom.AlertProvider
+func (provider *AlertProvider) ToCustomAlertProvider(service *core.Service, alert *core.Alert, result *core.Result, resolved bool) *custom.AlertProvider {
+	var message, results string
+	if resolved {
+		message = fmt.Sprintf("An alert for *%s* has been resolved:\\n—\\n    _healthcheck passing successfully %d time(s) in a row_\\n—  ", service.Name, alert.FailureThreshold)
+	} else {
+		message = fmt.Sprintf("An alert for *%s* has been triggered:\\n—\\n    _healthcheck failed %d time(s) in a row_\\n—  ", service.Name, alert.FailureThreshold)
+	}
+	for _, conditionResult := range result.ConditionResults {
+		var prefix string
+		if conditionResult.Success {
+			prefix = "✅"
+		} else {
+			prefix = "❌"
+		}
+		results += fmt.Sprintf("%s - `%s`\\n", prefix, conditionResult.Condition)
+	}
+	var text string
+	if len(alert.Description) > 0 {
+		text = fmt.Sprintf("⛑ *Gatus* \\n%s \\n*Description* \\n_%s_  \\n\\n*Condition results*\\n%s", message, alert.Description, results)
+	} else {
+		text = fmt.Sprintf("⛑ *Gatus* \\n%s \\n*Condition results*\\n%s", message, results)
+	}
+
+	return &custom.AlertProvider{
+		URL:     fmt.Sprintf("https://api.telegram.org/bot%s/sendMessage", provider.Token),
+		Method:  http.MethodPost,
+		Body:    fmt.Sprintf(`{"chat_id": "%s", "text": "%s", "parse_mode": "MARKDOWN" }`, provider.ID, text),
+		Headers: map[string]string{"Content-Type": "application/json"},
+	}
+}