Add Messagebird as an alerting provider

alerting/provider/messagebird/messagebird.go

@@ -0,0 +1,47 @@
+package messagebird
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/TwinProduction/gatus/alerting/provider/custom"
+	"github.com/TwinProduction/gatus/core"
+)
+
+const (
+	restAPIURL = "https://rest.messagebird.com/messages"
+)
+
+// AlertProvider is the configuration necessary for sending an alert using Messagebird
+type AlertProvider struct {
+	AccessKey  string `yaml:"access-key"`
+	Originator string `yaml:"originator"`
+	Recipients string `yaml:"recipients"`
+}
+
+// IsValid returns whether the provider's configuration is valid
+func (provider *AlertProvider) IsValid() bool {
+	return len(provider.AccessKey) > 0 && len(provider.Originator) > 0 && len(provider.Recipients) > 0
+}
+
+// ToCustomAlertProvider converts the provider into a custom.AlertProvider
+// Reference doc for messagebird https://developers.messagebird.com/api/sms-messaging/#send-outbound-sms
+func (provider *AlertProvider) ToCustomAlertProvider(service *core.Service, alert *core.Alert, _ *core.Result, resolved bool) *custom.AlertProvider {
+	var message string
+	if resolved {
+		message = fmt.Sprintf("RESOLVED: %s - %s", service.Name, alert.Description)
+	} else {
+		message = fmt.Sprintf("TRIGGERED: %s - %s", service.Name, alert.Description)
+	}
+
+	return &custom.AlertProvider{
+		URL:    restAPIURL,
+		Method: http.MethodPost,
+		Body: fmt.Sprintf(`{ "originator": "%s", "recipients": "%s", "body": "%s"}`,
+			provider.Originator, provider.Recipients, message),
+		Headers: map[string]string{
+			"Content-Type":  "application/json",
+			"Authorization": fmt.Sprintf("AccessKey %s", provider.AccessKey),
+		},
+	}
+}